EXPERIMENTAL INVESTIGATIONS OF Al-BASED INITIATIOR FOR (CO)POLYMERIZATION OF EPOXIDES AND EPISULFIDE AND APPLICATION TOWARD MEMBRANE SYNTHESIS By Niloofar Safaie Ashtiani A DISSERTATION Submitted to Michigan State University in partial fulfillment of the requirements for the degree of Chemistry- Doctor of Philosophy 2022 ABSTRACT EXPERIMENTAL INVESTIGATIONS OF Al-BASED INITIATIOR FOR (CO)POLYMERIZATION OF EPOXIDES AND EPISULFIDE AND APPLICATION TOWARD MEMBRANE SYNTHESIS By Niloofar Safaie Ashtiani We developed a novel aluminum-based initiator for epoxide polymerization which facilitated polymerization of various epoxides (epichlorohydrin, propylene oxide, etc.) and episulfide up to molecular weights of 100 kg/mol while maintaining relatively narrow polydispersity (Ð < 1.3). The initiator was simply synthesized through the reaction of a thiol ligand and trialkyl aluminum, with the thiol ligand choice enabling polymer end group control. Copolymerization of epichlorohydrin and propylene oxide and copolymerization of different epoxides with episulfide demonstrated the ability of this method to control polymer architecture. We further investigated the effect of catalyst concentration and initiator structure on the kinetics of epoxide polymerizations through 1H NMR spectroscopy. Finally, we combined our method of polymerization with another facile method, reversible addition fragmentation with chain transfer (RAFT) polymerization, to synthesize block-co-polymers made from vinyl and epoxide monomers. To do this, we made a macroinitiator from polystyrene (PS) and poly(methyl methacrylate) (PMMA), synthesized by RAFT polymerization, and further polymerized epoxide from it. Therefore, this new synthetic tool allows for the facile and controlled polymerization of epoxides into well-defined, functional, polyether materials. Furthermore, the introduced innovative and reliable methodology for the synthesis of SAl initiators enabled us to tune the polymer architecture to readily access more complex structure of polyepisulifides. We synthesized di-functional (d-H) and tetra-functional (t- H) SAl initiators to produce ABA and star-(co)polymers consisting of propylene sulfide and PO or ECH. Finally, polyethylene glycol (PEG) was used as a macroinitiator to create PEG-b-PPS block copolymers and characterized by 1H, 13C NMR spectroscopy, DOSY, DSC, and SEC. Motivated by the result, we prepared the star shape cross linked membrane from t-H initiator. The composition was controlled through the monomer feed ratio of propylene oxide (PO) and epichlorohydrin (ECH) for synthesis of PPO-PECH membrane in the presence of poly(ethylene oxide)-diglycidyl ether as a cross linker and the most optimized PPO-PECH with the ratio of 90:10 resulted optically clear and flexible film. We further modified the membrane with a range of amines like trimethylamine (TEA), dimethylamine (DMA), triethylamine (TEA), and diethylamine (DEA) by membrane dipping method. The chemical, physical, and mechanical properties of resultant secondary amine grafted and quartenized membranes were characterized as a candidate for CO2 transport. Moreover, we designed the facilitated transport membranes of crosslinked ether-based PPO-PECH membranes with the range of hindered and unhindered primary amines using previously reported mono(μ-alkoxo)- bis(alkylaluminum) (MOB). The physical and chemical properties of the membranes investigated by FT-IR spectroscopy, DSC, TGA, and rheology. This method demonstrated a simple and robust strategy to prepare copolymers cross linked membranes containing amines for CO2 transport. This enables us to compare the effect of different amines in the structure of facilitated transport membranes. In this thesis research we seek to develop a SAl initiator as a platform that is both simple to use and can synthesize new polymeric materials. This methodology is simple and tunable to produce robust crosslinked membranes for molecular transport. Copyright by NILOOFAR SAFAIE ASHTIANI 2022 To my parents, my husband, and my sister v ACKNOWLEDGMENTS I had a great time with my advisor Prof. Ferrier It was impossible to complete my Ph. D. without him. He truly guided me not only in science but also in my life. Also, I would like to thank all my committee members (Prof. Gary Blanchard, Prof. Ramani Narayan, and Prof. Shiwang Cheng) for their valuable inputs during my presentations. Furthermore, I would like to thank all my lab mates (Geetanjali Shukla, Shayylyn Crum, Gouree Kumbhar, Danielle DeJonge, and Mayson Wipple) for all their help and support on my research. Also, I like to say special thanks to my family and friends for their constructive support and help throughout my life. Last but not least, I wanted to thank Mohammad wo stood by me in bad and good days of life during PhD. vi TABLE OF CONTENTS LIST OF TABLES ..................................................................................................................... x LIST OF FIGURES .................................................................................................................. xi LIST OF SCHEMES ............................................................................................................. xxv Chapter 1. Introduction ............................................................................................................ 1 1.1 Background ......................................................................................................................1 BIBLIOGRAPHY.................................................................................................................... 10 Chapter 2. Aluminum-based Initiators from Thiols for Epoxide Polymerization ............ 15 2.1 Introduction ....................................................................................................................15 2.2 Experimental section ......................................................................................................17 2.2.1 Characterization .....................................................................................................18 2.2.2 Synthesis of trimethylaluminum and triethylamine adduct (NAl).26 .....................19 2.2.3 General procedure for synthesis of initiators .........................................................19 2.2.4 General procedure for synthesis and purification of polymers ..............................20 2.2.5 Procedure for synthesis and reactivity ratio measurement of P(PO-grad-ECH) ...22 2.2.6 General procedure for synthesis of P(PO-b-ECH).................................................22 2.2.7 Polymerization procedure for synthesis of P(MMA-b-ECH) ................................23 2.2.8 Detailed purification procedure for synthesized polymers ....................................25 2.2.9 Kinetic study for different concentrations of NAl by 1H NMR spectroscopy at specified time points ..............................................................................................................25 2.2.10 Kinetic study for different initiators by 1H NMR spectroscopy specified time .....25 2.2.11 Polymerization procedure for synthesis of poly(styrene-block-epichlorohydrin) (P(styerne-b-ECH)) ................................................................................................................26 2.3 Results and discussion ...................................................................................................27 2.4 Supporting information ..................................................................................................44 BIBLIOGRAPHY.....................................................................................................................81 Chapter 3. Investigation of Aluminum-based initiators for Propylene Sulfide (Co)Polymerization with Compositional and Architectural Control ..................................... 87 3.1 Introduction ....................................................................................................................87 3.2 Experimental section ......................................................................................................89 3.2.1 Materials ................................................................................................................89 3.2.2 Characterization .....................................................................................................90 3.2.3 Synthesis of trimethylaluminum and triethylamine Adduct (NAl)........................91 3.2.4 Synthesis of (Benzylthio)dimethylaluminum (BnSAlMe2), (benzyloxy)dimethylaluminum (BnOAlMe2) and dimethyl(propylthio)aluminum (PrSAlMe2) ............................................................................................................................92 3.2.5 Synthesis of di-functional initiator (d-H) ...............................................................92 3.2.6 Synthesis of tetra-functional initiator (t-H)............................................................93 vii 3.2.7 Procedure for synthesis of poly(propylene sulfide) and its purification using BnsAlMe2 or BnOAlMe2 .......................................................................................................93 3.2.8 Procedure for one-pot synthesis of poly(ECH-stat-PS) using BnSAlMe2 as an initiator .......................................................................................................94 3.2.9 Procedure for one-pot synthesis of poly(PO-stat-PS) using BnSAlMe2 as an initiator .......................................................................................................95 3.2.10 Procedure for synthesis of poly(ECH-b-PS) using BnSAlMe2 as an initiator .......95 3.2.11 Procedure for synthesis of poly(PO-b-PS) using BnSAlMe2 as an initiator ..........96 3.2.12 Procedure for synthesis of poly(PS-b-PO) by d-H initiator ...................................97 3.2.13 Procedure for synthesis of poly(PS-b-PO) by t-H initiator ....................................98 3.2.14 Procedure for control experiments by kinetics Studies using 1H NMR spectroscopy of BnSAlMe2 and NAl, only NAl, and only BnSAlMe2 or PS polymerization: With only BnSAlMe2 .............................................................................................................98 3.2.15 Procedure for Kinetics Studies by 1H NMR spectroscopy of d-H initiator and PrSAlMe2 for PS polymerization ...........................................................................................99 3.2.16 Procedure for synthesis of poly(EG-b-PS) ............................................................99 3.3 Results and discussion .................................................................................................100 3.4 Supporting information ................................................................................................116 BIBLIOGRAPHY.................................................................................................................. 133 Chapter 4. Two-steps Solvent Free Synthesis Method for Preparation of Star-shaped Cross-linked Polyether Membranes Containing Different Amines via SAl Initiator......... 137 4.1 Introduction ..................................................................................................................137 4.2 Experimental section ....................................................................................................139 4.2.1 Materials ..............................................................................................................139 4.2.2 Synthesis of Trimethylaluminum and Triethylamine Adduct (NAl) ...................139 4.2.3 Synthesis of Tetra-headed Initiator (t-H) .............................................................140 4.2.4 Membrane Preparation .........................................................................................140 4.2.5 Functionalization of the Membranes ...................................................................141 4.2.6 Structure Characterization ...................................................................................141 4.2.7 Thermal Characterization.....................................................................................141 4.2.8 Water Uptake and Swelling Ratio........................................................................142 4.2.9 Resistance Characterization .................................................................................142 4.2.10 Rheology Characterization...................................................................................143 4.2.11 Alkaline stability ..................................................................................................143 4.3 Results and discussion .................................................................................................143 4.3.1 Synthesis and Characterization of Modified Cross-linked Membranes ..............146 4.3.2 Structural characterization ...................................................................................147 4.3.3 Thermal characterization .....................................................................................148 4.3.4 Water uptake and swelling ratio ..........................................................................149 4.3.5 Conductivity.........................................................................................................150 4.3.6 Rheology ..............................................................................................................151 4.4 Supporting information ................................................................................................153 BILBIOGRAPHY.................................................................................................................. 156 viii Chapter 5. Development and Characterization of Crosslinked Amine Modified Membranes for CO2 separation and capture ......................................................................... 161 5.1 Introduction ..................................................................................................................161 5.2 Experimental section ....................................................................................................163 5.2.1 Material ................................................................................................................163 5.2.2 Synthesis of Bis(μ-oxo)alkylaluminum [(CH3)2NCH2CH2(μ2- O)Al(CH3)2·Al(CH3)3](MOB) .............................................................................................164 5.2.3 Synthesis of crosslinked membranes ...................................................................164 5.2.4 Crosslinked membrane functionalization ............................................................165 5.2.5 Structure Characterization ...................................................................................165 5.2.6 Thermal Characterization.....................................................................................165 5.2.7 Rheology Characterization...................................................................................166 5.3 Results and discussion .................................................................................................166 5.3.1 Chemical properties .............................................................................................167 5.3.2 Thermal and Rheological Properties ....................................................................169 5.4 Supporting information ................................................................................................172 BILBIOGRAPHY.................................................................................................................. 174 Chapter 6. Conclusion and Future Work............................................................................ 180 ix LIST OF TABLES Table 2-1 Control experiment. .................................................................................................... 30 Table 3-1 Polymerization and copolymerization characteristics. ............................................. 102 Table 4-1 Characterization of t-H-Initiated Cross-linked Membranes. ..................................... 145 Table 4-2 Characterization of amine modified t-H-Initiated Cross-linked Membranes. ........... 147 Table 5-1 Characterization of Amine Modified Cross-linked Membranes. ............................. 168 x LIST OF FIGURES Figure 2-1 (top) Chemical reaction scheme for the synthesis of BnSAlMe2. (bottom) Resultant chemical structure of the asymmetric structure determined by X-Ray crystallography. Thermal ellipsoids are shown at 50% probability level. ........................................................28 Figure 2-2 Plot of normalized ECH concentration over time with BnSAlMe2 initiator and NAl catalyst. Monomer concentration was monitored via 1H NMR spectroscopy. The full conversion was achieved in ca. 10 hours with the combined catalyst and initiator system, with kobs = 7.38 × 10-5 ± 5.41 × 10-6 s-1, whereas no conversion is present with just catalyst and slow conversion is present with just BnSAlMe2 as initiator. The inset is a plot of the kobs as a function of equivalents of NAl catalyst to BnSAlMe2 initiator, where a linear relationship was observed. .....................................................................................................31 Figure 2-3 Plot of Mn (left axis, blue circles) and Ð (right axis, red triangles) as a function of ECH to initiator BnSAlMe2 ratio ([ECH]/[BnSAlMe2]). Mn increased linearly at increasing ratio of epichlorohydrin, while Ð remained consistently low (Ð < 1.4) suggesting a controlled chain growth polymerization of ECH. ..................................................................33 Figure 2-4 Resultant structure of cPenSAlMe2 (a) and ClBnSAlMe2 (b) formed from the reaction of cyclopentyl thiol and 4-chlorobenzenemethanethiol, respectively, with trimethyl aluminum determined by X-Ray crystallography. cPenSAlMe2 forms a dimer (shown) consisting of a four membered thio-aluminum ring while the ClBnSAlMe2 forms a chain of initiator units connected via dative bonds to aluminum and sulfur atoms of adjacent initiators, like BnSAlMe2 (cf., Figure 1). Thermal ellipsoids are shown at 50% probability level. .......................................................................................................................................35 Figure 2-5 1H NMR Spectra of PECH initiated by PrSAlMe2 (a), cPenSAlMe2 (b), BnSAlMe2 (c), and ClBnSAlMe2 (d) in CD2Cl2 (c, d) or CDCl3 (a, b). The peaks corresponding to the various end groups are clearly visible in each of the spectra and are marked with letters ‘a’ through ‘c’ and their chemical shift and multiplicity is consistent with expectations. Peaks marked with ‘x’ correspond to CD2Cl2 and peaks marked with ‘y’ correspond to water impurity in CDCl3. Intensity increased to accentuate peaks corresponding to end groups. ..36 Figure 2-6 Plot of the –ln([ECH]/[ECH]0) as a function of time for the polymerization of ECH with SAl initiators PrSAlMe2 (red squares), BnSAlMe2 (blue circles), ClBnSAlMe2 (purple triangles), and cPenSAlMe2 (green diamonds). Monomer conversion was monitored via 1H NMR spectroscopy for 2.5 hours by taking aliquots from the reaction vessel and an observed rate constant (kobs) was determined to be kobs = (3.83 ± 0.15) × 10-4 s-1 (PrSAlMe2), (1.86 ± 0.08) × 10-4 s-1 (BnSAlMe2), (1.34 ± 0.05) × 10-4 s-1(ClBnSAlMe2), and (0.21 ± 0.03) × 10-4 s-1 (cPenSAlMe2). ...................................................................................38 Figure 2-7 1H and 13C NMR spectra and labeled chemical structures for PECH-grad-PPO (a and b, respectively) and PECH-b-PPO (c and d, respectively) in CDCl3. The 13C NMR spectrum xi of the PECH-grad-PPO (b) reveals additional cross-peaks compared with PECH-b-PPO (d). ................................................................................................................................................40 Figure 2-8 PMMA-block-PECH synthetic route. ..........................................................................42 Figure 2-9 SEC traces (RI) of RAFT synthesized PMMA (right, red curve) and P(MMA-b-ECH) (left, blue curve). The Mn and Đ was determined to be 6.3 kg/mol and 1.13 (PMMA) and 18.4 kg/mol and 1.05 (P(MMA-b-ECH)). .............................................................................43 Figure 2-10 . 1H NMR spectra in CDCl3 of RAFT synthesized PMMA (c), thiol-end terminated PMMA (b), and P(MMA-b-ECH) (a). The peak associated with the benzyl end group from the RAFT agent (cf., c) disappears after the aminolysis step (cf., b), which reveals a free thiol. .......................................................................................................................................43 Figure 2-11 1H NMR spectroscopy of BnSAlMe2. 1H NMR (500 MHz, Chloroform-d) δ 7.38 – 7.21 (m, 5H, PhCH2S-Al(CH3)2), 3.91 (s, 2H, PhCH2S-Al(CH3)2), -0.43 (s, 6H, PhCH2S- Al(CH3)2). ..............................................................................................................................44 Figure 2-12 13C NMR spectrum of BnSAlMe2. 13C NMR(126 MHz, CD2Cl2) δ 141.46, 128.56, 127.97, 126.89 PhCH2S-Al(CH3)2, 32.00 PhCH2S-Al(CH3)2, 28.78 PhCH2S-Al(CH3)2. .....45 Figure 2-13 Carbon labeling scheme for BnSAlMe2. There is a single molecule in the asymmetric unit, which is represented by the reported sum formula. In other words: Z is 4 and Z' is 1 for BnSAlMe2. ......................................................................................................45 Figure 2-14 The Unit structure of dimethyl aluminum bound to benzyl thiolate, consistent with trimethyl aluminum reacting with the benzyl mercaptan. This unit, we propose, defines our initiator for epoxide polymerizations. The entire crystal structure reveals these individual units to be datively bound to adjacent units in a linear chain. ...............................................46 Figure 2-15 Plot of the –ln([ECH]/[ECH]0) over time for the polymerization of ECH with BnSAl and 1 eq of NAl showing a linear slope consistent with a living polymerization. r2 = 0.96..46 Figure 2-16 1H NMR spectroscopy for ECH polymerizations with just NAl after 7 days which shows no conversion to PECH. 1H NMR (500 MHz, Chloroform-d) δ 3.62 – 3.50 (m, 2H, ECH OCH2CH(CH2Cl)), 3.22 (dddd, 1H, ECH OCH2CH(CH2Cl)), 2.88 (ddd, 1H, ECH OCH2CH(CH2Cl)), 2.67 (dd, 1H, ECH OCH2CH(CH2Cl)). .................................................47 Figure 2-17 1H NMR spectroscopy for ECH polymerizations with just BnSAlMe2 after 7 days which shows slow conversion (ca. 10% after 7 day). 1H NMR (500 MHz, Chloroform-d) δ 3.77- 3.49 (bm, PECH, -OCH2CH(CH2Cl)O-), 3.62 – 3.49 (m, 2H, ECH OCH2CH(CH2Cl)), 3.22 (dddd, 1H, ECH OCH2CH(CH2Cl)), 2.88 (ddd, 1H, ECH OCH2CH(CH2Cl)), 2.67 (dd, 1H, ECH OCH2CH(CH2Cl)). .................................................................................................47 Figure 2-18 1H NMR spectroscopy for ECH polymerizations with benzyl mercaptan (ligand) and NAl after 7 days which shows no conversion to PECH. 1H NMR (500 MHz, Chloroform- d3.62 – 3.50 (m, 2H, ECH OCH2CH(CH2Cl)), 3.22 (dddd, 1H, ECH OCH2CH(CH2Cl)), 2.88 (ddd, 1H, ECH OCH2CH(CH2Cl)), 2.67 (dd, 1H, ECH OCH2CH(CH2Cl)). ................48 xii Figure 2-19 RI trace of targeted 30k PECH synthesized by BnSAlMe2 initiator. The Mn is determined to be 30.7 with Ð =1.17. .....................................................................................48 Figure 2-20 DSC analysis of targeted 30k PECH with BnSAlMe2. The data from the second heating curve were collected which reveals one Tg at -26 °C. ..............................................49 Figure 2-21 1H NMR spectroscopy of 30K PECH treated with 1 M HCl in MeOH. This is magnified 1H NMR to verify benzyl signal loss. 1H NMR (500 MHz, Chloroform-d) δ 3.83- 3.39 (bm, -OCH2CH(CH2Cl)O-)............................................................................................49 Figure 2-22 Plot of normalized ECH concentration over time with BnSAlMe2 initiator and 0.25 eq. of NAl catalyst. Monomer concentration was monitored via 1H NMR spectroscopy and the rate of reaction calculated based on it (kobs = 5.06 × 10-6 ± 5.54 × 10-7 s-1). Sigmoidal shape of conversion curve for 0.25 eq. of NAl can be seen in this figure which is related to induction period. The kobs is calculated using the data collected after the induction period, where conversion is first order in monomer. .........................................................................50 Figure 2-23 Plot of normalized ECH concentration over time with BnSAlMe2 initiator and 0.5 eq. of NAL catalyst. Monomer concentration was monitored via 1H NMR spectroscopy, and the rate of reaction calculated based on it (kobs = 2.34 × 10-5 ± 2.21 × 10-6 s-1). Sigmoidal shape of conversion curve for 0.5 eq. of NAl can be seen in this figure which is related to induction period. The kobs is calculated using the data collected after the induction period, where conversion is first order in monomer. .........................................................................50 Figure 2-24 Plot of normalized ECH concentration over time with BnSAlMe2 initiator and 2 eq. of NAl. Monomer concentration was monitored via 1H NMR spectroscopy. Full conversion was achieved in ca. 10 hours with the combined catalyst and initiator system, with kobs = 1.91 × 10-4 ± 5.79 × 10-6 s-1. .................................................................................51 Figure 2-25 Plot of the –ln([ECH]/[ECH]0) over time for the polymerization of ECH with BnSAl and 2 equivalents of catalyst showing a linear slope consistent with a living polymerization. r2 = 0.96. ......................................................................................................51 Figure 2-26 RI trace of targeted 15k PECH synthesized by BnSAlMe2 initiator. The Mn is determined to be 17.7 with Ð = 1.37. ....................................................................................52 Figure 2-27 RI trace of targeted 50k PECH synthesized by BnSAlMe2 initiator. The Mn is determined to be 49.4 with Ð = 1.28. ....................................................................................52 Figure 2-28 RI trace of targeted 70k PECH synthesized by BnSAlMe2 initiator. The Mn is determined to be 75.7 with Ð = 1.25. ....................................................................................53 Figure 2-29 RI trace of targeted 100k PECH synthesized by BnSAlMe2 initiator. The Mn is determined to be 94.6 with Ð = 1.28. ....................................................................................53 Figure 2-30 RI trace of targeted 30k PBO synthesized by BnSAlMe2 initiator. The Mn is determined to be 23.6 with Ð = 1.16. ....................................................................................54 xiii Figure 2-31 RI trace of targeted 100k PBO synthesized by BnSAlMe2 initiator. The Mn is determined to be 80.2 with Ð = 1.02. ....................................................................................54 Figure 2-32 RI trace of targeted 30k PPO synthesized by PrSAlMe2 initiator. The Mn is determined to be 23.5 with Ð = 1.17. ....................................................................................55 Figure 2-33 RI trace of targeted 30k PPO synthesized by BnSAlMe2 initiator. The Mn is determined to be 38.9 with Ð = 1.04. ....................................................................................55 Figure 2-34 RI trace of targeted 100k PPO synthesized by BnSAlMe2 initiator. The Mn is determined to be 80.1 with Ð = 1.02. ....................................................................................56 Figure 2-35 DSC analysis of targeted 30k PPO with BnSAlMe2. The data from the second heating curve were collected which reveals one Tg at -70 °C. ...............................................56 Figure 2-36 DSC analysis of targeted 30k PBO with BnSAlMe2. The data from the second heating curve were collected which reveals one Tg at -73 °C................................................57 Figure 2-37 1H NMR spectroscopy of targeted 30K poly(allyl glycidyl ether) (PAGE) with BnSAlMe2. 1H NMR (500 MHz, Chloroform-d) δ 5.88 (m, –O–CH2–CH=CH2), 5.27-5.14 (doublet of doublets, –O–CH2–CH=CH2), 3.98 (d, –O–CH2–CH=CH2), 3.75-3.42 (bm, –O– CH2–CH(CH2–O–CH2–CH=CH2)–O–). ................................................................................57 Figure 2-38 13C NMR spectroscopy of targeted 30K poly(allyl glycidyl ether) (PAGE) with BnSAlMe2. 13C NMR (126 MHz, Chloroform-d) δ 134.93 (–O–CH2–CH=CH2), 116.74 (– O–CH2–CH=CH2), 78.89 (–O–CH2–CH(CH2–O–CH2–CH=CH2)–O–), 72.26 (–O–CH2– CH=CH2), 70.25-69.84 (–O–CH2–CH(CH2–O–CH2–CH=CH2)–O–, m), 69.74 (–O–CH2– CH(CH2–O–CH2–CH=CH2)–O–, rrm or mrr). ......................................................................58 Figure 2-39 DSC analysis of Targeted 30k PAGE with compound BnSAlMe2. The data from the second heating curve were collected which reveals one Tg at –76 °C. ..................................58 Figure 2-40 RI trace of targeted 30k PAGE synthesized with BnSAlMe2. The Mn is determined to be 29.6 Kg/mol with Ð = 1.45. The first modal peak is due to aggregation of polymer in presence of Al trace. ..............................................................................................................59 Figure 2-41 1H NMR spectrum of PrSAlMe2.1H NMR (500 MHz, Chloroform-d) δ 2.62 (m, 2H, CH3CH2CH2S-Al(CH3)2), 1.65 (dq, 2H, CH3CH2CH2S-Al(CH3)2), 1.04-0.95 (m, 3H, CH3CH2CH2S-Al(CH3)2), -0.49 (S, 6H, CH3CH2CH2S-Al(CH3)2). ......................................59 Figure 2-42 13C NMR spectrum of PrSAlMe2 13C NMR (126 MHz, Chloroform-d) δ 30.33 CH3CH2CH2S-Al(CH3)2, 25.97 CH3CH2CH2S-Al(CH3)2, 13.15 CH3CH2CH2S-Al(CH3)2, - 9.21 CH3CH2CH2S-Al(CH3)2. ...............................................................................................60 Figure 2-43 1H NMR spectrum of cPenSAlMe2. 1H NMR (500 MHz, Chloroform-d) δ 3.39 – 3.33 (m, 1H, cyclopentane -CH-), 2.10 – 1.99 (m, 2H, cyclopentane -CH2-CH2-), 1.83 – 1.73 (m, 2H, cyclopentane -CH2-CH2-), 1.62–1.53 (m, 4H, cyclopentane -CH2-CH2-), -0.49 (s, 6H, cyclopentane-S-Al(CH3)2)..........................................................................................60 xiv Figure 2-44 1H 13C NMR spectrum of cPenSAlMe2 13C NMR (126 MHz, Chloroform-d) δ 30.33 (cyclopentane -CH-), 25.97 (cyclopentane -CH2-CH2-), 13.15 (cyclopentane -CH2-CH2-), - 9.21 (cyclopentane-S-Al(CH3)2). ...........................................................................................61 Figure 2-45 1H NMR spectrum of ClBnSAlMe2. 1H NMR (500 MHz, Chloroform-d) δ 7.34 – 7.22 (m, 4H, (Cl)PhCH2S-Al(CH3)2), 3.89 (s, 2H, (Cl)PhCH2S-Al(CH3)2), -0.45 (s, 6H, (Cl)PhCH2S-Al(CH3)2). .........................................................................................................61 Figure 2-46 13C NMR spectrum of ClBnSAlMe2. 13C NMR (126 MHz, Chloroform-d) δ 127.50, 126.84 (Cl)PhCH2S-Al(CH3)2, 51.18 (Cl)PhCH2S-Al(CH3)2, 26.37 (Cl)PhCH2S-Al(CH3)2. ................................................................................................................................................62 Figure 2-47 RI trace of targeted 30k PECH synthesized by PrSAlMe2 initiator. The Mn is determined to be 30.2 with Ð = 1.24. ....................................................................................62 Figure 2-48 RI trace of targeted 30k PECH synthesized by cPenSAlMe2 initiator. The Mn is determined to be 29.3 with Ð = 1.25. ....................................................................................63 Figure 2-49 RI trace of targeted 30k PECH synthesized by ClBnSAlMe2 initiator. The Mn is determined to be 30.9 with Ð = 1.28. ....................................................................................63 Figure 2-50 Samples were analyzed by electrospray ionization in a solvent containing ammonium formate to facilitate ionization as ammonium adducts. Panel A shows the positive ion mode ESI spectrum with the inset showing the results of a deconvolution of charge states to show the neutral mass distribution of the polymer sample. Focusing on the higher m/z range where the charge states are lowest (panel B), the neutral mass can easily be calculated. The triply charged ion with m/z 1610.5194 [M+(NH4)3]3+ corresponds to a neutral mass of 4777.4568 (1610.5194 * 3 – 3 * 18.0338) which is consistent with a molecule containing 81 total propylene oxide units and a propylthiol end group (expected mass = 4777.426, 6.4 ppm mass error). The next abundant signal at m/z 1629.8662 corresponds to a neutral mass of 4835.4972, which is 58 Da heavier and represents one additional propylene oxide repeating unit..............................................................................64 Figure 2-51 Samples were analyzed by electrospray ionization in a solvent containing ammonium formate to facilitate ionization as ammonium adducts. Panel A shows the positive ion mode ESI spectrum with the inset showing the results of a deconvolution of charge states to show the neutral mass distribution of the polymer sample. Focusing on the higher m/z range where the charge states are lowest (panel B), the neutral mass can easily be calculated. The doubly charged ion with m/z 1386.0093 [M+(NH4)2]2+ corresponds to a neutral mass of 2735.951 (1386.0093 * 2 – 2 * 18.0338) which is consistent with a molecule containing 45 total propylene oxide units and a BnS end group (expected mass = 2735.919, 11.7 ppm mass error). The next abundant signal at m/z 1415.0305 corresponds to a neutral mass of 2793.9934, which is 58 Da heavier and represents one additional propylene oxide repeating unit...............................................................................................65 Figure 2-52 Samples were analyzed by electrospray ionization in a solvent containing ammonium formate to facilitate ionization as ammonium adducts. Panel A shows the positive ion mode ESI spectrum with the inset showing the results of a deconvolution of xv charge states to show the neutral mass distribution of the polymer sample. Focusing on the higher m/z range where the charge states are lowest (panel B), the neutral mass can easily be calculated. The doubly charged ion with m/z 1896.2792 [M+(NH4)2]2+ corresponds to a neutral mass of 3756.5252 (1896.2964 * 2 – 2 * 18.0338) which is consistent with a molecule containing 62 total propylene oxide units and a ClBnS end group (expected mass = 3756.591, -17.5 ppm mass error). The next abundant signal at m/z 1925.3075 corresponds to a neutral mass of 3814.5474, which is 58 Da heavier and represents one additional propylene oxide repeating unit...............................................................................................66 Figure 2-53 Samples were analyzed by electrospray ionization in a solvent containing ammonium formate to facilitate ionization as ammonium adducts. Panel A shows the positive ion mode ESI spectrum with the inset showing the results of a deconvolution of charge states to show the neutral mass distribution of the polymer sample. Focusing on the higher m/z range where the charge states are lowest (panel B), the neutral mass can easily be calculated. The doubly charged ion with m/z 1897.3320 [M+(NH4)2]2+ corresponds to a neutral mass of 3758.5964 (1897.3320 * 2 – 2 * 18.0338) which is consistent with a molecule containing 63 total propylene oxide units and a cyPenS end group (expected mass = 3758.688, 24.4 ppm mass error). The next abundant signal at m/z 1926.3486 corresponds to a neutral mass of 3816.6296, which is 58 Da heavier and represents one additional propylene oxide repeating unit...............................................................................................67 Figure 2-54 MALDI-TOF analysis of 5kg/mol PPO with 4 different initiators (A). The X-axis is the same for all four plots and is the mass range (in m/z). The mass distribution with MALDI-TOF matches with ESI-MS data. (B) Expanded prospective of MALDI-TOF. The difference between each subsequent peak is equal to mass of one propylene oxide. The order of polymers are the same for A and B. .........................................................................68 Figure 2-55 Fit of BSL to the conversion as a function of the normalized molar concentration of each monomer ([M]/[M]0). From BSL, the reactivity ratios for ECH (rECH) and PO (rPO) were determined to be rECH = 2.56 ± 0.29 and rPO = 0.44 ± 0.03, which suggests a gradient copolymer with ECH preferentially adding over PO. ............................................................69 Figure 2-56 600 MHz 2D Figure 2-57 DOSY NMR spectra obtained at 298 K in Chloroform-d solution of the PECH-b-PPO. 1H NMR (600 MHz, Chloroform-d) δ 3.70 (bm, (–O–CH2– CH (CH2–Cl)–O– and –O–CH2 (CH3)-O-), 1.13 (m, -CH3). .................................................69 Figure 2-58 13C NMR spectroscopy of P(MMA-b-ECH). 13C NMR (126 MHz, cdcl3) δ 178.12- 177.00 (-CH2-C(CH3)(COOCH3)-), 81.58-67.83 (–O–CH2–CH(CH2–Cl)–O–), 51.84 (-CH2- C(CH3)(COOCH3)-), 44.89 (-CH2-C(CH3)(COOCH3)-), 45.93-45.32 (H-T diads, –O–CH2– CH(CH2–Cl)–O–), 44.89-44.54 (-CH2-C(CH3)(COOCH3)-), 43.87-42.63 (H-H and T-T diads, –O–CH2–CH(CH2–Cl)–O–), 25.07 (–O–CH2–CH(CH2–Cl)–O–), 18.70-16.41(-CH2- C(CH3)(COOCH3)-). Different regiostructures of ECH monomer in the PECH block can be seen in this spectrum due to head-to-tail, head-to-head, and tail-to-tail diads. In H-T diads, γ gauche effect on the carbon of CH2 (–O–CH2–CH(CH2–Cl)–O–), cause related signals to be shifted and this is why two sets of peaks are observed in the 13C NMR spectrum. Peaks at 29.77, 19.78, and 9.42 are corresponded to hexanes. ............................................................70 xvi Figure 2-59 600 MHz 2D DOSY NMR spectra obtained at 298 K in Chloroform-d solution of the PMMA-b-PECH. 1H NMR (600 MHz, Chloroform-d) δ 3.99–3.62 (bm, - OCH2CH(CH2Cl)O-), 3.63-3.56 (bm,-CH2C(CH3)(COOCH3)-), 2.19-1.66 (bm, - CH2C(CH3)(COOCH3)-). .......................................................................................................70 Figure 2-60 1H NMR spectroscopy of thiol end-terminated PMMA without AlMe3, in the presence of ECH and NAl, at 50°C after 7 days. 1H NMR (500 MHz, Chloroform-d) δ 3.52-3.48 (bm-CH2-C(CH3)(COOCH3)-), 3.47–3.42 (d, J = 5.4 Hz, 2H, ECH, OCH2CH(CH2Cl)), 3.22 (tdd, J = 5.4, 3.9, 2.5 Hz, 1H, ECH, OCH2CH(CH2Cl)), 2.88 (dd, J = 4.8, 3.9 Hz, 1H, ECH, OCH2CH(CH2Cl)), 2.67 (dd, J = 4.8, 2.5 Hz, 1H, ECH OCH2CH(CH2Cl)), 2.03-1.59 (bm,-CH2-C(CH3)(COOCH3)-), 1.31-0.72 (bm -CH2- C(CH3)(COOCH3)-). The only NAl peaks correspond to Me groups on Al below zero but Et groups are overlapping with other peaks and cannot be specified. ........................................71 Figure 2-61 DSC analysis of P(MMA-b-ECH). The data from the second heating curve were collected which reveals a broad Tg centered at 0 °C. .............................................................71 Figure 2-62 13C NMR spectroscopy of P(styrene-b-ECH) which is consistent with a regioregular PECH block. 13C NMR (126 MHz, cdcl3) δ 145.21(-CH2-CH(Ph ,C)-) 128.00-127.11 (- CH2-CH(Ph ,CH)-), 125.68-125.25 (-CH2-CH(Ph, CH)-), 78.97 (–O–CH2–CH(CH2Cl)–O–), 69.33(–O–CH2–CH(CH2Cl)–O–), 43.57 (–O–CH2–CH(CH2Cl)–O–), 44.46(-CH2-CH(Ph)-), 40.21(-CH2-CH(Ph)-) 29.59(–CH2–Cl). ................................................................................72 Figure 2-63 DSC analysis of P(styrene-b-ECH). The data from the second heating curve were collected which reveals two Tg, one at –27 ºC corresponding to the PECH block and one at 74 ºC corresponding to the PS block. ....................................................................................72 Figure 2-64 600 MHz 2D DOSY NMR spectra obtained at 298 K in Chloroform-d solution of the PS-b-PECH. 1H NMR (600 MHz, Chloroform-d) δ 7.25- 6.30 (bm, -CH2-CH(Ph)-), 3.77- 3.49 (broad m, -OCH2CH(CH2Cl)O-), 2.07-1.10 (bm, -CH2-CH(Ph)-). ......................73 Figure 2-65 1H NMR spectroscopy of (P(styrene-b-ECH). 1H NMR (500 MHz, cdcl3) δ 7.25-6.30 (bm, -CH2-CH(Ph)-), 3.77- 3.49 (bm, -OCH2CH(CH2Cl)O-), 2.07-1.10 (bm, -CH2-CH(Ph)- ). .............................................................................................................................................73 Figure 2-66 1H NMR spectroscopy of targeted 30K PECH with BnSAlMe2 initiator. 1H NMR (500 MHz, Chloroform-d) δ 3.83-3.39 (bm, -OCH2CH(CH2Cl)O-). ....................................74 Figure 2-67 13C NMR spectroscopy of targeted 30K PECH with BnSAlMe2. 13C NMR (126 MHz, cdcl3) δ 79.18-79.09 (–O–CH2–CH(CH2-Cl)–O–), 69.80 (–O–CH2–CH(CH2-Cl)– O– m), 69.50 (–O–CH2–CH(CH2-Cl)–O– rrm or mrr)), 43.80 (–CH2–Cl). ..........................74 Figure 2-68 1H NMR spectroscopy of targeted 30K PPO with BnSAlMe2 initiator. 1H NMR (500 MHz, Chloroform-d) δ 3.80 – 3.17 (bm, –O–CH2–CH(CH3)–O–), 1.12 (m, -CH3). ............75 Figure 2-69 13C NMR spectroscopy of targeted 30K PPO with BnSAlMe2 initiator. 13C NMR (126 MHz, cdcl3) δ 75.89 (–O–CH2–CH(CH3)–O–, mm), 75.68 (–O–CH2–CH(CH3)–O– xvii , mr + rm), 75.48 (–O–CH2–CH(CH3)–O–, rr), 73.71 (–O–CH2–CH(CH3)–O–, m), 73.16 (– O–CH2–CH(CH3)–O–, rrm or mrr), 17.81 (–CH3). ...............................................................75 Figure 2-70 1H NMR spectroscopy of targeted 30K PBO with BnSAlMe2 initiator. 1H NMR (500 MHz, Chloroform-d) δ 3.68 – 3.25 (bm, –O–CH2–CH(CH2–CH3)–O–), 1.68 – 1.37 (m, CH2–CH3), 0.91 (t, –CH2–CH3). ............................................................................................76 Figure 2-71 13C NMR spectroscopy of targeted 30K PBO with BnSAlMe2 initiator. 13C NMR (126 MHz, cdcl3) δ 80.84-80.42 (–O–CH2–CH(CH2–CH3)–O–), 72.37 (–O–CH2–CH(CH2– CH3)–O–, m), 71.53 (–O–CH2–CH(CH2–CH3)–O–, rrm or mrr)), 24.72 (–CH2–CH3), 9.76 (–CH3). ...................................................................................................................................76 Figure 2-72 1H NMR spectroscopy of targeted 30K PECH with PrSAlMe2 initiator. 1H NMR (500 MHz, Methylene Chloride-d2) δ 3.80 – 3.51 (bm, -OCH2CH(CH2Cl)O-). ...................77 Figure 2-73 1H NMR spectroscopy of targeted 30K PECH with ClBnSAlMe2 initiator. 1H NMR (500 MHz, Methylene Chloride-d2) δ 3.80 – 3.51 (bm, -OCH2CH(CH2Cl)O-). ...................77 Figure 2-74 1H NMR spectroscopy of targeted 30K PECH with cPenSAlMe2 initiator. 1H NMR (500 MHz, Methylene Chloride-d2) δ 3.80 – 3.51 (bm, -OCH2CH(CH2Cl)O-). ...................78 Figure 2-75 1H NMR spectroscopy of P(MMA-b-ECH). 1H NMR (500 MHz, Methylene Chloride-d2) δ 3.99–3.62 (bm, -OCH2CH(CH2Cl)O-), 3.63-3.56 (bm,- CH2C(CH3)(COOCH3)-), 2.19-1.66 (bm, -CH2C(CH3)(COOCH3)-), 1.67 – 0.58 (bm, - CH2C(CH3)(COOCH3)-). .......................................................................................................78 Figure 2-76 DSC analysis of P(PO-grad-ECH). The data from the second heating curve were collected which reveals one Tg, one at -41 ºC........................................................................79 Figure 2-77 DSC analysis of P(ECH-b-PO). The data from the second heating curve were collected which reveals two Tg, one at –30 ºC corresponding to the PECH block and one at - 67 ºC corresponding to the PO block. ....................................................................................79 Figure 2-78 RI trace of targeted P(ECH-grad-PO). The Mn is determined to be 29.0 kg/mol with Ð = 1.28. ................................................................................................................................80 Figure 2-79 RI trace of targeted P(ECH-b-PO). The Mn is determined to be 33.4 kg/mol with Ð = 1.27……………………………………………………………………………………...… 80 Figure 3-1 a) Plot of Mn (left axis, blue circles) and Đ (right axis, red triangles) as a function of the PS to BnSAlMe2 ratio ([PS]/[BnSAlMe2]). Mn increased linearly at increasing ratio of propylene sulfide with Đ < 1.4. b) SEC traces for PPS with different targeted molecular weights. blue, for 15 kg/mol targeted PPS, the Mn is determined to be 14.8 kg/mol with Đ of 1.20. purple, for 30 kg/mol targeted PPS, the Mn is determined to be 33.7 kg/mol with Đ of 1.21. green, for 50 kg/mol targeted PPS, the Mn is determined to be 47.1 kg/mol with Đ of 1.32. pink, for 70 kg/mol targeted PPS, the Mn is determined to be 68.4 kg/mol with Đ of 1.35. red, for 100 kg/mol targeted PPS, the Mn is determined to be 98.2 kg/mol with Đ of 1.24.......................................................................................................................................103 xviii Figure 3-2 . a) Plot of normalized PS concentration over time with BnSAlMe2 initiator and NAl catalyst (green line), plot of normalized PS concentration over time with only BnSAlMe2 initiator (blue line), and plot of normalized PS concentration over time with only NAl catalyst (red line), for polymerization of targeted 20 Kg/mol PS. Monomer concentration was monitored via 1H NMR spectroscopy, and the rate of reactions calculated based on it. The rates are as followings from the slope of each plot, kobs = (1.70 ± 0.19) × 10-3 s -1 with both catalyst and initiator, kobs = 1.32 ± 0.04 × 10-5 s -1 with only catalyst). b) SEC traces of (green) targeted 20 Kg/mol PPS with both the catalyst and the initiator, (red) 20 Kg/mol PPS with only the catalyst, and (blue) 20 Kg/mol PPS with only the initiator. With both the catalyst and the initiator the Mn is close to the targeted MW, Mn = 21.2 Kg/mol and PDI of 1.23. However, by using only the catalyst and only the initiator we lose the control over the MW. In a red SEC trace (only catalyst), the Mn = 47.6 Kg/mol and PDI of 1.31 and blue SEC trace (only initiator) has the Mn = 45.3 Kg/mol with PDI of 1.30. ..............................105 Figure 3-3 Total conversion as a function of normalized monomer concentration for (a) poly(PO-stat-PS) and (b) poly(ECH-stat-PS). A fit to this data results in the reactivity ratios for each monomer. The reactivity ratios of the monomer pairs are determined to be rPO= 0.905 ± 0.082 and rPS = 1.138 ± 0.108 for poly(PO-stat-PS) and rECH = 0.906 ± 0.043 and rPS = 1.191 ± 0.059 for poly(ECH-stat-PS)..........................................................................107 Figure 3-4 DOSY NMR of statistical copolymers (a and b) and block copolymers (c and d). The DOSY spectra reveal that there is only one diffusing species for both the statistical and block copolymers, indicating that both monomers share a common backbone...................108 Figure 3-5 (a) Chemical reaction scheme for the synthesis of d-H initiator followed by PPS synthesis from d-H initiator and copolymerization form it. (b) chemical reaction scheme for the synthesis of t-H initiator followed by PPS synthesis from t-H initiator and copolymerization form it......................................................................................................111 Figure 3-6 (top) Reaction scheme for the d-h or PrSAlMe2 initiated polymerization of PS. (bottom) Plot of normalized PS concentration over time with PrSAlMe2 initiator and NAl catalyst (red line) and plot of normalized PS concentration over time with d-H initiator and NAl catalyst (blue line). Monomer concentration was monitored via 1H NMR spectroscopy, and the rate of reactions calculated. From the slope of the fit, the rate constant was calculated to be kobs = (7.11 ± 0.59) × 10−5 s −1 (PrSAlMe2) and (15.9 ± 0.86) × 10-5 s −1 (d- H). This experiment shows that the rate of polymerization is as twice as fast for d-H initiator in compare with PrSAlMe2, proving that the initiation is happening from both heads of the initiator. ................................................................................................................................112 Figure 3-7 DOSY NMR of (a) poly d-H (PS-b-PO) and (b) poly t-h (PS-b-PO). The results suggest both the epoxide and PS are in the same polymer chain.........................................113 Figure 3-8 a) Scheme for synthesis of PEG-b-PPS. b) DOSY NMR PEG-b-PPS c) SEC traces (LS) of PEG (right, blue curve) and PEG-b-PPS (left, red curve). The Mn and Đ were determined to be, respectively, 5.5 kg/mol and 1.24 (PEG) and 22.2 kg/mol and 1.18 PEG- b-PPS....................................................................................................................................115 xix Figure 3-9 1H NMR and 13C NMR spectra of BnSPPS. a) 1H NMR (500 MHz, CDCl3) δ 2.91- 2.80 (m, −S−CH2−CH(CH3)−S−), 2.65-2.58 (m, −S−CH2−CH(CH3)−S−), 1.39 (m, −S−CH2−CH(CH3)−S−). b) 13C NMR (126 MHz, CDCl3) δ 41.14 (−S−CH2−CH(CH3)−S), 38.18 (−S−CH2−CH(CH3)−S), 20.63 (−S−CH2−CH(CH3)−S−). ........................................116 Figure 3-10 DSC analysis of targeted 30k PPS with BnSAlMe2. The data from the second heating curve were collected which reveals one Tg at -41 °C. ............................................116 Figure 3-11 EIS-MS characterization of the targeted 5kg/mol PPS. ...........................................117 Figure 3-12 DSC analysis of (a) poly(ECH-stat-PS) and (b) poly(PO-stat-PS). The data from the second heating curve were collected which reveals one Tg at -40 °C for poly(ECH-stat-PS) and one Tg at -46 °C for poly(PO-stat-PS). .........................................................................117 Figure 3-13 SEC traces of (a) poly(ECH-stat-PS) and (b) poly(PO-stat-PS). For poly(ECH-stat- PS), the Mn is determined to be 29.2 kg/mol with Ð of 1.56. And for or poly(PO-stat-PS), the Mn is determined to be 30.8 kg/mol with Ð of 1.21.......................................................118 Figure 3-14 SEC traces of (a) P(ECH-b-PS) and (b) P(PO-b-PS). For poly(ECH-b-PS), the Mn is determined to be 29.9 kg/mol with Ð of 1.74. And for poly(PO-b-PS), the Mn is determined to be 29.6 kg/mol with Ð of 1.32. ........................................................................................118 Figure 3-15 DSC analysis of (a) poly(ECH-b-PS) and (b) poly(PO-b-PS). The data from the second heating curve were collected which reveals two Tg at -40 °C and -29 °C for PPS and PECH blocks, respectively. For poly(PO-b-PS) two Tg at -70 °C and -47 °C for PPO and PPS blocks, respectively. .....................................................................................................119 Figure 3-16 SAXS data for the synthesized copolymers. The block copolymer and statistical copolymer all have very weak phase separation as indicated by the broad shoulder peak at Q~0.02 Å − 1 .forpoly(ECH-b-S),Q~0.07 Å − 1 forpoly(PO-stat-PS),andQ~0.033 Å − 1 .for poly(PO-b-PS)......................................................................................................................119 Figure 3-17 1H NMR and 13C NMR spectra of BnOPPS. a) 1H NMR (500 MHz, CDCl3) δ 2.91- 2.80 (m, −S−CH2−CH(CH3)−S−), 2.65-2.58 (m, −S−CH2−CH(CH3)−S−), 1.39 (m, −S−CH2−CH(CH3)−S−). b) 13C NMR (126 MHz, CDCl3) δ 41.14 (−S−CH2−CH(CH3)−S), 38.18 (−S−CH2−CH(CH3)−S), 20.63 (−S−CH2−CH(CH3)−S−). ........................................120 Figure 3-18 SEC trace of targeted 30k BnOPPS. the Mn is determined to be 31.6 kg/mol with Ð of 1.32. .................................................................................................................................120 Figure 3-19 DSC trace of BnOPPS. The data from the second heating curve were collected which reveals one Tg at -42 °C. ...........................................................................................121 Figure 3-20 1H NMR and 13C NMR spectra of d-H initiator. (a) 1H NMR (500 MHz, CDCl3) δ 1.7-3.41 (b, 2(CH3)Al-CH2CH2CH2S-Al(CH3)2, 6H), -0.92-0.24 (b, 2(CH3)Al- CH2CH2CH2S-Al(CH3)2, 6H). Peaks at 0.88 and 1.26 in 1H NMR spectrum, are corresponded to hexane. (b) 13C NMR (126 MHz, CDCl3) δ 29.65 2(CH3)Al-CH2CH2CH2S- Al(CH3)2, 27.73 2(CH3)Al-CH2CH2CH2S-Al(CH3)2, 11.312(CH3)Al-CH2CH2CH2S- xx Al(CH3)2. Peaks at 14.14, 22.53, and 33.8 in 13C NMR spectra are corresponded to hexane. Broadening effects of the peaks are observed due to oligomerization in 1H NMR spectrum. ..............................................................................................................................................121 Figure 3-211H–1H correlation spectrum for d-H initiator. Only one half of the spectrum is shown for clarity. The spectrum suggests that there are three distinct species: single d-H initiator, dimerized, and trimerized form of d-H initiator, connect the peaks on the X- and Y-axes that are correlated with one another. The scheme below the diagonal represents the chemical structure of the species present. The peak assignments for the spectra are labeled here. Detailed peak assignments are listed in the methods section. .............................................122 Figure 3-22 1H NMR and 13C NMR spectra of t-H initiator. a) 1H NMR (500 MHz, CDCl3) δ 4.21-1.42 (24 H, -[C-CH2COOCH2CH2S-Al(CH3)2]4-), -0.36 to -1.09 (24 H, -[C- CH2COOCH2CH2S-Al(CH3)2]4-). b) 13C NMR (126 MHz, CDCl3) 198.53 -[C- CH2COOCH2CH2S-Al(CH3)2]4-), 42.42-[C-CH2COOCH2CH2S-Al(CH3)2]4-), 31.61-[C- CH2COOCH2CH2S-Al(CH3)2]4-), 29.61, -[C-CH2COOCH2CH2S-Al(CH3)2]4-), 25.10 -[C- CH2COOCH2CH2S-Al(CH3)2]4-), 9.81-[C-CH2COOCH2CH2S-Al(CH3)2]4-).Peaks at 14.14, 22.35, and 31.87 in 13C NMR spectra are corresponded to hexane. Broadening effects of the peaks are observed due to oligomerization in 1H NMR spectrum. ......................................123 Figure 3-23 SEC traces of (a) d-h PPS and (b) t-H PPS. For d-h PPS), the Mn is determined to be 34.5 kg/mol with Ð of 1.37. And for d-h PPS, the Mn is determined to be 88.7 kg/mol with Ð of 1.51. .............................................................................................................................123 Figure 3-24 1H NMR and 13C NMR spectrum of d-H poly(PS-b-PO). (a) 1H NMR (500 MHz, CDCl3) δ 3.72−3.2 (bm, −O−CH2−CH(CH3)−O−), 2.91-2.54 (bm, −S−CH2−CH(CH3)−S−), 1.31 (m, −S−CH2−CH(CH3)−S−), 1.11 (m, −O−CH2−CH(CH3)−O−). (b) 13C NMR (126 MHz, CDCl3) δ 75.26 (−O−CH2−CH(CH3)−O−), 73.35 (−O−CH2−CH(CH3)−O−), 40.6 (−S−CH2−CH(CH3)−S−), 37.9 (−S−CH2−CH(CH3)−S−), 20.98 (−S−CH2−CH(CH3)−S−), 16.83 (−O−CH2−CH(CH3)−O−). .........................................................................................124 Figure 3-25 1H NMR and 13C NMR spectrum of t-H poly(PS-b-PO). (a) 1H NMR (500 MHz, CDCl3) δ 2.97-2.81 (m, −S−CH2−CH(CH3)−S−), 2.71-2.57 (m, −S−CH2−CH(CH3)−S−), 1.40 (m, −S−CH2−CH(CH3)−S−). (b) 13C NMR (126 MHz, CDCl3) δ 75.26 (−O−CH2−CH(CH3)−O−), 73.35 (−O−CH2−CH(CH3)−O−), 40.6 (−S−CH2−CH(CH3)−S−), 37.9 (−S−CH2−CH(CH3)−S−), 20.98 (−S−CH2−CH(CH3)−S−), 16.83 (−O−CH2−CH(CH3)−O−). ...................................................................................................124 Figure 3-26 SEC traces of (a) d-H poly(PS-b-PO) and (b) t-H poly(PS-b-PO). For d-H poly(PS- b-PO), the Mn is determined to be 29.8 kg/mol with Ð of 1.39. And for t-H poly(PS-b-PO, the Mn is determined to be 84.0 kg/mol with Ð of 1.09.......................................................125 Figure 3-27 DSC analysis of (a) d-H poly(PS-b-PO) and (b) t-H poly(PS-b-PO). The data from the second heating curve were collected which reveals two Tgs at -66 °C and -45 for d-H poly(PS-b-PO) corresponded to PECH and PPS blocks. For t-H poly(PS-b-PO), DSC reveals two Tgs at -65 °C and -47 for d-H poly(PS-b-PO) corresponded to PECH and PPS blocks. ..................................................................................................................................125 xxi Figure 3-28 SAXS data for the synthesized copolymers. The phase behavior of the d-H poly(PS- b-PO) and t-H poly(PS-b-PO) are more obvious at Q~0.018 Å − 1 . and Q~0.022 Å − 1 .. .......................................................................................................................................126 Figure 3-29 1H NMR and 13C NMR spectrum of PEG-b-PPS a) 1H NMR (500 MHz, CDCl3) δ 3.65-3.48 (b, −O−CH2−CH2−O−), 2.92-2.78 80 (m, −S−CH2−CH(CH3)−S−), 2.66-2.59 (m, −S−CH2−CH(CH3)−S−), 1.38 (m, −S−CH2−CH(CH3)−S−). b) 13C NMR (126 MHz, cdcl3) δ 70.55 (−O−CH2−CH2−O−), 41.26 (−S−CH2−CH(CH3)−S−), 38.38 (−S−CH2−CH(CH3)−S−), 20.79 (−S−CH2−CH(CH3)−S−). ................................................126 Figure 3-30 DSC analysis of PEG-b-PPS. The data from the second heating curve were collected which reveals one Tg at -41 °C for PPS block and another Tm at 58 °C. .............................127 Figure 3-31 1H NMR and 13C NMR spectrum of BnSAlMe2. a) 1H NMR (500 MHz, CDCl3) δ 7.38 – 7.21 (m, 5H, PhCH2S-Al(CH3)2), 3.91 (s, 2H, PhCH2S-Al(CH3)2), -0.43 (s, 6H, PhCH2SAl(CH3)2). b) 13C NMR (126 MHz, CDCl3) δ141.46, 128.56, 127.97, 126.89 (PhCH2S-Al(CH3)2, 32.00 (PhCH2S-Al(CH3)2), 28.78 (PhCH2S-Al(CH3)2). .....................127 Figure 3-32 1H NMR and 13C NMR spectrum of PrSAlMe2. a) 1H NMR (500 MHz, CDCl3) δ 2.62 (m, 2H, CH3CH2CH2S-Al(CH3)2), 1.65 (dq, 2H, CH3CH2CH2S-Al(CH3)2), 1.04-0.95 (m, 3H, CH3CH2CH2S-Al(CH3)2), -0.49 (S, 6H, CH3CH2CH2S-Al(CH3)2). b) 13C NMR (126 MHz, CDCl3) δ 30.33 (CH3CH2CH2S-Al(CH3)2), 25.97 (CH3CH2CH2S-Al(CH3)2), 13.15 (CH3CH2CH2S-Al(CH3)2), -9.21 (CH3CH2CH2S-Al(CH3)2). ....................................128 Figure 3-33 1H NMR and 13C NMR spectra of poly(ECH-stat-PS). a) 1H NMR (500 MHz, CDCl3) δ 3.80-3.29 (bm, −O−CH2−CH(CH2Cl)−O−), 3.16-2.51 (bm, −S−CH2−CH(CH3)−S−), 1.63-1.54 (m, −O−CH2−CH(CH2Cl)−O− and −S−CH2−CH(CH3)−S−), 1.40-1.33 (m, −S−CH2−CH(CH3)−S−), 1.37-1.17 O−CH2−CH(CH2Cl)−O− and −S−CH2−CH(CH3)−S−). b) 13C NMR (126 MHz, CDCl3) 79.37(−O−CH2−CH(CH2Cl)−O−), 75.58 (−O−CH2−CH(CH2Cl)−O−), 44.72 (−O−CH2−CH(CH2Cl)−O−), 41.16 (−S−CH2−CH(CH3)−S−) , 38.39 (−O−CH2−CH(CH2Cl)−O− and −S−CH2−CH(CH3)−S−), 20.63 (−S−CH2−CH(CH3)−S−), 20.85 (−O−CH2−CH(CH2Cl)−O− and −S−CH2−CH(CH3)−S−), 18.59 (−S−CH2−CH(CH3)−S−). ..............................................128 Figure 3-34 1H NMR and 13C NMR spectrum of poly(PO-stat-PS). (a) 1H NMR (500 MHz, CDCl3) δ 3.83-3.24 (bm, −O−CH2−CH(CH3)−O−), 3.10-2.41 (bm, −S−CH2−CH(CH3)−S−, −O−CH2−CH(CH3)−O− and −S−CH2−CH(CH3)−S−), 1.32-1.42 (m, −S−CH2−CH(CH3)−S−), 1.30-1.19 (bm, −O−CH2−CH(CH3)−O− and −S−CH2−CH(CH3)−S−), 1.17-1.04 (m, −O−CH2−CH(CH3)−O−). (b) 13C NMR (126 MHz, CDCl3) δ75.85 (−O−CH2−CH(CH3)−O−), 73.34 (−O−CH2−CH(CH3)−O−), 72.90 (−O−CH2−CH(CH3)−O− and −S−CH2−CH(CH3)−S), 41.23 (−S−CH2−CH(CH3)−S−), 38.10 (−S−CH2−CH(CH3)−S−), 20.8 (−O−CH2−CH(CH3)−O− and −S−CH2−CH(CH3)−S), 19.3 (−S−CH2−CH(CH3)−S−), 17.4 (−O−CH2−CH(CH3)−O−). ........................................129 Figure 3-35 1H NMR and 13C NMR spectrum of poly(ECH-b-PS). (a) 1H NMR (500 MHz, CDCl3) δ 3.77-3.55 (bm, −O−CH2−CH(CH2Cl)−O−), 2.91-2.80 (m, xxii −S−CH2−CH(CH3)−S−), 2.65-2.58 (m, −S−CH2−CH(CH3)−S−), 1.35 (m, −S−CH2−CH(CH3)−S−). (b) 13C NMR (126 MHz, CDCl3) δ 78.97 (−O−CH2−CH(CH2Cl)−O−), 69.51 (−O−CH2−CH(CH2Cl)−O), 43.47 (−O−CH2−CH(CH2Cl)−O−), 41.17 (−S−CH2−CH(CH3)−S−), 38.24 (−S−CH2−CH(CH3)−S−), 20.86 (−S−CH2−CH(CH3)−S−). ................................................129 Figure 3-36 1H NMR and 13C NMR spectrum of poly(PO-b-PS). (a) 1H NMR (500 MHz, CDCl3) δ 3.72−3.2 (bm, −O−CH2−CH(CH3)−O−), 2.91-2.54 (bm, −S−CH2−CH(CH3)−S−), 1.31 (m, −S−CH2−CH(CH3)−S−), 1.11 (m, −O−CH2−CH(CH3)−O−). (b) 13C NMR (126 MHz, CDCl3) δ 75.26 (−O−CH2−CH(CH3)−O−), 73.35 (−O−CH2−CH(CH3)−O−), 40.6 (−S−CH2−CH(CH3)−S−), 37.9 (−S−CH2−CH(CH3)−S−), 20.98 (−S−CH2−CH(CH3)−S−), 16.83 (−O−CH2−CH(CH3)−O−). ..............................................130 Figure 3-37 1H NMR and 13C NMR spectrum of d-H PPS. (a) 1H NMR (500 MHz, CDCl3) δ 2.91-2.80 (m, −S−CH2−CH(CH3)−S−), 2.65-2.58 (m, −S−CH2−CH(CH3)−S−), 1.39 (m, −S−CH2−CH(CH3)−S−). (b) 13C NMR (126 MHz, CDCl3) δ13C NMR (126 MHz, CDCl3) δ 41.14 (−S−CH2−CH(CH3)−S), 38.18 (−S−CH2−CH(CH3)−S), 20.63 (−S−CH2−CH(CH3)−S−). ....................................................................................................130 Figure 3-38 1H NMR and 13C NMR spectrum of t-H PPS. (a) 1H NMR (500 MHz, CDCl3) δ 2.91-2.80 (m, −S−CH2−CH(CH3)−S−), 2.65-2.58 (m, −S−CH2−CH(CH3)−S−), 1.39 (m, −S−CH2−CH(CH3)−S−). (b) 13C NMR (126 MHz, CDCl3) δ 13C NMR (126 MHz, CDCl3) δ 41.14 (−S−CH2−CH(CH3)−S), 38.18 (−S−CH2−CH(CH3)−S), 20.63 (−S−CH2−CH(CH3)−S−). ....................................................................................................131 Figure 3-39 DSC analysis of (a) d-H PPS and (b) t-H PPS. The data from the second heating curve were collected which reveals one Tg at -41 °C for both these. ..................................131 Figure 3-40 1H NMR and 13C NMR spectrum of BnOAlMe2. a) 1H NMR (500 MHz, CDCl3) δ 7.47 – 7.38 (m, 5H, PhCH2O-Al(CH3)2), 3.33 (s, 2H, PhCH2O-Al(CH3)2), 0.15 - -0.6 (s, 6H, PhCH2OAl(CH3)2). b) 13C NMR (126 MHz, CDCl3) δ138.64, 137.57, 130.04, 126.69 (PhCH2O-Al(CH3)2, 50.76 (PhCH2O-Al(CH3)2), -7.71 (PhCH2O-Al(CH3)2). ....................132 Figure 4-1 FTIR spectrum of PPO-PECH (yellow color), PPO-PECH-TEA (green color), PPO- PECH-DEA (red color), PPO-PECH-TMA (blue color), and PPO-PECH-DMA (purple color). The C-N characteristic starching frequency of amin modified membranes are represented by a vertical line that is not presented in the pristine membrane. ....................148 Figure 4-2 DSC measurements (a) and TGA characterization of (b) PPO-PECH (yellow color), and amine modified membranes PPO-PECH-TEA (green color), PPO-PECH-DEA (red color), PPO-PECH-TMA (blue color), and PPO-PECH-DMA (purple color). ...................150 Figure 4-3 conductivity measurement of PPO-PECH and amine modified membranes PPO- PECH-TEA, PPO-PECH-DEA, PPO-PECH-TMA, and PPO-PECH-DMA. .....................152 Figure 4-4 rheology measurements of PPO-PECH and amine tethered membranes PPO-PECH- TEA, PPO-PECH-DEA, PPO-PECH-TMA, and PPO-PECH-DMA. .................................152 xxiii Figure 4-5 1H NMR and 13C NMR spectra of t-H initiator. a) 1H NMR (500 MHz, CDCl3) δ 4.21-1.42 (24 H, -[C-CH2COOCH2CH2S-Al(CH3)2]4-), -0.36 to -1.09 (24 H, -[C- CH2COOCH2CH2S-Al(CH3)2]4-). b) 13C NMR (126 MHz, CDCl3) 198.53 -[C- CH2COOCH2CH2S-Al(CH3)2]4-), 42.42-[C-CH2COOCH2CH2S-Al(CH3)2]4-), 31.61-[C- CH2COOCH2CH2S-Al(CH3)2]4-), 29.61, -[C-CH2COOCH2CH2S-Al(CH3)2]4-), 25.10 -[C- CH2COOCH2CH2S-Al(CH3)2]4-), 9.81-[C-CH2COOCH2CH2S-Al(CH3)2]4-). Peaks at 14.14, 22.35, and 31.87 in 13C NMR spectra are corresponded to hexane. Broadening effects of the peaks are observed due to oligomerization in 1H NMR spectrum. ......................................153 Figure 4-6 DSC measurement of star shape membrane with different ratios of PO:ECH ranging from 50:50 to 90:10. ............................................................................................................154 Figure 4-7 1H NMR spectroscopy of the polymeric solution with the ratio of PPO-PECH with ratio of PO:ECH (90:10). All the corresponding peaks are assigned. .................................154 Figure 4-8 water uptake and the swelling ratio of PPO-PECH and amine modified membranes PPO-PECH-TEA, PPO-PECH-DEA, PPO-PECH-TMA, and PPO-PECH-DMA. Red circle is corresponded to water uptake (WU) and blue dimond is corresponded to welling ratio (SR). .....................................................................................................................................155 Figure 5-1 FT-IR spectra of the copolymer membranes: pristine membrane PPO-PECH (red color) and amine modified membranes PPO-PECH-MeA (green color), PPO-PECH-nBuA (purple color), PPO-PECH-isoBuA (yellow line), and PPO-PECH-tBuA(wine color). Amine modified membranes are showing the characteristic peak of C-N at 1640 cm-1 (dashed line). ........................................................................................................................169 Figure 5-2 DSC measurements (a) and TGA characterization of (b) PPO-PECH (red color), and amine modified membranes PPO-PECH-MeA (green color), PPO-PECH-nBuA (purple color), PPO-PECH-isoBuA (yellow color), and PPO-PECH-tBuA(wine color). ...............170 Figure 5-3 the plateau modulus (G′) of the cross-linked membranes (PPO-PECH) and amine modified membranes PPO-PECH-MeA, PPO-PECH-nBuA, PPO-PECH-isoBuA, and PPO- PECH-tBuA. ........................................................................................................................171 Figure 5-4 1 H NMR and 13C NMR spectroscopy of MOB. 1 H NMR (CDCl3, 500 MHz) δ: -0.95 ([(CH3)2NCH2CH2(μ2- O)Al(CH3)2·Al(CH3)3], -0.74 3.46 ([(CH3)2NCH2CH2(μ2- O)Al(CH3)2·Al(CH3)3], 2.58 (s, CH3−N−), 2.92 (t, −N−CH2−CH2−O−), 3.98 (t, −N−CH2−CH2− O−). 13C NMR (CDCl3, 100 MHz) δ: 45.2 ([(CH3)2NCH2CH2(μ2- O)Al(CH3)2·Al(CH3)3], 55.11 (CH3−N−), 58.84 (−N−CH2−CH2−O−), 67.30 (−N−CH2−CH2−O−). ...........................................................................................................172 Figure 5-5 1H NMR spectroscopy of the polymeric solution with the ratio of PPO-PECH with ratio of PO:ECH (80:20). .....................................................................................................173 xxiv LIST OF SCHEMES Scheme 1-2 a) Using SAl for episulfide polymerization and copolymerization. b) general scheme for synthesis of ABA terblcok and star shape copolymer...................................................... 6 Scheme 1-3 chemical structure of star shape membrane. .............................................................. 7 Scheme 1-4 general of scheme of amine modified membranes. ................................................... 8 Scheme 2-1 SAl-initiated polymerization of ECH. ..................................................................... 31 Scheme 3-1 Data exclusion criteria with number of included and excluded subjects and measurement sets. .............................................................................................................. 101 Scheme 3-2 Statistical (a) and block (b) copolymerization of PS and epoxides. ...................... 106 Scheme 3-3 BnOAlMe2 initiated PS polymerization. ............................................................... 110 Scheme 4-1 Synthesis of cross-linked polyether membrane using the star shape initiator (PPO- PECH) ................................................................................................................................ 144 Scheme 4-2 Synthesis of amine modified cross-linked PPO-PECH Membranes Using the t-H Initiator. Image of the representative cross-linked polyether membrane demonstrating optical transparency and flexibility is presented. ............................................................... 146 Scheme 5-1 a) Synthesis of Amine Modified Cross-linked Polyether Membranes Using the MOB Initiator. b) Images of the representative cross-linked polyether membrane demonstrating optical transparency and flexibility. ................................................................................... 167 xxv Chapter 1. Introduction 1.1 Background Aluminum-containing polymerization platforms have been around for decades. Common industrial examples abound; For instance, the Vandenberg catalyst, produced in the 1960’s, allowed for the industrial synthesis of high molecular weight polyether copolymers.1-21 This catalyst was the result of a reaction of trialkylaluminum, water, and acetyl acetone. Prior to that, in the 1950’s, the Ziegler-Natta catalyst, which revolutionized industrial polymer production from olefins, utilized a co-catalyst containing a trialkylaluminum component.22, 23 Both of these polymerization schemes are still in use today. Aluminum-based polymerization platforms have also been used to create polymers from other monomers (e.g., anhydride,24 lactone,25, 26 CO227, 28 ). However, despite aluminum being a component in all of these polymerization schemes, there is no uniting chemistry or mechanism that forms a coherent polymerization platform to polymerize all of these monomers. Lewis’s acid-base pairs (LPs) have been increasingly utilized as catalysts for the polymerization of a diverse array of monomers. LPs consist of both a Lewis acid and base component that can be bound together as an adduct or exist separately as a frustrated LP.29, 30 There are a variety of Lewis acids and bases, but aluminum containing acids, such as methyl aluminum di(2,6-di-tert-butyl-4-methylphenoxy) (MAD), and nitrogen-containing bases, such as N-heterocyclic carbenes / olefins, are common.29-31 LPs are attractive as catalysts for polymerizations because they are easy to synthesize, highly tunable, and can polymerize a wide variety of monomers controllably and to high molecular weight.29, 30, 32, 33 There are some restrictions however. LPs are most compatible with polar monomers,30 although polymerization of nonpolar monomers has also been demonstrated.34 LP copolymerizations of homologous sets 1 of monomers are common,11, 35 as well as alternating polymerizations of disparate monomers,36, 37 but few demonstrations of statistical copolymerizations of disparate monomers have been demonstrated. This is most likely due to the efficiency of LP polymerizations being strongly tied to the chemistry of the LP and the monomer.29 Because of the strong catalyst chemistry- polymerization kinetics relationship, no single LP can polymerize all monomers efficiently or several disparate monomers simultaneously. Both the polymer backbone and polymer pendant are important in controlling polymer properties. The polymer backbone is borne from the chemical “handle” that is used to polymerize the chosen monomer (i.e., the vinyl group on styrene), while the polymer pendant comes from the monomer chemical substituents that persist after polymerization. However, most polymerization methods polymerize only a homologous set of monomers, that is monomers with different chemical substituents, but the same chemical “handle.” The incorporation of different monomer types into a polymer is important both from a property standpoint38 and from a sustainability standpoint.39 For instance, copolymerizations of disparate monomers have led to degradable polymers,40 sustainable polymers made from renewable feedstocks,41 and polymers with unique properties.42 Unfortunately, incorporation of disparate monomers into a growing polymer chain is non-trivial, but some recent examples highlight potential strategies. Work from Coates’ group utilized two catalysts, each active for a different monomer, and a chain shuttling agent to incorporate epoxides and lactones into a growing polymer chain.43 Rieger’s group created terpolymers of an epoxide, CO2, and butyrolactone, by using a single Zn catalyst that catalyzed each of the separate polymerization reactions, allowing them to control monomer sequence through CO2 concentration.42 Lynd’s group employed the aluminum-based Vandenberg catalyst to copolymerize epoxides and lactones.40 While these works represent interesting steps 2 forward for disparate monomer copolymerization, they are still restricted by monomer choice and, in some cases, complex polymerization procedures. A polymerization platform that can adroitly incorporate several disparate monomers in a facile way is necessary to realize the future of polymer science. This year is the 100th anniversary of Staudinger’s landmark work describing the macromolecular theory of polymers. To mark this occasion, several recent editorials have outlined the future of polymer science for the next 100 years.2, 44 In these articles, the authors have invariably described the future of polymer science as being defined by new, non-precious metal containing polymerization methods that create sustainable polymers with unique properties. We would also argue that ease of use of these methods is vitally important. The broad uptake of an easy-to-use method like reversible addition fragmentation with chain transfer (RAFT) polymerization underscores this point.3 Therefore, the future of polymer science lies in a universal polymerization platform borne of abundant pre- cursor materials that anyone can use. We believe that our recently described, aluminum-based polymerization platform achieves all of these goals. A polymerization strategy that combines the versatility of LP catalysts and aluminum- based initiators can usher in the future of polymer science. Recently, Lynd and co-workers described a general polymerization platform for epoxides.44, 45 The platform utilized a simple LP catalyst consisting of an organoaluminum and organoamine adduct along with an aluminum alkoxide initiator. The initiator and the catalyst were simple to synthesize, and polymerizations were simple to execute, requiring mild temperatures and no solvent. The initiator behaved like a traditional anionic initiator while the catalyst activated the monomers to add them more easily to the growing chain end. Both the catalyst and initiator were necessary for the polymerization to proceed. The result of the marriage of the LP catalyst and anionic initiator was a facile polymerization platform that allowed for the controlled polymerization of practically any 3 epoxide. Building on this, we found that by replacing the aluminum alkoxide initiator in Lynd’s work with a thio-aluminum initiator (SAl) results in not only the same ability to polymerize epoxides, but also allows for the polymerization of other monomer types, including vinyls and thiiranes. Furthermore, we found that we could use this strategy to copolymerize epoxides and vinyls, which we do not believe has been demonstrated before. Our goal is that we can utilize our SAl initiators and LP catalysts, both based on abundant aluminum pre-cursors, as a facile universal polymerization platform. In this way, we can continue the storied legacy of aluminum- based polymerization platforms, dating from the time of Staudinger, through to the next century of polymer science. As mentioned earlier, synthesis of polyethers using a previously reported anionic polymerization is facile and controlled, however, there is only few methods published in literature that targeting high molecular weight polyether to 100 kg/mol with end group control, especially for epoxides carrying a pendant group. Moreover, there is no methodology reported for copolymerization of epoxides and episulfides since the importance of this copolymer for drug delivery and biomedical application is well-known. As a result, introducing a new methodology for copolymerization is still essential. Furthermore, we investigated the application prospective of the introduced method to design a new strategy for synthesis of cross-linked membranes for CO2 separation. In the first study, we presented a new method for epoxide polymerizations utilizing, aluminum-based initiators, which leverage the chemical versatility of thiol compounds to control polymer end group. The homo- and co-polymerization of various epoxides, such as epichlorohydrin and propylene oxide, demonstrate the flexibility of the initiators. Polymer molecular weight was controlled up to 100 kg/mol for the epoxides studied while maintaining 4 relatively narrow dispersity (Ð < 1.4). We further characterized the kinetics of epoxide polymerizations through 1H NMR spectroscopy and studied how the initiator structure impacted the kinetics. Finally, we employed our initiators to polymerize from thiol-end functionalized poly(methyl methacrylate) (PMMA) synthesized through RAFT polymerization, which allows us to easily create block copolymers made from vinyl and epoxide monomers. Therefore, this new synthetic tool allows for the facile polymerization of epoxides into well-defined, functional, polyether materials. Polymerization Scheme Copolymerization Scheme Cl O O n m S O RS Al R O H n m N Al Cl Monomer or Initiator or Macroinitiator Block Chemistry Chemistry Monomer Chemistry Monomer or Block Chemistry NC NC NC NC NC NC OR’ = O O O O O PS PMMA Scheme 1-1 general method for (co)polymerization for different range of epoxides. Copolymerization Scheme Copolymerization Scheme In the secondClexperimental study, we examined the versatility of the mentioned O O Cl n m O O Sn m O RS method to produce propylene sulfide O (PS) homopolymers Oup to 100 Al H R S O kg/mol and PS – epoxide RS AlR n m H n m N Al NCl Al Cl statistical, block, ABA, and star copolymers using inexpensive and versatile thio-aluminum (SAl) based initiators. Homopolymerizations of PS with SAl initiators are living and controlled, with number averaged molecular weights (Mn) up to 100 kg/mol while maintaining narrow polydispersity (Ð < 1.4). Statistical and block-copolymers of PS and epichlorohydrin (ECH) or propylene oxide (PO) are synthesized and characterized by size-exclusion chromatography (SEC), differential scanning calorimetry (DSC), 1H and 13C NMR spectroscopy, diffusion 5 ordered spectroscopy (DOSY), and small angle X-ray scattering (SAXS). This work represents the first statistical copolymerization of PS and epoxides with similar reactivity ratios, allowing fine control over composition. Block-copolymers of PS and epoxides are synthesized by simple sequential addition, without intermediate preparative steps. Polymer architecture is controlled through modification of the initiator; we synthesized di-functional (d-H) and tetra-functional (t- H) SAl initiators to produce ABA tri-block and star-(co)polymers, respectively. Finally, polyethylene glycol (PEG) was used as a macroinitiator to create PEG-b-PPS block copolymers and characterized by 1H, 13C NMR spectroscopy, DOSY, DSC, and SEC. Scheme 1-2 a) Using SAl for episulfide polymerization and copolymerization. b) general scheme for synthesis of ABA terblcok and star shape copolymer Third, we further expanded upon application of the introduced method to target synthesis of ion exchange membranes. We used the star shape composition of initiator to present a one-pot 6 and solvent free platform for synthesis of architecturally controlled star shape polyether-based membrane. Tuning the monomer feed ratio of propylene oxide (PO) and epichlorohydrin (ECH) for synthesis of poly(propylene oxide-stat-epichlorohydrin (PPO-PECH) in the presence of poly(ethylene oxide)-diglycidyl ether as a cross linker evolute a 3-D structure of membrane. The copolymerizations produced optically clear, flexible films in all cases with different PO:ECH ratios. To provide compositional control of the chemical properties of the prepared films we explored their structure-property relationships within the context of monomer ratio. The optimized PPO-PECH with ratio of 90:10 further modified with a range of amines like trimethylamine (TEA), dimethylamine (DMA), triethylamine (TEA), and diethylamine (DEA) by membrane dipping method. The chemical, physical and mechanical properties of resultant secondary amine grafted and qaurtenized membranes were characterized. PPO-PECH-TMA shows higher conductivity, higher water uptake, swelling ratio, and alkaline stability in compare with pristine and the other modified membranes due to higher basicity of TMA in the structure of the membrane. This membrane will be characterized for CO2/CH4 selectivity and permeability to compare the effect of different amines in the membrane structure. Scheme 1-3 chemical structure of star shape membrane. Finally, we used previously reported Bis(μ-oxo)alkylaluminum (BOD) to synthesis crosslinked poly (propylene oxide-stat-epichlorohydrin) (PPO-PECH) membranes utilizing bifunctional, poly(ethylene glycol) diglycidyl ether as a cross linking agent. This enables us to 7 compare the efficiency different membrane structure, including star shape and linear membranes for CO2 transport. In this study, was post modified with the range of unhindered to hindered primary amine via dipping method. In this study, we also can compare the effect of amine groups with the previous membrane having quartenized and tertiary amines. The chemical structure and physical properties of the membranes were characterized by FT-IR, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and rheometer. Theses membranes are candidates for CO2 separation and capture due to favorable interaction of C-O bond in the backbone with CO2 and presence of grafted amine for facilitation of CO2 transport. Scheme 1-4 general of scheme of amine modified membranes. In the following chapters we are describing a novel, aluminum-based polymerization platform for epoxide monomers as well as episulfide to synthesis homo and copolymers of these monomers. The polymerization platform consists of a thio-aluminum (SAl) initiatior and organoamine-organoaluminum adduct (NAl) catalyst platform which allows for the controlled, living polymerization of epoxide monomers. We further expanded the architecture of SAl to synthesize star shape initiator which utilized further to prepare crosslinked amine grafted polyether-based membrane for CO2 transport. And finally, we designed robust, flexible, and optically transparent facilitated transport membranes that are tethered with hindered and unhindered primary amines for CO2 capture and separation. 8 9 BIBLIOGRAPHY 10 BIBLIOGRAPHY (1) Staudinger, H. Über Polymerisation. Berichte der deutschen chemischen Gesellschaft (A and B Series) 1920, 53 (6), 1073-1085. 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Well-controlled polymerization by metalloporphyrin. Synthesis of copolymer with alternating sequence and regulated molecular weight from cyclic acid anhydride and epoxide catalyzed by the system of aluminum porphyrin coupled with quaternary organic salt. Macromolecules 1985, 18 (6), 1049-1055. (25) Yasuda, T.; Aida, T.; Inoue, S. Synthesis of polyester-polyether block copolymer with controlled chain length from β-lactone and epoxide by aluminum porphyrin catalyst. Macromolecules 1984, 17 (11), 2217-2222. (26) Endo, M.; Aida, T.; Inoue, S. Immortal polymerization of .epsilon.-caprolactone initiated by aluminum porphyrin in the presence of alcohol. Macromolecules 1987, 20 (12), 2982-2988. (27) Wang, Y.; Zhao, Y.; Ye, Y.; Peng, H.; Zhou, X.; Xie, X.; Wang, X.; Wang, F. A One- Step Route to CO2-Based Block Copolymers by Simultaneous ROCOP of CO2/Epoxides and RAFT Polymerization of Vinyl Monomers. Angewandte Chemie International Edition 2018, 57 (14), 3593-3597. 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Catalytic Lewis Pair Polymerization of Renewable Methyl Crotonate to High-Molecular-Weight Polymers. ACS Catalysis 2018, 8 (10), 9877-9887. (34) Sajid, M.; Stute, A.; Cardenas, A. J. P.; Culotta, B. J.; Hepperle, J. A. M.; Warren, T. H.; Schirmer, B.; Grimme, S.; Studer, A.; Daniliuc, C. G.; Fröhlich, R.; Petersen, J. L.; Kehr, G.; Erker, G. N,N-Addition of Frustrated Lewis Pairs to Nitric Oxide: An Easy Entry to a Unique Family of Aminoxyl Radicals. JACS 2012, 134 (24), 10156-10168. (35) Chen, Y.; Shen, J.; Liu, S.; Zhao, J.; Wang, Y.; Zhang, G. High Efficiency Organic Lewis Pair Catalyst for Ring-Opening Polymerization of Epoxides with Chemoselectivity. Macromolecules 2018, 51 (20), 8286-8297. 13 (36) Ji, H.-Y.; Wang, B.; Pan, L.; Li, Y.-S. Lewis pairs for ring-opening alternating copolymerization of cyclic anhydrides and epoxides. Green Chemistry 2018, 20 (3), 641-648. (37) Yang, J.-L.; Wu, H.-L.; Li, Y.; Zhang, X.-H.; Darensbourg, D. J. Perfectly Alternating and Regioselective Copolymerization of Carbonyl Sulfide and Epoxides by Metal-Free Lewis Pairs. Angew. Chem. Int. Ed. 2017, 56 (21), 5774-5779. (38) Wang, H.; Wu, X.; Yang, Y.; Nishiura, M.; Hou, Z. Co-syndiospecific Alternating Copolymerization of Functionalized Propylenes and Styrene by Rare-Earth Catalysts. Angew. Chem. Int. Ed. 2020, 59 (18), 7173-7177. (39) Poland, S. J.; Darensbourg, D. J. A quest for polycarbonates provided via sustainable epoxide/CO2 copolymerization processes. Green Chemistry 2017, 19 (21), 4990-5011. (40) Chwatko, M.; Lynd, N. A. Statistical Copolymerization of Epoxides and Lactones to High Molecular Weight. Macromolecules 2017, 50 (7), 2714-2723. (41) Wang, Y.; Li, A.-L.; Liang, H.; Lu, J. Reversible addition–fragmentation chain transfer radical copolymerization of β-pinene and methyl acrylate. Eur. Polym. J. 2006, 42 (10), 2695- 2702. (42) Kernbichl, S.; Reiter, M.; Mock, J.; Rieger, B. Terpolymerization of β-Butyrolactone, Epoxides, and CO2: Chemoselective CO2-Switch and Its Impact on Kinetics and Material Properties. Macromolecules 2019, 52 (21), 8476-8483. (43) Clayman, N. E.; Morris, L. S.; LaPointe, A. M.; Keresztes, I.; Waymouth, R. M.; Coates, G. W. Dual catalysis for the copolymerisation of epoxides and lactones. Chem. Commun. 2019, 55 (48), 6914-6917. (44) Abd-El-Aziz, A. S.; Antonietti, M.; Barner-Kowollik, C.; Binder, W. H.; Böker, A.; Boyer, C.; Buchmeiser, M. R.; Cheng, S. Z. D.; D’Agosto, F.; Floudas, G.; Frey, H.; Galli, G.; Genzer, J.; Hartmann, L.; Hoogenboom, R.; Ishizone, T.; Kaplan, D. L.; Leclerc, M.; Lendlein, A.; Liu, B.; Long, T. E.; Ludwigs, S.; Lutz, J.-F.; Matyjaszewski, K.; Meier, M. A. R.; Müllen, K.; Müllner, M.; Rieger, B.; Russell, T. P.; Savin, D. A.; Schlüter, A. D.; Schubert, U. S.; Seiffert, S.; Severing, K.; Soares, J. B. P.; Staffilani, M.; Sumerlin, B. S.; Sun, Y.; Tang, B. Z.; Tang, C.; Théato, P.; Tirelli, N.; Tsui, O. K. 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Aluminum-based Initiators from Thiols for Epoxide Polymerization 2.1 Introduction Polyethers are important industrial polymers where they are used in the production polyurethanes,1, 2 and are found in common consumer products such as laxatives, eye drops, medicines, and lubricants as well as in the technological applications such as lithium ion batteries,3 separation membranes,4, 5 anti-fouling coatings6, 7 , and biomedical applications.8 The ubiquity and utility of polyether materials are the results of their functional monomer precursors, epoxides. Epoxides hold great promise as a polymeric materials platform due to their tunable functional group(s) and indiscriminate ring strain driving force for polymerization.9-11 Furthermore, epoxides are widely available, relatively inexpensive, and easy to synthesize making them prime candidates as a feedstock for polymeric materials.12 However, in traditional anionic ring opening polymerization (AROP) schemes, various epoxide substitutions such as alkyls and halides can cause side reactions during polymerization, such as chain transfer to monomer, resulting in a loss of control, limited molecular weight, and/or no conversion at all.13 To address these shortcomings, numerous catalytic strategies have been reported for epoxide polymerizations. Catalytic methods can result in polymers and also copolymers14, 15 with high molecular weight,16 narrow dispersity,17-19 and controlled stereochemistry.20-23 However, the catalyst synthesis in these methods can be complex and/or use expensive starting materials making them less suitable for non-experts that may want to utilize polyether materials. Recently developed mono(μ-alkoxo)bis(alkylaluminum) (MOB) compounds are tolerant to monomer functional group while still providing molecular weight control for epoxide polymerizations without any chain transfer reactions present.24, 25 Additionally, the MOB compounds are trivial to synthesize and use for epoxide polymerizations and therefore provide 15 access for non-experts to polyethers with tunable molecular weight, composition, and architecture.4, 24, 25 The MOB compounds can be split into two separate components that facilitate epoxide polymerization; one consisting of a polymerization catalyst portion (e.g., Et3NAlMe3) and one consisting of a bis((μ-alkoxo)-dialkylaluminum) (BOD) initiator portion (e.g., [Et2Al(μ- OCH2CH2OMe)]2).26 The result of this split was that the polymer end group could be controlled using different initiator chemistries with a limited effect on polymerization kinetics. Previously, all MOB / BOD initiators were based on alcohol-containing ligands, which limits the potential ligand moieties. Expanding the ligand system for aluminum-based initiators to include functional groups beyond alcohols can enhance the functionality of polyethers. Thiols are particularly attractive due to the vast library of thiol compounds available, allowing us to precisely tune polyether end group. Additionally, thiol-end terminated polymers are commercially available and easily synthesizable via post-modification of polymers obtained from techniques like reversible addition-fragmentation chain transfer polymerization (RAFT).27 Thus, block copolymers of vinyls and epoxides can be readily synthesized through a combination of simple-to-use techniques. While thiol-containing compounds have been utilized in polymerizations either through specific ‘click’ interactions28 or for ring-opening polymerizations of lactones,29 they have not been applied to epoxide polymerizations. In this work, we explore thiols as the ligand for aluminum-based initiators for epoxide polymerizations. Thio-aluminum initiators (SAls) can be easily synthesized from the reaction of a thiol containing ligand and trimethylaluminum. The kinetic and molecular weight control of epoxide polymerizations initiated by SAls was investigated by tuning catalyst concentration and monomer to initiator ratio and characterized by 1H NMR spectroscopy and size exclusion 16 chromatography (SEC). Initiator chemistry was varied to investigate polymer end-group control as well as the effect on polymerization kinetics. Finally, polymer compositional control was examined via the copolymerization of two different monomers. Polyethers with controlled end group were produced from a diverse set of thiol-containing small molecules and polymers. Macroinitiators derived from RAFT produced polymers allowed for the facile synthesis of vinyl- b-epoxide polymers without the need for hazardous reagents or complex synthetic procedures, providing access to these materials for non-chemists. 2.2 Experimental section Trimethylaluminum solution (AlMe3, Sigma-Aldrich, 2.0 M in hexane), triethylamine (TEA, Sigma-Aldrich, ≥99.5%), benzyl mercaptan (Sigma-Aldrich, 99%), 1-propane thiol (Sigma- Aldrich, 99%), cyclopentyl thiol (Sigma-Aldrich, 97%), 4-chlorobenzenemethanethiol (Sigma- Aldrich, 98%), 2-cyano-2-propyl benzodithioate (Sigma-Aldrich, >HPLC 97%), hexylamine (Sigma-Aldrich, 99%), 2,2′-azobisisobutyronitrile (Sigma-Aldrich, 98%), and sodium hydrogen sulfate (NaHSO4, Sigma-Aldrich, technical grade), CDCl3 (Cambridge Analytica), D2- dichloromethane (Cambridge Analytica) were used without any further purification. Hexanes (Sigma-Aldrich, anhydrous, >99%), tetrahydrofuran (THF, Sigma-Aldrich, anhydrous, ≥99.5%, inhibitor free) were used for experiments in the glove box. Methanol (MeOH, Fisher, Certified ACS), hexane (Fisher, Certified ACS) and dichloromethane (DCM, Fisher, Certified ACS) were used for washing polymers. Epichlorohydrin (ECH, Sigma-Aldrich, ≥99%), propylene oxide (PO, Sigma-Aldrich, GC, ≥99.5%), butylene oxide (BO, Sigam-Aldrich, 99%), and allyl glycidyl ether (AGE, Sigma-Aldrich, ≥ 99%) were all used as received. Methyl methacrylate (MMA, contains ≤30 ppm MEHQ as inhibitor, 99%) and styrene (contains 4-tert-butylcatechol as stabilizer, ≥99%) were filtered over activated basic alumina column to remove inhibitors. All air 17 and moisture sensitive reactions were prepared under a dry nitrogen atmosphere inside a glovebox. 2.2.1 Characterization 1 H NMR spectroscopy was performed on a 500 MHz Varian NMR spectrometer at room temperature and chemical shifts are reported in parts per million (ppm) and are referenced using the residual 1H peak from the deuterated solvent. The structure of the compounds was determined by 13C NMR spectroscopy on a 126 MHz Varian NMR spectrometer. All diffusion ordered spectroscopy (DOSY) measurements were performed at 25° C on a Varian Inova 600 spectrometer operating at 599.72 MHz and equipped with a 5mm Z-gradient HCN inverse probe capable of producing gradients in the Z direction with strength of 63 G/cm. All DOSY measurements were run using the dbppste pulse sequence with 128-160 scans and 20 increments with gradient strengths from 2.7 to 59.22 G/cm. The relaxation delay was set to 3s, the diffusion delay to 24ms, and the gradient length to 2.0ms. Size exclusion chromatography (SEC) was carried out on the Malvern OMNISEC system with an isocratic pump, degasser, and temperature-controlled column oven held at 35 °C containing 2 Viscotek 300×8.0 mm columns (T3000 and T4000) with an exclusion limit of 400 kDa. Triple detection with light scattering, viscometer, and refractive index has been used for absolute molecular weight determination of polymers. Calibration was carried out using polystyrene standards (from scientific polymer) in THF. Differential scanning calorimetric (DSC) tests were conducted on a TA250 instrument with a heating rate of 10 °C min−1 under a N2 atmosphere, and the data from the second heating curve were collected. Samples were analyzed by electrospray ionization with mass spectrometry in positive ion mode using a Waters Xevo G2XS Q-Tof mass spectrometer interfaced with a Waters Acquity UPLC. 5 ul of a sample (diluted in 90% methanol containing 1mM ammonium formate) 18 were flow-injected (no UPLC column) using a mobile phase of 80% methanol and 20% 10 mM ammonium formate in water pumped at 0.2 ml/min. Data were acquired over an m/z range of 200-6000 in continuum mode. Single crystal X-ray diffraction XRD data were collected using a Bruker APEX-II CCD diffractometer equipped with an Oxford Cryosystems low-temperature device, operating at T = 173.0 K. Data were measured using ω and φ of 1 ° per frame for 10 s using CuKα radiation (sealed tube, 40.0 kV, 30.0 mA). The total number of runs and images was based on the strategy calculation from the program COSMO (BRUKER, V1.61, 2009). MALDI- TOF spectra were acquired using a Shimadzu Axima cfr+ operating in linear mode with a laser power setting of 50. The matrix used was alpha-cyanohydroxycinnamic acid (CHCA, 10 mg/ml in acetonitrile/water (50:50 v/v) containing 0.1% TFA). 2.2.2 Synthesis of trimethylaluminum and triethylamine adduct (NAl).26 A reaction vial was charged with a stir bar, 6.35 mL anhydrous hexanes, and 2.0 M AlMe3 in hexane (6.35 mL, 12.7 mmol) in a dry nitrogen glove box and cooled to –78 ºC. Then, TEA (1.5 ml, 10.7 mmol) was added dropwise to the vial. The solution was set to stir and warm to room temperature overnight. To crystallize the desired product, the solution was then directly cooled to –40 ºC and the resultant crystals were washed three times with anhydrous hexanes (3×5 ml) and dried in vacuo. 1H NMR (500 MHz, CDCl3) δ 2.80 (q, 6H), 1.18 (t, 9H), -0.89 (s, 9H). 13C NMR (126 MHz, CDCl3) δ 47.78, 9.20. 2.2.3 General procedure for synthesis of initiators A vial of anhydrous hexane (6.35 ml) and 2.0 M AlMe3 in hexanes (6.35 mL, 12.7 mmol) equipped with a stir bar, cooled down to –78 ºC in a cold well. At a desired temperature, a thiol ligand (12.7 mmol) was added dropwise. Then, the solution was stirred at 900 rpm for 24 hours while warming to room temperature. To remove unreacted AlMe3 and purify the initiator, the 19 synthesized compound was washed three times with anhydrous hexanes (3×5 ml) and dried in vacuo. (Benzylthio)dimethylaluminum (BnSAlMe2) 1 H NMR (500 MHz, CD2Cl2) δ 9.43 – 8.98 (m, 5H), 5.88 (s, 2H), 1.51 (s, 6H). 13C NMR (126 MHz, CD2Cl2) δ 141.46, 128.56, 127.97, 126.89, 32.00, 28.78. ((4-Chlorobenzyl)thio)dimethylaluminum (ClBnSAlMe2) 1 H NMR (500 MHz, CDCl3) δ 7.34 – 7.22 (m, 4H), 3.89 (s, 2H), -0.45 (s, 6H).13C NMR (126 MHz, CDCl3) δ 127.50, 126.84, 51.18, 26.37. Dimethyl(propylthio)aluminum (PrSAlMe2) 1 H NMR (500 MHz, CDCl3) δ 2.63 (t, J = 7.3 Hz, 2H), 1.64 (m, 2H), 0.98 (t, J = 7.3 Hz, 3H), - 0.51 (s, 6H). 13C NMR (126 MHz, CDCl3) δ 30.33, 25.97, 13.15, -9.21. (Cyclopentylthio)dimethylaluminum (cPenSAlMe2) 1 H NMR (500 MHz, CDCl3) δ 2.62 (m, 2H), 1.65 (dq, 2H), 1.04-0.95 95 (m, 3H), -0.49 (S, 6H). 13 C NMR (126 MHz, CDCl3) δ 42.65, 37.24, 24.51, -7.83. 2.2.4 General procedure for synthesis and purification of polymers All polymerizations were performed neat in 20 ml septum-capped reaction vials and charged with a stir bar in the inert atmosphere. Initiator, NAl, and monomer were added to the vial. The solution was heated up to 50°C until completion of the polymerization. Reactions were quenched with methanol and dissolved in dichloromethane. Then, the resulting solution was added dropwise into acidic MeOH (0.01 M HCl in MeOH) to precipitate the desired polymer product. Then, it was washed 3 times with water to remove residual aluminum. After precipitation out of MeOH, the polymer was dried in vacuo overnight at 70 °C. 20 Mn was determined by 1H NMR spectroscopy by taking the ratio of the backbone proton signals to the integral of the end group signal on the initiator. Average molecular weights and dispersity (Ð) were determined by SEC with triple detection (refractive index, light scattering, and viscometry) with respect to polystyrene standards. All other polymerizations were performed under identical experimental conditions and characterized by 1H NMR, 13C NMR spectroscopy, and SEC. Poly(epichlorohydrin) (PECH) 1 H NMR (500 MHz, CDCl3) δ 3.70 (bm, –O–CH2–CH(CH2Cl)–O–). 13C NMR (126 MHz, CDCl3) δ 79.18-79.09 (–O–CH2–CH(CH2Cl)–O–), 69.80 (–O–CH2–CH(CH2Cl)–O– m), 69.50 (–O–CH2–CH(CH2Cl)–O– rrm or mrr), 43.80 (–CH2–Cl). Poly(propylene oxide) (PPO) 1 H NMR (500 MHz, CDCl3) δ 3.80 – 3.17 (bm, –O–CH2–CH(CH3)–O–), 1.12 (m, -CH3). 13C NMR (126 MHz, CDCl3) δ 75.89 (–O–CH2–CH(CH3)–O–, mm), 75.68 (–O–CH2–CH(CH3)–O–, mr + rm), 75.48 (–O–CH2–CH(CH3)–O–, rr), 73.71 (–O–CH2–CH(CH3)–O–, m), 73.16 (–O– CH2–CH(CH3)–O–, rrm or mrr), 17.81 (–CH3). Poly(butylene oxide) (PBO) 1 H NMR (500 MHz, CDCl3) δ 3.68 – 3.25 (bm, –O–CH2–CH(CH2–CH3)–O–), 1.68 – 1.37 (m, CH2–CH3), 0.91 (t, –CH2–CH3). 13C NMR (126 MHz, CDCl3 ) δ 80.84-80.42 (–O–CH2– CH(CH2–CH3)–O–), 72.37 (–O–CH2–CH(CH2–CH3)–O–, m), 71.53 (–O–CH2–CH(CH2–CH3)– O–, rrm or mrr)), 24.72 (–CH2–CH3), 9.76 (–CH3). Poly(allyl glycidyl ether) (PAGE) 1 H NMR (500 MHz, Chloroform-d) δ 5.88 (m, –O–CH2–CH=CH2), 5.27-5.14 (doublet of doublets, –O–CH2–CH=CH2), 3.98 (d, –O–CH2–CH=CH2), 3.75-3.42 (bm, –O–CH2–CH(CH2– 21 O–CH2–CH=CH2)–O–). 13C NMR (126 MHz, Chloroform-d) δ 134.93 (–O–CH2–CH=CH2), 116.74 (–O–CH2–CH=CH2), 78.89 (–O–CH2–CH(CH2–O–CH2–CH=CH2)–O–), 72.26 (–O– CH2–CH=CH2), 70.25-69.84 (–O–CH2–CH(CH2–O–CH2–CH=CH2)–O–, m), 69.74 (–O–CH2– CH(CH2–O–CH2–CH=CH2)–O–, rrm or mrr). 2.2.5 Procedure for synthesis and reactivity ratio measurement of P(PO-grad-ECH) A vial with a stir bar was charged with PrSAlMe2 (0.013 g, 0.1 mmol) and NAl (0.017 g, 0.1 mmol). A mixture of ECH (1.5 ml, 1.84 g, 0.019 mol) and PO (1.39 ml, 1.15g, 0.019 mol) was added to the vial slowly and then heated up to 50°C. To measure reactivity ratios of ECH and PO, small aliquots (ca. 30 µL) were taken out of reaction mixture and dissolved in CDCl3. The conversion of each monomer was calculated based on the integration of backbone area to the unreacted corresponding monomer by 1H NMR spectroscopy. After a given time, the mixture was diluted with DCM and precipitated in a threefold excess of acidic methanol (0.01 M). The polymer was dried under vacuum at room temperature. Dispersity and Mn were characterized by SEC and the structure of the copolymer was confirmed by 1H NMR and 13C NMR spectroscopy. 1 H NMR (500 MHz, CDCl3) δ 3.82 – 3.40 (bm, –O–CH2–CH(CH2Cl)–O– and –O–CH2– CH(CH3)–O–), 1.18 – 1.10 (bm, –O–CH2–CH(CH3)–O–). 13C NMR (126 MHz, CDCl3) δ 79.67- 78.65 (–O–CH2–CH(CH2Cl)–O–), 75.85-75.17 (–O–CH2–CH(CH3)–O–), 74.44-74.04 (–O– CH2–CH(CH3)–O– and –O–CH2–CH(CH2Cl)–O–), 73.37-72.84 (–O–CH2–CH(CH2Cl)–O–), 69.72-69.24 (–O–CH2–CH(CH3)–O–), 68.68-68.13 (–O–CH2–CH(CH3)–O– and –O–CH2– CH(CH2Cl)–O–), 44.05-43.23 (–CH2–Cl), 17.10 (–CH3). 2.2.6 General procedure for synthesis of P(PO-b-ECH) PrSAlMe2 (0.009 g, 0.068 mmol) and NAl (0.011 g, 0.063 mmol) were added into a vial with stir bar. After the addition of the ECH (0.84 ml,1g, 0.01 mol), the vial was placed in the hotplate at 22 50°C. Completion of polymerization was monitored by 1H NMR spectroscopy and when the first monomer is consumed, the PO (0.7 ml, 0.58 g, 0.01 mol) was injected to the vial. Stirring was continued at 50 °C for enough time until the second monomer is fully converted. The product was then dissolved in DCM and the resulting solution was precipitated out of MeOH to yield the desired polymer product. The supernatant was removed, and the polymer was dried in vacuo. Structure of the block copolymer characterized by 1H NMR and 13C NMR spectroscopy. Dispersity and Mn were characterized by SEC and glass transition temperature confirmed by DSC. 1 H NMR (500 MHz, CDCl3 δ 3.70 (bm, (–O–CH2–CH (CH2–Cl)–O– and –O–CH2 (CH3)-O-), 1.13 (m, -CH3). 13C NMR (126 MHz, CDCl3) δ 79.07-78.99 (–O–CH2–CH(CH2Cl)–O–), 75.52-75.11 (–O–CH2–CH(CH3)–O–), 73.35-72.79 (–O–CH2–CH(CH2Cl)–O–), 69.67- 69.35 (–O–CH2– CH(CH3)–O–), 43.65 (–CH2–Cl), (17.45-17.32) (–CH3). 2.2.7 Polymerization procedure for synthesis of P(MMA-b-ECH) Polymerization was performed in a round-bottom flask capped with a septum. The reaction vessel with a stir bar was loaded with THF (5 mL), MMA (1.87 ml, 2.0 × 10-2 mol), 2-cyano-2-propyl benzodithioate (0.022 g, 9.9 × 10-5 mol), and AIBN (0.005 g, 3.1 × 10-5 mol). The mixture was deoxygenated by sparging a reaction mixture with N2. The temperature was then raised to 90 °C using an oil bath and polymerization was carried out under N2 atmosphere. Monomer consumption was followed by 1H NMR spectroscopy and after 72 h, 70% of monomer was converted. Poly(methyl methacrylate) (PMMA) was precipitated out of MeOH and the excess monomer and solvent removed by evaporation at ambient temperature under vacuum. Mn and dispersity of the polymer were determined by SEC and the structure was confirmed by 1H and 13 C NMR spectroscopy. In the next step, the aminolysis of PMMA with hexylamine was performed for conversion of dithioester into a thiol end-group. The procedure was as follows. PMMA (0.5 g) was 23 dissolved in THF and 0.5 ml of NaHSO4 (5% aqueous solution) was added into a 50 ml 3-necks flask with a stir bar. The flask was sparged with N2 for 15 mins. Hexylamine (3.7 mmol, 0.38 g, 0.5 ml) was added dropwise, and the reaction was stirred for 10 h under N2. Solution color changed from pink to light yellow while adding the hexylamine and after aminolysis was done, the reaction mixture was light yellow (an indication of the conversion). Next, the reaction vessel was taken into the glove box and the solution was added dropwise into 5-fold excess of MeOH. The PMMA functionalized with thiol (PMMA-SH) was collected by precipitation and then drying in vacuo. In order to synthesis a macroinitiator, in one 20 ml vial, 0.14 g of PMMA-SH was dissolved on 1 ml of benzene and AlMe3 (0.3 ml of 2 M in hexane) added dropwise to the solution and stirred overnight at RT. To synthesize poly(methyl methacrylate)-block-(epichlorohydrin), NAl (0.003 g, 1.7 × 10-5 mol) and 0.2 ml of ECH (0.23 g, 2.4 mmol) were added into the same vial and heated up to 50 °C. Conversion of ECH was monitored by 1H NMR spectroscopy and the reaction terminated by MeOH after 3 days (full conversion). The block copolymer was purified by redissolving in DCM, precipitating out of MeOH, and drying in vacuo. The resulted poly(MMA)- b-(ECH) characterized by SEC, DSC, 1H NMR, and 13 C NMR spectroscopy. 1H NMR spectroscopy of P(MMA-b-ECH). 1H NMR (500 MHz, Methylene Chloride-d2) δ 3.99–3.62 (bm, -OCH2CH(CH2Cl)O-), 3.63-3.56 (bm,-CH2C(CH3)(COOCH3)-), 2.19-1.66 (bm, - CH2C(CH3)(COOCH3)-), 1.67 – 0.58 (bm, -CH2C(CH3)(COOCH3)-). 13C NMR spectroscopy of 13 P(MMA-b-ECH). C NMR (126 MHz, cdcl3) δ 178.12- 177.00 (-CH2-C(CH3)(COOCH3)-), 81.58-67.83 (–O–CH2–CH(CH2–Cl)–O–), 51.84 (-CH2-C(CH3)(COOCH3)-), 44.89 (-CH2- C(CH3)(COOCH3)-), 45.93-45.32 (H-T diads, –O–CH2–CH(CH2–Cl)–O–), 44.89-44.54 (-CH2- C(CH3)(COOCH3)-), 43.87-42.63 (H-H and T-T diads, –O–CH2–CH(CH2–Cl)–O–), 25.07 (–O– CH2–CH(CH2–Cl)–O–), 18.70-16.41(-CH2-C(CH3)(COOCH3)-). 24 2.2.8 Detailed purification procedure for synthesized polymers After completion of the polymerization monitored by 1H NMR spectroscopy, the reaction was quenched by exposing to the air and adding 0.1 ml of MeOH. Then, the polymer was dissolved in 3 ml of DCM by stirring and heating to 50 °C. The dissolved polymer was added dropwise to 6 ml of 0.01 M HCl in MeOH (acidic MeOH) to be precipitated. After sufficient time, the supernatant was removed. The polymer was re-dissolved in DCM, washed three times with DI water, and precipitated by adding to the 3 ml of MeOH. Finally, the polymer was dried in vacuo overnight at 70 °C. It should be noted that PPO did not precipitate out of a number of different solvents and so the above steps were followed without precipitation for PPO. 2.2.9 Kinetic study for different concentrations of NAl by 1H NMR spectroscopy at specified time points In a glove box, a reaction vial was charged with a stir bar, BnSAlMe (0.018 g, 0.099 mmol), NAl (0.25 eq. (0.004 g, 2.3 × 10-2 mmol), 0.5 eq. (0.008 g, 4.6 × 10-2 mmol), 1 eq. (0.0175 g, 0.1 mmol), 2 eq (0.035 g, 0.2 mmol), and epichlorohydrin (3 g, 2.5 ml). the reaction vessel then placed on a stir plate at 50 ºC. Small aliquots (ca. 30 µL) were taken at sp,ecified time points. These samples were dissolved in d-chloroform and conversion was determined using 1H NMR spectroscopy. The conversion of each monomer was calculated based on the integration of the backbone area to the unreacted corresponding monomer by 1H NMR spectroscopy. The samples were quenched by exposing them to the air which deactivates the catalyst. 2.2.10 Kinetic study for different initiators by 1H NMR spectroscopy specified time A reaction vial was charged with a stir bar, NAl (0.035 g, 0.2 mmol), epichlorohydrin (3 g, 2.5 ml), and initiator (0.099 mmol) and then it heated up to 50 ºC in a glove box. Small aliquots (ca. 30 µL) were taken at specified time points. These samples were dissolved in d-chloroform and the 25 conversion was determined using 1H NMR spectroscopy. The conversion of each monomer was calculated based on the integration of backbone area to the unreacted corresponding monomer by 1 H NMR spectroscopy. The samples were quenched by exposing to the air which deactivates the catalyst. 2.2.11 Polymerization procedure for synthesis of poly(styrene-block-epichlorohydrin) (P(styerne- b-ECH)) Polymerization was performed in a round-bottom flask capped with a septum. The reaction vessel with a stir bar was loaded with tetrahydrofuran (5 mL), styrene (2.3 ml, 2 × 10-2 mol), 2-cyano-2- propyl benzodithioate (0.022 g, 9.9 × 10-5 mol), and AIBN (0.005 g, 3.1 × 10-5 mol). The mixture was deoxygenated by sparging a reaction mixture with N2. The temperature was then raised to 90°C using an oil bath and polymerizations were carried out under N2 atmosphere. Monomer consumption was followed by 1H NMR analysis and after 72 h, 68% of monomer was converted. Poly(styrene) (PS) was precipitated out of MeOH, and the excess monomer and solvent removed by evaporation at ambient temperature under vacuum. In the next step, the aminolysis of PS with hexylamine was performed for conversion of dithioester into a thiol end-group. The procedure was as follows. Functionalized PS (0.1 g) was dissolved in THF and 0.1 ml of NaHSO4 (5% aqueous solution) were added to a 50 ml 3-necks flask with a stir bar. The flask was sparged with N2 for 15 mins. Hexylamine (0.69 mmol, 0.07 g, 0.1 ml) was added dropwise, and the reaction was stirred for 10 h under N2. Solution color changed from pink to light yellow while adding the hexylamine and after aminolysis was done, the reaction mixture was light yellow (an indication of conversion). Next, the reaction vessel was taken into the glove box and the solution was added dropwise into 5-fold excess of MeOH. The PS functionalized thiol (PS-SH) was collected by precipitation and then drying in vacuo. In order to synthesis a macroinitiator, 0.18 g of PS-SH was dissolved in 1 26 ml of benzene and added into a reaction vial with a septum. AlMe3 (0.3 ml of 2 M in hexane) added dropwise into the solution and stirred overnight at RT. To synthesis poly(styrene-block- epichlorohydrin), NAl (0.005 g, 2.8 × 10-3 mol), and 0.2 ml of ECH (0.4 ml, 0.472 g, 5.1mmol) were added into the same vial and heated up to 50 °C. Conversion of ECH was monitored by 1H NMR spectroscopy and the reaction terminated by MeOH after 6 days. The block copolymer was purified by redissolving in DCM, precipitating out of MeOH, and drying in vacuo. 2.3 Results and discussion A potential initiator for epoxide polymerizations, a thio-aluminum (SAl) compound, was synthesized from the reaction of benzyl mercaptan and trimethyl aluminum at –78 oC. The resulting SAl (BnSAlMe2) was crystallized from the reaction medium and characterized via X- Ray crystallography as seen in Figure 2-1 as well as 1H NMR and 13C NMR spectroscopy (SI, Figure 2-11 to 2-14). X-Ray crystallography revealed a unit structure of dimethyl aluminum bound to benzyl thiolate, consistent with trimethyl aluminum reacting with the benzyl mercaptan. This unit, we propose, defines our initiator for epoxide polymerizations. The entire crystal structure reveals these individual units to be datively bound to adjacent units in a linear chain (c.f., Figure 2-13, 2-14), which is consistent with other SAl structures in literature.30 Details of the crystallography can be found in the SI. 27 Figure 2-1 (top) Chemical reaction scheme for the synthesis of BnSAlMe2. (bottom) Resultant chemical structure of the asymmetric structure determined by X-Ray crystallography. Thermal ellipsoids are shown at 50% probability level. BnSAlMe2 was utilized as an initiator to polymerize the epoxide epichlorohydrin (ECH). Here, we targeted 30 kg/mol polyepichlorohydrin (PECH) using BnSAlMe2 in an equimolar ratio with NAl catalyst26 in the absence of a solvent, as shown in Scheme 2-1. The polymerization was monitored with 1H NMR spectroscopy until completion at 12 hours with >99% conversion of ECH. The observed rate constant (kobs) was determined from a fit to the kinetic data as seen in Figure 2-2 (a log-linear plot can be seen in SI Figure 2-15) and was calculated to be kobs = 7.38 × 10-5 ± 5.41 × 10-6 s-1. The first order in monomer kinetics suggests polymerizations initiated by BnSAlMe2 are living in nature. As a control, ECH conversion was monitored in the presence of just BnSAlMe2, just NAl catalyst, and benzyl mercaptan (ligand) and catalyst (i.e., no initiator). Using exclusively the initiator, slow conversion was observed (ca. 10% after 7 days), while just catalyst and catalyst and ligand resulted in no conversion after 7 days. This suggests that both catalyst and initiator are necessary for efficient conversion, which is consistent with previous work with BOD-initiated polymerizations.26 1H NMR spectra for ECH polymerizations with just NAl catalyst, just BnSAlMe2, and benzyl mercaptan with NAl can be found in the supplemental 28 information (SI, Figures 2-16, 2-17). Based on these results, we suggest that the polymerization follows an anionic coordination−insertion of activated monomer mechanism assisted by a Lewis pair (i.e., NAl), where the NAl adduct acts as a strong activator of the monomer via oxygen- aluminum coordination as proposed by Carlotti31 and the covalent nature of the Al-S bond suggests polymerization via a coordination mechanism.32, 33 The resulting PECH was characterized via size-exclusion chromatography (SEC). The Mn was found to be 30.7 kg/mol with Ð = 1.17, consistent with the targeted molecular weight, and compared favorably to the molecular weight calculated through 1H NMR spectroscopy via end group analysis of 31.6 kg/mol (SI, Figure 2-19). The results for this polymerization can be found in Table 2-1, sample 2. Differential scanning caolorimetry (DSC) was also performed on this polymer and showed a single glass transition temperature (Tg) at –26 °C (SI, Figure 2-20). We also have observed the hydrogenation reaction of the end group for BnSPECH in a higher concentration of acidic MeOH (1 M HCl in MeOH) confirmed by 1 H NMR spectroscopy (SI, Figure 2-21), which suggests we can achieve hetero-bifunctional polymers with two addressable end groups (i.e., alcohol and thiol). 29 Table 2-1 Control experiment. Sample Monomer Initiator Time Mn(theo) Mn(calc) b Mn c Đd (hr.)a (kg/mol) (kg/mol) (kg/mol) 1 ECH BnSAlMe2 6 15 17.5 17.7 1.37 2 ECH BnSAlMe2 10 30 31.6 30.7 1.17 3 ECH BnSAlMe2 48 50 46.8 49.4 1.28 4 ECH BnSAlMe2 70 70 75.0 75.7 1.25 5 ECH BnSAlMe2 102 100 97.1f 94.6 1.28 6 BO BnSAlMe2 48 30 22.7 23.6e 1.16 e 7 BO BnSAlMe2 97 100 81.2f 80.2 e 1.02 e 8 PO BnSAlMe2 40 30 38.1 38.9 e 1.04 e 9 PO BnSAlMe2 97 100 78.4f 80.1 e 1.02 e 10 AGE BnSAlMe2 22 30 28.3 29.6 1.45 11 ECH cPenSAlMe2 12 30 33.9 29.3 1.25 12 ECH ClBnSAlMe2 12 30 27.3 30.9 1.28 13 ECH PrSAlMe2 4 30 30.2 28.6 1.24 14 PO PrSAlMe2 22 30 19.9 19.8 e 1.07 e 15 BO PrSAlMe2 48 30 27.4 23.5 e 1.17 e 30 Scheme 2-1 SAl-initiated polymerization of ECH. Figure 2-2 Plot of normalized ECH concentration over time with BnSAlMe2 initiator and NAl catalyst. Monomer concentration was monitored via 1H NMR spectroscopy. The full conversion was achieved in ca. 10 hours with the combined catalyst and initiator system, with kobs = 7.38 × 10-5 ± 5.41 × 10-6 s-1, whereas no conversion is present with just catalyst and slow conversion is present with just BnSAlMe2 as initiator. The inset is a plot of the kobs as a function of equivalents of NAl catalyst to BnSAlMe2 initiator, where a linear relationship was observed. The effect of catalyst concentration on the polymerization rate was investigated with 1H NMR spectroscopy. We monitored the conversion of ECH with a targeted molecular weight of 30 kg/mol with varying ratio of catalyst to initiator concentration ([C0]/[I0]) = 0.25, 0.50, 1.00, and 2.00. The resulting kinetic data of normalized monomer concentration as a function of time can be seen in SI (supplemental information, Figure 2-22 to 2-25) and the kobs as a function of [C0]/[I0] can be seen in Figure 2-2 inset. A linear increase in kobs as a function of [C0]/[I0] was observed, which differs from Lynd’s work on the BOD system,26 but is consistent with other polymerization catalysts behavior in the literature.34, 35 It should also be noted that there is an apparent induction period,36 denoted by the characteristic sigmoidal shape of the conversion 31 curve for samples with [C0]/[I0] = 0.25 and 0.50 and the reported kobs was determined from a fit to the conversion after the induction period, where conversion is first order in monomer. The induction period can be observed in the full kinetic data plots found in the supplementary information (SI, Figures 2-22, 2-23). No induction period was observed for samples with [C0]/[I0] = 1.00 or 2.00. In work by Huang et al.37 for polymerization of PO using a double metal catalyst (DMC), they observed that when the ratio of [C]/[I] decreases, the induction period increases, which is the same observation for our catalyst and initiator system. The addition of more initiators can inhibit the addition of the monomer to the activated chain end, which may be due to the higher donor ability of sulfur anion to oxy anion which can deactivate the catalyst (NAl). Moreover, the ring opening reaction of epoxides and consequently activation of the monomer is directly dependent on the amount of NAl. This justifies the lower rate of this reaction at the first stage of polymerization, which refers to the induction period. The induction period of the NAl catalyst will be further addressed by a future paper from the Lynd laboratory at UT Austin. Molecular weight control was investigated for SAl-initiated polymerizations of ECH. Control over PECH molecular weight was achieved by varying the monomer to initiator ratio ([M0]/[I0]) with targeted molecular weights of 15, 30, 50 75, and 100 kg/mol. For these polymerizations, the NAl catalyst was pinned at 63.5 µmol, or equimolar with the BnSAlMe2 BnSAlMe2 initiator for a 30 kg/mol polymer. All polymerizations were carried out to full conversion prior to termination. The final Mn of the polymers was consistent with the targeted molecular weights as determined by both SEC and end group analysis via 1H NMR spectroscopy. The details of the polymers can be found in Table 2-1, samples 1–5. Figure 2-3 is a plot of Mn (blue left axis) and Ð (red right axis) as a function of [ECH]/[BnSAlMe2] 32 determined by SEC. A linear trend in the Mn as a function of [ECH]/[BnSAlMe2] can be seen in the plot, implying good control over Mn up to 100 kg/mol. Furthermore, Ð < 1.4 for all polymers produced suggests no side reactions are occurring. The corresponding SEC traces for each of these polymerizations can be found in the SI (supplemental information, Figure 2-26 to 2-29). Figure 2-3 Plot of Mn (left axis, blue circles) and Ð (right axis, red triangles) as a function of ECH to initiator BnSAlMe2 ratio ([ECH]/[BnSAlMe2]). Mn increased linearly at increasing ratio of epichlorohydrin, while Ð remained consistently low (Ð < 1.4) suggesting a controlled chain growth polymerization of ECH. Similar molecular weight control was demonstrated for polymerizations of propylene oxide (PO) and butylene oxide (BO). PO and BO are difficult to polymerize via traditional methods (i.e., AROP) to even moderate molecular weights (i.e., Mn > 10 kg/mol) due to their propensity to chain transfer,38 but work by several different researchers like Carlotti,39 Deffieux,40 Naumann,41 and Coates42 over the past two decades have demonstrated the high molecular weight synthesis of PPO by other means. However, high molecular PBO still remains a challenge. We targeted polymer molecular weights of 30 and 100 kg/mol for each monomer using BnSAlMe2 as the initiator and using 63.5 µmol of NAl catalyst. The results can be found in Table 2-1 and were generally consistent with the targeted molecular weights. Specifically, the Mn determined from SEC for the polymers were: 38.1 kg/mol (PPO, 30 kg/mol), 80.1 kg/mol 33 (PPO, 100 kg/mol), 23.1 kg/mol (PBO, 30 kg/mol), and 80.1 kg/mol (PBO, 100 kg/mol) all with narrow Ð < 1.1. Molecular weights determined by end group analysis from 1H NMR spectra of polymers were consistent with the Mn determined by SEC (SI, Figures 2-30 to 2-34) and no peaks suggesting any chain transfer occurred. DSC was also performed on the 30 kg/mol samples of PPO and PBO and showed single Tg consistent with the synthesized polymers The DSC data can be found in SI (Figures 2-36, 2-37). Therefore, the SAl initiator allows for facile and controlled synthesis of mid-range molecular weight (i.e., 100 kg/mol > Mn >10 kg/mol) PPO and PBO. As a further demonstration of functional monomer polymerization, allyl glycidyl ether (AGE) was polymerized. We targeted PAGE molecular weight of 30 kg/mol using BnSAlMe2 as the initiator and using 63.5 µmol of NAl catalyst. The results can be found in Table 2-1. Specifically, the Mn determined from SEC was 29.6 kg/mol with Ð = 1.45, which is consistent with the targeted molecular weight. The resulting PAGE was also characterized by 1H NMR spectroscopy with calculated molecular weight based on end group analysis to 31.2 kg/mol, consistent with the SEC results. NMR spectra and SEC trace for PAGE can be found in the supporting information (Figures 2-37 to 2-40). Three additional SAl initiators were synthesized from different thiol-containing ligands to tune polymer end-group. SAl initiators were synthesized in a similar way to the BnSAlMe2 initiator above but utilizing ligands of propyl thiol (PrSAlMe2), cyclopentylthiol (cPenSAlMe2), and chloro-benzyl thiol (ClBnSAlMe2) in a reaction with trimethylaluminum. These ligands were chosen due to their unique chemical signature in 1H NMR spectra compared with the polymer, allowing for a facile determination of the end group. All SAl initiators were characterized via 1H and 13C NMR spectroscopy (supplemental information, Figures 2-41 to 2-46) and cPenSAlMe2 34 and ClBnSAlMe2 were characterized by X-Ray crystallography (full XRD data are available in the SI). Characterization of PrSAlMe2 by X-Ray crystallography was unsuccessful due to the instability of the resulting crystals. The structure of cPenSAlMe2 and ClBnSAlMe2 determined by X-Ray crystallography can be seen in Figure 2-4. cPenSAlMe2 (Figure 2-4 a) consists of a dimer of dimethyl aluminum cyclopentyl sulfur forming a four-membered thio-aluminum ring. This structure is reminiscent of BODs from literature26, 43 as well as similar thio-aluminum compounds in the literature,29, 44, 45 but it is distinct from the crystal structure of BnSAlMe2. Meanwhile, ClBnSAlMe2 (Figure 2-4 b) is similar in structure to BnSAlMe2 and exists as a linear chain of adjacent initiator units connected through dative bonds of aluminum and sulfur. Figure 2-4 Resultant structure of cPenSAlMe2 (a) and ClBnSAlMe2 (b) formed from the reaction of cyclopentyl thiol and 4-chlorobenzenemethanethiol, respectively, with trimethyl aluminum determined by X-Ray crystallography. cPenSAlMe2 forms a dimer (shown) consisting of a four membered thio-aluminum ring while the ClBnSAlMe2 forms a chain of initiator units connected via dative bonds to aluminum and sulfur atoms of adjacent initiators, like BnSAlMe2 (cf., Figure 1). Thermal ellipsoids are shown at 50% probability level. Polymerizations of ECH with all SAl initiators were performed to demonstrate polymer end group control. The polymerizations of ECH were carried out in the bulk with a 2:1 ratio of NAl catalyst to SAl initiator with a targeted molecular weight of 30 kg/mol. A summary of the polymerizations initiated with all SAl initiators can be found in Table 2-1 and SEC traces can be found in SI (Figures 2-47 to 2-49). The resultant PECH were characterized by 1H NMR 35 spectroscopy and SEC. The molecular weights for all polymers were consistent with the targeted molecular weight of 30 kg/mol. The 1H NMR spectra for polymers synthesized from SAl initiators can be seen in Figure 2-5. All spectra are consistent with the anticipated ones. The molecular weight calculation via end group analysis (c.f., Table 2-1) is consistent with the SEC results. To further confirm the polymer end group, a 5 kg/mol molecular weight PPO was synthesized with all SAl initiators and the resultant polymers were characterized via electrospray ionization with mass spectroscopy (ESI-MS) and matrix assisted laser desorption/ionization time of flight (MALDI-TOF). The results from this analysis can be found in the SI (supplemental information, Figures 2-50 to 2-54). Figure 2-5 1H NMR Spectra of PECH initiated by PrSAlMe2 (a), cPenSAlMe2 (b), BnSAlMe2 (c), and ClBnSAlMe2 (d) in CD2Cl2 (c, d) or CDCl3 (a, b). The peaks corresponding to the various end groups are clearly visible in each of the spectra and are marked with letters ‘a’ through ‘c’ and their chemical shift and multiplicity is consistent with expectations. Peaks marked with ‘x’ correspond to CD2Cl2 and peaks marked with ‘y’ correspond to water impurity in CDCl3. Intensity increased to accentuate peaks corresponding to end groups. 36 Kinetic studies of ECH polymerization with all SAl initiators were performed to determine whether the initiator structure influenced polymerization kinetics. Based on our assumption of a coordination-insertion polymerization mechanism with ionic character, the initiator end group should play a little role in the reaction kinetics as the end group moves away from the site of insertion as the monomer is consumed. Polymerizations of ECH were carried out with each SAl initiator and two equivalents to initiator of NAl catalyst and monitored with 1H NMR spectroscopy over 2.5 hours. A plot of the resulting kinetic data can be seen in Figure 2-6. The kobs was determined from the slope of the fit to the –ln([ECH]/[ECH]0) and was kobs = (3.83 ± 0.15) × 10-4 s-1 (PrSAlMe2), (1.86 ± 0.08) × 10-4 s-1 (BnSAlMe2), (1.34 ± 0.05) × 10-4 s- 1 (ClBnSAlMe2), and (0.21 ± 0.03) × 10-4 s-1 (cPenSAlMe2). The results of the initiator kinetic study were unexpected, as they suggest initiator structure affects polymerization kinetics. The PrSAlMe2 initiator was approximately two times faster than either benzyl containing initiator (i.e., BnSAlMe2 and ClBnSAlMe2) and more than 10 times faster than cPenSAlMe2. The results of both end group analyses via 1H NMR spectroscopy and ESI-MS suggest that the polymer is growing linearly (i.e., the end group moves further away from the site of enchainment as polymerization progresses), so the exact role of the end group on kinetics remains unclear. However, the benzyl containing initiators have similar kobs to each other along with similar crystal structures, while the crystal structure, and resulting kobs, for cPenSAlMe2 differs significantly from them. Therefore, the more open structure of the benzyl containing initiators may facilitate monomer enchainment and enhance kinetics compared with cPenSAlMe2. Moreover, the electron density of the initiator may affect the rate of polymerization as an electron rich ligand like PrSAlMe2 is the fastest one, while ClBnSAlMe2, the most electron deficient, is the slowest between all initiators. This effect has been seen before for cationic 37 polymerizations.46 The crystallographic structure of PrSAlMe2 or an intermediate after enchainment would elucidate the genesis of these kinetic differences and this will be followed up further in future work. Figure 2-6 Plot of the –ln([ECH]/[ECH]0) as a function of time for the polymerization of ECH with SAl initiators PrSAlMe2 (red squares), BnSAlMe2 (blue circles), ClBnSAlMe2 (purple triangles), and cPenSAlMe2 (green diamonds). Monomer conversion was monitored via 1H NMR spectroscopy for 2.5 hours by taking aliquots from the reaction vessel and an observed rate constant (kobs) was determined to be kobs = (3.83 ± 0.15) × 10-4 s-1 (PrSAlMe2), (1.86 ± 0.08) × 10-4 s-1 (BnSAlMe2), (1.34 ± 0.05) × 10-4 s-1(ClBnSAlMe2), and (0.21 ± 0.03) × 10-4 s-1 (cPenSAlMe2). To investigate the generality of our method to target specific polymer architecture, we synthesized copolymers of ECH and PO. The copolymerization of ECH and PO in a 1:1 ratio was performed using PrSAlMe2, which was chosen due to the enhanced celerity over the other initiators. The polymerization was monitored by 1H NMR spectroscopy and the total conversion of monomers was determined. The reactivity ratios were fit to the non-terminal copolymerization model reported by Beckingham–Sanoja–Lynd (BSL)47, 48 and Figure 2-55 shows the fit of BSL to the conversion as a function of the normalized molar concentration of each monomer ([M]/[M]0). From BSL, the reactivity ratios for ECH (rECH) and PO (rPO) were determined to be 38 rECH = 2.56 ± 0.29 and rPO = 0.44 ± 0.03, which suggests a gradient copolymer with ECH preferentially adding over PO. The resulting polymer was also characterized by SEC with a Mn of 29.0 kg/mol and Đ of 1.28, consistent with the targeted molecular weight of 30 kg/mol. We further synthesized a block copolymer of ECH and PO by sequential addition of monomers initiated with PrSAlMe2. The resulting copolymer was characterized by SEC with Mn of 33.4 kg/mol and Đ of 1.27, consistent with the targeted molecular weight of 30 kg/mol (15 kg/mol for each block). The 1H and 13C NMR spectra for the block and gradient copolymers with labeled chemical structures can be seen in Figure 2-7. The 1H NMR spectra for the gradient and block copolymers, Figure 2-7a and 7c, respectively, are similar to each other and consistent with the anticipated spectra. The 13C NMR spectra for the gradient and block copolymers, Figure 2-7b and 2-7d, respectively, differ in that the gradient copolymer has additional carbon peaks compared with the block copolymer due to adjacency of the different monomers.24 Furthermore, the PECH-b-PPO sample was characterized by diffusion ordered spectroscopy (DOSY). The DOSY spectrum can be seen in supporting information (Figure 2-56) and is consistent with block copolymer formation. Copolymerization demonstrates the ability of our method to synthesize multifunctional polymeric materials with controlled compositions. 39 Figure 2-7 1H and 13C NMR spectra and labeled chemical structures for PECH-grad-PPO (a and b, respectively) and PECH-b-PPO (c and d, respectively) in CDCl3. The 13C NMR spectrum of the PECH-grad-PPO (b) reveals additional cross-peaks compared with PECH-b-PPO (d). We synthesized a block copolymer consisting of vinyl and epoxide units through a combination of reversible addition-fragmentation with chain transfer (RAFT) polymerization and AROP to demonstrate the utility of our method as a materials platform. Specifically, a block copolymer of poly(methyl methacrylate) (PMMA) and PECH was synthesized as outlined in Figure 2-8. Utilizing this method to synthesize vinyl-block-epoxide polymers has advantage over traditional anionic polymerization as the synthesis can be performed without the need for specialized glassware or the use of dangerous reagents (e.g., ethylene oxide). In the RAFT polymerization of MMA, 2-cyano-2-propyl benzodithioate was used as a chain transfer agent along with AIBN as a radical initiator to produce PMMA. The resultant PMMA was characterized via SEC (Figure 2-9, right trace, red) with Mn = 6.3 kg/mol and Đ = 1.13 and 1H NMR spectroscopy (Figure 2-10 c). The dithioester, which remained as an end group from the 40 RAFT polymerization, was cleaved down to a terminal thiol via aminolysis and the thiol terminated PMMA was characterized via 1H NMR spectroscopy, which revealed the loss of protons associated with the benzyl group (Figure 2-10 b). The thiol end terminated PMMA was transformed into a macro-initiator for epoxide polymerization through the reaction of the thiol group with trimethyl aluminum in benzene at room temperature overnight. A polymerization of ECH, initiated from the end of the thio-aluminum end-terminated PMMA, was carried out (for 3 days) at 50 °C in the presence of NAl catalyst. The resulting P(MMA-b-ECH) was characterized via SEC, 1H and 13C NMR spectroscopy, and DSC. The SEC trace (RI) of P(MMA-b-ECH) can be seen in Figure 2-9 (left trace, blue) and the Mn was determined to be 18.4 kg/mol with Đ = 1.05. A clear shift to smaller retention volume can be seen in SEC of the block-co-polymer compared with the homopolymer, consistent with the ECH block growing from the PMMA chain end. The 1H (Figure 2-10 a) and 13C (SI, Figure 2-57) NMR spectra are consistent with the expected polymer structure. DOSY was also performed on this sample and the resulting spectrum is consistent with block co polymer formation (supporting information, Figure 2-58). Moreover, in a control experiment, after working up the thiol end-terminated PMMA, we added epichlorohydrin into the reaction vial (without the addition of AlMe3) and monitored the conversion of ECH. No conversion for ECH was observed after 7 days (SI, Figure 2-59) by 1H NMR spectroscopy. This observation suggests that PECH is not forming separately and must be polymerized off of the macro-initiator. DSC (SI, Figure 60) reveals a single broad Tg which is to be expected as PMMA and PECH are miscible polymers.49, 50 The broadening behavior for glass transition has been observed due to miscibility of PMMA and PECH.51, 52 The 13C NMR spectrum shows additional peaks, which we think corresponds to different regiostructures of PECH. These peaks are consistent with head-to-head, tail-to-tail and head-to-tail addition of 41 ECH to the growing chain end.53 The regio-irregularity of the PECH block is inconsistent with polymerizations carried out above using SAl initiators and previous work with MOB24-26 and BOD26, 43 initiators. We suspect it has to do with the favorable interaction between MMA and ECH. To test this, we polymerized ECH from the end of RAFT synthesized polystyrene (PS) in a similar manner to the PMMA. The resulting 13C NMR spectrum (SI, Figure 2-61) for PS-b- PECH polymer is consistent with a regioregular PECH block. DSC (supplemental information, Figure 2-62) reveals two Tg, one at –27 ºC corresponding to the PECH block and one at 74 ºC corresponding to the PS block. DOSY was also performed on this sample and the resulting spectrum is consistent with block co polymer formation (SI, Figure 2-63). Therefore, vinyl- block-epoxide polymers can be synthesized through relatively simple means that are accessible to non-experts at polymer synthesis. S CN S S n O n NC AIBN, THF, 85 oC S O O O 4 NH2 S Al AlMe3 SH n n NC benzene , RT NC O O O O m O be Cl nz Cl Et ene , S H 3N :A 50 o n Om lM C NC e 3 O O Figure 2-8 PMMA-block-PECH synthetic route. 42 Figure 2-9 SEC traces (RI) of RAFT synthesized PMMA (right, red curve) and P(MMA-b-ECH) (left, blue curve). The Mn and Đ was determined to be 6.3 kg/mol and 1.13 (PMMA) and 18.4 kg/mol and 1.05 (P(MMA-b-ECH)). Figure 2-10 . 1H NMR spectra in CDCl3 of RAFT synthesized PMMA (c), thiol-end terminated PMMA (b), and P(MMA-b-ECH) (a). The peak associated with the benzyl end group from the RAFT agent (cf., c) disappears after the aminolysis step (cf., b), which reveals a free thiol. In conclusion, four different thio-aluminum compounds (SAls) were synthesized and their efficacy as initiators for epoxide polymerizations was investigated. SAl initiators performed 43 similarly to other recently reported Al-based initiators for epoxide polymerizations. SAl initiators resulted in the living polymerizations with controlled molecular weight, low dispersity, and were tolerant to the epoxide functional group. Polymer end group was tuned through the thiol ligand used in the SAl synthesis and was confirmed through both 1H NMR spectroscopy and electrospray ionization mass spectrometry (ESI-MS). Polymerization kinetics were investigated and found to depend on catalyst concentration and SAl end group. Finally, we synthesized poly(methyl methacrylate-b-epichlorohydrin) (P(MMA-b-ECH)) by combining the traditional RAFT polymerization technique with our SAl initiators, allowing for facile synthesis of vinyl-b- epoxide copolymers. This technique allows us to further tune polyether chemistry by giving us access to the vast array of thiol compounds that can act as end groups as well as facilitates the synthesis of block copolymers from disparate monomer classes. 2.4 Supporting information Figure 2-11 1H NMR spectroscopy of BnSAlMe2. 1H NMR (500 MHz, Chloroform-d) δ 7.38 – 7.21 (m, 5H, PhCH2S-Al(CH3)2), 3.91 (s, 2H, PhCH2S-Al(CH3)2), -0.43 (s, 6H, PhCH2S- Al(CH3)2). 44 Figure 2-12 13C NMR spectrum of BnSAlMe2. 13C NMR(126 MHz, CD2Cl2) δ 141.46, 128.56, 127.97, 126.89 PhCH2S-Al(CH3)2, 32.00 PhCH2S-Al(CH3)2, 28.78 PhCH2S-Al(CH3)2. Figure 2-13 Carbon labeling scheme for BnSAlMe2. There is a single molecule in the asymmetric unit, which is represented by the reported sum formula. In other words: Z is 4 and Z' is 1 for BnSAlMe2. 45 Figure 2-14 The Unit structure of dimethyl aluminum bound to benzyl thiolate, consistent with trimethyl aluminum reacting with the benzyl mercaptan. This unit, we propose, defines our initiator for epoxide polymerizations. The entire crystal structure reveals these individual units to be datively bound to adjacent units in a linear chain. Figure 2-15 Plot of the –ln([ECH]/[ECH]0) over time for the polymerization of ECH with BnSAl and 1 eq of NAl showing a linear slope consistent with a living polymerization. r2 = 0.96. 46 Figure 2-16 1H NMR spectroscopy for ECH polymerizations with just NAl after 7 days which shows no conversion to PECH. 1H NMR (500 MHz, Chloroform-d) δ 3.62 – 3.50 (m, 2H, ECH OCH2CH(CH2Cl)), 3.22 (dddd, 1H, ECH OCH2CH(CH2Cl)), 2.88 (ddd, 1H, ECH OCH2CH(CH2Cl)), 2.67 (dd, 1H, ECH OCH2CH(CH2Cl)). Figure 2-17 1H NMR spectroscopy for ECH polymerizations with just BnSAlMe2 after 7 days which shows slow conversion (ca. 10% after 7 day). 1H NMR (500 MHz, Chloroform-d) δ 3.77- 3.49 (bm, PECH, -OCH2CH(CH2Cl)O-), 3.62 – 3.49 (m, 2H, ECH OCH2CH(CH2Cl)), 3.22 (dddd, 1H, ECH OCH2CH(CH2Cl)), 2.88 (ddd, 1H, ECH OCH2CH(CH2Cl)), 2.67 (dd, 1H, ECH OCH2CH(CH2Cl)). 47 Figure 2-18 1H NMR spectroscopy for ECH polymerizations with benzyl mercaptan (ligand) and NAl after 7 days which shows no conversion to PECH. 1H NMR (500 MHz, Chloroform-d3.62 – 3.50 (m, 2H, ECH OCH2CH(CH2Cl)), 3.22 (dddd, 1H, ECH OCH2CH(CH2Cl)), 2.88 (ddd, 1H, ECH OCH2CH(CH2Cl)), 2.67 (dd, 1H, ECH OCH2CH(CH2Cl)). Figure 2-19 RI trace of targeted 30k PECH synthesized by BnSAlMe2 initiator. The Mn is determined to be 30.7 with Ð =1.17. 48 Figure 2-20 DSC analysis of targeted 30k PECH with BnSAlMe2. The data from the second heating curve were collected which reveals one Tg at -26 °C. Figure 2-21 1H NMR spectroscopy of 30K PECH treated with 1 M HCl in MeOH. This is magnified 1H NMR to verify benzyl signal loss. 1H NMR (500 MHz, Chloroform-d) δ 3.83-3.39 (bm, -OCH2CH(CH2Cl)O-). 49 Figure 2-22 Plot of normalized ECH concentration over time with BnSAlMe2 initiator and 0.25 eq. of NAl catalyst. Monomer concentration was monitored via 1H NMR spectroscopy and the rate of reaction calculated based on it (kobs = 5.06 × 10-6 ± 5.54 × 10-7 s-1). Sigmoidal shape of conversion curve for 0.25 eq. of NAl can be seen in this figure which is related to induction period. The kobs is calculated using the data collected after the induction period, where conversion is first order in monomer. Figure 2-23 Plot of normalized ECH concentration over time with BnSAlMe2 initiator and 0.5 eq. of NAL catalyst. Monomer concentration was monitored via 1H NMR spectroscopy, and the rate of reaction calculated based on it (kobs = 2.34 × 10-5 ± 2.21 × 10-6 s-1). Sigmoidal shape of conversion curve for 0.5 eq. of NAl can be seen in this figure which is related to induction period. The kobs is calculated using the data collected after the induction period, where conversion is first order in monomer. 50 Figure 2-24 Plot of normalized ECH concentration over time with BnSAlMe2 initiator and 2 eq. of NAl. Monomer concentration was monitored via 1H NMR spectroscopy. Full conversion was achieved in ca. 10 hours with the combined catalyst and initiator system, with kobs = 1.91 × 10- 4 ± 5.79 × 10-6 s-1. Figure 2-25 Plot of the –ln([ECH]/[ECH]0) over time for the polymerization of ECH with BnSAl and 2 equivalents of catalyst showing a linear slope consistent with a living polymerization. r2 = 0.96. 51 Figure 2-26 RI trace of targeted 15k PECH synthesized by BnSAlMe2 initiator. The Mn is determined to be 17.7 with Ð = 1.37. Figure 2-27 RI trace of targeted 50k PECH synthesized by BnSAlMe2 initiator. The Mn is determined to be 49.4 with Ð = 1.28. 52 Figure 2-28 RI trace of targeted 70k PECH synthesized by BnSAlMe2 initiator. The Mn is determined to be 75.7 with Ð = 1.25. Figure 2-29 RI trace of targeted 100k PECH synthesized by BnSAlMe2 initiator. The Mn is determined to be 94.6 with Ð = 1.28. 53 Figure 2-30 RI trace of targeted 30k PBO synthesized by BnSAlMe2 initiator. The Mn is determined to be 23.6 with Ð = 1.16. Figure 2-31 RI trace of targeted 100k PBO synthesized by BnSAlMe2 initiator. The Mn is determined to be 80.2 with Ð = 1.02. 54 Figure 2-32 RI trace of targeted 30k PPO synthesized by PrSAlMe2 initiator. The Mn is determined to be 23.5 with Ð = 1.17. Figure 2-33 RI trace of targeted 30k PPO synthesized by BnSAlMe2 initiator. The Mn is determined to be 38.9 with Ð = 1.04. 55 Figure 2-34 RI trace of targeted 100k PPO synthesized by BnSAlMe2 initiator. The Mn is determined to be 80.1 with Ð = 1.02. Figure 2-35 DSC analysis of targeted 30k PPO with BnSAlMe2. The data from the second heating curve were collected which reveals one Tg at -70 °C. 56 Figure 2-36 DSC analysis of targeted 30k PBO with BnSAlMe2. The data from the second heating curve were collected which reveals one Tg at -73 °C. Figure 2-37 1H NMR spectroscopy of targeted 30K poly(allyl glycidyl ether) (PAGE) with BnSAlMe2. 1H NMR (500 MHz, Chloroform-d) δ 5.88 (m, –O–CH2–CH=CH2), 5.27-5.14 (doublet of doublets, –O–CH2–CH=CH2), 3.98 (d, –O–CH2–CH=CH2), 3.75-3.42 (bm, –O– CH2–CH(CH2–O–CH2–CH=CH2)–O–). 57 Figure 2-38 13C NMR spectroscopy of targeted 30K poly(allyl glycidyl ether) (PAGE) with BnSAlMe2. 13C NMR (126 MHz, Chloroform-d) δ 134.93 (–O–CH2–CH=CH2), 116.74 (–O– CH2–CH=CH2), 78.89 (–O–CH2–CH(CH2–O–CH2–CH=CH2)–O–), 72.26 (–O–CH2–CH=CH2), 70.25-69.84 (–O–CH2–CH(CH2–O–CH2–CH=CH2)–O–, m), 69.74 (–O–CH2–CH(CH2–O–CH2– CH=CH2)–O–, rrm or mrr). Figure 2-39 DSC analysis of Targeted 30k PAGE with compound BnSAlMe2. The data from the second heating curve were collected which reveals one Tg at –76 °C. 58 Figure 2-40 RI trace of targeted 30k PAGE synthesized with BnSAlMe2. The Mn is determined to be 29.6 Kg/mol with Ð = 1.45. The first modal peak is due to aggregation of polymer in presence of Al trace. Figure 2-41 1H NMR spectrum of PrSAlMe2.1H NMR (500 MHz, Chloroform-d) δ 2.62 (m, 2H, CH3CH2CH2S-Al(CH3)2), 1.65 (dq, 2H, CH3CH2CH2S-Al(CH3)2), 1.04-0.95 (m, 3H, CH3CH2CH2S-Al(CH3)2), -0.49 (S, 6H, CH3CH2CH2S-Al(CH3)2). 59 Figure 2-42 13C NMR spectrum of PrSAlMe2 13C NMR (126 MHz, Chloroform-d) δ 30.33 CH3CH2CH2S-Al(CH3)2, 25.97 CH3CH2CH2S-Al(CH3)2, 13.15 CH3CH2CH2S-Al(CH3)2, -9.21 CH3CH2CH2S-Al(CH3)2. Figure 2-43 1H NMR spectrum of cPenSAlMe2. 1H NMR (500 MHz, Chloroform-d) δ 3.39 – 3.33 (m, 1H, cyclopentane -CH-), 2.10 – 1.99 (m, 2H, cyclopentane -CH2-CH2-), 1.83 – 1.73 (m, 2H, cyclopentane -CH2-CH2-), 1.62–1.53 (m, 4H, cyclopentane -CH2-CH2-), -0.49 (s, 6H, cyclopentane-S-Al(CH3)2). 60 Figure 2-44 1H 13C NMR spectrum of cPenSAlMe2 13C NMR (126 MHz, Chloroform-d) δ 30.33 (cyclopentane -CH-), 25.97 (cyclopentane -CH2-CH2-), 13.15 (cyclopentane -CH2-CH2-), -9.21 (cyclopentane-S-Al(CH3)2). Figure 2-45 1H NMR spectrum of ClBnSAlMe2. 1H NMR (500 MHz, Chloroform-d) δ 7.34 – 7.22 (m, 4H, (Cl)PhCH2S-Al(CH3)2), 3.89 (s, 2H, (Cl)PhCH2S-Al(CH3)2), -0.45 (s, 6H, (Cl)PhCH2S-Al(CH3)2). 61 Figure 2-46 13C NMR spectrum of ClBnSAlMe2. 13C NMR (126 MHz, Chloroform-d) δ 127.50, 126.84 (Cl)PhCH2S-Al(CH3)2, 51.18 (Cl)PhCH2S-Al(CH3)2, 26.37 (Cl)PhCH2S-Al(CH3)2. Figure 2-47 RI trace of targeted 30k PECH synthesized by PrSAlMe2 initiator. The Mn is determined to be 30.2 with Ð = 1.24. 62 Figure 2-48 RI trace of targeted 30k PECH synthesized by cPenSAlMe2 initiator. The Mn is determined to be 29.3 with Ð = 1.25. Figure 2-49 RI trace of targeted 30k PECH synthesized by ClBnSAlMe2 initiator. The Mn is determined to be 30.9 with Ð = 1.28. 63 Figure 2-50 Samples were analyzed by electrospray ionization in a solvent containing ammonium formate to facilitate ionization as ammonium adducts. Panel A shows the positive ion mode ESI spectrum with the inset showing the results of a deconvolution of charge states to show the neutral mass distribution of the polymer sample. Focusing on the higher m/z range where the charge states are lowest (panel B), the neutral mass can easily be calculated. The triply charged ion with m/z 1610.5194 [M+(NH4)3]3+ corresponds to a neutral mass of 4777.4568 (1610.5194 * 3 – 3 * 18.0338) which is consistent with a molecule containing 81 total propylene oxide units and a propylthiol end group (expected mass = 4777.426, 6.4 ppm mass error). The next abundant signal at m/z 1629.8662 corresponds to a neutral mass of 4835.4972, which is 58 Da heavier and represents one additional propylene oxide repeating unit. 64 Figure 2-51 Samples were analyzed by electrospray ionization in a solvent containing ammonium formate to facilitate ionization as ammonium adducts. Panel A shows the positive ion mode ESI spectrum with the inset showing the results of a deconvolution of charge states to show the neutral mass distribution of the polymer sample. Focusing on the higher m/z range where the charge states are lowest (panel B), the neutral mass can easily be calculated. The doubly charged ion with m/z 1386.0093 [M+(NH4)2]2+ corresponds to a neutral mass of 2735.951 (1386.0093 * 2 – 2 * 18.0338) which is consistent with a molecule containing 45 total propylene oxide units and a BnS end group (expected mass = 2735.919, 11.7 ppm mass error). The next abundant signal at m/z 1415.0305 corresponds to a neutral mass of 2793.9934, which is 58 Da heavier and represents one additional propylene oxide repeating unit. 65 Figure 2-52 Samples were analyzed by electrospray ionization in a solvent containing ammonium formate to facilitate ionization as ammonium adducts. Panel A shows the positive ion mode ESI spectrum with the inset showing the results of a deconvolution of charge states to show the neutral mass distribution of the polymer sample. Focusing on the higher m/z range where the charge states are lowest (panel B), the neutral mass can easily be calculated. The doubly charged ion with m/z 1896.2792 [M+(NH4)2]2+ corresponds to a neutral mass of 3756.5252 (1896.2964 * 2 – 2 * 18.0338) which is consistent with a molecule containing 62 total propylene oxide units and a ClBnS end group (expected mass = 3756.591, -17.5 ppm mass error). The next abundant signal at m/z 1925.3075 corresponds to a neutral mass of 3814.5474, which is 58 Da heavier and represents one additional propylene oxide repeating unit. 66 Figure 2-53 Samples were analyzed by electrospray ionization in a solvent containing ammonium formate to facilitate ionization as ammonium adducts. Panel A shows the positive ion mode ESI spectrum with the inset showing the results of a deconvolution of charge states to show the neutral mass distribution of the polymer sample. Focusing on the higher m/z range where the charge states are lowest (panel B), the neutral mass can easily be calculated. The doubly charged ion with m/z 1897.3320 [M+(NH4)2]2+ corresponds to a neutral mass of 3758.5964 (1897.3320 * 2 – 2 * 18.0338) which is consistent with a molecule containing 63 total propylene oxide units and a cyPenS end group (expected mass = 3758.688, 24.4 ppm mass error). The next abundant signal at m/z 1926.3486 corresponds to a neutral mass of 3816.6296, which is 58 Da heavier and represents one additional propylene oxide repeating unit. 67 Figure 2-54 MALDI-TOF analysis of 5kg/mol PPO with 4 different initiators (A). The X-axis is the same for all four plots and is the mass range (in m/z). The mass distribution with MALDI- TOF matches with ESI-MS data. (B) Expanded prospective of MALDI-TOF. The difference between each subsequent peak is equal to mass of one propylene oxide. The order of polymers are the same for A and B. 68 Figure 2-55 Fit of BSL to the conversion as a function of the normalized molar concentration of each monomer ([M]/[M]0). From BSL, the reactivity ratios for ECH (rECH) and PO (rPO) were determined to be rECH = 2.56 ± 0.29 and rPO = 0.44 ± 0.03, which suggests a gradient copolymer with ECH preferentially adding over PO. Figure 2-56 600 MHz 2D Figure 2-57 DOSY NMR spectra obtained at 298 K in Chloroform-d solution of the PECH-b-PPO. 1H NMR (600 MHz, Chloroform-d) δ 3.70 (bm, (–O–CH2–CH (CH2–Cl)–O– and –O–CH2 (CH3)-O-), 1.13 (m, -CH3). 69 Figure 2-58 13C NMR spectroscopy of P(MMA-b-ECH). 13C NMR (126 MHz, cdcl3) δ 178.12- 177.00 (-CH2-C(CH3)(COOCH3)-), 81.58-67.83 (–O–CH2–CH(CH2–Cl)–O–), 51.84 (-CH2- C(CH3)(COOCH3)-), 44.89 (-CH2-C(CH3)(COOCH3)-), 45.93-45.32 (H-T diads, –O–CH2– CH(CH2–Cl)–O–), 44.89-44.54 (-CH2-C(CH3)(COOCH3)-), 43.87-42.63 (H-H and T-T diads, – O–CH2–CH(CH2–Cl)–O–), 25.07 (–O–CH2–CH(CH2–Cl)–O–), 18.70-16.41(-CH2- C(CH3)(COOCH3)-). Different regiostructures of ECH monomer in the PECH block can be seen in this spectrum due to head-to-tail, head-to-head, and tail-to-tail diads. In H-T diads, γ gauche effect on the carbon of CH2 (–O–CH2–CH(CH2–Cl)–O–), cause related signals to be shifted and this is why two sets of peaks are observed in the 13C NMR spectrum. Peaks at 29.77, 19.78, and 9.42 are corresponded to hexanes. Figure 2-59 600 MHz 2D DOSY NMR spectra obtained at 298 K in Chloroform-d solution of the PMMA-b-PECH. 1H NMR (600 MHz, Chloroform-d) δ 3.99–3.62 (bm, -OCH2CH(CH2Cl)O- ), 3.63-3.56 (bm,-CH2C(CH3)(COOCH3)-), 2.19-1.66 (bm, -CH2C(CH3)(COOCH3)-). 70 Figure 2-60 1H NMR spectroscopy of thiol end-terminated PMMA without AlMe3, in the presence of ECH and NAl, at 50°C after 7 days. 1H NMR (500 MHz, Chloroform-d) δ 3.52-3.48 (bm-CH2-C(CH3)(COOCH3)-), 3.47–3.42 (d, J = 5.4 Hz, 2H, ECH, OCH2CH(CH2Cl)), 3.22 (tdd, J = 5.4, 3.9, 2.5 Hz, 1H, ECH, OCH2CH(CH2Cl)), 2.88 (dd, J = 4.8, 3.9 Hz, 1H, ECH, OCH2CH(CH2Cl)), 2.67 (dd, J = 4.8, 2.5 Hz, 1H, ECH OCH2CH(CH2Cl)), 2.03-1.59 (bm,-CH2- C(CH3)(COOCH3)-), 1.31-0.72 (bm -CH2- C(CH3)(COOCH3)-). The only NAl peaks correspond to Me groups on Al below zero but Et groups are overlapping with other peaks and cannot be specified. Figure 2-61 DSC analysis of P(MMA-b-ECH). The data from the second heating curve were collected which reveals a broad Tg centered at 0 °C. 71 Figure 2-62 13C NMR spectroscopy of P(styrene-b-ECH) which is consistent with a regioregular PECH block. 13C NMR (126 MHz, cdcl3) δ 145.21(-CH2-CH(Ph ,C)-) 128.00-127.11 (-CH2- CH(Ph ,CH)-), 125.68-125.25 (-CH2-CH(Ph, CH)-), 78.97 (–O–CH2–CH(CH2Cl)–O–), 69.33(– O–CH2–CH(CH2Cl)–O–), 43.57 (–O–CH2–CH(CH2Cl)–O–), 44.46(-CH2-CH(Ph)-), 40.21(-CH2- CH(Ph)-) 29.59(–CH2–Cl). Figure 2-63 DSC analysis of P(styrene-b-ECH). The data from the second heating curve were collected which reveals two Tg, one at –27 ºC corresponding to the PECH block and one at 74 ºC corresponding to the PS block. 72 Figure 2-64 600 MHz 2D DOSY NMR spectra obtained at 298 K in Chloroform-d solution of the PS-b-PECH. 1H NMR (600 MHz, Chloroform-d) δ 7.25- 6.30 (bm, -CH2-CH(Ph)-), 3.77- 3.49 (broad m, -OCH2CH(CH2Cl)O-), 2.07-1.10 (bm, -CH2-CH(Ph)-). Figure 2-65 1H NMR spectroscopy of (P(styrene-b-ECH). 1H NMR (500 MHz, cdcl3) δ 7.25-6.30 (bm, -CH2-CH(Ph)-), 3.77- 3.49 (bm, -OCH2CH(CH2Cl)O-), 2.07-1.10 (bm, -CH2-CH(Ph)-). 73 Figure 2-66 1H NMR spectroscopy of targeted 30K PECH with BnSAlMe2 initiator. 1H NMR (500 MHz, Chloroform-d) δ 3.83-3.39 (bm, -OCH2CH(CH2Cl)O-). Figure 2-67 13C NMR spectroscopy of targeted 30K PECH with BnSAlMe2. 13C NMR (126 MHz, cdcl3) δ 79.18-79.09 (–O–CH2–CH(CH2-Cl)–O–), 69.80 (–O–CH2–CH(CH2-Cl)–O– m), 69.50 (–O–CH2–CH(CH2-Cl)–O– rrm or mrr)), 43.80 (–CH2–Cl). 74 Figure 2-68 1H NMR spectroscopy of targeted 30K PPO with BnSAlMe2 initiator. 1H NMR (500 MHz, Chloroform-d) δ 3.80 – 3.17 (bm, –O–CH2–CH(CH3)–O–), 1.12 (m, -CH3). Figure 2-69 13C NMR spectroscopy of targeted 30K PPO with BnSAlMe2 initiator. 13C NMR (126 MHz, cdcl3) δ 75.89 (–O–CH2–CH(CH3)–O–, mm), 75.68 (–O–CH2–CH(CH3)–O– , mr + rm), 75.48 (–O–CH2–CH(CH3)–O–, rr), 73.71 (–O–CH2–CH(CH3)–O–, m), 73.16 (–O– CH2–CH(CH3)–O–, rrm or mrr), 17.81 (–CH3). 75 Figure 2-70 1H NMR spectroscopy of targeted 30K PBO with BnSAlMe2 initiator. 1H NMR (500 MHz, Chloroform-d) δ 3.68 – 3.25 (bm, –O–CH2–CH(CH2–CH3)–O–), 1.68 – 1.37 (m, CH2– CH3), 0.91 (t, –CH2–CH3). Figure 2-71 13C NMR spectroscopy of targeted 30K PBO with BnSAlMe2 initiator. 13C NMR (126 MHz, cdcl3) δ 80.84-80.42 (–O–CH2–CH(CH2–CH3)–O–), 72.37 (–O–CH2–CH(CH2– CH3)–O–, m), 71.53 (–O–CH2–CH(CH2–CH3)–O–, rrm or mrr)), 24.72 (–CH2–CH3), 9.76 (– CH3). 76 Figure 2-72 1H NMR spectroscopy of targeted 30K PECH with PrSAlMe2 initiator. 1H NMR (500 MHz, Methylene Chloride-d2) δ 3.80 – 3.51 (bm, -OCH2CH(CH2Cl)O-). Figure 2-73 1H NMR spectroscopy of targeted 30K PECH with ClBnSAlMe2 initiator. 1H NMR (500 MHz, Methylene Chloride-d2) δ 3.80 – 3.51 (bm, -OCH2CH(CH2Cl)O-). 77 Figure 2-74 1H NMR spectroscopy of targeted 30K PECH with cPenSAlMe2 initiator. 1H NMR (500 MHz, Methylene Chloride-d2) δ 3.80 – 3.51 (bm, -OCH2CH(CH2Cl)O-). Figure 2-75 1H NMR spectroscopy of P(MMA-b-ECH). 1H NMR (500 MHz, Methylene Chloride-d2) δ 3.99–3.62 (bm, -OCH2CH(CH2Cl)O-), 3.63-3.56 (bm,-CH2C(CH3)(COOCH3)-), 2.19-1.66 (bm, -CH2C(CH3)(COOCH3)-), 1.67 – 0.58 (bm, -CH2C(CH3)(COOCH3)-). 78 Figure 2-76 DSC analysis of P(PO-grad-ECH). The data from the second heating curve were collected which reveals one Tg, one at -41 ºC. Figure 2-77 DSC analysis of P(ECH-b-PO). The data from the second heating curve were collected which reveals two Tg, one at –30 ºC corresponding to the PECH block and one at -67 ºC corresponding to the PO block. 79 Figure 2-78 RI trace of targeted P(ECH-grad-PO). The Mn is determined to be 29.0 kg/mol with Ð = 1.28. Figure 2-79 RI trace of targeted P(ECH-b-PO). The Mn is determined to be 33.4 kg/mol with Ð = 1.27. 80 BIBLIOGRAPHY 81 BIBLIOGRAPHY (1) Scharfenberg, M.; Hofmann, S.; Preis, J.; Hilf, J.; Frey, H. Rigid Hyperbranched Polycarbonate Polyols from CO2 and Cyclohexene Based Epoxides. 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Simple and Accurate Determination of Reactivity Ratios Using a Nonterminal Model of Chain Copolymerization. Macromolecules 2015, 48 (7), 6922− 6930. 86 Chapter 3. Investigation of Aluminum-based initiators for Propylene Sulfide (Co)Polymerization with Compositional and Architectural Control 3.1 Introduction Poly(propylene sulfide) (PPS) is a versatile, non-toxic, sulfur-containing polymer that has widespread use in biomedical1-3 and patterning4, 5 contexts. The sulfur in the polymer backbone can readily be converted to hydrophilic sulfone groups in the presence of oxidative species, making PPS ideal for targeted drug delivery.6 Additionally, PPS consisting of pure converted sulfone groups undergoes interesting solvent-mediated self-assembly.7 Sigwalt and co-workers demonstrated classical anionic polymerization of PS in the 1960’s using sodium naphthalene as an initiator.8 Modern anionic synthesis of PPS utilizes thiolate anions as an initiator either produced directly from deprotonation of a thiol or via protected thiol ala acyl group transfer.6 While these methods are effective, they typically produce polymers with molecular weight ca. 10 kg/mol. Very recent work by Rumyantsev demonstrated PPS at molecular weights above 100 kg/mol at Ð < 1.4 using xanthates, but molecular weight control was not straightforward.9 Initiation from thiolates is robust, and several thiols with a variety of chemistries and structures are available for end group and / or architecture control. For instance, dithiols can be employed to create ABA co-polymers10 and multi-armed thiols11, 12 can be used to create star polymers. This architectural and chemical control over PPS, along with the ability of PPS to switch from a hydrophobic to hydrophilic character as well as PPS inherent biocompatibility has made it practically ubiquitous as a component in drug delivery schemes. PPS is frequently paired with other biologically relevant polymers. PPS acts as the hydrophobic block in a block copolymer paired with a hydrophilic polymer, like poly(ethylene glycol) (PEG). Amphiphilic block copolymers consisting of PPS and another hydrophilic block have been used 87 to create vesicular13, 14 and micellar structures11 through self-assembly that hold medicinal cargo, which can be released in the presence of oxidative species that causes the PPS block to become hydrophilic. Hubbell and Tirelli have develop synthetic methods for block-co-polymers containing PPS. Typically, either a macroinitiator6, 15, 16 or a coupling strategy16 is employed for block copolymer synthesis; in the former case the second polymer is polymerized from the first polymer and in the latter case two pre-formed polymers are coupled end to end (e.g., through a ‘click’ reaction). Both methods require multiple steps. Recently, Frey and co-workers17 demonstrated the use of a multifunctional initiator, cysteine, to synthesize copolymers of PPS and sarcosine of varying ratio by a protection / deprotection strategy for the cysteine. Wang and co-workers employed a combined RAFT and AROP polymerization strategy to copolymerize PPS with N-isopropylmethacrylamide (NIPMAM).18 However, this resulted in some incorporation of the NIPMAM into the PS block. Developing facile synthetic techniques that allow for synthesizing PS containing block copolymers, especially those with epoxides, through sequential addition of monomer would allow for finer control over copolymer physical properties and increase access to these materials. Aside from block copolymers, copolymers containing both ethers and sulfur in the backbone have found use in optical and electronic applications.19, 20 Frequently, these polymers are produced through the alternating copolymerization of epoxides and sulfur containing species like carbonyl sulfide21 and carbon disulfide.22 Aside from alternating copolymers, limited compositional control over copolymers from epoxides and thiol containing monomers has been demonstrated. Episulfides in particular are difficult to copolymerize with epoxides due to the propensity of the episulfide to homopolymerize20, 23 resulting in block- instead of statistical- copolymers. While some patents exist involving statistical-copolymers of epoxides and 88 episulfides, they only achieve a small percentage (<10%) of epoxide incorporation.24, 25 Diversifying the epoxide monomers compatible with PS in copolymerization schemes will allow for new PPS materials with tunable or unique property sets. In this work, we investigate our previously report SAl initiators26 with NAl catalyst for PS and PS-co-epoxide polymerizations. We explore molecular weight control of PPS by tuning PS to initiator ratio and quantify this by size exclusion chromatography (SEC) and NMR spectroscopy. The influence of catalyst and initiator interaction on polymerization control and kinetics is characterized through 1H NMR spectroscopy and SEC. Copolymerization of PS and epoxides are performed to determine polymer compositional control. Finally, we demonstrate both block and statistical copolymers and characterize these polymers through 1H, 13C, and diffusion ordered NMR spectroscopy as well as SEC, differential scanning calorimetry (DSC), and small angle X-ray scattering (SAXS). Initiator chemistry was varied to control polymer architecture, and we synthesized both ABA copolymers and star (co)polymers. Synthesis of biomedically applicable poly(EG-b-PS) was achieved by the addition of PS to macroinitiator PEG. This work demonstrates methods that allow for the direct synthesis of PS-block-epoxide polymers as well as the statistical copolymerization of PS and epoxide, which has been difficult to achieve in the past. 3.2 Experimental section 3.2.1 Materials Trimethylaluminum solution (AlMe3, 2.0 M in hexane), triethylamine (TEA, ≥99.5%), benzyl mercaptan (99%), benzyl alcohol, 1-propane thiol (99%), 1,3-Propanedithiol (Sigma-Aldrich, 99%), pentaerythritol tetrakis(3-mercaptopropionate) (99%), and polyethylene glycol (5500 g/mol) were purchased from Sigma-Aldrich. CDCl3 (Cambridge Analytica) was used without 89 any further purification. Hexanes (Sigma Aldrich, anhydrous, >99%) was used for initiator / catalyst purification in the glovebox. Methanol (MeOH, Fisher, Certified ACS), hexane (Fisher, Certified ACS), and dichloromethane (DCM, Fisher, Certified ACS) were used for washing the polymers. Propylene sulfide (PS, 96%, ACROS Organics), propylene oxide (PO, Sigma-Aldrich, GC, ≥99.5%), and epichlorohydrin (ECH, Sigma-Aldrich, ≥99%), were all used as received. All air and moisture-sensitive reactions were prepared under a dry nitrogen atmosphere inside a glovebox. 3.2.2 Characterization 1 H NMR spectroscopy was performed on a 500 MHz Varian NMR spectrometer at room temperature, and chemical shifts are reported in parts per million (ppm), referenced using the residual 1H peak from the deuterated solvent. The structure of the compounds was determined by 13C NMR spectroscopy on a 126 MHz Varian NMR spectrometer. All diffusion ordered spectroscopy (DOSY) measurements were performed at 25 °C on a Varian Inova 600 spectrometer operating at 599.72 MHz and equipped with a 5 mm Z-gradient HCN inverse probe capable of producing gradients in the Z direction with a strength of 63 G/cm. All DOSY measurements were run using the dbppste pulse sequence with 128−160 scans and 20 increments with gradient strengths from 2.7 to 59.22 G/cm. The relaxation delay was set to 3 s, the diffusion delay to 24 ms, and the gradient length to 2.0 ms. Size-exclusion chromatography (SEC) was carried out on the Malvern OMNISEC system with an isocratic pump, degasser, and temperature-controlled column oven held at 35 °C containing 2 Viscotek 300 × 8.0 mm2 columns (T3000 and T4000) with an exclusion limit of 400 kDa. Triple detection with light scattering, viscometer, and the refractive index has been used for the absolute molecular weight determination of the polymers. The reported Mn are all absolute molecular weights. Differential 90 scanning calorimetric (DSC) tests were conducted on a TA250 instrument with a heating rate of 10 °C/min under a N2 atmosphere, and the data from the second heating curve were collected. PPS homopolymer was analyzed by electrospray ionization with mass spectrometry (ESI-MS) in positive ion mode using a Waters Xevo G2XS Q-Tof mass spectrometer interfaced with a Waters Acquity UPLC. Five microlitres of a sample (diluted in 90% methanol containing 1 mM ammonium formate) was flow-injected (no UPLC column) using a mobile phase of 80% methanol and 20% 10 mM ammonium formate in water pumped at 0.2 mL/min. SAXS measurements were performed at the beamline 12-ID-B at Advanced Photon Source of Argonne National Laboratory with the x-ray energy of 13.3 keV with a two-dimensional (2-D) Pilatus 2M detector. The sample to detector distance was set to 2.0 m. In all measurements, the sample thickness was kept around 0.1 mm and the exposure time of 0.5 s. The scattering of the air has been measured as the background noise. 3.2.3 Synthesis of trimethylaluminum and triethylamine Adduct (NAl) In a reaction vial with a stir bar, 6.35 mL of anhydrous hexanes and 2.0 M AlMe3 in hexane (6.35 mL, 12.7 mmol) were added and cooled to −78 °C. Then, triethylamine (1.5 mL, 10.7 mmol) was added dropwise into the vial. The solution was set to stir and warm to room temperature overnight. To crystallize the desired product, the solution was then directly cooled to −40 °C and the resultant crystals were washed three times with anhydrous hexanes (3 × 5 mL) and dried in vacuo. 1H NMR (500 MHz, CDCl3) δ 2.80 (q, 6H, 3(CH3CH2)N:Al(CH3)3), 1.18 (t, 9H, 3(CH3CH2)N:Al(CH3)3), −0.89 (s, 9H, 3(CH3CH2)N:Al(CH3)3). 13C NMR (126 MHz, CDCl3) δ 64.54 3(CH3CH2)N:Al(CH3)3), 47.78 3(CH3CH2)N:Al(CH3)3, 9.20 3(CH3CH2)N:Al(CH3)3). 91 3.2.4 Synthesis of (Benzylthio)dimethylaluminum (BnSAlMe2), (benzyloxy)dimethylaluminum (BnOAlMe2) and dimethyl(propylthio)aluminum (PrSAlMe2) In a 20 mL vial, anhydrous hexane (6.35 mL) and 2.0 M AlMe3 in hexanes (6.35 mL, 12.7 mmol) were added and cooled down to −78 °C. Then, benzyl mercaptan/benzyl alcohol/propyl thiol (12.7 mmol) was added dropwise, and the solution was stirred for 24 h while warming to room temperature. To remove unreacted AlMe3 and purify the initiator, the synthesized compound was washed three times with anhydrous hexanes (3 × 5 mL) and dried in vacuo. BnSAlMe2: 1H NMR and 13C NMR spectrum of BnSAlMe2. 1H NMR (500 MHz, CDCl3) δ 7.38 to 7.21 (m, 5H, PhCH2S-Al(CH3)2), 3.91 (s, 2H, PhCH2S-Al(CH3)2), -0.43 (s, 6H, PhCH2SAl(CH3)2). 13C NMR (126 MHz, CDCl3) δ141.46, 128.56, 127.97, 126.89 (PhCH2S- Al(CH3)2, 32.00 (PhCH2S-Al(CH3)2), 28.78 (PhCH2S-Al(CH3)2). BnOAlMe2: 1H NMR (500 MHz, CDCl3) δ 7.47 – 7.38 (m, 5H, PhCH2O-Al(CH3)2), 3.33 (s, 2H, PhCH2O-Al(CH3)2), 0.15 - -0.6 (s, 6H, PhCH2OAl(CH3)2). b) 13C NMR (126 MHz, CDCl3) δ138.64, 137.57, 130.04, 126.69 (PhCH2O-Al(CH3)2, 50.76 (PhCH2O-Al(CH3)2), -7.71 (PhCH2O-Al(CH3)2). PrSAlMe2: 1H NMR (500 MHz, CDCl3) δ 2.62 (m, 2H, CH3CH2CH2S-Al(CH3)2), 1.65 (dq, 2H, CH3CH2CH2S-Al(CH3)2), 1.04-0.95 (m, 3H, CH3CH2CH2S-Al(CH3)2), -0.49 (S, 6H, CH3CH2CH2S-Al(CH3)2). 13C NMR (126 MHz, CDCl3) δ 30.33 (CH3CH2CH2S-Al(CH3)2), 25.97 (CH3CH2CH2S-Al(CH3)2), 13.15 (CH3CH2CH2S-Al(CH3)2), -9.21 (CH3CH2CH2S- Al(CH3)2). 3.2.5 Synthesis of di-functional initiator (d-H) A reaction vial was charged with a stir bar and AlMe3 (12.7 mmol, 6.35 mL) and anhydrous hexane (6.35 mL), cooled to −78 °C. 1,3-propanedithiol (12.7 mmol, 1.37 g, 1.27 ml) was added 92 dropwise into the reaction vial containing trimethylaluminum. The solution was set to stir and warm to room temperature overnight. The resultant white powders were washed three times with anhydrous hexanes and dried in vacuo. 1H NMR and 13C NMR spectra of the d-H initiator. 1H NMR (500 MHz, CDCl3) δ 3.41-1.70 (b, 2(CH3)Al-CH2CH2CH2S-Al(CH3)2, 6H). -0.24 to -0.92 (b, 2(CH3)Al-CH2CH2CH2S-Al(CH3)2, 6H), 13C NMR (126 MHz, CDCl3) δ 29.65 2(CH3)Al- CH2CH2CH2S-Al(CH3)2, 27.73 2(CH3)Al-CH2CH2CH2S-Al(CH3)2, 11.312(CH3)Al- CH2CH2CH2S-Al(CH3)2. 3.2.6 Synthesis of tetra-functional initiator (t-H) To a solution of AlMe3 (12.7 mmol, 6.35 mL) and anhydrous hexane (6.35 mL) at −78 °C, pentaerythritol tetrakis(3-mercaptopropionate) (12.7 mmol, 6.20 g, 4.85 ml) was added dropwise. The reaction mixture was stirred and warmed up to room temperature overnight. The resultant yellow powders were washed three times with anhydrous hexanes and dried in vacuo. 1H NMR (500 MHz, CDCl3) δ 4.21-1.42 (24 H, -[C-CH2COOCH2CH2S-Al(CH3)2]4-), -0.36 to -1.09 (24 H, -[C-CH2COOCH2CH2S-Al(CH3)2]4-). 13C NMR (126 MHz, CDCl3) 198.53 -[C- CH2COOCH2CH2S-Al(CH3)2]4-), 42.42-[C-CH2COOCH2CH2S-Al(CH3)2]4-), 31.61-[C- CH2COOCH2CH2S-Al(CH3)2]4-), 29.61, -[C-CH2COOCH2CH2S-Al(CH3)2]4-), 25.10 -[C- CH2COOCH2CH2S-Al(CH3)2]4-), 9.81-[C-CH2COOCH2CH2S-Al(CH3)2]4-). 3.2.7 Procedure for synthesis of poly(propylene sulfide) and its purification using BnsAlMe2 or BnOAlMe2 In a 20 mL septum-capped scintillation vial with a stir bar and under nitrogen atmosphere, BnSAlMe2 (0.018 g, 0.01 mmol) or BnOAlMe2 (0.016 g, 0.01 mmol), NAl (0.0175 g, 0.01 mmol), and propylene sulfide (3.19 mL, 3g, 0.040 mol) were added. The solution was heated to 50 °C until the completion of the polymerization. The 93 reaction was quenched with methanol and dissolved in dichloromethane. The resulting solution was added dropwise into acidic MeOH (0.01 M HCl in MeOH) to precipitate and washed three times with water to remove residual aluminum. After precipitation out of MeOH, the polymer was dried in vacuo overnight at 70 °C. SEC with refractive index, light scattering, and viscosity detectors determined absolute molecular weights and polydispersities. Also, Mn was determined by 1H NMR spectroscopy by taking the ratio of the backbone proton signals to the integral of the end group signal on the initiator. Resultant PPS is also characterized by 1H NMR spectroscopy, 13C NMR spectroscopy, and DSC. 1H NMR (500 MHz, CDCl3) δ 2.91- 2.80 (m, −S−CH2−CH(CH3)−S−), 2.65-2.58 (m, −S−CH2−CH(CH3)−S−), 1.39 (m, −S−CH2−CH(CH3)−S−). 13C NMR (126 MHz, CDCl3) δ 41.14 (−S−CH2−CH(CH3)−S), 38.18 (−S−CH2−CH(CH3)−S), 20.63 (−S−CH2−CH(CH3)−S−). 3.2.8 Procedure for one-pot synthesis of poly(ECH-stat-PS) using BnSAlMe2 as an initiator Polymerization was performed in a septum-capped reaction vial. The vial was charged with BnSAlMe2 (0.022 g, 0.12 mmol), NAl (0.020 g, 0.12 mmol), 1.6 g of PS (0.021 mol, 1.69 ml), ECH (1.69 mL, 2 g, 0.021 mol), and a stir bar at 50 °C. After the full conversion of monomers, the mixture was diluted with DCM and precipitated in a 3-fold excess of acidic methanol (0.01 M). The copolymer was dried under a vacuum at room temperature. Polydispersity and Mn were characterized by SEC, and the structure of the copolymer was investigated by 1H NMR, 13C NMR, and DOSY NMR spectroscopy. The thermal properties of the copolymer were studied using DSC. Poly(ECH-stat-PS): 1H NMR (500 MHz, CDCl3) δ 3.80-3.29 (bm, −O−CH2−CH(CH2Cl)−O−), 3.16-2.51 (bm, −S−CH2−CH(CH3)−S−), 1.63-1.54 (m, −O−CH2−CH(CH2Cl)−O− and −S−CH2−CH(CH3)−S−), 1.40-1.33 (m, −S−CH2−CH(CH3)−S−), 1.37-1.17 O−CH2−CH(CH2Cl)−O− and −S−CH2−CH(CH3)−S−). 13C NMR (126 MHz, CDCl3) 94 79.37(−O−CH2−CH(CH2Cl)−O−), 75.58 (−O−CH2−CH(CH2Cl)−O−), 44.72 (−O−CH2−CH(CH2Cl)−O−), 41.16 (−S−CH2−CH(CH3)−S−) , 38.39 (−O−CH2−CH(CH2Cl)−O− and −S−CH2−CH(CH3)−S−), 20.63 (−S−CH2−CH(CH3)−S−) , 20.85 (−O−CH2−CH(CH2Cl)−O− and −S−CH2−CH(CH3)−S−), 18.59 (−S−CH2−CH(CH3)−S−). 3.2.9 Procedure for one-pot synthesis of poly(PO-stat-PS) using BnSAlMe2 as an initiator Polymerization was performed in a septum-capped reaction vial. The vial was charged with BnSAlMe2 (0.027 g, 0.15 mmol), NAl (0.026 g, 0.15), PS (2.69 mL, 0.034 mol), PO (2.4 mL, 2 g, 0.034 mol) and a stir bar at 50 °C. After the full conversion of monomers, the mixture was diluted with DCM and precipitated in a 3-fold excess of acidic methanol (0.01 M). The copolymer was dried under a vacuum at room temperature. Polydispersity and Mn were characterized by SEC, and the structure of the copolymer was investigated by 1H NMR, 13C NMR, and DOSY NMR spectroscopy. The thermal properties of the copolymer were studied using DSC. Poly(PO-stat-PS): 1H NMR (500 MHz, CDCl3) δ 3.83-3.24 (bm, −O−CH2−CH(CH3)−O−), 3.10-2.41 (bm, −S−CH2−CH(CH3)−S−, −O−CH2−CH(CH3)−O− and −S−CH2−CH(CH3)−S−), 1.32-1.42 (m, −S−CH2−CH(CH3)−S−), 1.30-1.19 (bm, −O−CH2−CH(CH3)−O− and −S−CH2−CH(CH3)−S−), 1.17-1.04 (m, −O−CH2−CH(CH3)−O−).13C NMR (126 MHz, CDCl3) δ75.85 (−O−CH2−CH(CH3)−O−), 73.34 (−O−CH2−CH(CH3)−O−), 72.90 (−O−CH2−CH(CH3)−O− and −S−CH2−CH(CH3)−S), 41.23 (−S−CH2−CH(CH3)−S−), 38.10 (−S−CH2−CH(CH3)−S−), 20.8 (−O−CH2−CH(CH3)−O− and −S−CH2−CH(CH3)−S), 19.3 (−S−CH2−CH(CH3)−S−), 17.4 (−O−CH2−CH(CH3)−O−). 3.2.10 Procedure for synthesis of poly(ECH-b-PS) using BnSAlMe2 as an initiator BnSAlMe2 (0.024 g, 0.13 mmol) and NAl (0.023 g, 0.13 mmol) were added into a vial with a stir bar. After adding ECH (1.69 mL, 2 g, 0.0216 mol), the vial was placed on the hotplate at 50 95 °C. When the first monomer was fully converted (determined by 1H NMR spectroscopy), PS (1.69 mL, 1.6 g, 0.0216 mol) was injected into the vial. The stirring was continued at 50 °C for enough time until the second monomer is fully converted. The product was then dissolved in DCM, and the resulting solution was precipitated out of MeOH to yield the desired polymer product. The supernatant was removed, and the copolymer was dried in vacuo at 70 °C. The block copolymer was characterized by 1 H NMR, 13C NMR, and DOSY NMR spectroscopy. SEC analysis was performed to determine Mn and polydispersity. The glass transition corresponding to each block confirmed by DSC. Poly(ECH-b-PS): 1H NMR (500 MHz, CDCl3) δ 3.72−3.2 (bm, −O−CH2−CH(CH3)−O−), 2.91-2.54 (bm, −S−CH2−CH(CH3)−S−), 1.31 (m, −S−CH2−CH(CH3)−S−), 1.11 (m, −O−CH2−CH(CH3)−O−). 13 C NMR (126 MHz, CDCl3) δ 78.97 (−O−CH2−CH(CH2Cl)−O−), 69.51 (−O−CH2−CH(CH2Cl)−O), 43.47 (−O−CH2−CH(CH2Cl)−O−), 41.17 (−S−CH2−CH(CH3)−S−), 38.24 (−S−CH2−CH(CH3)−S−), 20.86 (−S−CH2−CH(CH3)−S−). 3.2.11 Procedure for synthesis of poly(PO-b-PS) using BnSAlMe2 as an initiator BnSAlMe2 (0.024 g, 0.13 mmol) and NAl (0.023 g, 0.13 mmol) were added into a vial with a stir bar. Adding of the PO (2.4 mL, 2 g, 0.034 mol), the vial was placed on the hotplate at 50 °C. When the first monomer was fully converted (determined by 1H NMR spectroscopy), PS (2.69 mL, 2.5 g, 0.034 mol) was injected into the vial. Stirring was continued at 50 °C for enough time until the second monomer is fully converted. The product was then dissolved in DCM, and the resulting solution was precipitated out of MeOH to yield the desired polymer product. The supernatant was removed, and the polymer was dried in vacuo at 70 °C. The block copolymer was characterized by 1H NMR, 13C NMR, and DOSY NMR spectroscopy. SEC analysis was performed to determine Mn and polydispersity and the glass 96 transition corresponded to each block confirmed by DSC. Poly(PO-b-PS): 1H NMR (500 MHz, CDCl3) δ 3.77-3.55 (bm, −O−CH2−CH(CH2Cl)−O−), 2.91-2.80 (m, −S−CH2−CH(CH3)−S−), 2.65-2.58 (m, −S−CH2−CH(CH3)−S−), 1.35 (m, −S−CH2−CH(CH3)−S−). 13C NMR (126 MHz, CDCl3) δ 75.26 (−O−CH2−CH(CH3)−O−), 73.35 (−O−CH2−CH(CH3)−O−), 40.6 (−S−CH2−CH(CH3)−S−), 37.9 (−S−CH2−CH(CH3)−S−), 20.98 (−S−CH2−CH(CH3)−S−), 16.83 (−O−CH2−CH(CH3)−O−). 3.2.12 Procedure for synthesis of poly(PS-b-PO) by d-H initiator To a mixture of NAl (0.0175 g, 0.1 mmol) and di-functional initiator (0.0220 g, 0.1 mmol) in a septum-capped vial, 3 g of PS (3.17 mL, 0.04 mol) was added. The reaction mixture was placed at 50 °C bath. Conversion of PS was followed by 1H NMR spectroscopy, and after full conversion of monomer, 2.32 g of PO (2.8 mL, 0.04 mol) was added to the vessel. The polymerization was quenched by MeOH after completion of the polymerization. The product was then dissolved in DCM, and the resulting solution was precipitated out of MeOH to yield the desired copolymer product. The supernatant was removed, and the polymer was dried in vacuo at 70 °C. Block copolymers were characterized by 1H NMR, 13C NMR, and DOSY NMR spectroscopy. SEC analysis was performed to determine Mn and Đ. Glass transition corresponded to each block confirmed by DSC. d-H poly(PO-b-PS): 1H NMR (500 MHz, CDCl3) δ 3.72−3.2 (bm, −O−CH2−CH(CH3)−O−), 2.91-2.54 (bm, −S−CH2−CH(CH3)−S−), 1.31 (m, −S−CH2−CH(CH3)−S−), 1.11 (m, −O−CH2−CH(CH3)−O−). 13C NMR (126 MHz, CDCl3) δ 75.26 (−O−CH2−CH(CH3)−O−), 73.35 (−O−CH2−CH(CH3)−O−), 40.6 (−S−CH2−CH(CH3)−S−), 37.9 (−S−CH2−CH(CH3)−S−), 20.98 (−S−CH2−CH(CH3)−S−), 16.83 (−O−CH2−CH(CH3)−O−). 97 3.2.13 Procedure for synthesis of poly(PS-b-PO) by t-H initiator NAl (0.017 g, 0.1 mmol), tetra-functional initiator (0.022 g, 0.1 mmol), and PS (2 g, 0.033mmol, 2.11 mL) were heated in a vial until full conversion of PS (followed by 1H NMR spectroscopy). Then, PO (1.93 g, 0.033 mmol, 2.3 mL) was added to the reaction vial. The polymerization was quenched by MeOH when all the PO was polymerized. The crude product was precipitated in acidic methanol, and the precipitate was dried in vacuo a 70 °C overnight to obtain pure copolymer product. The copolymer was fully characterized by SEC, DSC, 1H NMR, 13C NMR, and DOSY NMR spectroscopy. t-H poly(PO-b-PS): 1H NMR (500 MHz, CDCl3) δ 3.72−3.2 (bm, −O−CH2−CH(CH3)−O−), 2.91-2.54 (bm, −S−CH2−CH(CH3)−S−), 1.31 (m, −S−CH2−CH(CH3)−S−), 1.11 (m, −O−CH2−CH(CH3)−O−). 13C NMR (126 MHz, CDCl3) δ 75.26 (−O−CH2−CH(CH3)−O−), 73.35 (−O−CH2−CH(CH3)−O−), 40.6 (−S−CH2−CH(CH3)−S−), 37.9 (−S−CH2−CH(CH3)−S−), 20.98 (−S−CH2−CH(CH3)−S−), 16.83 (−O−CH2−CH(CH3)−O−). 3.2.14 Procedure for control experiments by kinetics Studies using 1H NMR spectroscopy of BnSAlMe2 and NAl, only NAl, and only BnSAlMe2 or PS polymerization: With only BnSAlMe2 In a glove box, a reaction vial was charged with a stir bar, BnSAlMe2 (0.063 g, 0.349 mmol), and PS (1 mL, 1 g, 0.013 mol). With only NAl: In a glove box, a reaction vial was charged with a stir bar, NAl (0.057 g, 0.332 mmol), and PS (1 mL, 1 g, 0.013 mol). With both NAl and BnSAlMe2: In a glove box, a reaction vial was charged with a stir bar, NAl (0.057 g, 0.332 mmol), BnSAlMe2 (0.063 g, 0.349 mmol), and PS (1 mL, 1 g, 0.013 mol). For all these experiments, the reaction vials heated up to 50 °C and small aliquots (ca. 30 µL) every 15 minutes were taken. These samples were dissolved in d-chloroform and conversion was determined using 1H NMR spectroscopy. The conversion of each monomer was calculated 98 based on the integration of the backbone area to the unreacted corresponding monomer by 1H NMR spectroscopy. The samples were quenched by exposing them to the air, which deactivates the catalyst. 3.2.15 Procedure for Kinetics Studies by 1H NMR spectroscopy of d-H initiator and PrSAlMe2 for PS polymerization In a glove box, a reaction vial was charged with a stir bar, d-H (0.0044, 0.1 mmol) or PrSAlMe2 (0.0026 g, 0.1 mmol), and NAl (0.0034 g, 0.1 mmol for PrSAlMe2 and 0.0068 g, 0.2 mmol for d-H initiator). Then, PS (2 g, 0.033 mol, 2.11 mL) was added. The reaction vial heated up to 50 °C and small aliquots (ca. 30 µL) every 15 minutes for 3 hours were taken. These samples were dissolved in d-chloroform, and conversion was determined using 1H NMR spectroscopy. The conversion of each monomer was calculated based on the integration of the backbone area to the unreacted corresponding monomer by 1H NMR spectroscopy. The samples were quenched by exposing them to the air, which deactivates the catalyst. 3.2.16 Procedure for synthesis of poly(EG-b-PS) In a vial equipped with a stir bar, 1.5 g of PEG dissolved in 3 ml anhydrous benzene and purged with N2. After dissolution, 0.1 ml of AlMe3 solution was added dropwise to the dissolved PEG forming a macroinitiator. Further, PS (1 g, 0.013 mol, 0.092 ml) and NAl (0.03 g, 0.041 mmol) were added to the solution, and the reaction heated up to 50 °C overnight. After full consumption of PS, the solution was exposed to air and, the excess benzene was evaporated. The residue then dissolved in 2 ml DCM, precipitated out of MeOH, and dried on the vacuum at 70 °C. 1H NMR (500 MHz, CDCl3) δ 3.65-3.48 (b, −O−CH2−CH2−O−), 2.92-2.78 80 (m, −S−CH2−CH(CH3)−S−), 2.66-2.59 (m, −S−CH2−CH(CH3)−S−), 1.38 (m, 99 −S−CH2−CH(CH3)−S−). 13C NMR (126 MHz, CDCl3) δ 70.55 (−O−CH2−CH2−O−), 41.26 (−S−CH2−CH(CH3)−S−), 38.38 (−S−CH2−CH(CH3)−S−), 20.79 (−S−CH2−CH(CH3)−S−). 3.3 Results and discussion Previously, we developed a thio-aluminum based (SAl) initiator that quickly and controllably polymerized epoxides in the presence of a Lewis pair (LP) catalyst consisting of triethyl amine and trimethyl aluminum (NAl).26 Since we suspect initiation occurs from a thiolate ion, we hypothesized that this would be amenable to episulfide polymerization. To test this idea, we investigated the homopolymerization of propylene sulfide (PS) with our SAl initiator (BnSAlMe2) and NAl (Et3NAlMe3) catalyst. BnSAlMe2 and NAl were synthesized by previously reported methods.26, 27 PS polymerization was performed neat at 50 °C in the presence of BnSAlMe2 and NAl catalyst in an equimolar ratio, which resulted in PPS with a yield of 94.2% after purification procedure. A scheme of this reaction can be seen in Scheme 3-1. PPS was characterized via size-exclusion chromatography (SEC) with triple detection and the absolute Mn was found to be 33.7 kg/mol with polydispersity (Đ) = 1.21 (Figure 3-1b, purple line), consistent with the targeted molecular weight of 30 kg/mol. The Mn determined by SEC compared favorably to the molecular weight calculated through 1H NMR spectroscopy via end group analysis of 36.2 kg/mol (SI, Figure 3-9 a). The 13C NMR revealed an atactic PPS, in line with polyethers synthesized previously.26 The results for this polymerization can be found in Table 3-1, entry 2. It should be noted that the polymerization time in the table refers to the time at which the polymerization was terminated with conversion > 99%. This polymer was further characterized by differential scanning calorimetry (DSC) and showed one glass transition temperature (Tg) at –41 °C (SI, Figure 3-10), in accordance with the literature value.28 100 Scheme 3-1 Data exclusion criteria with number of included and excluded subjects and measurement sets. Control over PPS molecular weight was achieved by varying the monomer to initiator ratio ([M0]/[I0]) with constant catalyst concentration (63.5 μmol). Molecular weights of 15, 30, 50, 75, and 100 kg/mol were targeted. Here, we have direct control over Mn through [M0]/[I0], which differs from a recent report that demonstrates high Mn PPS.9 The Mn determined by SEC and end group analysis via 1H NMR spectroscopy was consistent with the targeted molecular weights. Bottom is a plot of the molecular weight (left) and Đ (right) as a function of the [M0]/[I0]. A linear fit (blue line) to the molecular weight data is provided to emphasize the controlled nature of the polymerization. The commensurate SEC traces for these polymers can be seen in the Figure. The molecular weight was narrow with Đ ≈ 1.25 in most cases, further suggesting a controlled polymerization. We also synthesized 5 kg/mol PPS and characterized it with ESI-MS (SI, Figure 3-11) to confirm end group structure. The ESI-MS shows that a single end group from the initiator ligand remains on each polymer, suggesting linear chain growth proceeding from the BnSAlMe2 initiator. 101 Table 3-1 Polymerization and copolymerization characteristics. Entry Polymer Initiator Time Mn(theo) Mnb Mnc Đc (hr.)a (kg/mol) (kg/mol) (kg/mol) 1 PPS BnSAlMe2 6 15 14.8 14.3 1.20 2 PPS BnSAlMe2 10 30 33.7 36.2 1.21 3 PPS BnSAlMe2 48 50 47.1 46.7 1.32 4 PPS BnSAlMe2 70 70 68.4 67.7 1.35 5 PPS BnSAlMe2 102 100 98.2 97.1 1.24 6 P(ECH-stat-PS) BnSAlMe2 168 30 29.2 27.3 1.56 7 P(PO-stat-PS) BnSAlMe2 72 30 30.8 28.6 1.21 8 P(ECH-b-PS) BnSAlMe2 168 30 29.9 30.3 1.74 9 P(PO-b-PS) BnSAlMe2 72 30 29.6 27.8 1.32 10 PPS d-H 5 30 34.5 - 1.37 11 P(PS-b-PO) d-H 24 30 29.8 - 1.39 12 PPS d t-H 10 80 88.7 - 1.51 13 (PS-b-PO) d t-H 24 80 84.3 - 1.09 14 PPS PrSAlMe2 5 30 32.3 31.1 1.21 15 PPS BnOAlMe2 48 30 31.7 32.4 1.24 16 P(EG-b-PS)e mPEGAlMe2 18 20 22.2 23.8 1.18 a Time terminated at > 99% conversion as determined by 1H NMR spectroscopy. b Absolute molecular weight and Đ determined from SEC with LS, RI, and viscometry triple detection system. c Determined from end group analysis of the 1H NMR spectra. d Polymerizations were conducted at room temperature. Reaction condition: NAl (1 mmol), initiator (1 mmol), PS (0.4 mol), and for synthesis of copolymers we used (1:1) ratio of monomers. e Initiated from macroinitiator. 102 Figure 3-1 a) Plot of Mn (left axis, blue circles) and Đ (right axis, red triangles) as a function of the PS to BnSAlMe2 ratio ([PS]/[BnSAlMe2]). Mn increased linearly at increasing ratio of propylene sulfide with Đ < 1.4. b) SEC traces for PPS with different targeted molecular weights. blue, for 15 kg/mol targeted PPS, the Mn is determined to be 14.8 kg/mol with Đ of 1.20. purple, for 30 kg/mol targeted PPS, the Mn is determined to be 33.7 kg/mol with Đ of 1.21. green, for 50 kg/mol targeted PPS, the Mn is determined to be 47.1 kg/mol with Đ of 1.32. pink, for 70 kg/mol targeted PPS, the Mn is determined to be 68.4 kg/mol with Đ of 1.35. red, for 100 kg/mol targeted PPS, the Mn is determined to be 98.2 kg/mol with Đ of 1.24. We investigated the polymerization kinetics of PS in the presence of only initiator (BnSAlMe2), only catalyst (NAl), and both catalyst and initiator. For each experiment, we targeted 20 kg/mol PPS. The polymerization kinetics were determined by monitoring the monomer conversion with 1H NMR spectroscopy over time and a linear fit to -ln([PS]/[PS]0) vs. time was used to determine the observed rate constant (kobs). For the case with catalyst and initiator, the polymerization proceeded swiftly, and the kobs was found to be 1.67 ± 0.19 ×10-3 s-1, which corresponds to conversion > 95% after time < 1 hour. Furthermore, characterization with SEC reveals a Mn = 21.2 kg/mol with a Ð = 1.23, in line with the targeted Mn. The first order in monomer nature of the kinetics and low Ð suggests the PS polymerization is living. The turnover frequency (TOF) was also calculated and found to be 40.4 hr-1. Unexpectedly, the polymerization 103 rate of PS with only initiator kobs = 1.30 ± 0.16 × 10−3 s−1 was comparable to PPS synthesized using NAl and BnSAlMe2. However, the Mn obtained from SEC for the PPS is 45.3 kg/mol, with Đ = 1.30 more than double the targeted Mn. In the presence of only NAl, PS polymerizes markedly slower than using both catalyst and the initiator with a kobs of 1.32 ± 0.04 × 10−5 s −1 which has an Mn = 47.6 kg/mol and Đ = 1.31, determined by SEC, which also suggests a lack of control. The fact that the presence of only catalyst is sufficient to polymerize PS is in stark contrast to what is observed with epoxides, in which no polymerization occurs without presence of both catalyst and initiator.26, 27 PPS synthesized with only NAl is a classic Lewis pair polymerization; however, without the initiator the Mn cannot be controlled due to irreversible interaction of Lewis pairs (LP) which causes low initiator efficiency and it is the case for several reported LP systems.29-31 Therefore, catalyst and initiator together are involved in a Lewis pair assisted coordination insertion mechanism with an anionic character for PS polymerization. The NAl only polymerization deserves further study and will be investigated as future work. 104 Figure 3-2 . a) Plot of normalized PS concentration over time with BnSAlMe2 initiator and NAl catalyst (green line), plot of normalized PS concentration over time with only BnSAlMe2 initiator (blue line), and plot of normalized PS concentration over time with only NAl catalyst (red line), for polymerization of targeted 20 Kg/mol PS. Monomer concentration was monitored via 1H NMR spectroscopy, and the rate of reactions calculated based on it. The rates are as followings from the slope of each plot, kobs = (1.70 ± 0.19) × 10-3 s -1 with both catalyst and initiator, kobs = 1.32 ± 0.04 × 10-5 s -1 with only catalyst). b) SEC traces of (green) targeted 20 Kg/mol PPS with both the catalyst and the initiator, (red) 20 Kg/mol PPS with only the catalyst, and (blue) 20 Kg/mol PPS with only the initiator. With both the catalyst and the initiator the Mn is close to the targeted MW, Mn = 21.2 Kg/mol and PDI of 1.23. However, by using only the catalyst and only the initiator we lose the control over the MW. In a red SEC trace (only catalyst), the Mn = 47.6 Kg/mol and PDI of 1.31 and blue SEC trace (only initiator) has the Mn = 45.3 Kg/mol with PDI of 1.30. We investigated the statistical copolymerization of PS with epoxides to tune polymer composition. Combining PS with functional epoxides could lead to new biologically relevant materials. Inoue noted the difficulty in typical epoxide-episulfide copolymerization due to the increased reactivity of the episulfide over the epoxide.32 We copolymerized epichlorohydrin (ECH) and propylene oxide (PO) with PS ] in a 1:1 molar ratio with a targeted molecular weight of 30 kg/mol in the presence of BnSAlMe2 and NAl at 50 °C to achieve statistical copolymers, poly(ECH-stat-PS) and poly(PO-stat-PS), respectively. The copolymerizations were monitored 105 by 1H NMR spectroscopy, and the reactivity ratios fit to the nonterminal copolymerization model reported by Beckingham−Sanoja−Lynd (BSL)33 ]. For poly(ECH-stat-PS), the reactivity ratios for ECH (rECH) and PS (rPS) were determined to be rECH = 0.906 ± .043 and rPS = 1.191 ± 0.059 and for poly(PO-stat-PS), the rPO and rPS were calculated to be rPO= 0.905 ± 0.082 and rPS = 1.138 ± 0.108, commensurate with a statistical copolymer that favors PS over epoxide addition. From DSC analysis, P(ECH-stat-PS) and P(PO-stat-PS) presented only one glass transition temperature (Tg) at –40 °C and –46 °C, respectively, consistent with a statistical copolymer of these two monomers (SI, Figure 3-12). SEC and diffusion ordered spectroscopy (DOSY) further corroborate the copolymer structure. SEC (SI, Figure 3-13) showed a single peak with Mn of 29.2 kg/mol and Đ of 1.56 for poly(ECH-stat-PS) (Table 3-1, entry 6) and Mn of 30.8 kg/mol and Đ of 1.21 for poly(PO-stat-PS) (Table 3-1, entry 7). It is unclear why the Đ is much higher for the ECH containing copolymer when compared with the PO containing copolymer. From the 1 H and 13C NMR spectra, there are no additional peaks due to an unexpected side reaction. Furthermore, the DOSY spectra (Figure 3-4, a and b) exhibit the same diffusion coefficient for all the protons pertaining to the polymers, suggesting only one polymer chain is present. Scheme 3-2 Statistical (a) and block (b) copolymerization of PS and epoxides. 106 Figure 3-3 Total conversion as a function of normalized monomer concentration for (a) poly(PO-stat-PS) and (b) poly(ECH-stat-PS). A fit to this data results in the reactivity ratios for each monomer. The reactivity ratios of the monomer pairs are determined to be rPO= 0.905 ± 0.082 and rPS = 1.138 ± 0.108 for poly(PO-stat-PS) and rECH = 0.906 ± 0.043 and rPS = 1.191 ± 0.059 for poly(ECH-stat-PS). 107 Figure 3-4 DOSY NMR of statistical copolymers (a and b) and block copolymers (c and d). The DOSY spectra reveal that there is only one diffusing species for both the statistical and block copolymers, indicating that both monomers share a common backbone. We further synthesized block copolymers of PS and ECH or PO via sequential addition initiated with BnSAlMe2 (Scheme 3-2, b) in the presence of NAl to obtain poly(ECH-b-PS) and poly(PO-b-PS), respectively. The synthetic method does not require any intermediate steps and epoxide, or PS can be directly polymerized from the living chain end of the other. DOSY of the copolymers revealed spectroscopic signals corresponding to PECH or PPO and PPS detected at a similar diffusion coefficient for both block copolymers, at 8.37 × 10−7 cm2/sec for P(ECH-b-PS) and 1.17 × 10−6 cm2/sec for P(PO-b-PS) (Figure 3-4, c and d). This finding suggests that both blocks are in the same polymer chain. Both copolymers were characterized by SEC where poly(ECH-b-PS) had an Mn= 29.9 kg/mol and Đ = 1.74 (Table 3-1, entry 8) and poly(PO-b-PS) 108 had an Mn= 29.6 kg/mol and Đ = 1.32 (Table 3-1, entry 9) and (SI, Figure 3-14). For P(ECH-b- PS), two Tg at -29 °C and -40 °C were observed for PECH block and PS block, respectively (SI, Figure 3-15). For P(PO-b-PS), we observed two Tgs at –70 °C and –47 °C, in agreement with expected values (SI, Figure 3-15 b). Small angle X-ray scattering (SAXS) revealed much stronger scattering intensity than the statistical copolymer at low wavevector, Q <0.3 Å-1, indicating weak phase separation behavior for both block copolymers (SI, Figure 3-16) consistent with the DSC results. Therefore, this is a facile method to produce functional block copolymers of PS and epoxide. As mentioned, true statistical copolymers of episulfides and epoxides were difficult to achieve in the past due to episulfide’s proclivity to homopolymerize when initiated by the thiolate ion. However, in this work, we were able to achieve statistical copolymers of these two disparate monomers suggesting that PS can add similarly as well to what we hypothesize to be a thiolate (from the PS) or oxyanion (from the epoxide) polymer chain end. We, therefore, wondered: does the initiating anion matter? To this end, we polymerized PS from a benzyl alcohol aluminum initiator (BnOAlMe2) in the presence of NAl catalyst. The resultant PPS was characterized by 1H and 13C NMR spectroscopy (SI, Figure 3-17) and Mn (SI, Figure 3-18), characterized by SEC. Both the 1H and 13C NMR spectra were similar to the PPS initiated by the SAl. The Mn was found to be 31.7 kg/mol from SEC which compared favorably with the targeted Mn of 30 kg/mol with Đ =1.24. The Tg was also determined for this polymer from DSC and found to be –42 ºC (SI, Figure 3-19), consistent with the PPS initiated from BnSAlMe2. The difference between the PPS initiated by BnOAlMe2 and BnSAlMe2 was the overall polymerization time. PS was > 99% converted after 48 hours with BnOAlMe2 compared with 10 hours for BnSAlMe2. It has been previously noted34 that the electronegativity of the substituent 109 groups at the aluminum can have a significant effect on the propagation rate for polymerization of heterocycles (i.e., lactones) and so the difference may be due to the difference in electronegativity between sulfur and oxygen. Ultimately, this result suggests that a PS polymerization initiated by either the oxyanion or the thiolate proceed by the same mechanism, but with the oxyanion-initiated polymerization proceeding more slowly. This may explain why we are able to achieve statistical copolymers of epoxides and PS. Work is ongoing to better understand this interaction Scheme 3-3 BnOAlMe2 initiated PS polymerization. Inspired by the previous reports of PS containing ABA and star polymers,10, 11 we investigated (co)polymer architecture through initiator design and di-functional (d-H) (Figure 3- 3a, compound 1) and tetra-functional (t-H) (Figure 3-5a, compound 4) initiators were synthesized. The d-H initiator was synthesized from 1,3 propane dithiol and the t-H from pentaerythritol tetrakis(3-mercaptopropionate) with trimethylaluminum at –78 °C. d-H initiator was characterized by 1H and 13C NMR spectroscopy as well as 1H – 1H correlated spectroscopy (COSY). The NMR spectra of the d-H initiator were consistent with our suggested structure. (SI, Figures 3-20 and 3-21). The 1H NMR spectrum of the t-H initiator (SI, Figure 3-11a) suggested a complex structure which might be due to the formation of polymeric compounds with trimethyl aluminum like dimeric or trimeric or larger complexes [(CH3)2AlS(ligand)]n. 110 Figure 3-5 (a) Chemical reaction scheme for the synthesis of d-H initiator followed by PPS synthesis from d-H initiator and copolymerization form it. (b) chemical reaction scheme for the synthesis of t-H initiator followed by PPS synthesis from t-H initiator and copolymerization form it. The d-H and t-H initiators were used to synthesize linear PPS from the d-H initiator and star-shaped PPS (3-5 b, compound 5) from the t-H initiator. The homopolymers were characterized by SEC (SI, Figure 3-23). The d-H PPS had Mn = 34.5 and Ð = 1.37 (Table 3-1, Entry 10), consistent with the targeted molecular weight of 30 kg/mol. To test whether the PPS formed from both ends of the d-H initiator, we conducted a kinetic study. The d-H initiator and an analogous mono-functional initiator (PrSAlMe2) polymerized PS at a controlled monomer to initiator ratio at 50 °C. The reactions were monitored over time by 1H NMR spectroscopy, and the -ln([PS]/[PS]0) vs. time (s) was plotted to determine kobs, as seen in Figure 3-6. From the slope of the fit, the rate constant was calculated to be kobs = 7.11 ± 0.59 × 10−5 s −1 (PrSAlMe2) and (15.9 ± 0.86) × 10-5 s −1 (d-H). The polymerization is approximately twice as fast for the d-H 111 initiator than for the mono-functional initiator, commensurate with propagation co-occurring at two ends. The t-H PPS had an Mn = 88.7 kg/mol and Ð = 1.51 (Table 3-1, Entry 12), in line with the targeted molecular weight of 80 kg/mol. Furthermore, the radius of gyration (Rg) measured by SEC for t-H PPS = 4.23 nm is smaller than PPS synthesized by BnSAlMe2 (Rg = 18.78 nm), consistent with the branched architecture of the star polymer. Figure 3-6 (top) Reaction scheme for the d-h or PrSAlMe2 initiated polymerization of PS. (bottom) Plot of normalized PS concentration over time with PrSAlMe2 initiator and NAl catalyst (red line) and plot of normalized PS concentration over time with d-H initiator and NAl catalyst (blue line). Monomer concentration was monitored via 1H NMR spectroscopy, and the rate of reactions calculated. From the slope of the fit, the rate constant was calculated to be kobs = (7.11 ± 0.59) × 10−5 s −1 (PrSAlMe2) and (15.9 ± 0.86) × 10-5 s −1 (d-H). This experiment shows that the rate of polymerization is as twice as fast for d-H initiator in compare with PrSAlMe2, proving that the initiation is happening from both heads of the initiator. The d-H and t-H initiators were used to synthesize tri-block-copolymers (3-5 a, compound 3) and star-block-copolymers (Figure 3-5 b, compound 6) of PS and PO through sequential addition. The resultant copolymers were characterized by 1H and 13C NMR 112 spectroscopy and the spectroscopic peaks were commensurate with the anticipated polymer structure (SI, Figure 3-24 and 3-25). DOSY experiments, Figure 3-7, revealed a single diffusion coefficient for all polymer peaks for both the d-H and t-H initiated copolymers. Copolymers were further characterized by SEC (SI, Figure 3-26). For d-H P(PS-b-PO) (Table 3-1, entry 11), the Mn = 29.8 kg/mol and Ð = 1.39, which is consistent with the targeted Mn of 30 kg/mol. For t-H P(PS-b-PO) (Table 1, entry 13), the Mn = 84.3 kg/mol and Ð = 1.09. DSC (SI, Figure 3-27) of these polymers revealed two Tgs at –66 °C and –45 °C for d-H poly(PS-b-PO) and two Tgs at –65°C and –47 °C for t-H poly(PS-b-PO), which agrees with the block-copolymer architecture. Furthermore, SAXS reveals clear microphase separation for the block polymers synthesized with both the d-H and t-H initiators. (SI, Figure 3-28). Therefore, this polymerization method allows us to synthesize block copolymers of PS and epoxide and allows us to tune polymer architecture through initiator design. Figure 3-7 DOSY NMR of (a) poly d-H (PS-b-PO) and (b) poly t-h (PS-b-PO). The results suggest both the epoxide and PS are in the same polymer chain. Finally, we synthesized a block copolymer consisting of ethylene glycol (EG) and PS units to further demonstrate the utility of our synthetic platform. PEG-b-PS is an important polymer in 113 drug delivery applications and is often synthesized through a two-step process. Here, we reacted 5 kg/mol monomethyl ether-PEG (mPEG) with AlMe3 in benzene to create a macroinitiator mPEGAlMe2, as seen in Figure 3-8 a. PS was then polymerized from the end of the mPEGAlMe2 in benzene at 50 ºC in the presence of NAl catalyst. The final PEG-b-PPS was characterized via 1H NMR and 13C NMR spectroscopy (SI, Figure 3-29) as well as DOSY NMR, Figure 3-8 b. The 1H and 13C NMR spectra were consistent with the anticipated block-co- polymer and the DOSY NMR revealed a single diffusion coefficient, suggesting PEG and PPS units are in the same polymer chain. The mPEG and PEG-b-PPS was also characterized via SEC and the LS traces can be seen in Figure 3-8 c. A shift to a lower retention time can be seen upon polymerization of PPS from the mPEGAlMe2 macroinitiator, consistent with the expected increase in the molecular weight. The SEC of mPEG revealed a Mn of 5.5 kg/mol and Đ of 1.24, matching data provided by the vendor. The SEC of the block-co-polymer revealed a Mn of 22.2 kg/mol and Đ = 1.18, commensurate with the targeted Mn. Finally, DSC (SI, Figure 3-30) revealed a single Tg at –41 ºC, matching that of the PPS block, and a melting point (Tm) of 58 ºC, consistent with the thermal data provided by the vendor. The Tg of the PEG block is not evident as it is most likely out of the temperature range accessible by our DSC, but the appearance of the Tm is strong evidence the PEG block is present. Therefore, we have demonstrated a facile method to produce PEG-b-PPS via our method. In summary, we presented a new methodology for (co)polymerization of PS with a recently reported SAl initiator. This method is living and produces polymers with controlled molecular weight up to 100 kg/mol and low Ð. We demonstrated statistical copolymerization of PS and epoxides to obtain unique, compositionally controlled copolymers. Polymer structure was characterized by various means such as 1H and 13C NMR spectroscopy, DOSY, SEC, DSC, and SAXS. Further, the chemical flexibility of our SAl 114 initiators enabled us to impart architectures on the PS containing (co)polymers in the form of ABA copolymers and star (co)polymers. Finally, we synthesized a PEG-b-PPS from a PEG macroinitiator and characterized it by 1H and 13C NMR spectroscopy, DOSY, DSC, and SEC. This facile and tunable aluminum initiator system opens the door for a more robust and controlled synthesis of PS-epoxide copolymers that can be applied in biomedical and other contexts. Figure 3-8 a) Scheme for synthesis of PEG-b-PPS. b) DOSY NMR PEG-b-PPS c) SEC traces (LS) of PEG (right, blue curve) and PEG-b-PPS (left, red curve). The Mn and Đ were determined to be, respectively, 5.5 kg/mol and 1.24 (PEG) and 22.2 kg/mol and 1.18 PEG-b-PPS. 115 3.4 Supporting information Figure 3-9 1H NMR and 13C NMR spectra of BnSPPS. a) 1H NMR (500 MHz, CDCl3) δ 2.91- 2.80 (m, −S−CH2−CH(CH3)−S−), 2.65-2.58 (m, −S−CH2−CH(CH3)−S−), 1.39 (m, −S−CH2−CH(CH3)−S−). b) 13C NMR (126 MHz, CDCl3) δ 41.14 (−S−CH2−CH(CH3)−S), 38.18 (−S−CH2−CH(CH3)−S), 20.63 (−S−CH2−CH(CH3)−S−). Figure 3-10 DSC analysis of targeted 30k PPS with BnSAlMe2. The data from the second heating curve were collected which reveals one Tg at -41 °C. 116 Figure 3-11 EIS-MS characterization of the targeted 5kg/mol PPS. Figure 3-12 DSC analysis of (a) poly(ECH-stat-PS) and (b) poly(PO-stat-PS). The data from the second heating curve were collected which reveals one Tg at -40 °C for poly(ECH-stat-PS) and one Tg at -46 °C for poly(PO-stat-PS). 117 Figure 3-13 SEC traces of (a) poly(ECH-stat-PS) and (b) poly(PO-stat-PS). For poly(ECH-stat- PS), the Mn is determined to be 29.2 kg/mol with Ð of 1.56. And for or poly(PO-stat-PS), the Mn is determined to be 30.8 kg/mol with Ð of 1.21. Figure 3-14 SEC traces of (a) P(ECH-b-PS) and (b) P(PO-b-PS). For poly(ECH-b-PS), the Mn is determined to be 29.9 kg/mol with Ð of 1.74. And for poly(PO-b-PS), the Mn is determined to be 29.6 kg/mol with Ð of 1.32. 118 Figure 3-15 DSC analysis of (a) poly(ECH-b-PS) and (b) poly(PO-b-PS). The data from the second heating curve were collected which reveals two Tg at -40 °C and -29 °C for PPS and PECH blocks, respectively. For poly(PO-b-PS) two Tg at -70 °C and -47 °C for PPO and PPS blocks, respectively. Poly(ECH-b-PS) 103 Poly(ECH-stat-PS) Poly(PO-b-PS) Poly(PO-stat-PS) 102 I(q) (cm-1) 101 100 10-1 10-2 o 10-1 -1 Q (A ) Figure 3-16 SAXS data for the synthesized copolymers. The block copolymer and statistical copolymer all have very weak phase separation as indicated by the broad shoulder peak at Q~0.02 Å − 1 for poly(ECH-b-S), Q~0.07 Å − 1 for poly(PO-stat-PS), and Q~0.033 Å − 1 for poly(PO-b-PS). 119 Figure 3-17 1H NMR and 13C NMR spectra of BnOPPS. a) 1H NMR (500 MHz, CDCl3) δ 2.91- 2.80 (m, −S−CH2−CH(CH3)−S−), 2.65-2.58 (m, −S−CH2−CH(CH3)−S−), 1.39 (m, −S−CH2−CH(CH3)−S−). b) 13C NMR (126 MHz, CDCl3) δ 41.14 (−S−CH2−CH(CH3)−S), 38.18 (−S−CH2−CH(CH3)−S), 20.63 (−S−CH2−CH(CH3)−S−). Figure 3-18 SEC trace of targeted 30k BnOPPS. the Mn is determined to be 31.6 kg/mol with Ð of 1.32. 120 Figure 3-19 DSC trace of BnOPPS. The data from the second heating curve were collected which reveals one Tg at -42 °C. Figure 3-20 1H NMR and 13C NMR spectra of d-H initiator. (a) 1H NMR (500 MHz, CDCl3) δ 1.7-3.41 (b, 2(CH3)Al-CH2CH2CH2S-Al(CH3)2, 6H), -0.92-0.24 (b, 2(CH3)Al-CH2CH2CH2S- Al(CH3)2, 6H). Peaks at 0.88 and 1.26 in 1H NMR spectrum, are corresponded to hexane. (b) 13C NMR (126 MHz, CDCl3) δ 29.65 2(CH3)Al-CH2CH2CH2S-Al(CH3)2, 27.73 2(CH3)Al- CH2CH2CH2S-Al(CH3)2, 11.312(CH3)Al-CH2CH2CH2S-Al(CH3)2. Peaks at 14.14, 22.53, and 33.8 in 13C NMR spectra are corresponded to hexane. Broadening effects of the peaks are observed due to oligomerization in 1H NMR spectrum. 121 Figure 3-211H–1H correlation spectrum for d-H initiator. Only one half of the spectrum is shown for clarity. The spectrum suggests that there are three distinct species: single d-H initiator, dimerized, and trimerized form of d-H initiator, connect the peaks on the X- and Y-axes that are correlated with one another. The scheme below the diagonal represents the chemical structure of the species present. The peak assignments for the spectra are labeled here. Detailed peak assignments are listed in the methods section. 122 Figure 3-22 1H NMR and 13C NMR spectra of t-H initiator. a) 1H NMR (500 MHz, CDCl3) δ 4.21-1.42 (24 H, -[C-CH2COOCH2CH2S-Al(CH3)2]4-), -0.36 to -1.09 (24 H, -[C- CH2COOCH2CH2S-Al(CH3)2]4-). b) 13C NMR (126 MHz, CDCl3) 198.53 -[C- CH2COOCH2CH2S-Al(CH3)2]4-), 42.42-[C-CH2COOCH2CH2S-Al(CH3)2]4-), 31.61-[C- CH2COOCH2CH2S-Al(CH3)2]4-), 29.61, -[C-CH2COOCH2CH2S-Al(CH3)2]4-), 25.10 -[C- CH2COOCH2CH2S-Al(CH3)2]4-), 9.81-[C-CH2COOCH2CH2S-Al(CH3)2]4-).Peaks at 14.14, 22.35, and 31.87 in 13C NMR spectra are corresponded to hexane. Broadening effects of the peaks are observed due to oligomerization in 1H NMR spectrum. Figure 3-23 SEC traces of (a) d-h PPS and (b) t-H PPS. For d-h PPS), the Mn is determined to be 34.5 kg/mol with Ð of 1.37. And for d-h PPS, the Mn is determined to be 88.7 kg/mol with Ð of 1.51. 123 Figure 3-24 1H NMR and 13C NMR spectrum of d-H poly(PS-b-PO). (a) 1H NMR (500 MHz, CDCl3) δ 3.72−3.2 (bm, −O−CH2−CH(CH3)−O−), 2.91-2.54 (bm, −S−CH2−CH(CH3)−S−), 1.31 (m, −S−CH2−CH(CH3)−S−), 1.11 (m, −O−CH2−CH(CH3)−O−). (b) 13C NMR (126 MHz, CDCl3) δ 75.26 (−O−CH2−CH(CH3)−O−), 73.35 (−O−CH2−CH(CH3)−O−), 40.6 (−S−CH2−CH(CH3)−S−), 37.9 (−S−CH2−CH(CH3)−S−), 20.98 (−S−CH2−CH(CH3)−S−), 16.83 (−O−CH2−CH(CH3)−O−). Figure 3-25 1H NMR and 13C NMR spectrum of t-H poly(PS-b-PO). (a) 1H NMR (500 MHz, CDCl3) δ 2.97-2.81 (m, −S−CH2−CH(CH3)−S−), 2.71-2.57 (m, −S−CH2−CH(CH3)−S−), 1.40 (m, −S−CH2−CH(CH3)−S−). (b) 13C NMR (126 MHz, CDCl3) δ 75.26 (−O−CH2−CH(CH3)−O−), 73.35 (−O−CH2−CH(CH3)−O−), 40.6 (−S−CH2−CH(CH3)−S−), 37.9 (−S−CH2−CH(CH3)−S−), 20.98 (−S−CH2−CH(CH3)−S−), 16.83 (−O−CH2−CH(CH3)−O−). 124 Figure 3-26 SEC traces of (a) d-H poly(PS-b-PO) and (b) t-H poly(PS-b-PO). For d-H poly(PS- b-PO), the Mn is determined to be 29.8 kg/mol with Ð of 1.39. And for t-H poly(PS-b-PO, the Mn is determined to be 84.0 kg/mol with Ð of 1.09. Figure 3-27 DSC analysis of (a) d-H poly(PS-b-PO) and (b) t-H poly(PS-b-PO). The data from the second heating curve were collected which reveals two Tgs at -66 °C and -45 for d-H poly(PS-b-PO) corresponded to PECH and PPS blocks. For t-H poly(PS-b-PO), DSC reveals two Tgs at -65 °C and -47 for d-H poly(PS-b-PO) corresponded to PECH and PPS blocks. 125 Figure 3-28 SAXS data for the synthesized copolymers. The phase behavior of the d-H poly(PS- b-PO) and t-H poly(PS-b-PO) are more obvious at Q~0.018 Å − 1 and Q~0.022 Å − 1 . Figure 3-29 1H NMR and 13C NMR spectrum of PEG-b-PPS a) 1H NMR (500 MHz, CDCl3) δ 3.65-3.48 (b, −O−CH2−CH2−O−), 2.92-2.78 80 (m, −S−CH2−CH(CH3)−S−), 2.66-2.59 (m, −S−CH2−CH(CH3)−S−), 1.38 (m, −S−CH2−CH(CH3)−S−). b) 13C NMR (126 MHz, cdcl3) δ 70.55 (−O−CH2−CH2−O−), 41.26 (−S−CH2−CH(CH3)−S−), 38.38 (−S−CH2−CH(CH3)−S−), 20.79 (−S−CH2−CH(CH3)−S−). 126 Figure 3-30 DSC analysis of PEG-b-PPS. The data from the second heating curve were collected which reveals one Tg at -41 °C for PPS block and another Tm at 58 °C. Figure 3-31 1H NMR and 13C NMR spectrum of BnSAlMe2. a) 1H NMR (500 MHz, CDCl3) δ 7.38 – 7.21 (m, 5H, PhCH2S-Al(CH3)2), 3.91 (s, 2H, PhCH2S-Al(CH3)2), -0.43 (s, 6H, PhCH2SAl(CH3)2). b) 13C NMR (126 MHz, CDCl3) δ141.46, 128.56, 127.97, 126.89 (PhCH2S- Al(CH3)2, 32.00 (PhCH2S-Al(CH3)2), 28.78 (PhCH2S-Al(CH3)2). 127 Figure 3-32 1H NMR and 13C NMR spectrum of PrSAlMe2. a) 1H NMR (500 MHz, CDCl3) δ 2.62 (m, 2H, CH3CH2CH2S-Al(CH3)2), 1.65 (dq, 2H, CH3CH2CH2S-Al(CH3)2), 1.04-0.95 (m, 3H, CH3CH2CH2S-Al(CH3)2), -0.49 (S, 6H, CH3CH2CH2S-Al(CH3)2). b) 13C NMR (126 MHz, CDCl3) δ 30.33 (CH3CH2CH2S-Al(CH3)2), 25.97 (CH3CH2CH2S-Al(CH3)2), 13.15 (CH3CH2CH2S-Al(CH3)2), -9.21 (CH3CH2CH2S-Al(CH3)2). Figure 3-33 1H NMR and 13C NMR spectra of poly(ECH-stat-PS). a) 1H NMR (500 MHz, CDCl3) δ 3.80-3.29 (bm, −O−CH2−CH(CH2Cl)−O−), 3.16-2.51 (bm, −S−CH2−CH(CH3)−S−), 1.63-1.54 (m, −O−CH2−CH(CH2Cl)−O− and −S−CH2−CH(CH3)−S−), 1.40-1.33 (m, −S−CH2−CH(CH3)−S−), 1.37-1.17 O−CH2−CH(CH2Cl)−O− and −S−CH2−CH(CH3)−S−). b) 13C NMR (126 MHz, CDCl3) 79.37(−O−CH2−CH(CH2Cl)−O−), 75.58 (−O−CH2−CH(CH2Cl)−O−), 44.72 (−O−CH2−CH(CH2Cl)−O−), 41.16 (−S−CH2−CH(CH3)−S−) , 38.39 (−O−CH2−CH(CH2Cl)−O− and −S−CH2−CH(CH3)−S−), 20.63 (−S−CH2−CH(CH3)−S−), 20.85 (−O−CH2−CH(CH2Cl)−O− and −S−CH2−CH(CH3)−S−), 18.59 (−S−CH2−CH(CH3)−S−). 128 Figure 3-34 1H NMR and 13C NMR spectrum of poly(PO-stat-PS). (a) 1H NMR (500 MHz, CDCl3) δ 3.83-3.24 (bm, −O−CH2−CH(CH3)−O−), 3.10-2.41 (bm, −S−CH2−CH(CH3)−S−, −O−CH2−CH(CH3)−O− and −S−CH2−CH(CH3)−S−), 1.32-1.42 (m, −S−CH2−CH(CH3)−S−), 1.30-1.19 (bm, −O−CH2−CH(CH3)−O− and −S−CH2−CH(CH3)−S−), 1.17-1.04 (m, −O−CH2−CH(CH3)−O−). (b) 13C NMR (126 MHz, CDCl3) δ75.85 (−O−CH2−CH(CH3)−O−), 73.34 (−O−CH2−CH(CH3)−O−), 72.90 (−O−CH2−CH(CH3)−O− and −S−CH2−CH(CH3)−S), 41.23 (−S−CH2−CH(CH3)−S−), 38.10 (−S−CH2−CH(CH3)−S−), 20.8 (−O−CH2−CH(CH3)−O− and −S−CH2−CH(CH3)−S), 19.3 (−S−CH2−CH(CH3)−S−), 17.4 (−O−CH2−CH(CH3)−O−). Figure 3-35 1H NMR and 13C NMR spectrum of poly(ECH-b-PS). (a) 1H NMR (500 MHz, CDCl3) δ 3.77-3.55 (bm, −O−CH2−CH(CH2Cl)−O−), 2.91-2.80 (m, −S−CH2−CH(CH3)−S−), 2.65-2.58 (m, −S−CH2−CH(CH3)−S−), 1.35 (m, −S−CH2−CH(CH3)−S−). (b) 13C NMR (126 MHz, CDCl3) δ 78.97 (−O−CH2−CH(CH2Cl)−O−), 69.51 (−O−CH2−CH(CH2Cl)−O), 43.47 (−O−CH2−CH(CH2Cl)−O−), 41.17 (−S−CH2−CH(CH3)−S−), 38.24 (−S−CH2−CH(CH3)−S−), 20.86 (−S−CH2−CH(CH3)−S−). 129 Figure 3-36 1H NMR and 13C NMR spectrum of poly(PO-b-PS). (a) 1H NMR (500 MHz, CDCl3) δ 3.72−3.2 (bm, −O−CH2−CH(CH3)−O−), 2.91-2.54 (bm, −S−CH2−CH(CH3)−S−), 1.31 (m, −S−CH2−CH(CH3)−S−), 1.11 (m, −O−CH2−CH(CH3)−O−). (b) 13C NMR (126 MHz, CDCl3) δ 75.26 (−O−CH2−CH(CH3)−O−), 73.35 (−O−CH2−CH(CH3)−O−), 40.6 (−S−CH2−CH(CH3)−S−), 37.9 (−S−CH2−CH(CH3)−S−), 20.98 (−S−CH2−CH(CH3)−S−), 16.83 (−O−CH2−CH(CH3)−O−). Figure 3-37 1H NMR and 13C NMR spectrum of d-H PPS. (a) 1H NMR (500 MHz, CDCl3) δ 2.91-2.80 (m, −S−CH2−CH(CH3)−S−), 2.65-2.58 (m, −S−CH2−CH(CH3)−S−), 1.39 (m, −S−CH2−CH(CH3)−S−). (b) 13C NMR (126 MHz, CDCl3) δ13C NMR (126 MHz, CDCl3) δ 41.14 (−S−CH2−CH(CH3)−S), 38.18 (−S−CH2−CH(CH3)−S), 20.63 (−S−CH2−CH(CH3)−S−). 130 Figure 3-38 1H NMR and 13C NMR spectrum of t-H PPS. (a) 1H NMR (500 MHz, CDCl3) δ 2.91-2.80 (m, −S−CH2−CH(CH3)−S−), 2.65-2.58 (m, −S−CH2−CH(CH3)−S−), 1.39 (m, −S−CH2−CH(CH3)−S−). (b) 13C NMR (126 MHz, CDCl3) δ 13C NMR (126 MHz, CDCl3) δ 41.14 (−S−CH2−CH(CH3)−S), 38.18 (−S−CH2−CH(CH3)−S), 20.63 (−S−CH2−CH(CH3)−S−). Figure 3-39 DSC analysis of (a) d-H PPS and (b) t-H PPS. The data from the second heating curve were collected which reveals one Tg at -41 °C for both these. 131 Figure 3-40 1H NMR and 13C NMR spectrum of BnOAlMe2. a) 1H NMR (500 MHz, CDCl3) δ 7.47 – 7.38 (m, 5H, PhCH2O-Al(CH3)2), 3.33 (s, 2H, PhCH2O-Al(CH3)2), 0.15 - -0.6 (s, 6H, PhCH2OAl(CH3)2). b) 13C NMR (126 MHz, CDCl3) δ138.64, 137.57, 130.04, 126.69 (PhCH2O- Al(CH3)2, 50.76 (PhCH2O-Al(CH3)2), -7.71 (PhCH2O-Al(CH3)2). 132 BIBLIOGRAPHY 133 BIBLIOGRAPHY (1) Ford, C. A.; Spoonmore, T. J.; Gupta, M. K.; Duvall, C. L.; Guelcher, S. A.; Cassat, J. E., Diflunisal-loaded poly(propylene sulfide) nanoparticles decrease S. aureus-mediated bone destruction during osteomyelitis. Journal of Orthopaedic Research 2021, 39 (2), 426-437. (2) Reddy, S. T.; Rehor, A.; Schmoekel, H. G.; Hubbell, J. A.; Swartz, M. A., In vivo targeting of dendritic cells in lymph nodes with poly(propylene sulfide) nanoparticles. J. Controlled Release 2006, 112 (1), 26-34. (3) Hirosue, S.; Kourtis, I. C.; van der Vlies, A. 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Different polymeric membrane materials like perfluoro polymer, polyimides, polyamides have been used for CO2 separation from the gas mixture13,16–19. Mostly, the concern about these membranes is related to their low permeability and selectivity20,21. The addition of the polar groups into the membrane matrix, such as ether oxygen (R-O-R), cyano (- C-N), carbonate (CO32-), and ester (-COOR) groups helps to increase the selectivity of the membrane for CO2 separation22. Thus, from that idea, multiple polymer membranes have been reported previously, which help to enhance membrane selectivity and permeability. 23–25 Among them, polyethylene glycol (PEG) is an attractive polymeric tool for the gas separation processes due to the presence of polar ether linkage in their backbone, which enables favorable interaction with CO2 24,26,27. However, the widely used PEG has a crystalline nature, which reduces the mechanical stability of the membrane26. Therefore, controlling the physical and chemical properties of polyether's-based membranes for CO2 separation is still crucial. The cross-linking strategy is considered one of the ideal methods to decrease crystallization properties28. In a series of works by Dr. Freeman, the cross-linked PEO membranes demonstrate excellent CO2 permeability and selectivity, including cross-linked PEG 29, cross-linked poly(ethylene glycol diacrylate)30 31,32, and cross-linked poly(propylene glycol diacrylate ). 137 Moreover, combining different epoxide monomers into a single polymer backbone is another interesting method to achieve a tunable copolymeric structure to improve the permeability by reducing the crystallization of the membrane 33. In a recent work by Lynd 34, they used 1,4 butanediol-diglycidyl ether as a crosslinker to prepare a wide range of copolymers, such as n- butyl glycidyl ether and allyl glycidyl ether, epichlorohydrin, and glycidol which exhibited high selectivity for CO2 separation. The architecture of the membrane also has a significant impact on the efficiency of gas separation. Yin et al. 27 suggested that the star-shaped polymers with a three-dimensional structure are suitable for gas separation applications since the intermolecular packing of the star- like polymer may be different from the inter-segmental packing of linear polymer chains. They suggested that the star-shaped polymers had lower glass transition temperatures (Tg) and higher chain flexibility. In another study by Zhao et al.,35 denoted that the decrease of chain flexibility and the increase of inter-segment distance have the opposite effects on gas permeation performance. In addition, fabricated membranes with different amine (primary, secondary and tertiary) showed that the fixed site carriers facilitate the transport properties (reactive diffusion pathway for CO2 transport). Furthermore, quaternary amine-based anion exchange membrane also studied for CO2 transport, where hydroxide ions act as a mobile carrier helping to improve the selectivity and permeability36–38. This research aims to develop a new and straightforward one-step method to prepare a membrane with specific architecture functionalized with different amines. There are three key elements to address in the strategy for cross-linked membrane synthesis, specifically for CO2 separation. First, we need a specific star shape structure to facilities cross-linking due to the vicinity and flexibility of the polymer arms. Second, the presence of PO and ECH is a copolymer 138 composition that provides control over glass transition temperature (Tg) in the membrane structure since polypropylene oxide (PPO), and poly epichlorohydrin (PECH) differs significantly in the Tg. And finally, the Cl group of ECH can further react with an amine to improve the charged nature of the membrane for CO2 separation. 4.2 Experimental section 4.2.1 Materials Trimethylaluminum solution (TMA) (AlMe3, 2.0 M in hexane), triethylamine (TEA) (≥99.5%), diethylamine (DEA) (40% in water), trimethylamine (TMA) (40% in EtOH), dimethylamine solution (DMA) (2.0 M in THF), pentaerythritol tetrakis(3-mercaptopropionate) (99%), and NaOH (ACS reagent, ≥97.0%, pellets) were purchased from Sigma-Aldrich. Propylene oxide (PO, Sigma-Aldrich, GC, ≥99.5%), epichlorohydrin (ECH, Sigma-Aldrich, ≥99%), and poly(ethylene glycol) diglycidyl ether (Sigma-Aldrich, average Mn 500) were all used as received. CDCl3 (Cambridge Analytica) was used without any further purification inside a glovebox. 4.2.2 Synthesis of Trimethylaluminum and Triethylamine Adduct (NAl) In a reaction vial with a stir bar, 6.35 mL of anhydrous hexanes and 2.0 M AlMe3 in hexane (6.35 mL, 12.7 mmol) were added and cooled to −78 °C. Then, triethylamine (1.5 mL, 10.7 mmol) was added dropwise to the vial. The solution was set to stir and warm to room temperature overnight. To crystallize the desired product, the solution was then directly cooled to −40 °C, and the resultant crystals were washed three times with anhydrous hexanes (3 × 5 mL) and dried in vacuo. 1H NMR (500 MHz, CDCl3) δ 2.80 (q, 6H, 3(CH3CH2)N:Al(CH3)3), 1.18 (t, 139 9H, 3(CH3CH2)N:Al(CH3)3), −0.89 (s, 9H, 3(CH3CH2)N:Al(CH3)3). 13C NMR (126 MHz, CDCl3) δ 64.54 3(CH3CH2)N:Al(CH3)3), 47.78 3(CH3CH2)N:Al(CH3)3, 9.20 3(CH3CH2)N:Al(CH3)3). 4.2.3 Synthesis of Tetra-headed Initiator (t-H) To a solution of AlMe3 (12.7 mmol, 12.7 mL) and anhydrous hexane (12.7 mL) at −78 °C, pentaerythritol tetrakis(3-mercaptopropionate) (12.7 mmol, 6.20 g, 4.85 ml) was added dropwise. The reaction mixture was stirred and warmed up to room temperature overnight. The resultant yellow powders were washed three times with anhydrous hexanes and dried in vacuo.1H NMR (500 MHz, CDCl3) δ 4.21-1.42 (24 H, -[C-CH2COOCH2CH2S-Al(CH3)2]4-), -0.36 to -1.09 (24 H, -[C-CH2COOCH2CH2S-Al(CH3)2]4-). 13C NMR (126 MHz, CDCl3) 198.53 -[C- CH2COOCH2CH2S-Al(CH3)2]4-), 42.42-[C-CH2COOCH2CH2S-Al(CH3)2]4-), 31.61-[C- CH2COOCH2CH2S-Al(CH3)2]4-), 29.61, -[C-CH2COOCH2CH2S-Al(CH3)2]4-), 25.10 -[C- CH2COOCH2CH2S-Al(CH3)2]4-), 9.81-[C-CH2COOCH2CH2S-Al(CH3)2]4-). 4.2.4 Membrane Preparation Membrane polymeric solutions were all initially prepared in a 20 mL vial with the t-H initiator, NAl, epoxide monomers, and diglycidyl ether cross-linker. Under a nitrogen atmosphere in the glove box, the reaction mixture was heated to 50 °C until viscosity visibly increased (typically after 2-3 h). The resultant viscous solution was poured uniformly onto the quartz glass plate and placed directly on the top of the hotplate at 80 °C overnight under a nitrogen atmosphere. The film was peeled off from the glass plate with addition of water. To remove impurities from the membrane matrix, the membranes were washed with DI water and kept in DI water overnight, and dried in a vacuum oven overnight at 50 °C. The obtained membrane is transparent and homogenous with a thickness of approximately 200-300 μm. The solid films obtained by this 140 process were shows three-dimensional networks as suggested in the recently published work by Lynd group. 34 4.2.5 Functionalization of the Membranes For the functionalization of membranes (amine grafted membrane and quaternized amine grafted anion exchange membrane), post-modification method has been opted because of the crosslinked (insoluble in desired solvents) nature of it. The synthesized membranes were cut in varied sizes (2 x 2 cm2) and dipped into a different amine solution. For preparing tertiary amine grafted membrane, we dipped the membranes in DMA and DEA solutions, whereas for making quaternized anion exchange membrane, we dipped membranes in the TMA and TEA amine solution for 48-72 h respectively at RT. To remove the excess amine from the membranes surface membranes kept in the DI water overnight, moved in the vacuum oven at 50 °C to dry these overnight. 4.2.6 Structure Characterization 1 H NMR spectroscopy was performed on a 500 MHz Varian NMR spectrometer at room temperature, and chemical shifts are reported in parts per million (ppm) and are referenced using the residual 1H peak from the deuterated solvent to characterize the structure of the pristine membrane before poring the viscous material in the quartz glass. FTIR spectra were measured on a Thermo Nicolet iS5 (Thermo Nicolet, USA) spectrometer for pristine membranes and fabricated ones to further characterize the structures. 4.2.7 Thermal Characterization Differential scanning calorimetry (DSC) was performed on a TA250 series analyzer (TA Instruments). A membrane (5−6 mg) was loaded in an aluminum pan and crimped with an 141 aluminum hermetic lid. The sample was heated from −90 °C to a maximum of 50 °C with heating and cooling rates of 1 °C/min under a N2 atmosphere. Data from the second heating curve were collected. Thermogravimetric analysis (TGA) was performed on TGA 500 (TA Instruments, USA) under a N2 atmosphere with a heating rate of 10 °C/min. Approximately 5 mg of the membrane sample was loaded in an aluminum pan and heated to a maximum of 500 °C. 4.2.8 Water Uptake and Swelling Ratio The samples the most optimized PPO:PECH 90:10 and their derivatives (amine attached) were immersed in deionized water at RT to investigate the water uptake (WU) for 24 h. For swelling ratio measurements, the samples were immersed in DI water for 48 h at 50 °C. The membranes' water uptake and swelling ratio were determined by the change of weight and length between dried and hydrated membranes, respectively based on the following equations. 𝑾𝑼 = 𝒘 𝒘𝒆𝒕 − 𝒘 𝒅𝒓𝒚 𝒘 𝒅𝒓𝒚 𝑺𝑹 = 𝒍 𝒘𝒆𝒕 − 𝒍 𝒅𝒓𝒚 𝒍 𝒅𝒓𝒚 4.2.9 Resistance Characterization The most optimized PPO:PECH 90:10 and their derivatives (amine attached) were soaked overnight in 0.1 M NaOH and rinsed with DI water prior to measurement. The membranes were loaded in a Biologic Controlled Environment Sample Holder (CESH), consisting of two parallel anodized aluminum plates, a fixed bottom disc of 47 mm diameter on which a gold electrode (1/4 inch) is installed, and an upper metallic plate, moveable vertically versus the bottom plate. Electrochemical impedance spectroscopy measurements were performed with a Biologic VSP Potentiostat. The ionic conductivity was obtained by electrical measurements using a four-probe 142 testing cell by the Nyquist plot fitting simulation method. The ion conductivity (σ) of the membranes was calculated using the following equation. σ = 𝑙 𝑅𝐴 Where R (Ω) is the membrane impedance, l (cm) is the distance between reference electrodes, A (cm) is the thickness of the membranes, respectively. 4.2.10 Rheology Characterization The viscoelastic properties of cross-linked polyether films (the most optimized PPO:PECH 90:10 and mine modified membranes) were determined with MCR 302 rheometer from Anton Paar instrument rotational rheometer equipped with 8 mm diameter stainless steel parallel plate geometry. Oscillatory rheological measurements were conducted to measure the moduli of the films as a function of shear strain amplitude and as a function of frequency. The film sample was fixed between the upper parallel plate and stationary surface, with the gap size set according to individual film thickness (100−200 μm). All tests were performed in triplicate at 23 ± 0.1 °C. 4.2.11 Alkaline stability PPO-PECH-TMA and PPO-PECH-TMA were soaked in the 2 M NaOH for 216 h at 50 °C and the conductivity were measured by EIS. 4.3 Results and discussion Herein, we investigated the use of the thio-aluminum based (SAl) initiator to prepare cross- linked polyether-based membranes. We have previously used the SAl initiator in the presence of NAl, as a Lewis pair catalyst, to synthesize linear copolymers consisting of different epoxides with molecular weight control and relatively low polydispersity [39]. To further expand the 143 generality of this synthetic technique and achieve higher molecular weight in a shorter reaction time, we prepared the tetra functional (t-H) initiator from the reaction of pentaerythritol tetrakis(3-mercaptopropionate) with TEA solution (Scheme 4-1a). We further characterized the t-H initiator by 1H NMR and 13C NMR spectroscopy (SI, Figure 4-5) The t-H initiator allows us to polymerize four arm star polymers, which may enhance the mechanical properties of crosslinked polyether-based membranes. O Al O O O S Al HS SH S O AlMe3 O O O O O O O hexane HS SH -78 °C Al S S O O O Al O (a) Cl Cl O Oo o Cl O Om O O m O O 4n 4m O O n O n S O S p p O O O O O O O O S S O O p O O O O O O Et3N:AlMe3 n n O m m O Neat, 50 °C o Cl (b) Cl o Scheme 4-1 Synthesis of cross-linked polyether membrane using the star shape initiator (PPO- PECH) Membranes were prepared from the copolymerization of epichlorohydrin (ECH), propylene oxide (PO) and a crosslinker from t-H initiator. Scheme 4-1,b represents a general scheme for membrane preparation. ECH was chosen for these membranes because it is an inexpensive epoxide monomer containing a functional chloromethyl group, which can be easily modified with amine groups. PO was chosen as a comonomer to tune the ratio of ECH and due to its low Tg and non-crystalizing nature of it. The t-H initiator and NAl were first weighed in a scintillation vial, followed by the addition of the epoxide monomers in different ratios and a diglycidyl ether as a cross-linker. All the obtained membranes exhibited transparency with the 144 light-yellow color. Further, cross-linked nature of the membranes was confirmed by the solubility test in different solvents (DCM, CHCl3, DMSO, DMAc, and DI water). None of the membranes dissolved in any of the solvents, which supports the cross-linked characteristic of them. Different ratios of PO:ECH were used to tune the chemical and physical properties of the membrane. Reaction conditions and characteristics of the resultant cross-linked films are summarized in Table 4-1. Table 4-1 Characterization of t-H-Initiated Cross-linked Membranes. Entry PO:ECHa Time (h) Tg (°C)b 1 40:60 5 - 2 50:50 4.5 -38 3 60:40 4 -39 4 70:30 3 -43 5 80:20 3 -44 6 90:10 3 -45 a reaction condition: membranes were prepared by using 12 mg of t-H initiator, 24 mg of NAl, and diglycidyl ether (0.2 ml) as a cross-linker with different ratios of PO and ECH b measured from second heating curve of DSC. The structural properties of the membrane were characterized by FTIR spectroscopy and DSC. (Table 4-1, entries 1-6). The spectrum of PPO-PECH with the ratio of 90:10 (PO :ECH) showed all the functional groups in the membrane matrix (Figure 4-1, yellow line). Peaks present at 1620, 1611, 1110, and 750 cm-1suggest the presence of C=O, C-O, C-S, and C-Cl, respectively. From the DSC measurements (Table 4-1, entries 1-6), we observed a decrease in Tg due to continuous decrement of ECH content, which is consistent with the lower Tg of PPO compared with PECH. The DSC figure of membranes is presented in the SI, Figure 4-6, showing the shift from -38 °C for membrane having 50:50 of PO:ECH to -45 °C for membrane having 90:10 of PO:ECH. This is noteworthy because low Tg values have been shown to mitigate physical aging and promote high permeabilities in membrane materials. The prepared membrane of PO:PECH with the ratio of 90:10 (Table 4-1, entry 6) showed the desirable mechanical 145 robustness as well as the lowest Tg. Therefore, we opted to further modify this membrane with various amines. The chemical structure of the membrane with the ratio of 90:10 was studied by 1 H NMR spectroscopy, depicted in the SI, Figure 4-7), showing all the corresponding 1H NMR peaks. Scheme 4-2 Synthesis of amine modified cross-linked PPO-PECH Membranes Using the t-H Initiator. Image of the representative cross-linked polyether membrane demonstrating optical transparency and flexibility is presented. 4.3.1 Synthesis and Characterization of Modified Cross-linked Membranes We have chosen the post-modification solvent dip method to functionalize the membranes because of the membrane's cross-linked nature. The 90:10 PO:ECH membrane was dipped in TMA, TEA, DMA, and DEA solution for 48-72 h at room temperature where the free Cl group of the pristine membrane reacted with these amines to form quarternized (TMA and TEA) (Table 2, entries 2 and 4), and tertiary amines (DMA and DEA) (Table 2, entries 3 and 5) tethered to the polymer backbone . To remove the excess amine from the membrane surface, membranes 146 were kept in DI water for 24 h and dried in a vacuum oven for 24 hr. Scheme 2 represents a general method for the post-modification of the membranes. Table 4-2 Characterization of amine modified t-H-Initiated Cross-linked Membranes. Entry Samplea Tg WU SR G′d Conductivitye (°C)c (%) (%) (MPa) (S/cm) 1 PPO-PECHb -45 11.3 5.5 0.12 0.08 x 10-3 2 PPO-PECH-TMA -38 38.6 26.1 0.07 1.40 x 10-3 3 PPO-PECH-DMA -39 30.3 18.8 0.05 0.58 x 10-3 4 PPO-PECH-TEA -43 34.3 23.2 0.06 0.21 x 10-3 5 PPO-PECH-DEA -44 28.9 15.4 0.06 0.15 x 10-3 a reaction condition: amine solution (20 ml) at RT. b pristine membrane. c measured from second heating curve of DSC. d The plateau shear modulus was measured by rheometry. e calculated by EIS. 4.3.2 Structural characterization FT-IR spectroscopy was utilized to provide information about amine attachment to the membrane structure. Figure 4-1 depicted FT-IR spectra of PPO-PECH (yellow color) showing stretching frequencies around 1102, 903, and 611 cm-1 suggesting the presence of C-O, C-C-O and C-Cl in the pristine membrane matrix. Whereas amine tethered PPO-PECH membranes, PPO-PECH-TEA, PPO-PECH-DEA, PPO-PECH-TMA, PPO-PECH-DMA presented an extra characteristic frequency of C-N at 1253 cm1 (showed by vertical dashed line) followed by PPO- PECH peaks, suggesting the successful amine attachment with the polyether backbone in the membrane structure. 147 Figure 4-1 FTIR spectrum of PPO-PECH (yellow color), PPO-PECH-TEA (green color), PPO- PECH-DEA (red color), PPO-PECH-TMA (blue color), and PPO-PECH-DMA (purple color). The C-N characteristic starching frequency of amin modified membranes are represented by a vertical line that is not presented in the pristine membrane. 4.3.3 Thermal characterization The thermal stability of the amine-modified membranes was measured by TGA under air atmosphere as shown in Figure 4-2, a. to investigate the successful amine modification. According to the TGA curves, all membranes showing three stages degradation profile. The pristine membrane showed the weight losses due to water loss, functional group (C-O, C-Cl) breakage, and backbone decomposition. For the amine tethered membranes, the first slight stage for weight loss below 100-200 °C is due to adsorbed humidity or residual solvent evaporation in the membranes. The second weight loss at 200–380 °C is associated with the degradation of functional amine groups. The third weight loss above 400 °C is related to the decomposition of the polymer backbone. Moreover, quaternary membranes, PPO-PECH-TMA and PPO-PECH- 148 TEA showed more weight loss in the second stage than the pristine and secondary amine (PPO- PECH-DEA, and PPO-PECH-DMA) grafted membranes due to their charge nature. Figure 4-2, b, presents a DSC analysis of the PPO-PECH and amine modified membranes. The Tg corresponded to PPO-PECH comes at -45 °C and it shifted to the lower Tgs for the amine grafted membranes matrix. All the resultant Tg’s of the amine modified cross-linked films were generally less than −50 °C. This is noteworthy because low Tg values have been shown to mitigate physical aging and promote high permeabilities in membrane materials. There were also no signs of melting or crystallization in any of the films. 4.3.4 Water uptake and swelling ratio Sufficient bound and free water is essential for hydration and ion conduction in membranes, which is originated from the quaternary amines group and other functional groups. However, too much absorbed water could give rise to the decline of conductivity and mechanical strength for hydrated membranes, due to the dilution effect and excessive swelling. Therefore, we have used PPO-PECH (90:10) where less amount of PECH as compared to PPO helps to balance the ionic conductivity and dimensional stability. As depicted in SI Figure 4-8, both the water uptake and the swelling ratio increases after the secondary and tertiary amines are attached to the membrane. Secondary amines attached membrane show less water uptake than tertiary amines of the hydrophilic nature of these, respectively (Table 4-2, entries 1-5). Moreover, the tertiary amines attached to the polyether backbone membrane will act as a quaternary anion exchange membrane, helping to transport the hydroxide and chloride ions. This observation suggests the conducting nature of the quartenized membranes compared to the PPO-PECH-DMA, PPO-PECH-DMA DEA, and pristine membranes. 149 Figure 4-2 DSC measurements (a) and TGA characterization of (b) PPO-PECH (yellow color), and amine modified membranes PPO-PECH-TEA (green color), PPO-PECH-DEA (red color), PPO-PECH-TMA (blue color), and PPO-PECH-DMA (purple color). 4.3.5 Conductivity The ionic conductivity is an essential property for the membranes which plays a key role in the different applications. The hydroxide ion conductivity is significantly influenced by the water uptake and swelling ratio of the membranes. The ionic conductivity of the amine tethered membranes values at RT are also included in Table 4-2, entries 1-6. As shown in Figure 4-3, all amine grafted membranes showed higher conductivity in comparison with the PPO-PECH membrane. PPO-PECH-DMA and PPO-PECH-DEA showed comparable conductivity as compared to the pristine membrane. The minor difference in the conductivity of the PPO-PECH-DMA (0.58 x 10-3 S/cm) and PPO-PECH-DEA (0.21 x 10-3 S/cm) in comparison with the pristine membrane stem from the absence of the ionic channels (counter ions) in the PPO-PECH-DMA and PPO-PECH-DEA membranes. On the other hand, the quartenized membranes, PPO-PECH-TEA and PPO-PECH- TMA, have higher conductivity in comparison with the pristine membrane and PPO-PECH- 150 DMA and PPO-PECH-DEA. Because these quartenized membranes contain labile hydroxide counter ion, helping to create a better transport pathway owing to the enhancement of the mobility of anions. In addition, the membrane containing TMA (1.40 x 10-3 S/cm) showed higher conductivity due to the more basic nature of TMA than TEA. This fact explains more conductivity of PPO-PECH-DMA than PPO-PECH-DEA due to more basic characteristics of DMA. It is noted that the design of a copolymer with high conductivity improves the performance of membranes in fuel cell applications. It is clear from the data shown in Table 2 and Figure 3 that the OH– conductivity of quartenized membranes has a direct correlation with water uptake and swelling ratio of the membrane which are dependent on both the polymer backbone and the nature of the amine. 4.3.6 Rheology Further evidence of compositional control of structure−property relationships in the network polyether materials was evident in the rheological properties of the resultant films. We have used the rheology data to determine the mechanical stability of the pristine and modified membranes as Figure 4 presents the shear modulus (G′) vs different membrane names. For the pristine membrane the shear modulus comes nearby 0.12 MPa whereas for the charged membranes it decreases (form 0.07-0.05 MPa) due to the successful amine attachment to the membrane matrix. 151 Figure 4-3 conductivity measurement of PPO-PECH and amine modified membranes PPO- PECH-TEA, PPO-PECH-DEA, PPO-PECH-TMA, and PPO-PECH-DMA. Figure 4-4 rheology measurements of PPO-PECH and amine tethered membranes PPO-PECH- TEA, PPO-PECH-DEA, PPO-PECH-TMA, and PPO-PECH-DMA. In summary, a novel star-shaped with a Cl-bearing monomer ether-based backbone was synthesized and readily fabricated with different amines for CO2 transport. Star shape structure of the initiator facilities cross-linking due to vicinity of the arms and helps to improve the mechanical stability of the membrane. The monomer ratio in the polymer backbone PO:ECH was controlled ranging from 40:60 to 90:10, respectively. Further the physical and chemical characteristic of these membranes studied by FT-IR, DSC and TGA and the optimized PPO- 152 PECH membrane with the ratio of PO:ECH (90:10) have further modified with different amines. The post-modification of the PPO-PECH with TMA, DMA, TEA, and DEA was opted for amin grafting to the polyether backbone achieving amine tethered cross-linked polyether films with uniform and complete incorporation of comonomers into polymer films with thermal stability, optical transparency, and flexibility. The low Tg of amine grafted PPO-PECH membrane (below - 54 °C) considered to play an important role in the permeability of the membranes. This unique amine modified membranes are the great candidates for CO2 transport because of favorable C-O interaction in the polymer backbone with CO2 as well as amine presence in the structure facilitates the CO2 selectivity and permeability. These features signify great potential for these membranes in the practical applications for CO2 separation. 4.4 Supporting information Figure 4-5 1H NMR and 13C NMR spectra of t-H initiator. a) 1H NMR (500 MHz, CDCl3) δ 4.21-1.42 (24 H, -[C-CH2COOCH2CH2S-Al(CH3)2]4-), -0.36 to -1.09 (24 H, -[C- CH2COOCH2CH2S-Al(CH3)2]4-). b) 13C NMR (126 MHz, CDCl3) 198.53 -[C- CH2COOCH2CH2S-Al(CH3)2]4-), 42.42-[C-CH2COOCH2CH2S-Al(CH3)2]4-), 31.61-[C- CH2COOCH2CH2S-Al(CH3)2]4-), 29.61, -[C-CH2COOCH2CH2S-Al(CH3)2]4-), 25.10 -[C- CH2COOCH2CH2S-Al(CH3)2]4-), 9.81-[C-CH2COOCH2CH2S-Al(CH3)2]4-). Peaks at 14.14, 22.35, and 31.87 in 13C NMR spectra are corresponded to hexane. Broadening effects of the peaks are observed due to oligomerization in 1H NMR spectrum. 153 Figure 4-6 DSC measurement of star shape membrane with different ratios of PO:ECH ranging from 50:50 to 90:10. Figure 4-7 1H NMR spectroscopy of the polymeric solution with the ratio of PPO-PECH with ratio of PO:ECH (90:10). 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Membranes have been used for applications including fuel cell 2–6, water desalination 7–11, redox batteries 12–16, and CO2 separation 17–20. Over the past decade, issues relating to climate change have enhanced focus on CO2 separation and capture technologies resulting in innovative designs for CO2 selective membranes. Precisely, membranes that allow separation from other gases or directly capture CO2 from the air have been increasingly studied. These studies have led to an enhanced fundamental understanding of membrane design 21–25. For nearly 50 years, polymeric membranes have enjoyed the most significant share of the gas-separation membrane market because of the polymer membrane’s lower cost and superior processability 26. Generally, gas transport through polymeric membranes follows the solution- diffusion mechanism, in which permeability is the product of gas solubility and diffusivity 27,28. The critical shortcoming of solution-diffusion membranes is the trade-off between permeability and selectivity, governed by Robeson’s upper bound 29,30. However, the transport mechanism is different inside facilitated transport membranes (FTMs); both high permeability and selectivity can be obtained simultaneously. The advantage of facilitated transport membranes becomes even more favorable when applied for CO2 capture from low CO2 pressure streams, e.g., flue gas in coal-fired power plants 1. Facilitated transport membranes containing amines have shifted the paradigm in CO2 membrane design. FTMs generally include amines with various substitutions either attached 161 (‘fixed’) to the membrane backbone or dissolved (‘free’) in the membrane matrix 31,32. These amines are further broken down into two categories, hindered and unhindered. Hindered amines have a tertiary carbon attached to a primary amine or secondary or tertiary carbon atom attached to a secondary amine 33,34. The reaction between CO2 and fixed carriers is an intermediate that deprotonates with another amine to form a carbamate. In this case, if the amino group is sterically hindered, the rotation of the C–N bond in the carbamate product is restricted, and hence the carbamate product is destabilized by the surrounding bulky substituents 35 1,32,36–38. In the presence of water, the hindered carbamate can be easily hydrolyzed, resulting in the formation of bicarbonate and the regeneration of a free amino group, hereby doubling the CO2 loading capacity 39 40–424344. Zhao and Ho grafted sec-butyl, isopropyl, and tert-butyl groups on the primary amino sites in PAA. A moderately hindered PAA, poly(N-isopropylallylamine) exhibited a high CO2 permeability of 297 Barrer, nearly 5.5 times more permeable than the unhindered PAA 45. Polyether-based membranes are particularly attractive for CO2 separations. The high mobility of C-O polymeric chain and favorable interaction between the C-O bond and CO2 make it desirable for CO2 application 46,47. In addition, it has been observed that crosslinking of polyether and its derivatives (like polyethylene glycol) can enhance the membrane’s permeability due to the flexibility of the chains 48. In the recent work in 2020 by Lynd 49, they presented a chain-growth network polymerization of epoxides to address the need for new synthetic concepts using mono(μ-alkoxo)- bis(alkylaluminum) (MOB) 50,51 initiators were further crosslinked to result in a thin film for CO2 separation. Inspired from the previous studies, we prepared facilitated transport membranes combining the enhanced selectivity and permeability of ether-based membranes with the 162 increased loading capacity and transport properties of amines tethered membranes. Specifically, we synthesized robust, crosslinked polyether membranes containing functional chloromethyl groups at a controlled ratio. This one-pot solvent-free synthesis of the membrane was achieved by the reaction of MOB in the presence of epoxides monomer and poly (ethylene glycol) glycidyl ether as a crosslinker. The membranes were modified via post-polymerization with various amines to understand how the structure of the tethered amines affected the physicochemical properties of the membranes. Furthermore, the effect of a steric hindrance for different primary amines (hindered and unhindered amines) has been explored for CO2 transport. The chemical structure, thermal properties, and single-gas permeation of the resultant membranes are investigated here by various characterization techniques. 5.2 Experimental section 5.2.1 Material Trimethylaluminum solution (TMA) (AlMe3, 2.0 M in hexane), 1-Methoxy-2-ethanol (anhydrous, 99.8%), (40% in EtOH), dimethylamine solution (DMA) (2.0 M in THF), n- butylamine (99%) (n-BuA), isobutyl amine (99%) (iso-BuA), tert-Butylamine (99%) (t-BuA) were purchased from Sigma-Aldrich. Propylene oxide (PO, Sigma-Aldrich, GC, ≥99.5%), epichlorohydrin (ECH, Sigma-Aldrich, ≥99%), and poly(ethylene glycol) glycidyl ether (Sigma- Aldrich, average Mn 500) were all used as received. CDCl3 (Cambridge Analytica) was used without any further purification inside a glovebox. All the air and sensitive reaction were carried out in the glovebox. 163 5.2.2 Synthesis of Bis(μ-oxo)alkylaluminum [(CH3)2NCH2CH2(μ2- O)Al(CH3)2·Al(CH3)3](MOB) A reaction vial was charged with a stir bar and trimethylaluminum (12.7 mmol, 12.7 mL) and cooled to −78 °C. 1-Methoxy-2-ethanol (12.7 mmol, 0.966 g) was added dropwise into the reaction vial containing trimethylaluminum. The solution was set to stir and warm to room temperature overnight. The solution was then directly cooled to −40 °C to crystallize the desired product. The resultant crystals were washed three times with anhydrous hexanes and dried in vacuo. 1 H NMR (CDCl3, 500 MHz) δ: -0.95 ([(CH3)2NCH2CH2(μ2- O)Al(CH3)2·Al(CH3)3], - 0.74 3.46 ([(CH3)2NCH2CH2(μ2-O)Al(CH3)2·Al(CH3)3], 2.58 (s, CH3−N−), 2.92 (t, −N−CH2−CH2−O−), 3.98 (t, −N−CH2−CH2− O−). 13 C NMR (CDCl3, 100 MHz) δ: 45.2 ([(CH3)2NCH2CH2(μ2-O)Al(CH3)2·Al(CH3)3], 55.11 (CH3−N−), 58.84 (−N−CH2−CH2−O−), 67.30 (−N−CH2−CH2−O−). 1H and 13C NMR spectrum are presented in the SI, Figure 5-6. 5.2.3 Synthesis of crosslinked membranes Polymeric membrane solution prepared in a 20 mL vial with the initiator (14 mg), propylene oxide (0.74 ml), epichlorohydrin (0.11 ml), and diglycidyl ether (0.1 ml) as a cross-linker. Under a nitrogen atmosphere in the glove box, the reaction mixture was heated to 60 °C until viscosity visibly increased (5 hrs). The resultant viscous solution was casted uniformly onto the quartz glass plate and placed directly on the top of the hotplate at 80 °C overnight under a nitrogen atmosphere. The film was peeled off from the glass plate with addition of water. To remove impurities from the membrane matrix, the membranes were washed with DI water and kept in DI water overnight, and dried in a vacuum oven overnight at 40 °C. The obtained membrane is transparent and homogenous with a thickness of approximately 200-300 μm. 164 5.2.4 Crosslinked membrane functionalization To synthesize the different amine grafted membranes, post- modification method has been opted because of the crosslinked nature of it (insoluble in desired solvents). The synthesized membranes were cut in varied sizes (2 x 2 cm2) and dipped into a different amine solution including MeA, nBu-A, iso-BuA, t-BuA for 48-72 h at RT. To remove the excess amine from the membranes, the membranes kept in the DI water. 5.2.5 Structure Characterization The structure of the MOB was determined by 13C NMR spectroscopy on a 126 MHz Varian NMR spectrometer, as well as 1H NMR spectroscopy on a 500 MHz Varian NMR spectrometer at room temperature. 1H NMR spectroscopy of pristine membrane was performed on the same instrument and referenced using the residual 1H peak from the deuterated solvent before poring the viscous material in the quartz glass. FTIR spectra were measured on a Shimadzu IRAffinity- 1 spectrometer equipped with MIRacle ATR attachment. The spectra were recorded between the wavelength of 500-4000 cm-1 in absorption mode for the pristine membranes and fabricated ones to further characterize the structures. 5.2.6 Thermal Characterization Differential scanning calorimetry (DSC) was performed on a TA250 series analyzer (TA Instruments). A membrane (5−6 mg) was loaded in an aluminum pan and crimped with an aluminum hermetic lid. The sample was heated from −90 °C to a maximum of 50 °C with heating and cooling rates of 1 °C/min under a N2 atmosphere. Data from the second heating curve were collected. Thermogravimetric analysis (TGA) was performed on TGA 500 (TA Instruments, USA) under a N2 atmosphere with a heating rate of 10 °C/min. Approximately 5 165 mg of the membrane sample was loaded in an aluminum pan and heated to a maximum of 500 °C. 5.2.7 Rheology Characterization The shear modulus of the pristine and amine modified membranes were determined with a MCR 302 rheometer from Anton Paar equipped with 8 mm diameter stainless steel parallel plate geometry. Oscillatory rheological measurements were conducted to measure the moduli of the films as a function of shear strain amplitude and as a function of frequency. The film sample was fixed between the upper parallel plate and stationary surface, with the gap size set according to individual film thickness (100−200 μm). All tests were performed in triplicate at 23 ± 0.1 °C. 5.3 Results and discussion MOB initiators were utilized for the synthesis of cross-linked, functional polyether membranes. In the recent work by Lynd and Freeman, MOB initiators were shown to exhibit tolerance of chemical functionality, provide control of molecular weight, and access to high reaction rates under some conditions. They also reported a cross-linked polyether membranes with a range of epoxide substrates using MOB that exhibited tolerance toward chemical functionality. This series of cross-linked polyether-based films demonstrated relatively high CO2 permeability and permselectivity under both dry and humidified conditions. Motivated by these results, we prepared the crosslinked-propylene oxide (PO) and epichlorohydrin (ECH) membrane to further investigate the effect of amine functionalization on the selectivity and permeability of polymeric ether-based cross-linked membranes. ECH was chosen for these membranes because it is an inexpensive epoxide monomer containing a functional chloromethyl group, which can be easily modified with amine groups. PO was chosen as a comonomer to tune the ratio of ECH and due 166 to its low Tg and non-crystalizing nature of it. Therefore, crosslinked membranes were prepared solvent free by only adding PO, ECH, and poly(ethylene glycol) glycidyl ether crosslinker to a scintillation vial charged with MOB initiator. When the crosslinking membrane became apparently viscous, it was casted on a quartz plate to form a thin and uniform membrane. Scheme 5-1a depicts the concept for the crosslinked polyether membranes. The resulting membrane was free-standing, optically transparent, and flexible as can be seen in Scheme 5-1b. The membranes were post-modified with primary amines: methyl amine (MeA), n-butyl amine (nBuA), iso-butyl amine (isoBuA), and tert-butyl amine (tBuA). Since Cl groups of PECH can easily react with these amines, dipping method for membrane fabrication has been chosen. Scheme 5-1 a) Synthesis of Amine Modified Cross-linked Polyether Membranes Using the MOB Initiator. b) Images of the representative cross-linked polyether membrane demonstrating optical transparency and flexibility. 5.3.1 Chemical properties To investigate the polymerization of PO and ECH in the structure of membrane, 1H NMR spectroscopy was utilized by taking the aliquot of PPO-PECH before the viscose solution casted on the quartz plate. 1H NMR spectroscopy of the polymeric solution during reaction (SI, Figure 5-7) showed the Me group of PPO at 1.32 ppm, and protons corresponded to PPO and PECH 167 backbone are presented at 3.21-3.76 ppm. Residual peaks of monomers can be observed due to incomplete polymerization at this point. This is the only possible 1H NMR spectroscopy as cross- linked membranes cannot dissolve in a solvent for NMR spectroscopy characterization. FT-IR spectroscopy was utilized to provide information about successful cross-linked PPO-PECH membrane preparation and amine attachment through post modification mechanism. As shown in Figure 5-1, the FT-IR spectrum of pristine membrane, PPO-PECH, has peaks around 1102, 903, and 611 cm-1 suggesting the presence of C-O, C-C-O and C-Cl in the membrane structure. The amine modified membranes, PPO-PECH-MeA, PPO-PECH-nBuA, PPO-PECH-isoBuA, and PPO-PECH-tBuA presenting a characteristic peak of C-N at 1640 cm-1, which is not visible in the PPO-PECH, suggesting the successful attachment of the amines into the polyether backbone membranes. Moreover, the broad peak around 3300-3451 cm-1 for amine modified membranes suggests the presence of N-H in the amine tethered membranes. Table 5-1 Characterization of Amine Modified Cross-linked Membranes. Entry Samplea Tg G′e (°C)d (MPa) 1 PPO-PECHb -35 0.057 2 PPO-PECH-DMAc -30 0.021 3 PPO-PECH-nBuAc -29 0.025 4 PPO-PECH-iso-BuAc -31 0.037 5 PPO-PECH-t-BuAc -34 0.043 a reaction condition: pristine membrane was prepared on using 14 mg of MOB initiator, propylene oxide (0.74 ml), epichlorohydrin (0.11 ml), and diglycidyl ether (0.1 ml) as a cross-linker. b pristine membrane. c the membrane was dipped in the amine solution (20 ml) at RT. d measured from second heating curve of DSC. e the plateau shear modulus was measured by rheometer. 168 Figure 5-1 FT-IR spectra of the copolymer membranes: pristine membrane PPO-PECH (red color) and amine modified membranes PPO-PECH-MeA (green color), PPO-PECH-nBuA (purple color), PPO-PECH-isoBuA (yellow line), and PPO-PECH-tBuA(wine color). Amine modified membranes are showing the characteristic peak of C-N at 1640 cm-1 (dashed line). 5.3.2 Thermal and Rheological Properties Thermal and rheological properties of the membranes were characterized to further explore polymer composition – property relationships. Measured and derivative values from these experiments can be found in Table 5-1. For pristine membrane, one endotherm peak at -35 °C is evident, attributed to the glass transition of the membrane. The endothermic peak for the amine membranes shift to higher values after amine post-modification. These results suggest successful attachment of the amines. The DSC result and corresponding Tgs are depicted in the Figure 5-2, a. The thermal stability of the amine-modified membranes was measured by TGA under air 169 atmosphere as shown in Figure 5-2,b. PPO-PECH shows only two stages of weight loss due to both water loss and backbone decomposition. According to TGA curves, amine modified membranes have a three-stage degradation profile; The first slight stage for weight loss below 100-200 °C is due to adsorbed humidity or residual solvent evaporation in the membranes. The second weight loss at 200–380 °C is associated with the degradation of amine attached to the backbone. The third weight loss above 400 °C is related to the decomposition of the polymer backbone (PPO-PECH-MeA, PPO-PECH-nBuA, PPO-PECH-iso-BuA, PPO-PECH-tBuA). Figure 5-2 DSC measurements (a) and TGA characterization of (b) PPO-PECH (red color), and amine modified membranes PPO-PECH-MeA (green color), PPO-PECH-nBuA (purple color), PPO-PECH-isoBuA (yellow color), and PPO-PECH-tBuA(wine color). All polymeric systems are known to encompass different physical, chemical, and mechanical properties. These depend mainly on (1) macromolecular makeup, (2) inter-chain bonding and packing, and (3) chemical and thermomechanical history. Figure 5-3 shows the plateau shear modulus (Mpa) for pristine and all amine modified membranes. For the pristine membrane the shear modulus comes nearby 56 10-3 Mpa whereas for the amine modified 170 membranes the shear modulus decreases due to the presence of the amine in the membrane matrix. The enhancement of shear modulus for PPO-PECH-tBuA and PPO-PECH-isoBuA in comparison with PPO-PECH-nBuA and PPO-PECH-MeA membranes which is ascribed to the increased chain rigidity imparted due to steric hindrance of tBuA and isoBuA in comparison with isoBuA and MeA. Figure 5-3 the plateau modulus (G′) of the cross-linked membranes (PPO-PECH) and amine modified membranes PPO-PECH-MeA, PPO-PECH-nBuA, PPO-PECH-isoBuA, and PPO- PECH-tBuA. In occlusion, we reported a cross linked polyether-based membrane using a MOB initiator for CO2 transport. Post modification of the membranes by dipping method is easy and efficient resulting in the amine tethered membrane for primary amines attachment (PPO-PECH- MeA, PPO-PECH-nBuA, PPO-PECH-isoBuA, and PPO-PECH-tBuA). All the prepared membranes exhibited uniform structure and complete incorporation of comonomers into polymer films with thermal stability, optical transparency, and flexibility. The chemical composition of 171 the membranes was investigated by FT-IR to determine successful amine attachments as well as membrane physical properties which characterized by DSC, TGA, and rheometer. These membranes are the candidate for permeation–separation of CO2/N2 due to favorable interaction of C-O with CO2. Also, the effect of hindered amines as comparison with unhindered ones in the structure of the amine can be investigated for permeation–separation through CO2. 5.4 Supporting information Figure 5-4 1 H NMR and 13C NMR spectroscopy of MOB. 1 H NMR (CDCl3, 500 MHz) δ: -0.95 ([(CH3)2NCH2CH2(μ2- O)Al(CH3)2·Al(CH3)3], -0.74 3.46 ([(CH3)2NCH2CH2(μ2- O)Al(CH3)2·Al(CH3)3], 2.58 (s, CH3−N−), 2.92 (t, −N−CH2−CH2−O−), 3.98 (t, −N−CH2−CH2− O−). 13C NMR (CDCl3, 100 MHz) δ: 45.2 ([(CH3)2NCH2CH2(μ2-O)Al(CH3)2·Al(CH3)3], 55.11 (CH3−N−), 58.84 (−N−CH2−CH2−O−), 67.30 (−N−CH2−CH2−O−). 172 Figure 5-5 1H NMR spectroscopy of the polymeric solution with the ratio of PPO-PECH with ratio of PO:ECH (80:20). 173 BILBIOGRAPHY 174 BIBLIOGRAPHY (1) Han, Y.; Ho, W. S. W. Recent Advances in Polymeric Facilitated Transport Membranes for Carbon Dioxide Separation and Hydrogen Purification. J. Polym. Sci. A 2020, 58 (18), 2435– 2449. (2) Ramasubramanian, K.; Zhao, Y.; Winston Ho, W. S. 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We further expanded upon the architecture of SAl initiator by only changing the ligand to control the shape of homopolymers and copolymers. Then, we utilized the SAl star shape initiator to design novel amin tethered membrane for CO2 separation. In the last chapter, we developed a new membrane grafted with primary hindered and unhindered amines to investigate the efficacy of this membrane for CO2 capture. In the first step, we presented a new platform for synthesis of aluminum-based initiator for polymerization of different epoxides. We investigated the synthesis of four different thio- aluminum compounds (SAls) and evaluated the efficacy as initiators for epoxide polymerization. These initiators showed living polymerizations with controlled molecular weight, low dispersity, and were tolerant to the epoxide functional group. We used electrospray ionization mass spectrometry (EIS-MS) and 1H NMR spectroscopy to confirm the end group. We studied the kinetic behavior of this platform which showed the dependence on catalyst concentration and SAl end group. Next, we used SAl initiator for copolymerization (statistical and block copolymers) of different epoxides with targeted 30 kg/mol molecular weight and we used DOSY NMR to further investigate the presence of only one diffusion coefficient in the polymer matrix. We also combined the traditional RAFT polymerization technique with our SAl initiators, allowing for facile synthesis of vinyl-b-epoxide copolymers to easily and readily synthesis of poly(methyl methacrylate-b-epichlorohydrin) (P(MMA-b-ECH)). This technique will allow us to further tune polyether chemistry by giving us access to the vast array of thiol compounds that can 180 act as end groups as well as facilitates the synthesis of block copolymers from disparate monomer classes. In the second step, we showed that SAl initiators also can polymerize episulfides with a excellent control over molecular weights, relatively low polydispersity, and in short reaction time. Taken together, we copolymerized epoxides and episulfide to present a novel method for synthesis of statistical epoxide-stat-episulfide for the first time with control over molecular weight. We also synthesized a block copolymer of the same monomer to show the versatility of this method. We demonstrated statistical copolymerization of PS and epoxides to obtain unique, compositionally controlled copolymers. Polymer structure was characterized by various means such as 1H and 13C NMR spectroscopy, DOSY, SEC, DSC, and SAXS. In the next step, we synthesized a new class of SAl initiators to show chemical flexibility of our method to tune the initiator structure enabling us to impart architectures on the PS containing (co)polymers in the form of ABA copolymers and star (co)polymers. Finally, we synthesized a PEG-b-PPS from a PEG macroinitiator and characterized it by 1H and 13C NMR spectroscopy, DOSY, DSC, and SEC. This facile and tunable aluminum initiator system opens the door for a more robust and controlled synthesis of PS-epoxide copolymers that can be applied in biomedical and other contexts. In the third step, we investigated the use of t-H initiator to present a one-pot and solvent free platform for synthesis of architecturally controlled star shape polyether-based membrane. To design a membrane suitable for CO2 transport, we tuned the monomer feed ratio of propylene oxide (PO) and epichlorohydrin (ECH) for synthesis of poly(propylene oxide-stat- epichlorohydrin (PPO-PECH) in the presence of poly(ethylene oxide)-diglycidyl ether as a cross 181 linker evolute a 3-D structure of membrane. The produced films were optically clear and flexible films in all cases with different PO:ECH ratios. We used the optimized PPO-PECH with ratio of 90:10 to further modify the film with a range of amines like trimethylamine (TEA), dimethylamine (DMA), triethylamine (TEA), and diethylamine (DEA) by membrane dipping method. We characterized chemical, physical, and mechanical properties of resultant secondary amine grafted and qaurtenized membranes. PPO-PECH-TMA showed higher conductivity, higher water uptake, swelling ratio, and alkaline stability in compare with pristine and the other modified membranes due to higher basicity of TMA in the structure of the membrane. In the last step, we used previously reported MOB initiator to synthesis a (propylene oxide-stat-epichlorohydrin) (PPO-PECH) membranes utilizing bifunctional, poly(ethylene glycol) diglycidyl ether as a cross linking agent. We used of previously modified PO:ECH ratio (80:20) to be able to compare the capability of multi-armed membrane with the linear one for CO2 separation. We also modified the prepared membrane with the range of unhindered to hindered primary amines via dipping method. We investigated the chemical structure and physical properties of the membranes were characterized by FT-IR spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and rheometer. These membrane as facilitated transport membranes are designed specifically for CO2 transport and will be studied for CO2/CH4 separation. We will investigate the permeability and selectivity of the amine tethered membranes and compare the effect of hindered and unhindered amines for the mentioned application. This conclusion suggests that the innovative and easy to synthesis SAl initiator is a versatile platform for polymerization of epoxides and episulfide and it may be used as a general 182 method for polymerization of other heterocycle monomers like lactides and lactones. This might be single and simple system to controllably polymerize all of these monomers like epoxide, episulfide, lactide, and lactone either individually or simultaneously. Our investigations into an aluminum-based catalyst and initiator system demonstrate a single system can also copolymerize these monomers to prepare new and novel materials that will have different applications. Also, as we should that using SAl we can polymerize off of another polymer chain or combine it with traditional methods like RAFT, may be further used ti design new methodologies for polymerization Moreover, The SAl initiator can be modified to target different architecture of polymer as different thiols are commercially available as we synthesized ABA triblock copolymers and star shape copolymers. The only need to control the architecture is utilizing new thiol ligands that can be readily react with AlMe3 to yield in specific shape of initiator and eventually (co)polymer. Furthermore, by addition of a cross linker we could expand the use of the SAl initiators to synthesis membranes and design the membrane matrix to be utilized for important applications like CO2 separation. In future, combining different heterocycle monomers will result new copolymeric material and with using the same approach, different membrane with diverse applications can be synthesized. 183