SYNTHESIS AND CHARACTERIZATION OF ISOMERS OF FUNCTIONALIZED DOUBLE-DECKER-SHAPED SILSESQUIOXANES By Aditya N Patil A DISSERTATION Submitted to Michigan State University in partial fulfillment of the requirements for the degree of Chemical Engineering – Doctor of Philosophy 2023 ABSTRACT Functionalizing the incompletely condensed octaphenyl double-decker silsesquioxane tetrasilanol, Ph8-DDSQ(OH)4, with reactive dichlorosilanes forms condensed, hybrid molecules with reactive organic groups on the opposite edge of the inorganic SiO1.5 core, surrounded by phenyl moiety. This unique phenyl moiety surrounded SQ core provides additional thermo-oxidative stability for high temperatures, organic thermoplastics, and thermosetting polymers. Unlike corner-capped functional POSS, condensing DDSQ with dichlorosilane enables different chemical moieties on the opposite side of the SQ core, allowing SQ to act as the "bridging" chemical needed for bonding two different classes of materials. In addition, another benefit that is unique when condensing DDSQ-tetrol is the formation of isomers. Ph8DDSQ(OH)4, when fully condensed with R1R2SiCl2, is the formation of conformational isomers or regioisomers. (Isomers about the SQ core) The conformational isomer mixture often exhibited lower liquidus temperature than pure isomers, which benefits when mixed with organic resins at lower temperatures. Structural isomerism is the most radical type wherein the two compounds have the same number of atoms, but their chemical and physical properties are entirely different since they have logically distinct bonds. This work examines an asymmetrically capped DDSQ system synthesized as a coupling agent between graphene oxide (GO) nanofiller and styrene vinyl ester (VE) resin. The DDSQ-modified GO is dispersed into VE resin with only a simple mechanical stirring at room temperature. This work studies the different isomers of the DDSQ system. Firstly, meta and para isomeric moieties of phenyl ethynyl phenyl (PEP) dichlorosilane were obtained via the Sonogashira reaction and by subsequent reaction with trichlorosilane. The synthesized dichlorosilanes were reacted with DDPh8T8(OH)4, and the relevant reaction conditions and yield were presented. The reaction led to the formation of cis and trans isomers. These isomers form a eutectic mixture with a sharp melting point upon varying the ratio of cis and trans products. Upon using a mixture of meta and para dichlorosilanes as capping reagents, the reaction yielded a 6-isomer mixture of compounds. This isomeric mixture did not exhibit sharp melting characteristics as the individual isolated compounds exhibited. The sharpness of the solid-liquid transition character can also be dampened when long- chain chlorosilanes are used as capping agents for tetrol. This work also investigated the effect of constitutional isomerism in cage-like silsesquioxanes. Precisely, edge-open octaphenyl silsesquioxane diol condensed with tetramethyl dichlorosiloxane and double-decker-shaped silsesquioxane tetraol condensed with dimethyl dichlorosilanes form structural isomers. The interactions between the organic group bonded to the D-Si and the adjacent phenyl group connected to the T-Si of DDSQ molecules have a defining effect on the internal configuration of the DDSQ cage. This change affects phase transformation between liquid and solid states, forming a glassy state in a pure isolated compound. Copyright by ADITYA N PATIL 2023 TO MY FAMILY v ACKNOWLEDGMENTS Sitting down to write the last section of my Ph.D. thesis, I cannot believe that my days in the state of Michigan are numbered. This transformative graduate school experience at Michigan State University has affected my core principles and helped me to revise and refine my fundamentals. My method to approach a problem, to access, read, think, and process knowledge, to write and analyze scientific reports, to view the world as a research scientist, to interconnect with colleagues, behave myself in a professional environment, and manage resources and time, have all been strengthened over the last six years. This remodel occurred because of the people surrounding me and my workplace. I will eternally be grateful to them. It is nearly not probable to name every person that contributed to helping me in graduate school, as well as the individuals with whom I spent a fantastic time in Michigan. To start with, I need to eternally thank my family. To my parents, Narendra and Aruna, and my sister Chinmayee: your constant belief in me made all the difference. Next, I want to acknowledge the professors on my research committee. Firstly, I would like to highlight the guidance and patience of my advisor Dr. Andre Lee. He accepted me as his student in the Fall of 2017, and every day, he challenged me to change my method of thinking, how to work experimentally to achieve targets, to optimize the efforts to become a better researcher, and formulate questions to find solutions to any scientific problem. His contribution was beyond his duty, and he helped me to become a better scientist. Secondly, I would like to highlight Dr. Robert Maleczka for his guidance through the organic chemistry problems and his disposition to answer my questions every time his door was open. His contributions to this project were invaluable. Next, I would like to highlight Dr. Shiwang Cheng for his dedication to quality science, and I have always admired his passion for the students. Lastly, I would like to highlight Dr. Ramanini Narayan for his support. I recognize he plays many roles, but I have never met a PI that better encompasses the term mentor. Beyond vi the committee members, I would like to express my gratitude to my friends in chemistry. To my lab mates, Jonathan Dannett, Fangyi Shen, Badru-Deen Barry, Pepe Montero, Emmanuel Maloba, Thomas Oleskey, Arzoo Chhabra, Anshu Yadav, David Vogelsang, and Tyler Johnson: Working with you guys has been an honor, and I dearly hope to keep in close contact over the years. To my close friends:- Kalyani Jangam – The ‘USA exploration’ experience and amazing cuisines we have sampled cannot be put into words. Apoorva Kulkarni – From fighting over home-works to fun cookouts we had , Affan Malik – From playing board games, to real life games and sports, Gouree Kumbhar – From trying Pumpkin Spice Lattes to trying out new cafes, Shalin Patil – My flatmate, COD teammate and in being together in all crazy scenarios, Ishita Chandra – From the Neehes trips and unlimited gossips, Vishal Asnani – From playing FIFA to going places for a simple cup of coffee, Nikita Sharma – Eating good food together, Nidhi Kalani: From trying bougie places to home cooked Paneer dishes I have learned so much from you both in and outside the realm of science. I could never ask for a better group of friends. I want to mention to the CHEMS department staff that all of them did a great job with paperwork, orders, solving visa issues, and much more. Also, in the CHEMS department faculties, from whom I learn several new ideas and concepts through seminars, conferences, and classes. I want to thank Michigan State University through the CHEMS department for the unconditional financial support. vii TABLE OF CONTENTS LIST OF ABBREVIATIONS ...................................................................................................... x 1 INTRODUCTION ................................................................................................................ 1 1.1 Background ..................................................................................................................... 2 1.2 Silsesquioxanes ............................................................................................................... 7 1.3 Capped DDSQ systems ................................................................................................. 11 1.4 Isomers of capped DDSQ compounds .......................................................................... 11 1.5 Motivation ..................................................................................................................... 14 REFERENCES ......................................................................................................................... 16 2 APPLICATION OF ASYMMETRICALLY CAPPED DDSQ AS A BRIDGING AGENT ........................................................................................................................................ 19 2.1 Introduction ................................................................................................................... 20 2.2 Formulation of modified Derakene™ resins ................................................................ 23 2.3 Characterization of cured Derakene™ resin samples ................................................... 26 2.4 Experimental Details ..................................................................................................... 30 REFERENCES ......................................................................................................................... 35 APPENDIX ............................................................................................................................... 39 3 PHENYL ETHYNYL PHENYL DDSQ SYSTEMS........................................................ 45 3.1 Introduction ................................................................................................................... 46 3.2 Reagent synthesis .......................................................................................................... 47 3.3 Synthesis of dichlorosilanes .......................................................................................... 52 3.4 Capping of DDPh8T8(OH)4 ........................................................................................... 60 3.5 Separation of DDPh8T8 isomers.................................................................................... 60 3.6 Experimental details...................................................................................................... 62 REFERENCES ......................................................................................................................... 68 APPENDIX ............................................................................................................................... 69 4 EFFECTS OF USING BULKY CAPPING GROUPS .................................................... 80 4.1 Introduction ................................................................................................................... 81 4.2 Synthesis of isomers of capped DDSQ structures ........................................................ 82 4.3 Thermal Analysis using DSC........................................................................................ 86 4.4 Experimental details...................................................................................................... 91 REFERENCES ......................................................................................................................... 95 APPENDIX ............................................................................................................................... 97 5 SOLVENT EFFECT FOR CAPPING OF DDPh8T8(OH)4 .......................................... 111 5.1 Introduction ................................................................................................................. 112 5.2 DDSQ tetrol capping reaction using a good solvent ................................................... 113 5.3 DDSQ tetrol capping reaction using a poor solvent ................................................... 117 5.4 Experimental Details ................................................................................................... 120 REFERENCES ....................................................................................................................... 125 APPENDIX ............................................................................................................................. 127 viii 6 INCOMPLETELY CONDENSED CAGE-LIKE SILSESQUIOXANES ................... 138 6.1 Introduction ................................................................................................................. 139 6.2 Synthesis of Incompletely Condensed Cage diol........................................................ 140 6.3 Thermal properties of model compounds ................................................................... 144 6.4 Synthesis and Characterization of constitutional isomers .......................................... 146 6.5 Thermal and Rheological Property of isomers: TGA, DSC, and Viscosity ............... 152 6.6 Rheological data.......................................................................................................... 155 6.7 Experimental Details ................................................................................................... 157 REFERENCES ....................................................................................................................... 169 APPENDIX ............................................................................................................................. 172 7 SIGNIFICANCE AND PERSPECTIVE ........................................................................ 229 7.1 Significance................................................................................................................. 230 7.2 Perspectives................................................................................................................. 231 ix LIST OF ABBREVIATIONS AB Asymmetric double-decker-shaped silsesquioxane BCl3 Boron Trichloride BMI bismaleimides BODA bis-odiynyl arene CDCl3 Deuterated chloroform CuI Cuprous iodide CuCl2 Cupric Chloride DABPA O, O’-diallyl bisphenol A DCM Dichloromethane DDSQ Double-decker shaped silsesquioxane DDPh8T8(OH)4 Tetra-silanol double-decker-shaped silsesquioxane DDPh8T8(2(R1R2) Difunctional capped Double-decker-shaped silsesquioxane DSC Differential scanning calorimetry Et3N Triethylamine GC- MS Gas chromatography – Mass spectroscopy GO Graphene Oxide LiAlH4 Lithium Aluminium hydride LiBr Lithium Bromide Me Methyl MeSiCl3 Methyl trichlorosilane Mg Magnesium NMR Nuclear magnetic resonance x PdCl2(PPh3)2 Bis(triphenylphosphine)palladium (II) dichloride PEB Phenyl ethynyl benzene PEP Phenyl ethynyl phenyl PEPI Phenyl ethynyl phenyl imide PETIs Polyetherimide POSS Polyhedral oligomeric silsesquioxane PMR Polymerization of Monomer Reactants R.T. Room temperature RTM Resin transfer molding R1R2SiCl2 Difunctional dichlorosilane , SOPh8T8 Side open di-silanol silsesquioxane t-BuLi tertiary butyl lithium TCCA Trichloroisocyanuric acid TGA Thermogravimetric Analysis THF Tetrahydrofuran VARTM Vacuum-assisted Resin transfer molding xi 1 INTRODUCTION 1 1.1 Background High-performance thermosets are three-dimensional cured network structures. High-temperature polymeric materials exhibit high glass transition temperature (>300 °C) and excellent mechanical properties along with high decomposition temperature (>450 °C). These polymeric materials must be thermally and oxidatively stable without affecting the mechanical properties. Such materials often had an extensive aromatic backbone as the sp2 hybridized carbon atoms have higher bond dissociation energy than the sp3 hybridized carbon atoms.1 Although various thermosets could withstand high-temperature ranges (300 °C-400 °C), processing these thermosets was a tenuous task due to the inherent rigidity of the aromatic backbone of these thermosets. Polyimides have shown remarkable potential as thermally stable materials suitable as advanced structural resins for a wide range of applications.2,3 Polyimides contain a repeating imide structural unit and can be generally synthesized using condensation polymerization of dianhydride and diamine monomers. Avimid N™ is a commercially used condensation polyimide. It has a glass transition temperature of 360 °C. The polyimides synthesized using condensation usually produce intermediate isoimide structures, leading to incomplete polymerization. It affects the mechanical strength of the polymer due to the poor mechanical strength of lower molecular-weight polymer chains. Also, the fabrication process must be carefully designed considering the high pressure required for molding and dissipating the volatile byproducts formed. To find a solution to the issues mentioned above, a new approach, PMR (in-situ Polymerization of Monomer Reactants), was used by NASA4. This technique was highly successful because of the ease of processability of the reactant monomer and the ensuing oligomers. Also, the polymerization proceeds via an addition type reaction rather than a condensation type, thus avoiding the formation of volatile byproducts. The mechanical properties 2 of the cured network can be tailor-made by simple variation of the chemical structure of aromatic diamines or the diester acids used or by changing the stoichiometry of monomers used in the reaction. Along with this approach, many reactive groups have been used to end cap the thermoset resins. The mechanical properties of the cured network depend on the chemistry of cross-linking, cure rate, and the number of end groups. The end groups remain dormant during the fabrication process. After the fabrication step, temperature increases to induce homo-polymerization of the end groups, the final cured network cannot be reprocessed by melting, but it has enhanced thermochemical properties. Figure 1-1 : Functional groups used as end-capping reagents. Cyanate-terminated polyamide thermosets can be used as flame retardant agents. These thermosets can be used in the microelectronics industry, as they have low dielectric constant and high dielectric breakdown strength.5 Maleimide terminated thermosets are widely used as high- performance thermosets in oil-field operations. These thermosets can effectively perform in got/wet fluid conditions with pressure up to 70MPa and temperatures in the 200 °C.3 Nadimide- terminated thermosets can be used as high-temperature adhesives to bond metals.6 LARC-13 is a commercialized nadimide end-capped thermoset with a low softening temperature of 266-316 °C. 3 Hence, it can be used for specialized bonding applications. Despite the ease of processability of maleimide-terminated oligomers via melt-based processing, the after-cure products are brittle with low toughness and may contain voids because of the out-gassing of volatiles. PMR-15 is an alternative norbornene end capped addition type cured thermoset used for various aircraft engine applications. It has post-cure Tg of 365 °C and can withstand temperatures up to 230 °C for longer than 10,000 h. The drawback of PMR-15 lies in using methylene di-aniline monomer, a carcinogenic material. Also, the cost of processing was still very high for commercial usage of PMR-15. These issues led to exploring new end-group chemistries that could circumvent the existing issues. Acetylene functionalized moieties have been shown to be promising alternatives as reactive end-groups. They can undergo thermally induced addition reactions yielding a complex cross-linked network.7 The acetylene group formed an aromatic ring through cyclo-trimerization for low molecular weight compounds, but for the high molecular weight oligomers, the procedure involved forming ene-yne type structures. These structures are then further homopolymerized to give the cross-linked structure. The final cross-linked structure consists of polycyclic aromatic structures, bridged structures, backbone addition structures, and cyclotrimerized aromatic structures. Thermid 600®, developed by Gulf Chemicals, was the most widely used acetylene- terminated oligomer for polyimides. Thermid 600® has a glass transition temperature of 370 °C, a tensile strength of 96.5MPa, and a modulus of 3.79 GPa. It was found to be an excellent adhesive for titanium. The shortcoming of these end groups was the homopolymerization temperature around 200 °C. It led to a limited processing window for oligomers, and hence high melting, all aromatic backbone oligomers could not be processed. These limitations were overcome by replacing the terminal proton of the acetylene end group with a phenyl ring.8 This feature helped to postpone the cross-linking temperature beyond 300 °C, providing a larger window for 4 processing of the oligomers. NASA demonstrated the promising nature of these end groups in the High-Speed Civil Transport Program, where a series of phenyl-ethynyl terminated polyetherimides (PETIs) were synthesized and characterized.8,9. PETI-5 has a molecular weight of 5000 g/mol and has a glass transition temperature of 270 °C after curing it at 371 °C for one hour. It also shows 32% elongation at break with a modulus 3.0GPa and 130MPa tensile strength. To make further improvements to the thermal and oxidative stability of the polymer as well as to improve the ease of processing the oligomer melt and the AFR-PE-n class of thermosets was introduced in 1994.10 The oligomers for the synthesis of AFR-PE- n thermosets were synthesized by cyclodehydration reaction between hexafluoro dianhydride and phenyldiamine. Phenylethynyl phthalic anhydride was used as an end-capping reagent. These oligomers are then thermally cured to obtain the final cross-linked network. The length of the repeating units in the oligomer was represented by ‘n.’ The value of ‘n’ varied from 1,2,4, and 8. This value determined all the mechanical and thermal properties and the ease of processability of the oligomer. Oligomer characterization using chromatography and mass spectrometry revealed a broad molecular weight distribution for n =1,2,8. The distribution was narrow in the n =4 system, with an average of 4. AFR-PE- n systems exhibit a glass transition temperature of around 450 °C, significantly improving the mechanical properties of the previously studied polyimides.11 The rheological properties and thermal stability of the systems were studied. The AFR-PE-2 system exhibited minimum complex viscosity of 10 Poise at a cure temperature of 371 °C, whereas the minimum complex viscosity for AFR-PE-8 systems was 540 Poise. By interpolating, it can be assumed that the minimum complex viscosity for AFR-PE-4 systems lies in this range. The study of thermal decomposition temperatures showed that the cured networks were stable up to a range of 489 °C - 548 °C based on the heating rates used irrespective of the value of ‘n’. Despite the promising 5 properties polyamides synthesized from AFR-PE-4 oligomers, the moisture absorption rate was considerably high making them unsuitable for marine applications. Scheme 1-1 : Synthesis of AFR-PE-n imide oligomers11 Also, the value and temperature of the minimum melt viscosity of the oligomeric system, along with the solid-liquid phase transition temperature, needed to be lowered to facilitate the increase to increase the processing window. Additionally, the molecular weight for the oligomeric systems was not constant since the value of n varies, and therefore the properties vary with the molecular weight of the oligomeric systems.12 6 1.2 Silsesquioxanes 1.2.1 Condensed Polyhedral Oligomeric Silsesquioxanes. Organo-functionalized silsesquioxanes have emerged as a fascinating novel field for modern technology.13–16 Polyhedral oligomeric silsesquioxanes (POSS) are unique hybrid organic- inorganic materials with a general chemical composition of (RSiO1.5) n, where each silicon atom is connected to three oxygen atoms. The R group can be a hydrogen atom, or it can be any alkyl, alkylene, aryl, arylene, or organo-functional derivatives of alkyl, alkylene, aryl, or arylene groups17, and the shape of the structure varies between partial cages, closed cages Figure 1-2 : Random, ladder and cage-like structures of silsesquioxanes or random cages as shown in Figure 1-2. The term oligo- denotes the presence of several silsesquioxane units in the compound. The term silsesquioxane can be divided as sil- silicon; sesqui- each Si atom is bound to an average of one and a half oxygens; ane- each Si atom is attached to one hydrocarbon group; the silicon-oxygen cluster forms a polyhedron (cage) and not a cube as the bond angles between Si-O-Si and O-Si-O is not equal to 90 °C. Among these POSS materials, octa-silsesquioxanes (R8Si8O12, T8) have been primarily investigated; they consist of a rigid, cubic inorganic silica core with eight organic corner groups. Silsesquioxane was first synthesized in 1946 from the thermal analysis of the polymeric products of the hydrolysis of methyl trichlorosilane reaction by Scott.18 The two-step synthetic process involves the hydrolysis of methyl trichlorosilane to form the trisilanol derivative, followed by condensation to form thermally- stable organofunctional silsesquioxanes. Sprung and Guenther19 7 later initiated the development of this area by modifying and optimizing the method done by Scott. The most used reaction for synthesizing POSS is via hydrolytic condensation of trifunctional monomers where ‘X’ can be a reactive group such as halogen or alkoxy, or acetoxy group and ‘R’ Scheme 1-2 : Synthesis of POSS molecule via hydrolytic condensation of monomers is a thermally stable group such as alkyl or phenyl.20 The yield of the reaction depends on various processing factors such as the type of the functional group used, the concentration of the reactants and the intermediates in the reaction, the nature of the solvent used for the reaction, the type of catalyst used, the temperature at which the reaction is carried out and finally upon the rate and quantity of water addition in the reaction. After numerous optimization trials, the silsesquioxanes can now be obtained in the 88-89 % yield range. These POSS molecules have some definite advantages over the other nanosized fillers. To begin with, most of the other nanoscale inorganic agents have a size distribution, which leads to non-uniform dispersion in the matrices of the thermosets. The POSS moieties have a well-defined shape and can be well dispersed in polymer matrices with proper functionalization. Also, the number of active functional groups on other nanoscale agents is poorly defined. This various number of active functional groups led to variations in the properties of the final product with variations in synthesis batches. POSS has an exact number of organic groups on the corners. These groups can be altered to be reactive or non- reactive to suit the application's needs. One of the most synthesized POSS cages around the year 1980s was Hydridooctasilsesquioxane, (H8Si8O12) and Octakis-(Hydridodimethylsiloxy)Octasilsesquioxane, (H(CH3)2SiO8Si8O12). The POSS cages were further modified via hydrosilylation reaction using polymerizable groups to form 8 octa-functional macromers to modify various polymers. POSS can be introduced into polymer matrices to produce novel composite materials with various advantageous properties.21–24 1.2.2 Incompletely Condensed Polyhedral Oligomeric Silsesquioxanes Incompletely condensed polyhedral oligomeric silsesquioxanes [R7Si7O9(OH)3] contain Si-OH groups, which can be found in silica or silicate surfaces, thus providing a pathway for a suitable model compound for investigating and the study of silica surfaces and their interactions with polymeric surfaces. The incompletely condensed contain freely available hydroxyl groups, which can be readily reacted with alkoxysilanes or chlorosilanes to form functional end groups. Despite synthesizing and characterizing various incompletely condensed silsesquioxanes, the commonly synthesized incompletely condensed silsesquioxane is the trisilanol POSS [R7T4D3(OH)4], which is readily available on a multi-kilogram scale. The most pioneering work performed on these trisilanol cages is done by the Faher group.25–29 The group synthesized incompletely condensed silsesquioxanes via acid/base mediated hydrolytic cleavage of condensed POSS cages. The reaction can be carried out using triflic acid or methanesulfonic acid, which can cause cleavage of the Si - O framework, leading to the rearrangement of the cages to form incompletely condensed silsesquioxanes. A base such as NEt3OH can also be used to rearrange the cages and, upon further hydrolysis, form trisilanol cages. Kawakami et.al30,31 developed incompletely condensed octa-phenyl double-decker-shaped silsesquioxane tetra-silanol (DDPh8T8(OH)4) by cleavage and rearrangement of POSS cages. These DDPh8T8(OH)4 moieties can be mono-, di- or tetra-functionalized using chlorosilanes. Functionalization usually occurs via side capping of the silanol groups in the presence of a weak base. Numerous functional groups can be side capped onto the DDPh8T8(OH)4, forming a stable 9 DDSQ cage that can be further used as a monomer to form thermally stable thermosets, as a filler in a polymer matrix, or as a nanosized coupling agent between polymer matrix and carbon filler. Figure 1-3 : Partially condensed Octa phenyl double-decker shaped silsesquioxane tetra-silanol Barry et al. have established a novel synthetic route to obtain the symmetrical partially condensed Octa phenyl double-decker-shaped silsesquioxane tetra-silanol using dodecaphenylT12 (Ph12T12) as a starting material. Ph12T12 was treated with four equivalents of aqueous NaOH in isobutanol at 90 °C for 24 h. It was found that reacting completely condensed Ph12T12 with NaOH affected the selective fissure of Si-O-Si bonds. Figure 1-4 : Graphical abstract for Base-Promoted Hydrolysis of Dodecaphenyl Silsesquioxane into partially condensed octaphenyl silsesquioxane The crude product was silylated with TMSCl in order to aid in the identification of the reaction products; upon studying the mass spectral data from a time-resolved point to early formation of a tetracyclo siloxane as a critical intermediate for the formation of the ‘double-decker’ shaped silsesquioxane. 10 1.3 Capped DDSQ systems The DDSQ tetrol can be capped using dichlorosilanes, leading to the unavoidable production of isomers. The capping reaction and the ratio of the isomers depend on the type of dichlorosilane used. The work on the isolation of these isomers has been minimal. The primary method of separating these isomers is based on solubility differences and hence via fractional recrystallization. The isomers have vastly different properties when isolated compared to the isomeric mixture. Properties such as melting temperature and rheology of the isolated compounds are vastly different from the isomeric mixture and vary with the compounds' ratio in the isomeric mixture. Scheme 1-3 : Capping of DDSQ tetrol using dichlorosilanes. 1.4 Isomers of capped DDSQ compounds 33 In 2013, low-viscosity DDSQ-based polyamides were reported by Schoen . meta and para methyl-amino phenyl dichlorosilanes were used together to condense Ph8DDSQ(OH)4. This capping scheme created a mixture containing regio- (meta and para) and stereo- (cis and trans) isomers in the final condensed product. Once the products had been synthesized, phenyl ethynyl phthalic anhydride was used to form fully imidized oligomers (DDSQ-PEPI) (Figure 1-5). Compound 3a is a symmetrical meta-meta structure, 3c is a symmetrical para-para structure, and 3b is an asymmetrical meta-para structure. 11 All the systems have cis and trans isomers concerning the DDPh8T8 cage about the D-Silicon. Based on the assumption of a rate-independent reaction between dichlorosilane and silanol, the isomer mixture as prepared (in Figure 1-5) should contain 25% of isomer AA, 25% of isomer BB, and 50% isomer AB. The thermal stability of all these five samples in air and nitrogen was evaluated using thermogravimetric Analysis (TGA). The steady-state shear results suggest that the mixture's viscosity can be altered by orders-of-magnitude by altering the ratios of isomers. The trans para-DDSQ-PEPI showed a more substantial effect on the viscosity alteration than the cis para-DDSQ-PEPI. No significant differences were found. The mixtures also exhibited eutectic- like characteristics. Due to the organic content of the imide group, the amount of crystallinity is lowered, but the trans-cis mixture retains its crystallinity. Thus, the inorganic core provides the durability needed at elevated temperatures and relatively low-moisture uptake, while organic moiety enables processing to composite structures. This class of low-viscosity oligoimide thermosetting materials can provide needed control in viscosity which is expected to reduce the processing hurdles of reinforced composites by controlling the ratio of isomers in resin while retaining oxidative thermal stability over the current organic oligoimide resins. 12 Figure 1-5 : Different isomers of octaphenyl double-decker shaped silsesquioxane tetrasilanol - (i) trans-Ph8DDSQ (meta-aminophenyl)2(Me)2 (ii) cis Ph8DDSQ (meta-aminophenyl)2(Me)2 (iii) trans-Ph8DDSQ (para-aminophenyl)2(Me)2 (iv) cis Ph8DDSQ (meta-aminophenyl)2(Me)2 (v) trans-Ph8DDSQ (meta-aminophenyl)(para-aminophenyl)(Me)2 (vi) cis Ph8DDSQ (meta- aminophenyl)(para-aminophenyl)(Me)2 The attempted synthesis of DDPh8T8-PEPI possessed several disadvantages, such as diminished yields and being time intensive. Even though the moisture uptake has been reduced compared to AFR-PE-4 material, it may be possible to further reduce the uptake by eliminating the imide group and directly capping the DDPh8T8(OH)4 cage with phenylethynyl end-capped chlorosilanes. 13 Vogelsang D.34 also successfully separated the cis and trans isomers of capped DDSQ compounds using HPLC. He discovered that a polar group's presence could significantly help separate the isomers from obtaining nearly pure cis and near pure trans compounds. It was observed that with the addition of two different chlorosilanes for capping sites on DDPh8T8(OH)4, symmetrically and Figure 1-6 : Viscosity measurements for PEP amide based isomeric system asymmetrically capped DDPh8T8 mixtures are produced. Separating these products was possible because various hydroxyl groups are present in each molecule. By changing the ratios of the chlorosilanes, an attempt can be made to achieve the statistical ratio of isomers. The deviations from the statistical ratio of isomers are due to the difference in the rate of side-capping being significantly affected by steric hindrance from the side-capping agent. 1.5 Motivation The AFR PE-n system of organic polyamides provides high thermal stability and good mechanical properties for high-temperature applications. The system can be tuned to meet the application's specific requirements using a blend of AFR PE-n systems. This fine-tuning might lead to a lowering of Tg. Also, water is formed during the synthesis step, which might get trapped in the final structure leading to weakening mechanical properties. DDSQ PEPI systems have a robust hybrid core that helps achieve high Tg values. These capped DDSQ structures can be easily 14 synthesized using dichlorosilanes, and based on the polarity difference in the isomers, nearly pure forms of the isomers can be obtained by column chromatography techniques. By adjusting the ratio of cis and trans isomers, it is possible to adjust the final properties of the network structure. Also, it may be possible to alter the crystallinity and viscosity of the system by having different isomeric configurations of a capped functional group on either side of the cage, thereby helping to improve the cure kinetics. To this effect, a clean, optimized route must be developed to synthesize the chlorosilanes required to side-cap the cage structures. The structure's mechanical, thermal, and rheological properties must be studied. The aims of this report include the following: 1. To explore material applications based on the possible capped cage structures to be synthesized from this work. 2. To explore an alternative methodology for capping DDSQ tetrol to study the effect of non- solvent on the ratio of isomeric products. 3. Design and carefully analyze the synthesis routes to obtain clean chlorosilanes and synthesize an isomeric mixture of phenylethynyl end-capped DDPh8T8 cages. 4. Synthesis of a novel partially capped Ph8T8 diol and further capping with chlorosilanes to synthesize capped basket-like asymmetrical DDSQ compounds. 5. Study of thermal and structural characteristics for capped DDPh8T8 cages. 15 REFERENCES (1) Luo, Y.-R. Bond Dissociation Energies. CRC Handbook of Chemistry and Physics 2012, 89, 89. (2) Kreuz, J. A. Copolyimide-Iosimide Polymers. 3413267, November 26, 1968. https://pdfpiw.uspto.gov/67/132/034/1.pdf (accessed 2020-03-22). (3) Broome, J. T.; Voll, B. A.; Corbett, G.; GB; Goodson, J.; Yuan, Y.; Peterson, E. R. 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Structure-Property Processing Relationships and the Effects of Physical Structure on the Hygro-Thermal Durability and Mechanical Response of Polyimides, Michigan State University, 2001. 16 (12) Simone, C. D.; Scola, D. A. Phenylethynyl End-Capped Polyimides Derived from 4,4‘- (2,2,2-Trifluoro-1-Phenylethylidene)Diphthalic Anhydride, 4,4‘- (Hexafluoroisopropylidene)Diphthalic Anhydride, and 3,3‘,4,4‘-Biphenylene Dianhydride: Structure−Viscosity Relationship. Macromolecules 2003, 36 (18), 6780–6790. https://doi.org/10.1021/ma0300701. (13) Constable, G. S.; Lesser, A. J.; Coughlin, E. B. Morphological and Mechanical Evaluation of Hybrid Organic−Inorganic Thermoset Copolymers of Dicyclopentadiene and Mono- or Tris(Norbornenyl)-Substituted Polyhedral Oligomeric Silsesquioxanes. Macromolecules 2004, 37 (4), 1276–1282. https://doi.org/10.1021/ma034989w. (14) Xu, H.; Kuo, S.-W.; Lee, J.-S.; Chang, F.-C. Preparations, Thermal Properties, and T g Increase Mechanism of Inorganic/Organic Hybrid Polymers Based on Polyhedral Oligomeric Silsesquioxanes. Macromolecules 2002, 35 (23), 8788–8793. https://doi.org/10.1021/ma0202843. (15) Harrison, P. G. Silicate Cages: Precursors to New Materials. Journal of Organometallic Chemistry 1997, 542 (2), 141–183. https://doi.org/10.1016/S0022-328X(96)06821-0. (16) Fu, B. X.; Lee, A.; Haddad, T. S. Styrene−Butadiene−Styrene Triblock Copolymers Modified with Polyhedral Oligomeric Silsesquioxanes. Macromolecules 2004, 37 (14), 5211–5218. https://doi.org/10.1021/ma049753m. (17) Baney, R. H.; Itoh, M.; Sakakibara, A.; Suzuki, T. Silsesquioxanes. Chem. Rev. 1995, 95 (5), 22. https://doi.org/10.1021/cr00037a012. (18) Scott, D. W. Thermal Rearrangement of Branched-Chain Methylpolysiloxanes 1. J. Am. Chem. Soc. 1946, 68 (3), 356–358. https://doi.org/10.1021/ja01207a003. (19) Sprung, M. M.; Guenther, F. O. The Partial Hydrolysis of Ethyltriethoxysilane. J. Am. Chem. Soc. 1955, 77 (15), 3996–4002. https://doi.org/10.1021/ja01620a014. (20) Voronkov, M. G.; Lavrent’yev, V. I. Polyhedral Oligosilsesquioxanes and Their Homo Derivatives. (21) Gnanasekaran, D.; Madhavan, K.; Reddy, B. S. R. Developments of Polyhedral Oligomeric Silsesquioxanes (PaSS), Pass Nanocomposites and Their Applications: A Review. 28. (22) Han, D.; Wen, T.; Han, G.; Deng, Y.; Deng, Y.; Zhang, Q.; Fu, Q. Synthesis of Janus POSS Star Polymer and Exploring Its Compatibilization Behavior for PLLA/PCL Polymer Blends. Polymer 2018, 136, 84–91. https://doi.org/10.1016/j.polymer.2017.12.050. (23) Han, D.; Zhang, Q.; Chen, F.; Fu, Q. Using POSS–C 60 Giant Molecules as a Novel Compatibilizer for PS/PMMA Polymer Blends. RSC Adv. 2016, 6 (23), 18924–18928. https://doi.org/10.1039/C6RA00218H. (24) Fina, A.; Monticelli, O.; Camino, G. POSS-Based Hybrids by Melt/Reactive Blending. J. Mater. Chem. 2010, 20 (42), 9297. https://doi.org/10.1039/c0jm00480d. 17 (25) Feher, F. J.; Newman, D. A.; Walzer, J. F. Silsesquioxanes as Models for Silica Surfaces. J. Am. Chem. Soc. 1989, 111 (5), 1741–1748. https://doi.org/10.1021/ja00187a028. (26) Lichtenhan, J. D.; Vu, N. Q.; Carter, J. A.; Gilman, J. W.; Feher, F. J. Silsesquioxane- Siloxane Copolymers from Polyhedral Silsesquioxanes. Macromolecules 1993, 26 (8), 2141–2142. https://doi.org/10.1021/ma00060a053. (27) Jones, W. D.; Feher, F. J. Comparative Reactivities of Hydrocarbon Carbon-Hydrogen Bonds with a Transition-Metal Complex. Acc. Chem. Res. 1989, 22 (3), 91–100. https://doi.org/10.1021/ar00159a002. (28) Feher, F. J.; Budzichowski, T. A.; Blanski, R. L.; Weller, K. J.; Ziller, J. W. Facile Syntheses of New Incompletely Condensed Polyhedral Oligosilsesquioxanes: [(C- C5H9)7Si7O9(OH)3], [(c-C7H13)7Si7O9(OH)3], and [(c-C7H13)6Si6O7(OH)4]. Organometallics 1991, 10 (7), 2526–2528. https://doi.org/10.1021/om00053a070. (29) Feher, F. J.; Budzichowski, T. A.; Rahimian, K.; Ziller, J. W. Reactions of Incompletely- Condensed Silsesquioxanes with Pentamethylantimony: A New Synthesis of Metallasilsesquioxanes with Important Implications for the Chemistry of Silica Surfaces. J. Am. Chem. Soc. 1992, 114 (10), 3859–3866. https://doi.org/10.1021/ja00036a038. (30) Lee, D. W.; Kawakami, Y. Incompletely Condensed Silsesquioxanes: Formation and Reactivity. Polym J 2007, 39 (3), 230–238. https://doi.org/10.1295/polymj.PJ2006169. (31) Li, Z.; Kawakami, Y. Formation of Incompletely Condensed Oligosilsesquioxanes by Hydrolysis of Completely Condensed POSS via Reshuffling. Chem. Lett. 2008, 37 (7), 804–805. https://doi.org/10.1246/cl.2008.804. (32) Humphreys, J.; Pop, F.; Hume, P. A.; Murphy, A. S.; Lewis, W.; Davies, E. S.; Argent, S. P.; Amabilino, D. B. Solid State Structure, and Properties of Phenyl Diketopyrrolopyrrole Derivatives. CrystEngComm 2021, 23 (8), 1796–1814. https://doi.org/10.1039/D1CE00039J. (33) Schoen, B. Aminophenyl Double Decker Silsesquioxanes: Spectroscopic Elucidation, Physical and Thermal Characterization, and Their Applications, Michigan State University. (34) Vogelsang, D. F.; Dannatt, J. E.; Maleczka, R. E.; Lee, A. Separation of Asymmetrically Capped Double-Decker Silsesquioxanes Mixtures. Polyhedron 2018, 155, 189–193. https://doi.org/10.1016/j.poly.2018.08.016. 18 2 APPLICATION OF ASYMMETRICALLY CAPPED DDSQ AS A BRIDGING AGENT 19 2.1 Introduction Vinyl ester resins belong to the thermoset polymeric materials widely used in the composites industry.1,2 Vinyl ester resin is synthesized by esterifying epoxy resins with unsaturated monocarboxylic acids. Vinyl ester resins have numerous applications requiring high chemical and corrosion resistance. They are also used in applications where properties such as enhanced water barrier and low moisture uptake, low shrinkage, and good dimensional stability are required. Generally, these resins are used in marine, pipeline, automotive, and electronics industries.3–9 A graphene sheet is a single atomic layer of carbon atoms (sp2 hybridized) in a two-dimensional array. Since the discovery of graphene in 2004,10 various graphene-filled composites have been synthesized and studied to achieve better mechanical, thermal, and electrical properties.3,11–14 The improved properties are due to the large surface area of graphene compared to other carbon-based nano-fillers. The graphene sheets help improve the material's fracture toughness, mitigating the crack propagation mechanism. The moisture uptake is reduced as the path of fluids becomes more tortuous through the polymer matrix. The graphene sheets must be well dispersed in the matrix and strongly bond with the matrix to enhance the graphene composites' properties.4 But they tend to agglomerate due to strong Van-der Wall forces between the sheets.15 The surface is almost inert with the presence of a small percentage of non-carbon functional groups leading to a poor bonding between the matrix and the filler. There are several common approaches to the surface treatment of graphene, each serving a specific purpose and achieving distinct modifications16. Some prominent techniques include chemical functionalization, physical modifications, and deposition of thin films or coatings.16 Chemical functionalization involves introducing various chemical groups or molecules onto the graphene surface, altering its properties. Functionalization can enhance the dispersibility of graphene in 20 solvents, improve its compatibility with polymers or other materials, and introduce specific functionalities. Standard chemical functionalization methods include covalent functionalization and non-covalent functionalization17–19. In covalent functionalization, reactive species, such as diazonium salts or organic molecules containing functional groups (e.g., -OH, -COOH), react with the carbon atoms on the graphene surface, forming covalent bonds. Covalent functionalization can alter graphene's electronic structure, surface energy, and chemical reactivity. The most used covalent functionalization technique is oxidation. Oxidation treatment involves exposing graphene to oxidizing agents such as oxygen, ozone, or nitric acid. This process introduces oxygen- containing functional groups, such as hydroxyl (-OH), carbonyl (C=O), or carboxyl (-COOH) groups, onto the graphene surface. Oxidation can render graphene more hydrophilic, increase its compatibility with other materials, and provide sites for further functionalization. In the non- covalent functionalization approach, the adsorption of molecules or nanoparticles onto the graphene surface through weak molecular interactions such as Van der Waals forces or π-π stacking. Non-covalent functionalization can improve the dispersion of graphene in solvents or matrices, and it is reversible, allowing for easy removal of the functionalizing agents. Physical treatments can alter the graphene surface by mechanical, thermal, or plasma-based methods.20–23 These modifications can enhance graphene's structural integrity, wettability, and adhesion. The various types of physical treatment techniques are listed. In .mechanical exfoliation, the controlled application of mechanical forces, such as rubbing or peeling, to detach graphene flakes from a graphite source is done. Mechanical exfoliation is the basis for obtaining high-quality graphene flakes, such as those used in research or device fabrication. The next type of physical treatment is annealing. Annealing refers to the controlled heating of graphene to modify its structure and properties. Thermal treatment can improve the crystallinity, remove defects, and 21 restore the sp² carbon network of graphene, leading to improved electrical conductivity and carrier mobility. Plasma treatment involves subjecting graphene to low-pressure plasma, which can introduce functional groups, etch the surface, or enhance its adhesion to other materials. Plasma treatment can also improve the hydrophilicity or hydrophobicity of graphene, depending on the specific plasma chemistry used. Surface treatments can also involve depositing thin films or coatings onto the graphene surface to impart specific functionalities or enhance performance16,20,24–26. These methods include chemical vapor deposition and atomic layer deposition. CVD is a widely used technique to grow thin films or layers of materials on graphene. By controlling the deposition parameters, various materials like metals, metal oxides, or polymers can be deposited onto graphene, imparting properties such as electrical conductivity, barrier properties, or mechanical strength. Atomic layer deposition (ALD) is a precise thin film deposition technique that enables the growth of conformal and uniform coatings on graphene. ALD can deposit thin layers of materials like metal oxides or organic polymers with controlled thickness and composition, offering precise tailoring of surface properties. The oxidized graphene (GO) derivative increases the surface's quantity of non-carbon functional groups. GO sheet has epoxide and hydroxyl groups on the basal plane, whereas the edges have carboxyl and carbonyl functional groups. The functional groups make GO water dispersible and can be used to improve nanofiller dispersion in the matrix27 GO is usually synthesized from Graphene nanoplatelets using the modified Hummer’s process.28,29 To meet the ever-increasing demand for high-performance thermosets, efforts have been made to incorporate GO nanofillers into polymer matrices.4,5,14,29–32 The most common way to dispersion these GO nanofillers is using sonicators. Sonicators use large amounts of energy and can be challenging to use commercially. 22 Also, SEM images show the agglomeration of GO nanofillers in the matrix. The bonding between the GO surfaces functional groups and the matrix was improved using various coupling agents. These coupling agents include small molecules such as silanes or organo-amines, but they can also include polymeric macromolecules such as epoxy or nylon, or polypropylene. The surface of GO was intercalated with organic moieties to ensure the separation of layers, but due to the absence of a rigid three-dimensional structure, the method proved to be ineffective. 2.2 Formulation of modified Derakene™ resins POSS has been proved to be an effective dispersant in multiple cases. Based on this approach, an asymmetrically capped DDSQ system was developed as a coupling agent between the GO nanofiller and the polymer matrix. Derakene 411-350™ is a styrene-vinyl ester resin used as the polymer matrix. One end of the DDSQ system was capped with a cyanate group, while the other was capped with styrene moiety. The coupling between the nanofiller and the coupling agents can be done by simple mechanical stirring using a magnetic stirrer. Although using a molecule that has isocyanate and styrene at the opposite ends may enable GO to form a covalent bond to VE resin, the advantage of using the asymmetric DDSQ is the 3D nature of the SiO core and (maybe the phenyl group surrounding the SiO core). Using X-ray diffraction, we observed increases in the layer spacing of graphene nanoplate when GO is modified with isocyanate-DDSQ-styrene. Increases in the layer spacing of plate-like reinforcement such as GO can significantly improve mechanical performance and reduce moisture transport of polymer with the addition of plate-like reinforcement. The cyanate moiety on DDSQ is bounded covalently with the hydroxyl groups on GO, whereas the styrene moiety is incorporated along with the polymer matrix as seen from Scheme 2-2 23 The asymmetrically capped DDSQ compound was synthesized by capping with methyl propyl isocyanate dichlorosilane and styrene trichlorosilane. These chlorosilanes were synthesized using starting from essential reagents. The detailed synthesis of these chlorosilanes has been shown in SI. Once the dichlorosilanes have been synthesized, the capping reaction onto the DDSQ tetrol has Scheme 2-1 : Asymmetrically capped DDSQ coupling agent grafting with graphene oxide. been done using DCM as a capping solvent, as shown in Scheme 2-1The capping reaction produces three different isomeric products. These isomeric products can be separated based on the polarity of the products using flash column chromatography. The hydroxyl group on the capped isomers helps to impart polarity to the capped DDSQ structures. The isomer with two hydroxyl groups is the most polar elutes last from the column, and the asymmetrical product elutes in between the three isomeric products, whereas the compound with no hydroxyl group elutes first from the column. After separation, the asymmetrically capped DDSQ compound is then grafted onto GO. No high-energy methods, such as sonicators, were used to perform the grafting. A simple grafting method, such as mechanical stirring using a magnetic stirrer, has been employed. The solvent used to disperse GO was a 70/30 v/v mixture of THF and DMF. The solution was stirred 24 for 5 minutes. Afterward, the asymmetrically capped DDSQ was added and stirred for 72 hours. The isocyanate group on asymmetrical DDSQ covalently bonds to the hydroxyl group on the GO surface, giving a firm connection between the GO and the bridging agent. The other end of the asymmetrical DDSQ compound has a styrene handle that can copolymerize with styrene groups in the Derakene™ resin. The grafted DDSQ-GO complex was then dispersed in Derakene resin with a magnetic stirrer for 24 hours. Methyl ethyl ketone peroxide was added to the resin mixture and stirred with a glass rod. The sample was then cast in silicon molds for room temperature curing for 24 hours, followed by curing at 120 °C for 2 hours. Scheme 2-2 : Grafting of asymmetrically capped DDSQ onto GO surface 25 2.3 Characterization of cured Derakene™ resin samples In order to confirm the bridging between GO, the hybrid organic-inorganic bridging material, IR analysis was done, as shown in Figure 2-1. The peaks of interest in this IR data are the peak representing the -OH group and the peak representing the -NH group. The -OH peak present on GO disappears from the grafted DDSQ-GO complex. The -NH group peak can be seen almost overlapping with the peak of the carbonyl group, but it can be distinguished between the peaks seen in GO versus those seen in the DDSQ-GO complex. Also, the -NCO peak in the asymmetrically capped DDSQ compound disappears from the grafted DDSQ-GO complex. This Figure 2-1 : IR analysis to verify grafting of GO with DDSQ compound. 26 peak demonstrates the strong covalent bonding between the DDSQ and GO. The dispersion of grafted DDSQ-GO complex was studied using optical imaging, as seen in Figure 2-2. The optical analysis of post-cured resin showed the effectiveness of DDSQ as a coupling agent and a dispersant. As seen in Figure 2-2, the top image is the neat Derakene™ resin with no GO added to it. It is a clear transparent sample. The middle sample represents the Derakene™ sample Figure 2-2 : Optical analysis of post cured Derakene resin mixed with non-treated GO. The image shows that the GO is not well dispersed in the resin. The agglomerated GO spots are visible in the image. The third image shows Derakene™ resin mixed Table 2-1 : Mechanical properties of modified Derakene™ samples 27 with grafted DDSQ-GO complex. The image shows that GO has been well dispersed throughout the resin. Resin samples treated with 0.1, 0.2, and 0.4 wt % DDSQ-GO complex have been formulated, and mechanical testing has been carried out on these samples. The mechanical testing shows that the strength and strain to failure increase upon adding a modified DDSQ-GO complex Control: Treated Neat resin resin Ductile Brittle fracture fracture surface surface Figure 2-3 : Optical images post fracture surface testing of the samples to the resin. As the table above shows, adding 0.2 wt % of modified DDSQ-GO complex doubles the strain to failure and the strength of resins. Continued addition above 0.2 wt % results in no change in the strain to failure and the strength of resins. The fracture surface of the resin samples was studied post-sample fracture, as seen in Figure 2-3. Due to GO sheets in the resin samples, the fracture surface and characteristics change from brittle to ductile fracture. This transition is evident from the clean and sharp surface cuts in the control resin, whereas the treated sample has the plastic deformation characteristics as seen in ductile fracture. In conclusion, a simple, efficient way to disperse Graphene oxide into a polymeric matrix such as Derakene™ was developed. This methodology used simple magnetic stirring to disperse modified GO into polymeric resin compared to high-energy techniques such as sonicators. The bridging between the polymeric matrix and GO has been done using capped DDSQ. Asymmetrically capped 28 DDSQ formed an amide bridge between the isocyanate group on the DDSQ and the hydroxyl groups on the Graphene oxide surface; the styrene group on DDSQ was polymerized with the Derakene network structure. The nanocomposites of Derakene™ and graphene oxide exhibit a significant improvement in strength and ductility compared to the neat sample. 29 2.4 Experimental Details 2.4.1 General Information All manipulations were done under a nitrogen atmosphere using standard Schlenk techniques except otherwise stated. All commercially available chemicals were used as received unless otherwise indicated. Methyl trichlorosilane (MeSiCl3), Karstedt’s catalyst, styrene trimethoxysilane, methyldichlorosilane, vinyl cyanate, boron trichloride (1.0M in hexanes), deuterated chloroform with 1 vol % tetramethylsilane (CDCl3-1%TMS), were purchased from Sigma-Aldrich. Graphene nanoplatelet was obtained from XG Sciences. DDPh8T8(OH)4 was obtained from Hybrid Plastics. Triethylamine (Et3N) was purchased from Avantor and distilled over calcium hydride before use. Tetrahydrofuran (THF), dichloromethane (DCM), and methanol (MeOH) n-hexanes were purchased from Sigma-Aldrich. THF was distilled over benzophenone and sodium metal at 50 °C under nitrogen. Toluene was distilled over calcium hydride at a temperature of 120 °C. The other solvents were used as purchased without further purification, and the glassware was oven dried. All 1H, 13 C, and 29 Si NMR were acquired on an Agilent DirectDrive2 500 MHz NMR spectrometer equipped with a OneProbe operating at 500 MHz for 1 H NMR, 126 MHz for 13C NMR, and 99 MHz for 29Si NMR using CDCl3 and recorded at 25 ºC. 1 H-NMR spectra were recorded with eight scans, a relaxation delay of 1s, and a pulse angle of 45° 13 and referenced to the residual protonated solvent in CDCl3 (7.24 ppm). C-NMR spectra were collected with 254 scans, a relaxation delay of 0.1 s, and a pulse angle of 45°. 29Si NMR spectra were recorded with either 256 scans, a relaxation delay of 25 s, and a pulse angle 45°. Column chromatography was performed on EMD Millipore silica gel 60 columns of 40– 63 Å silica, 230– 400 mesh. Thin-layer chromatography (TLC) was performed on plates of EMD 250-µm silica 60- F254. 30 2.4.2 Synthesis of methyl(3-propyl isocyanate)dichlorosilane Scheme 2-3 : Reaction scheme for the synthesis of methyl(3-propyl isocyanate)dichlorosilane To a 100 mL round bottom flask, vinyl isocyanate (1 g, 0.012 mol, one equiv) and a stir bar were added under the N2 atmosphere. Karstedt’s catalyst (~ 2 % Pt in Xylene) (28 μL), methyl dichlorosilane (2.76 g, 0.024 mol, two equiv), and THF (20 mL) were charged to the flask. The reaction was stirred at room temperature for two h. The solvent and excess methyl dichlorosilane were evaporated at the end of the reaction time. The liquid obtained is then subjected to vacuum distillation (0.01 torr) at 90 °C to obtain the pure product as a liquid in the condensation flask, which was used as is for the next step. The yield of the reaction is 72% 1 H NMR (500 MHz, Chloroform-d) δ 3.37 (t, J = 6.6 Hz, 2H), 1.85 – 1.76 (m, 2H), 1.22 – 1.14 (m, 2H), 0.80 (d, J = 3.6 Hz, 3H). 13C NMR (126 MHz, Chloroform-d) δ 44.74, 24.44, 18.59, 5.11. 29 Si NMR (99 MHz, Chloroform-d) δ 32.19. 2.4.3 Synthesis of styryl trichlorosilane Scheme 2-4 : Reaction scheme for the synthesis of styryl trichlorosilane To a 100 mL round bottom flask, styrene trimethoxysilane (5 g, 0.022 mol, one equiv) and a stir bar under the N2 atmosphere were added. The reaction flask was placed in an acetonitrile/ dry ice cooling bath. Boron trichloride (1M in heptane) (78 mL, 0.078 mol, 3.5 equiv) and n-heptane (15 31 ml) was charged to the flask. The reaction flask was then placed in the ice bath for one h, followed by stirring at room temperature for 18 h. At the end of the rection time, vacuum distillation was carried out at 0 °C to remove the volatiles and then at room temperature to obtain the product in a condensation flask as a pale-yellow liquid. The yield of the reaction was 89% 1 H NMR (500 MHz, Chloroform-d) δ 7.83 – 7.72 (m, 2H), 7.56 – 7.49 (m, 2H), 6.77 (dd, J = 17.6, 10.9 Hz, 1H), 5.95 – 5.86 (m, 1H), 5.46 – 5.36 (m, 1H). 29Si NMR (99 MHz, Chloroform-d) δ - 1.19. 2.4.4 Synthesis of (1R,3R,5S,7R,9s,11S,13S,15R,17S,19r)-19-(3- isocyanatopropyl)-19-methyl-1,3,5,7,11,13,15,17-octaphenyl-9- (4-vinylphenyl)-2,4,6,8,10,12,14,16,18,20,21,22,23,24- tetradecaoxa-1,3,5,7,9,11,13,15,17,19- decasilapentacyclo[11.7.1.13,11.15,17.17,15]tetracosan-9-ol Scheme 2-5 : Synthesis of asymmetrically capped DDSQ nanobridge To a 250 mL round bottom flask was added DDPh8T8(OH)4 (2.15 g, 0.002 mol, one equiv), styrene trichlorosilane (0.48 g, 0.002 mol, one equiv), methyl(propyl isocyanate)dichlorosilane (0.40 g, 0.002 mol, one equiv) and a stir bar. The flask was placed under an N2 atmosphere, and freshly 32 distilled DCM (~50 mL) was added. Et3N (0.815 g, 0.008 mol, 4 equiv) was added dropwise to this solution. Upon complete addition of the triethylamine, the white-colored reaction mixture turned colorless. The reaction mixture was stirred for 5 min, after which solvent was removed using a rotary evaporator, and then THF (~ 15 mL) was added to create a slurry. This slurry was filtered through a medium frit funnel to obtain the crude product. It should be noted that this is a mixture of the three isomers - two symmetrically capped DDSQ systems and one asymmetrically capped DDSQ system. The products were isolated using silica column chromatography. A glass preparatory chromatography column, 60 cm long and 4 cm internal diameter, with a 500 mL round top reservoir, was packed with Si-gel, resulting in a packing height of about 75% of the total column height. DCM used as a mobile phase was flushed through the packed bed under pressure generated by a dry N2 stream. The mobile phase was passed through the column multiple times until no air bubbles or dry space was observed. A concentrated solution of the product mixture with DCM was gently injected from the top of the wet Si-gel bed and pushed into the packed bed until no solution was observed above the packed bed. The column was then gently charged with 500 mL of DCM and flushed using the N2 stream. Fractions of 20 mL were collected at the bottom of the column until the DCM reached the top of the bed. Each fraction was seated on 5 cm TLC plates of Si-gel supported on aluminum. Fractions were eluted with DCM and then analyzed under a 245 nm UV-lamp. Similar fractions were combined and dried. The asymmetrically capped DDSQ compound is eluted out as the second batch of fractions from the column. The yield is 12 %. 2.4.5 Graphene oxide sample preparation To a 100 mL round bottom flask, graphene oxide(GO) (0.12 g) and a stir bar were added under the N2 atmosphere. A solvent mixture of 7:3 THF: DMF (~ 50 mL) was charged into the flask. 33 Asymmetrically capped DDSQ synthesized in the previous step (0.21 g) was added to the flask. The reaction mixture was stirred for 72 h. At the end of the reaction time, the solvent was removed using a rotary evaporator. The reaction mixture was washed with fresh DCM (~3x15 mL) to remove the excess asymmetrically capped DDSQ. The black-colored solid GO was filtered and dried. 2.4.6 Composite sample preparation To a 20 mL flask, a stir bar and Derakene™ resin were added. 0.1wt% GO with asymmetrically capped DDSQ was added. The reaction mixture was stirred at room temperature for 24 h. At the end of the reaction time, 1% methyl ethyl ketone peroxide was the curing agent added to the mixture. Rectangular slabs were cast using silicone casts. 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Solar Energy Materials and Solar Cells 2010, 94 (2), 232–245. https://doi.org/10.1016/j.solmat.2009.09.008. 38 APPENDIX Figure 2-4 : 1H NMR (CDCl3, 99 MHz) 39 Figure 2-5 : 13C-NMR (CDCl3, 126 MHz) 40 Figure 2-6 : 29Si{1H}-NMR (CDCl3, 99 MHz) 41 Figure 2-7 : 1H NMR (CDCl3, 99 MHz) 42 Figure 2-8 : 13C-NMR (CDCl3, 126 MHz) 43 29 Figure 2-9 : Si{1H}-NMR (CDCl3, 99 MHz) 44 3 PHENYL ETHYNYL PHENYL DDSQ SYSTEMS 45 3.1 Introduction Polyhedral oligomeric silsesquioxanes (POSS) are unique hybrid organic-inorganic materials with a general chemical composition of (RSiO1.5) n. The R group can be a hydrogen atom or alkyl, alkylene, aryl, arylene, or organo-functional derivatives of alkyl, alkylene, aryl, or arylene groups.1 The structures of silsesquioxanes can be cage structures, partial cage structures, ladder structures, or random structures. POSS can be introduced into polymer matrices to produce novel composite materials with various advantageous properties.2–5 In 2013, low-viscosity DDSQ-based polyamides were reported by Schoen 6. meta and para methyl-aminophenyl dichlorosilanes were used together to condense Ph8DDSQ(OH)4. This capping scheme created a mixture containing regio- (meta and para) and stereo- (cis and trans) isomers in the final condensed product. The attempted synthesis of DDPh8T8-PEPI possessed several disadvantages, such as diminished yields and being time intensive. Even though the moisture uptake has been reduced compared to AFR-PE-4 material, it may be possible to further reduce the uptake by eliminating the imide group and directly capping the DDPh8T8(OH)4 cage with phenylethynyl end-capped chlorosilanes. The work presented in this report begins with the synthesis of meta/para phenylethynylphenylbromide – the precursor reagent for synthesizing dichlorosilanes. The amount of Palladium catalyst used in this reaction was optimized to obtain maximum yield with the least amount of Palladium catalyst. Grignard and lithiation routes were explored upon successfully synthesizing the precursors to obtain clean dichlorosilanes. The advantages and disadvantages of each route have been thoroughly explained, and an optimized reaction pathway to obtain clean dichlorosilanes has been demonstrated. These dichlorosilanes were then capped on to DDSQ to 46 obtain cis/trans isomeric mixtures. The conversion of dichlorosilanes to silanes has been explored to solve storage issues. 3.2 Reagent synthesis A general class of dichlorosilane is used to get the various chlorosilanes for side-capping of DDPh8T8(OH)4. These dichlorosilanes are synthesized starting from brominated phenylethynyl benzene. Different isomers of the starting reagent can be obtained depending on the position of the bromine group to the triple bond. The reaction to obtain these reagents using the Sonogashira reaction was given by Dannatt7, as shown in Scheme 3-1. A study of the effects of reaction conditions on the kinetics of the reaction was studied. The catalyst concentration was varied, and the extent of reaction completion was obtained from GCMS by calculating the area under the peak for the product molecule. Similarly, the amount of base equivalence was optimized to get a higher product yield. Scheme 3-1 : Reaction pathway for synthesis of bromo-phenyl ethynyl benzene 3.2.1 Reaction kinetics The reaction rate depends on the temperature at which the reaction is carried out. As the general thumb rule, the rate of reaction doubles for every 10 °C rise in temperature of the reaction conditions. This observation is known as the Arrhenius equation and is supported by the collision theory of chemical reactions. According to the Arrhenius equation, the rate constant (k) of a reaction is directly proportional to the exponential factor of the activation energy (Ea) divided by the product of the gas constant (R) and the temperature (T) in Kelvin: 47 −𝐸𝑎 𝑘 = 𝐴 ∗ 𝑒 ( 𝑅∗𝑇 ) Where: k: Rate constant of the reaction A: Pre-exponential factor (related to the frequency of collisions between reactant molecules) Ea: Activation energy (the minimum energy required for a reaction to occur) R: Gas constant (8.314 J/(mol*K)) T: Temperature in Kelvin The equation shows that an increase in temperature (T) will lead to a higher value for the exponential factor, resulting in a higher rate constant and a faster reaction rate. This effect is because as the temperature rises, the kinetic energy of the reactant molecules also increases. Consequently, the molecules move faster, leading to more frequent and energetic collisions, which enhances the likelihood of a successful reaction. The limiting factors in increasing the reaction mixture's temperature are either the reactants' stability concerning temperature or the boiling point of the solvent used in the reaction. In this case, the reactants bromoiodine and phenylacetylene are stable up to their melting points. The solvent used in this case is THF which has a boiling point of 66 °C and hence is the limiting factor for the reaction temperature conditions. Thus, the temperature is set to reflux conditions to facilitate the increase in reaction rate. The reaction rate also depends on the two reactants used in the reaction. The effects of sterics and electronics of the reactants used in the reaction have been discussed below. 3.2.2 Catalyst Cycle Various physical pathways suggest a plausible pathway for the reaction; based on identifying some of the transient species formed in the catalytic reactions, it is a challenging task to isolate 48 and characterize the organometallic intermediates to validate a mechanism beyond any doubt. The copper co-catalyzed Sonogashira reaction is predicted to be following the pathway shown in Figure 3-1 Figure 3-1 : Catalyst cycle for Sonogashira reaction8 The Pd (II) catalyst generates in-situ Pd (0) species, the actual catalytic moiety participating in the reaction. The palladium cycle proceeds via a fast-oxidative addition of aryl halide to the 14 electron Pd(0)L2 intermediate. The kinetics of this step depends on how efficiently the electron density around the carbon-halide bond is lowered. The copper cycle proceeds via the activation of aryl alkyne by the base. Usually, the base is not strong enough to deprotonate the alkyne. Hence, using copper salts generate a π-alkyne-Cu complex, making the alkyne proton more acidic for more accessible abstraction by the weak base. This use of copper salts leads to the formation of copper acetylide, which undergoes transmetalation with the intermediate formed in the palladium cycle. Transmetalation is the rate-determining step in which the intermediate formed undergoes reductive elimination to give the final product and, thus, regenerate the catalyst. 49 3.2.3 1-bromo-3-(phenylethynyl)benzene The palladium Cycle 0.05 mol% 0.1 mol% 0.2 mol% 0.5 mol% time (h) Figure 3-2 : Effect of varying Pd catalyst concentration on the extent of reaction. The bar graphs represent different amounts of catalyst loading used in the reaction. In the first optimization scenario, following procedure from the literature7, the initial Pd (PPh3)2Cl2 catalyst amount was set at 0.05 mol%, and the base used was one equivalent. After every hour, 0.1 mL of the reaction mixture was quenched with 1.5 mL methanol and then analyzed by GCMS. After analyzing the area under the peak for product molecules in the GCMS spectrum, it was found that 85 % of the reaction was completed in the first hour. In 2 h, 89 % of the reaction was completed, and the rate plateaued out after that, evident from the 90 % completion at the end of 3 h. On increasing the catalyst loading to 0.2 mol%, the initial rate of the reaction improved to 91% completion of the reaction in the first hour. Continued analysis at the 2 h and 3 h mark gave an extent of conversion of 96% and 100%, respectively. On increasing the catalyst amount to 0.3% and 0.5%, the extent of reaction at 1 h was around 97%, reaching completion within the 2 h mark. The base equivalency The base in the reaction is used to neutralize the byproduct hydrogen halide and activate the aryl acetylene. The reactions were carried out using optimized palladium catalyst conditions, varying 50 the base amount used in the order 1 equiv/2 equiv. After every hour, 0.1 mL of the reaction mixture was quenched with methanol and then analyzed by GCMS. After analyzing the area under the peak for product molecule by GCMS, it is evident from Figure 3-3 that the reaction reaches the experimental maximum value in 2 h. 1 equiv 2 equiv Figure 3-3 : Effect of varying the base equivalence on the extent of conversion of reaction 3.2.4 1-bromo-4- (phenyl ethynyl) benzene Based on the optimization conditions for synthesizing 1-bromo-3-phenylethynyl benzene, optimum conditions for the efficient synthesis of 1-bromo-3-phenylethynyl benzene can be obtained. In order to achieve the optimized conditions, the amount of CuI and Et3N were kept constant, and the amount of palladium catalyst was varied starting from 0.05 mol%. The rate of conversion increases as the amount of palladium catalyst increases. It can be observed from the reaction kinetics that the extent of the reaction for para systems is lower than the meta systems for given reaction conditions. Also, due to the even distribution of electron cloud density in 1-bromo- 4-iodobenzene, the oxidative addition step is slower than that of 1-bromo-3-iodobenzene. 51 0.05 mol% 0.1 mol% 0.2 mol% 0.5 mol% Figure 3-4 : Effect of varying Pd catalyst concentration on the extent of reaction. The bar graphs represent different amounts of catalyst loading used in the reaction. 3.2.5 Summary An analysis of optimization conditions for the Sonogashira reaction was carried out for iodobromobenzene. Based on the catalyst cycle, the amount of CuI was kept constant, whereas the amount of palladium catalyst used was varied. It was found that 0.2mol% of the Pd(PPh3)Cl2 catalyst was the optimum condition for the synthesis of 1-bromo-4-(phenyl ethynyl)benzene. 2 equivalents of base are used in the reaction. This excess base amount helps extract the phenylacetylene's acidic hydrogen. Also, due to the even distribution of electron cloud density in 1-bromo-4-iodobenzene compared to 1-bromo-3-iodobenzene, the oxidative addition step is slower than that of 1-bromo-3-iodobenzene. Hence the reaction time is almost doubled from 2 h to 4 h. 3.3 Synthesis of dichlorosilanes Once the (para/meta) bromo-phenyl ethynylbenzene (Br-PEB) has been synthesized, the next step is converting them into suitable chlorosilanes to act as side-capping agents to DDPh8T8(OH)4. The dichlorosilanes are highly moisture sensitive and readily decompose into silanols on exposure to moisture. Conversion to dichlorosilanes begins with the metalation of the C-Br bond present in the 52 precursor. The use of magnesium or organo-lithium agents has been explored for this purpose. Once the metalation is complete, the next step involves using trichlorosilanes to convert the organometal compounds to dichlorosilanes. 3.3.1 Grignard reaction pathway The use of Grignard reagents for forming new carbon-carbon bonds has been known for a century. Magnesium is used to generate the Grignard reagent. The reaction pathway for the generation of Grignard reagent from Br-PEB is shown in Scheme 3-2 Scheme 3-2 : Reaction pathway for Grignard reagent synthesis The outer layer of Mg is covered with magnesium oxide making it inert for the halo-organic compound to react. The reactant Mg must be activated using sonication or rapid stirring. Water or even air in ppm quantities can destroy the reagent by protonolysis. In order to analyze the progress during the reaction, a sample aliquot is quenched in methanol and tested using a GCMS. The Grignard species reacts with the proton from the alcohol to give diphenylacetylene which is detected by mass spectrometry. 53 Synthesis of para-dichlorosilane In order to synthesize the desired dichlorosilane, methyl trichlorosilane is reacted with the Grignard reagent formed in the previous step. Scheme 3-3 : Reaction pathway for para-dichlorosilane synthesis An excess of trichlorosilane is required to ensure the conversion to the desired dichlorosilane and to avoid the formation of undesired monochlorosilane in the process, as shown in Scheme 3-4. Scheme 3-4 : Undesired side reaction during the dichlorosilane synthesis step The reaction leads to the formation of MgBrCl salt. If the crude reaction mixture is used directly in the DDPh8T8(OH)4 capping, the salt causes significant issues leading to scrambled cage-like structures and hence needs to be filtered out from the reaction mixture. Thus, to isolate the clean dichlorosilane, distilling the chlorosilane was suggested. In practice, distillation causes charring of the product molecule. Sublimation proved to be adequate to isolate the dichlorosilane. A 53% yield was obtained. Synthesis of meta-dichlorosilane The meta-isomer of the dichlorosilane has been synthesized using the same approach as that of the para isomer, as shown in Scheme 3-5Scheme 3-5. 54 Scheme 3-5 : Reaction pathway for meta-dichlorosilane synthesis GCMS proved to be an efficient way to monitor the real-time progress of the reaction. Upon completion of the reaction, the solvent was evaporated, and the mixture was washed with hexanes. The organic products dissolved in hexanes were separated from the salts via filtration. Sublimation under vacuum conditions was attempted to isolate pure meta-dichlorosilane. The temperature varied from room to 120 °C, and the vacuum was maintained at 0.01 torr. It was found that no solid product was obtained throughout the whole temperature range. As the temperature increased, the reaction mixture became a charred mass lump. Distillation was also not effective in isolating the final product. Column chromatography techniques cannot be used as chlorosilanes would react with the column material to form silanols. The chlorosilanes can also cause erosion of the columns, thus rendering the HPLC technique inappropriate. In the case of para-dichlorosilane, the mixture in the sublimator was analyzed after the completion of the sublimation step. It was found that there was still a finite amount of para-dichlorosilane left. This leftover product could not be distilled off despite increasing the sublimation temperature from 70 °C to 120 °C, beyond which complete charring was observed. 3.3.2 n-Butyl lithium reaction pathway In order to convert the Br-PEB to dichlorosilanes, a metal-halogen exchange is required. In order to achieve this, n-butyl lithium is used as a lithiation agent, as shown in Scheme 3-6. 55 Scheme 3-6 : Reaction pathway for lithiation of Br-PEB The reaction needs to be carried out in a moisture-free atmosphere. n-Butyl lithium is a highly active pyrophoric compound. Hence, all the glassware used is heat dried and flushed with nitrogen. The temperature needs to be maintained low because n-butyl lithium is a highly reactive species that can lead to the formation of undesired products, as shown in Scheme 3-7. Scheme 3-7 : Reaction pathway for side reactions in lithiation reaction A sample aliquot is quenched in methanol and analyzed by GCMS to analyze the reaction progress. The lithiated species reacts with the proton from the alcohol to give diphenylacetylene which is detected by mass spectrometry. Despite maintaining the temperature at -78 °C, almost 30% of the reactant is wasted as the undesired side product. Due to the poor yields and difficulty in handling the reagents, this route does not seem to be a promising reaction pathway. 3.3.3 tert-butyllithium reaction pathway With multiple obstacles in obtaining the pure meta-PEP dichlorosilane, a better and more efficient route was taken to fulfill the objective. The reagent used for metalation was tertiary butyl lithium. t-Butyllithium is a pyrophoric organolithium compound that acts as a strong base and can deprotonate many carbon acids, including benzene. Ether solvents can also decompose; hence, low temperatures must be used to conduct the reactions. The metalation of meta-bromoPEB is shown in Scheme 3-8. The flask was thoroughly flushed with nitrogen to make sure the atmosphere within 56 the flask was air-free. Although the solvent was diethyl ether, the reaction temperature was kept at -78 °C using a dry ice-acetone bath. This low reaction temperature avoided the degradation of the organolithium compound via the solvent. Two equivalents of t-butyllithium reagent are required as the tertbutyl bromide product formed during the reaction further reacts with the organolithium compound to form LiBr, isobutylene, and isobutane and smaller hydrocarbons. In order to monitor the progress during the reaction, a sample aliquot is quenched in methanol and analyzed by GCMS. The reaction color was initially colorless and turned yellow upon adding the organolithium compound and finally to a reddish-brown color. The reaction is complete in 1 h with no undesired side products. Scheme 3-8 : Reaction pathway for lithiation of Br-PEB Upon completion of the lithiation reaction, the reaction mixture is cannula transferred into a flask containing methyl trichlorosilane. This flask is kept at -78 °C to avoid the degradation of the lithiated compound during the transfer. Upon completion of the transfer, the flask is taken out of the cold bath and allowed to warm up to room temperature. The reaction mixture turned bright red upon adding the lithiated compound; the color eventually turned light yellow. 57 Scheme 3-9 : Reaction pathway for meta-dichlorosilane synthesis. In order to monitor the progress during the reaction, a sample aliquot is quenched in methanol and analyzed by GCMS. The reaction was completed in 3 h. After completion, the salts were filtered off the reaction mixture using a cannula filter. The filtrate that contains the excess unreacted methyl trichlorosilane and other side products, along with the desired dichlorosilane, is subjected to vacuum distillation leaving behind the meta-PEPdichlorosilane along with diphenyl ethynyl. Although the formation of this compound leads to the loss of yield of dichlorosilane, it does not interfere with the capping of DDPh8T8(OH)4 and hence does not affect the project's overall goal. 3.3.4 Silanes as a long-term storage option Dichlorosilanes are highly moisture sensitive and need special storage conditions. The purification of dichlorosilanes requires vacuum distillation, leading to poor yield of dichlorosilanes. Silanes are not water sensitive and can be isolated using column chromatography. Long-term storage is also not an issue, as the silanes are not air-sensitive. They can be stored in a sealed container for considerably more extended than chlorosilanes without considering the need to replenish the inert atmosphere in the container constantly. The chlorosilanes can be converted to corresponding silanes via reduction using lithium aluminum hydride, as shown in Scheme 3-10. Scheme 3-10 : Reaction pathway for silane synthesis from dichlorosilane 58 The reduction is an exothermic reaction that must be cooled using an ice bath. Once dichlorosilanes are added to the flask, the reaction mixture can warm to room temperature to ensure complete silane conversion. The progress is monitored using GCMS. Upon completion of the reaction, hexanes are added to extract the organic products, and the excess hydride is quenched with DI water. The solids are separated by filtration. The crude mixture is concentrated and then passed through a silica chromatography column to isolate the pure meta-silane. The conversion of these silanes back to chlorosilanes was attempted using various chlorinating agents. GCMS analyzed the reaction mixture. It was found that the triple bond of ethynyl was chlorinated along with the Si-H silane bonds. The capping of silanes directly to DDPh8T8(OH)4 was somewhat explored. The reaction yield was poor (<10%), and NMR analysis of the reaction mixture indicated that the cages were scrambled/broken due to the reaction conditions used. 3.3.5 Summary Isomeric para/meta dichlorosilanes were synthesized using t-butyl lithium as a metalation reagent. This route yielded better results than the Grignard reagent route or the n-butyl lithium route. An excess of t-butyl lithium reagent is used to ensure complete conversion. The byproduct formed in the reaction is in a gaseous state at room temperature and hence can be easily separated. To improve the shelf life of chlorosilanes and yield, LiAlH4 is used as a reducing agent to convert chlorosilanes to silanes to improve the shelf life and yield. The silanes can be 01purified using column chromatography, which yields better than sublimation/ distillation. Multiple reaction pathways were studied to convert silanes back to chlorosilanes, but in most cases, the ethynyl bond gets chlorinated, leading to undesired side products. Hence, one-pot synthesis of dichlorosilanes was a better reaction pathway than converting chlorosilanes to silanes and back to chlorosilanes. 59 3.4 Capping of DDPh8T8(OH)4 DDPh8T8(OH)4 can be capped using various chlorosilanes to get up to four functional groups on the silicon core moiety. Depending on the type of side groups used, the DDSQ structures can be used as coupling agents or as nano-fillers to improve the mechanical properties of thermosets. The functionalized DDSQ structure can also be incorporated as the polymer backbone using monomeric functional units as capping reagents, followed by a polymerization reaction. Scheme 3-11 : Reaction pathway for capping of DDPh8T8(OH)4 using dichlorosilanes 3.5 Separation of DDPh8T8 isomers Fractional crystallization can be used to isolate nearly pure trans and enriched cis DDSQ-2((R1) (R2)) isomers. In order to facilitate the separation of the mixture, the compounds were dissolved in DCM, and the addition of hexanes resulted in the crystallization and precipitation of the trans isomers. This step led to the enrichment of cis isomer in the mother liquor. The thermal behavior of nearly pure isomers was studied using DSC. The melting point of nearly pure cis isomer was 270 °C which was 33 °C lower than that of nearly pure trans isomer (303 °C). The entropy at 60 melting was higher for trans isomers indicating that the packing in trans isomers was more ordered than cis, leading to a higher melting point. A eutectic mixture was formed upon mixing the isomers with a mass fraction of trans isomer equal to 0.3. This eutectic mixture had a melting point of Figure 3-5 : DSC data for mixture of isomers about 250 °C, lower than the melting temperatures of nearly pure cis and trans isomers. The heat of fusion is the same, while the heat of reaction for curing is higher for the eutectic mixture, indicating a higher degree of curing. The TGA data show that the isomeric mixture can withstand thermal degradation up to almost 500 °C. 61 3.6 Experimental details 3.6.1 General Information All manipulations were done under a nitrogen atmosphere using standard Schlenk techniques except otherwise stated. All commercially available chemicals were used as received unless otherwise indicated. 1-Bromo-4-iodobenzene (C6H4BrI), 1-bromo-3-iodobenzene (C6H4BrI), ethynylbenzene(C8H6), cuprous iodide (CuI), Bis(triphenylphosphine)palladium(II) dichloride (PdCl2(PPh3)2), magnesium turnings, n-butyl lithium (2.5M solution in hexanes), tertbutyl lithium (1.6M solution in hexanes), methyl trichlorosilane (MeSiCl3), Karstedt’s catalyst, styrene trimethoxysilane, methyldichlorosilane, vinyl cyanate, boron trichloride (1.0M in hexanes), deuterated chloroform with 1 vol % tetramethylsilane (CDCl3-1%TMS), were purchased from Sigma-Aldrich. Graphene nanoplatelet was obtained from XG Sciences. DDPh8T8(OH)4 was obtained from Hybrid Plastics. Triethylamine (Et3N) was purchased from Avantor and distilled over calcium hydride before use. Tetrahydrofuran (THF), dichloromethane (DCM), and methanol (MeOH) n-hexanes were purchased from Sigma-Aldrich. THF was distilled over benzophenone and sodium metal at 50 °C under nitrogen. Toluene was distilled over calcium hydride at a temperature of 120 °C. The other solvents were used as purchased without further purification, and the glassware was oven dried. All 1H, 13 C, and 29 Si NMR were acquired on an Agilent DirectDrive2 500 MHz NMR spectrometer equipped with a OneProbe operating at 500 MHz for 1 H NMR, 126 MHz for 13C NMR, and 99 MHz for 29Si NMR using CDCl3 and recorded at 25 ºC. 1 H-NMR spectra were recorded with 8 scans, a relaxation delay of 1s, and a pulse angle of 45° and 13 referenced to the residual protonated solvent in CDCl3 (7.24 ppm). C-NMR spectra were collected with 254 scans, a relaxation delay of 0.1 s, and a pulse angle of 45°. 29Si NMR spectra were recorded with either 256 scans, a relaxation delay of 25 s, and a pulse angle 45°. Column 62 chromatography was performed on EMD Millipore silica gel 60 columns of 40– 63 Å silica, 230– 400 mesh. Thin-layer chromatography (TLC) was performed on plates of EMD 250-µm silica 60- F254. 3.6.2 Synthesis procedure for meta Br-phenyl ethynyl benzene To a 100 mL oven-dried round bottom flask CuI (0.0673 g, 0.353 mmol, 0.1 mol %), a varying quantity of Pd(PPh3)2Cl2 (m mol % / m = 0.05, 0.1, 0.2, 0.5) and a stir bar was added. A rubber septum was used to seal the flask and flush it with nitrogen. The flask was placed in an oil bath preheated to 60 °C. THF (50 mL) was added to the flask fitted with a condenser. The reactants 1- bromo-3-iodobenzene (2.25 mL, 17.6 mmol, one equiv) and ethynylbenzene (2.15 mL, 19.4 mmol, 1.1 equiv) were charged into the flask. Finally, triethylamine (2 equiv) was charged to the flask. The contents of the reaction flask were stirred at room temperature. The mixture turned from light yellow to dark brown as the reaction progressed. The formation of triethylammonium chloride salt precipitate was observed. At time intervals of 1 hr, 0.1 mL of the reaction mixture was drawn out and quenched in 1.5 mL of methanol. GCMS then analyzed the quenched products. At the end of the reaction time (3 h), the solvent was evaporated using a rotary evaporator, and the resulting liquid mixture was stirred with DI water (30 mL) and extracted using DCM (50 mL). The solvent was evaporated to obtain a yellow liquid. The crude product was further purified using silica column chromatography. A glass preparatory chromatography column, 60 cm long and 4 cm internal diameter, with a 500 mL round top reservoir, was packed with Si-gel, resulting in a packing height of about 75% of the total column height. n-Hexanes used as mobile phase were flushed through the packed bed under pressure generated by a dry N2 stream. The mobile phase was passed through the column multiple times until no air bubbles or dry space was observed. A concentrated solution of the crude mixture with n-hexanes 63 was gently injected from the top of the wet Si-gel bed and pushed into the packed bed until no solution was observed above the packed bed. The column was then gently charged with 500 mL of n-hexanes and flushed using the N2 stream. Fractions of 20 mL were collected at the bottom of the column until the n-hexanes reached the top of the bed. Each fraction was seated on 5 cm TLC plates of Si-gel supported on aluminum. Fractions were eluted with n-hexanes and then analyzed under a 245 nm UV lamp. Similar fractions were combined and dried. 13 C NMR (126 MHz, Chloroform-d) δ 134.32, 131.69, 131.38, 130.15, 129.79, 128.64, 128.43, 125.30, 122.74, 122.18, 90.68, 87.80. 1 H NMR (500 MHz, Chloroform-d) δ 7.70 (t, J = 1.7 Hz, 1H), 7.57 – 7.50 (m, 2H), 7.50 – 7.44 (m, 2H), 7.41 – 7.33 (m, 3H), 7.22 (t, J = 7.9 Hz, 1H). 3.6.3 Synthesis of Grignard Reagent To a 100 mL round bottom flask were added activated Mg (0) turnings (0.2 g, 8.5 mmol, 1.1 equiv) and a stir bar. The Mg (0) turnings were stirred under a reduced pressure atmosphere for 2 h, after which the contents were put under an N2 atmosphere. 1-Bromo-3-(phenyl ethynyl) benzene (2 g, 7.7 mmol, 1 equiv) was dissolved in 20 mL freshly distilled THF and injected into the flask containing the Mg (0) turnings. This reaction mixture was stirred for 3 h. The color of the solution turned from colorless to dark green. An aliquot of the reaction mixture (0.1 mL) was dissolved in 1.5 mL of methanol to be analyzed by GCMS. The GCMS analysis showed only one peak with an m/z of 178, suggesting that complete Grignard formation was achieved. 3.6.4 Synthesis of lithiation reagent Using n-butyl lithium as a reagent To a 100 mL round bottom flask, a stir bar, 1-bromo-3-(phenyl ethynyl) benzene (2 g, 7.7 mmol, 1 equiv) was dissolved in 20 mL freshly distilled THF was added. The flask was flushed with N2 64 and was placed in a dry ice and acetone bath to maintain the reaction temperature at -78 °C. A 25 mL syringe flushed with N2 was used to dropwise add the solution of n-butyl lithium (3.4 mL, 1.1 equiv, 2.5 M in hexanes) to the flask. This mixture was stirred for 3 h, and the initial colorless solution turned dark brown. An aliquot of the reaction mixture (0.1 mL) was dissolved in 1.5 mL of methanol to be analyzed by GCMS. The GCMS analysis showed only one peak with an m/z of 178, suggesting complete lithiated agent formation was achieved. Using t-butyl lithium as a reagent To a 100 mL round bottom flask, a stir bar and 1-Bromo-3-(phenyl ethynyl) benzene (2 g, 0.0077 mol, 1 equiv) was dissolved in 20 mL freshly distilled THF was added. The flask was flushed with N2 and was placed in a dry ice and acetone bath to maintain the reaction temperature at -78 °C. A solution of t-butyl lithium (10 mL, 2.1 equiv, 1.6 M in hexanes) was added to the flask. This mixture was stirred for 3 h, and the initial colorless solution turned dark brown. An aliquot of the reaction mixture (0.1 mL) was dissolved in 1.5 mL of methanol to be analyzed by GCMS. The GCMS analysis showed only one peak with an m/z of 178, suggesting complete lithiated agent formation was achieved. 3.6.5 Synthesis of PEP dichlorosilane In a 500 mL round bottom flask equipped with a stir bar under an N2 atmosphere, MeSiCl3 (1 mL, 0.0085 mol, 1.1 equiv) and 40 mL THF were added. The MeSiCl3 was freshly distilled over CaH2 at 66 °C. The organometallic solution (Grignard/lithiated) was cannula transferred into the 500 mL flask containing MeSiCl3 while maintaining both flasks at -78 °C during the transfer. The reaction was removed from the dry ice and acetone bath and warmed to room temperature. Aliquots of the reaction mixture (0.1 mL) were dissolved in 1.5 mL of methanol and were analyzed by GCMS at 65 certain time intervals. The reaction mixture was stirred for 6-9 h, and upon completion, GCMS analysis showed complete conversion. It should be noted that the initial color of the solution was colorless, which turned red-brown upon the addition of organometallic solution and finally yellow-green upon completion of the reaction. At the end of the reaction, the solvent and MeSiCl3 were evaporated, leaving behind a yellow solid mass. Fresh hexanes (~150 mL) were added to the powder creating a slurry. This slurry was filtered through a medium frit funnel using hexanes (~200 mL) to aid transfer and wash the solid on the frit. The solvent from the filtrate was evaporated. The solid mass obtained is then subjected to reduced pressure (0.01 torr) conditions to isolate the pure dichlorosilane. The dichlorosilanes obtained were stored under an N2 atmosphere to be used for subsequent reactions. 3.6.6 Synthesis of silanes A 500 mL round bottom flask of lithium aluminum hydride (0.9 g, 0.024 mol, 3.5 equiv) and a stir bar were added under the N2 atmosphere. The flask was kept in an ice bath Methyl-phenyl ethynyl phenyl dichlorosilane (2 g, 0.0068 mol, 1 equiv) and THF (50 mL) were charged to the flask. The reaction mixture was stirred for 3 h. Then, hexanes (~150 mL) were added to the flask, stirring the reaction mass for 0.5 h. Then the reaction mixture was put in an ice bath, and DI water was added drop-wise to quench the excess hydride forming H2, LiOH, and Al(OH)3 salts. This slurry was filtered through a medium frit funnel using hexanes (~200 mL) to aid transfer and wash the solid on the frit. The solvent from the filtrate evaporated, leaving a crude yellow mixture behind. This crude mixture was further purified using silica column chromatography. A glass preparatory chromatography column, 60 cm in length 4 cm internal diameter, with a 500 mL round top reservoir, was packed with Si-gel, resulting in a packing height of about 75% of the total column height. 66 n-Hexanes used as mobile phase were flushed through the packed bed under pressure generated by a dry N2 stream. The mobile phase was passed through the column multiple times until no air bubbles or dry space was observed. A concentrated solution of the crude mixture with n-hexanes was gently injected from the top of the wet Si-gel bed and pushed into the packed bed until no solution was observed above the packed bed. The column was then gently charged with 500 mL of n-hexanes and flushed using the N2 stream. Fractions of 20 mL were collected at the bottom of the column until the n-hexanes reached the top of the bed. Each fraction was seated on 5 cm TLC plates of Si-gel supported on aluminum. Fractions were eluted with n-hexanes and then analyzed under a 245 nm UV lamp. Similar fractions were combined and dried. 3.6.7 Capping of DDPh8T8(OH)4 To a 250 mL round bottom flask were added DDPh8T8(OH)4 (1.5 g, 0.0014 mol, 0.5 equiv), dichloro(methyl)((phenylethynyl)phenyl) silane (1 g, 0.0028 mol, 2 equiv), and a stir bar under N2 atmosphere. Freshly distilled DCM (~50 mL) was then added. Et3N (0.8 mL, 0.0056 mol, 2.0 equiv) was added dropwise to this solution. Upon addition of the triethylamine, a white precipitate was observed. The reaction mixture was stirred for 5 min, after which the solvent was evaporated, and THF was added to create a slurry. This slurry was filtered through a medium frit funnel to obtain the crude product in the filtrate. This filtrate was further concentrated and purified by silica column chromatography (DCM mobile phase) to afford the desired product. It should be noted that this is a mixture of the cis and trans isomers. para- DDSQ (Si(Me)(PEP))2: 29Si NMR (99 MHz, Chloroform-d) δ -30.84, -78.36, -79.23, -79.51, -79.74. meta- DDSQ (Si(Me)(PEP))2: 29Si NMR (99 MHz, Chloroform-d) δ -31.28, -78.14, -79.02, -79.32, -79.58. 67 REFERENCES (1) Baney, R. H.; Itoh, M.; Sakakibara, A.; Suzuki, T. Silsesquioxanes. Chem. Rev. 1995, 95 (5), 22. https://doi.org/10.1021/cr00037a012. (2) Gnanasekaran, D.; Madhavan, K.; Reddy, B. S. R. Developments of Polyhedral Oligomeric Silsesquioxanes (PaSS), Pass Nanocomposites and Their Applications: A Review. 28. (3) Han, D.; Wen, T.; Han, G.; Deng, Y.; Deng, Y.; Zhang, Q.; Fu, Q. Synthesis of Janus POSS Star Polymer and Exploring Its Compatibilization Behavior for PLLA/PCL Polymer Blends. Polymer 2018, 136, 84–91. https://doi.org/10.1016/j.polymer.2017.12.050. (4) Han, D.; Zhang, Q.; Chen, F.; Fu, Q. Using POSS–C 60 Giant Molecules as a Novel Compatibilizer for PS/PMMA Polymer Blends. RSC Adv. 2016, 6 (23), 18924–18928. https://doi.org/10.1039/C6RA00218H. (5) Fina, A.; Monticelli, O.; Camino, G. POSS-Based Hybrids by Melt/Reactive Blending. J. Mater. Chem. 2010, 20 (42), 9297. https://doi.org/10.1039/c0jm00480d. (6) Schoen, B. Aminophenyl Double Decker Silsesquioxanes: Spectroscopic Elucidation, Physical and Thermal Characterization, and Their Applications, Michigan State University. (7) Dannatt, J. E. Advancing Frontiers in Reactive and Selective Iridium C–H Borylation Catalysis and Targeted Silsesquioxane Synthesis, Michigan State University. (8) Chinchilla, R.; Nájera, C. The Sonogashira Reaction: A Booming Methodology in Synthetic Organic Chemistry †. Chem. Rev. 2007, 107 (3), 874–922. https://doi.org/10.1021/cr050992x. 68 APPENDIX Figure 3-6 : 1H NMR (CDCl3, 99 MHz) 69 Figure 3-7 : 13C-NMR (CDCl3, 126 MHz) 70 Figure 3-8 : 1H NMR (CDCl3, 99 MHz) 71 Figure 3-9 : 13C-NMR (CDCl3, 126 MHz) 72 Figure 3-10 : 1H-NMR (CDCl3, 500 MHz) 73 Figure 3-11 : 29Si{1H}-NMR (CDCl3, 99 MHz) 74 Figure 3-12 : 29Si{1H}-NMR (CDCl3, 99 MHz) 75 Converting silanes to dichlorosilanes Upon successful isolation of pure silane, the next step is converting the silane back to chlorosilane for side-capping of DDPh8T8(OH)4. In order to achieve this moiety, various chlorinating agents can be used. The list of the chlorinating agents and the reaction condition is given in Scheme 3-12. The first reagent used for the attempted conversion was Boron trichloride (BCl3). Scheme 3-12 : Reaction pathway for dichlorosilane synthesis from silane BCl3 is a colorless gas usually available as a 1.0 molar solution in heptane. It is highly reactive towards water decomposing readily to give off HCl gas and needs to be handled carefully. The reaction progress was monitored by quenching a sample aliquot in methanol and then analyzed by GCMS. As shown in Table 3-1, after 5 min of reaction time, there were no products formed. The dechlorinated product and the initial reactant and undesired side product- tetrachlorinated silane- were observed as time progressed. After 3 h, no traces of the desired product were found, but there was still a finite amount of reactant and various fragments of the chlorinated products. Trichloroisocyanuric acid (TCCA) or 1,3,5-trichloro1,3,5-2,4,6, -(1H,3H,5H)-trione) is a white crystalline powder with a strong chlorine smell. It is an excellent chlorinating agent for ketones, alkenes and an oxidizing agent for secondary alcohols, aldehydes, and ethers. The choice of solvent is essential while using TCCA. At temperatures above 0 °C, TCCA can chlorinate ether solvents such as THF to give undesired side products. In order to avoid this formation of side products, the reaction must be carried at below 0 °C. Initially, it was assumed that the reactivity of TCCA decreases as the chlorine atoms get replaced by hydrogen atoms, and hence the ratio of equivalents 76 of ‘Cl’ in TCCA to the equivalents of ‘H’ in reactants was kept at 3:1. As seen from Table 3-1, the first set of experiments was carried out using 2.2 equivalents of TCCA with THF as solvent at 0 °C. The reaction progress was monitored by quenching a sample aliquot in methanol and then analyzed by GCMS. At the end of 5 min, mono- and di-chlorinated products were observed in the mass spectrum. Tetra- chlorinated products were also observed. This problem is because the TCCA can chlorinate the triple bond present in the reactant. The reaction was completed by testing the following sample at 20 min, but di- and tetra-chlorinated products were observed. These results lead to the conclusion that the kinetics of the undesired reaction is as fast as the kinetics of the desired reaction. The reaction was cooled.to slow down the undesired reaction, two different reaction conditions: 0 °C and -78 °C, were tested to achieve the goal. On testing both reaction conditions at the end of 20 min, the ratio of area under the peak in the mass spectrum for tetra- to di-chlorinated products decreased, but the tetra-chlorinated products were still observed. The next step was to decrease the ratio of equivalents of ‘Cl’ in TCCA to the equivalents of ‘H’ in reactants to 3:2. The reaction completion time increased from 20 min to 40 min. On inspecting the mass spectrum at the end of the reaction, undesired tetra-chlorinated products were still observed, but the area under the peak had further decreased compared to previous reaction conditions. Decreasing the ratio of equivalents of ‘Cl’ in TCCA to the equivalents of ‘H’ in reactants to 1:1, the reaction yielded only mono and dichlorinated products even after 100 min. 77 Table 3-1 : List of chlorinating agents for converting silane to dichlorosilanes. Equivalents Chlorinating agent Reaction conditions Product(s) obtained of reagent 0 °C, THF, 5 min Reactant Reactant, mono, and dichlorinated products, fragments of 2.2 0 °C, THF, 15 min reactant 0 °C, THF, 180 min Reactant, fragments of reactant rt, THF, 5 min Reactant, di- and tetrachlorinated products rt, THF, 20 min di- and tetrachlorinated products 2.2 0 °C, THF, 5 min Reactant, mono-, di- and tetrachlorinated products 0 °C, THF, 20 min di- and tetrachlorinated products -78 °C, THF, 5 min Reactant, mono-, di- and tetrachlorinated products -78 °C, THF, 20 min di- and tetrachlorinated products rt, diethyl ether, 5 min Reactant, mono- and dichlorinated, and products. 1.1 rt, diethyl ether, 20 min Reactant, mono-, di- and tetrachlorinated products rt, diethyl ether, 40 min di- and tetrachlorinated products. 78 Table 3-1 (cont’d) rt, diethyl ether, 20 min mono- and dichlorinated products. 0.66 rt, diethyl ether, 100 min mono- and dichlorinated products. rt, diethyl ether, 60 min mono and di- chlorinated products 10 rt, diethyl ether, 180 min mono and di- chlorinated products 0.07 rt, diethyl ether, 2880 min mono and di- chlorinated products 10 rt, diethyl ether, 360 min mono and di- chlorinated products 0.2 rt, diethyl ether, 630 min mono and di- chlorinated products Reactant monochlorinated product dichlorinated product tetrachlorinated product Figure 3-13 : List of products and byproducts formed during the chlorination reaction 79 4 EFFECTS OF USING BULKY CAPPING GROUPS 80 4.1 Introduction Polyhedral Oligomeric Double decker-shaped silsesquioxanes (DDSQ) are cage-like silsesquioxanes with a 3-dimensional well-defined inorganic core with an inert organic corona compatible with the surrounding polymeric matrix and containing well-defined reactive sites. The incompletely condensed DDSQ tetrol, when capped with two equivalents of dichlorosilanes, forms a capped DDSQ structure. This capping provides up to four additional reactive sites, which can impart polarity to the compounds to improve the separation of isomers, increase the miscibility with the polymeric matrix, or improve the nanocomposites' thermal and rheological characteristics.1–9 Figure 4-1 : DDSQ tetrol capped with 4 different functional groups Adding functionalized DDSQ to polymeric matrices without using solvents is an environmentally friendly method to integrate these cage structures to form polymeric nanocomposites. This step can be achieved by melting the nanostructured cage silsesquioxanes and mixing them with the polymeric material. Solid nanostructured materials are usually considered amorphous solids with a low solid-to-liquid transition temperature for more efficient mixing.10–15 The previous work reported on changing the peripheral structures of capped DDSQ structures has been reported by Vogelsang and Schoen.11–14,16–20 The work done has been summarized in Scheme 4-1. Although most of the work done focuses on using DDSQ structures with phenyl rings as peripheral groups, there has been some work done on corner capped heptaphenyl POSS-(phenylethynylphthalimide). This structure did not exhibit melting characteristics. So, the focus was shifted to using phenyl 81 DDSQ tetrol as a starting reagent. Using two different functional groups on chlorosilanes leads to the formation of cis and trans isomers. Usually, one functional group is smaller, such as a methyl group, whereas the other group is a bulkier functional group. The bulkier functional groups used in the previous work are phenylethynylphthalimides, phenylethynylphenyl, aniline, and phenyl. Scheme 4-1 : Reaction Scheme for capping of DDSQ tetrol with difunctional dichlorosilane It was hypothesized that the melting of DDSQ-2(R1R2) was caused by higher entropy as compared to POSS-R1 because the as-synthesized DDSQ-2(R1R2) products contain cis and trans isomers about the inorganic core. To verify this hypothesis that increasing the entropy of the functional groups affects the melting characteristics of the caged structures and to take advantage of the effect of isomers on the melting characteristics of the DDSQ cage structures, an analogous series of DDSQ cage structures were synthesized. The thermal characteristics of these compounds were studied using Differential Scanning Calorimetry (DSC). 4.2 Synthesis of isomers of capped DDSQ structures The series synthesis started via DDSQ tetrol capping using two equivalents of methyl trichlorosilane as a capping agent. The two ‘Cl’ functional groups on the chlorosilane react with the hydroxyl group on the DDSQ. The remaining third ‘Cl’ functional group is hydrolyzed to an - OH group in the subsequent step, as depicted in Scheme 4-2. 82 Scheme 4-2 : Capping of DDSQ tetrol with methyl trichlorosilane The synthesis, as shown, depicts the presence of stereoisomers. This step does lead to an increase in the entropy of the system. It has already been established that the cis and trans isomers affect the compounds' solid-to-liquid transition characteristics. A reaction involving two different chlorosilanes has been used to increase further the system's entropy to obtain a six-isomer mixture, as seen in Scheme 4-3. To begin with, the functional groups attached to the cage structures are small non-bulky groups such as methyl or hydrogen groups. Hence, there are two types of chlorosilanes used in this reaction; the first set is methyl hydrogen dichlorosilane and methyl trichlorosilane, whereas the second set is dimethyl dichlorosilane and methyl trichlorosilane. This addition leads to the formation of 3 major groups of isomeric compounds. Each isomeric group may have cis and trans isomers depending on the functional groups sued in chlorosilanes. Isomer AA has been capped with the first type of dichlorosilane on both sides; isomer AB has been capped on either side by functional groups from both the dichlorosilanes and isomer BB has been capped with the second type of dichlorosilane on both sides. 83 The asymmetrically capped AB isomer has been isolated using column chromatography based on the polarity differences of the isomers. The AB isomer is then further used to extend one side of the functional groups while the other side of the cage has constant functional groups. The extension leads to asymmetry on the ends of the cages, leading to increased system entropy. Scheme 4-3 : Capping of DDSQ tetrol using two different chlorosilanes to obtain an isomer mixture Like compound 4, compound 8 was synthesized starting with dimethyl dichlorosilane and isobutyl trichlorosilane. The resulting asymmetric AB product forms an analogous compound to the 4 synthesized previously. 84 Scheme 4-4 : Capping of DDSQ tetrol with RSiCl2 type chlorosilanes It has been found that the presence of hydroxy groups in the cage system might render them unsuitable to be analyzed with DSC. The extension of the side chain of capped DDSQ cages can be easily sone using chlorosilane. The silanol group on the cage structure reacts with the chlorosilane to add an ‘M’ silicon onto the cage, as seen in Scheme 4-5. Scheme 4-5 : Capping of the hydroxyl group with a dichlorosilane 29 Si NMR analysis of the product has been shown in Figure 4-2. The silicon NMR depicts seven groups of silicon atoms present in compound 6. There are 1 group of ‘M’ silicon atoms, two groups of ‘D’ silicon atoms, and 4 types of ‘T’ silicon atoms. The red ‘M’ silicon atom comes around 10.0 ppm, the green ‘D’ silicon atom comes around -15 ppm, the yellow ‘D’ silicon atom comes around -64 ppm, and the remaining four groups of ‘T’ silicon atoms show up between -78.5 ppm to -80 ppm. A similar methodology can be used to modify the hydroxyl groups on the cage shown in Scheme 4-5. 85 Figure 4-2 : 29Si NMR analysis 4.3 Thermal Analysis using DSC DSC analysis was performed to study the thermal characteristics of the synthesized series of analogous cage-like structures. Melting behavior, as expressed in DSC trace for pure compounds, is usually observed as a single sharp endothermic peak in which the onset temperature (Tonset) is very similar to the peak temperature (Tpeak).11 Presence of isomers usually broadens the solid-to- liquid transition peak.17 Table 4-1 depicts the melting temperatures, enthalpy, and entropy for 6 isomer mixtures synthesized using Scheme 4-3. The asymmetric isomer has a lower entropy as compared to the symmetrical isomers. 5’ has the highest entropy in the set of isomers. It means the isomer with hydroxyl groups has a more ordered crystal structure than any other isomer. 86 Table 4-1 : DSC obtained experimental values for DDSQ-2(R1R2). Compound Tpeak (°C) Tm (°C) ΔHm (kJ/mol) ΔSm (J/mol K) 3’ 279 (Major) 276 39.7 144 5’ 267 262 40.6 155 4’ 286 282 31.7 111 6 isomer 287 ( Broad peak ) 272 33.2 122 mixture This value might be attributed to hydrogen bonding contributing to a more ordered crystal structure. Also, the 6-isomer mixture exhibits a broad solid-to-liquid transition peak of about 15 °C indicating that although the individual isomers do show a sharp melting transition, the mixture of isomers eventually disrupts the ordered packing leading to glassy like solid to liquid transition temperatures. Table 4-2 : Experimental values obtained for DDSQ-2[(RMe)(MeOH)] by DSC. Compound Tpeak (°C) Tm (°C) ΔHm (kJ/mol) ΔSm (J/mol K) R (4*) Hydrogen 286 282 33.6 119 Methyl 290 290 39.5 137 Propyl 223 (Major) 219 28.6 131 chloride 4* is the analogous series of compounds where the R group keeps increasing in size from hydrogen to methyl to propyl chloride group. 4* with the methyl group has the sharpest melting point, with the onset and peak temperatures being the same. The enthalpy and entropy are the highest amongst 87 the series of compounds. In the case when the ‘R’ group is a hydrogen atom, the system has the lowest entropy overall in the system. The melting point is almost similar to that of the methyl group as the ‘R’ substituent, but the enthalpy is lower than that of the ‘R’ substituents. The system with propyl chloride with the substituent has the lowest melting point of the three compounds. Correspondingly, it also has the lowest enthalpy of the three compounds. Table 4-3 : Experimental values obtained for DDSQ-2[(RMe)(MeOTMS)] by DSC. Compound Tpeak (°C) Tm (°C) ΔHm (kJ/mol) ΔSm (J/mol K) R (6*) Hydrogen 206 200 37 185 Methyl 210 206 38.7 188 Propyl 208 (Broad) 190 19.5 103 chloride 6* is the analogous series of compounds where the hydroxy group on 4* has been modified by shielding it via reaction with trimethylchlorosilane (TMSCl). The ‘R’ group keeps increasing from hydrogen to methyl to propyl chloride group. As seen from Table 4-3, the melting point of the compounds where the ‘R’ group is either a hydrogen atom or methyl group, the melting point of the system drops by almost 80 °C by adding a bulky TMS group on the cages. This instance is the first indication that increasing the asymmetry on one side of the cage leads to a significant swing in the melting temperature of the compounds. Surprisingly, the enthalpy and entropy for 6* in the case where the ‘R ’ group is an H or Me is higher than the corresponding values in 4*. However, the solid-to-liquid transition temperature changes by about 20 ° when the' R' group is propyl 88 chloride. The nature of the peak changes to a relatively broad peak with about a 15 °C difference between the onset and peak points. Table 4-4 : Experimental values obtained for DDSQ-2[(Me2)(RR')] by DSC. Compound Tpeak (°C) Tm (°C) ΔHm (kJ/mol) ΔSm (J/mol K) R (6*) 290 290 39.5 137 210 206 38.7 188 152 (Broad) 138 21.6 157 The last comparison system of the capped cages studied in this work is based on Scheme 4-5. In this case, the isobutyl group has replaced the methyl group. Upon DSC analysis of the system, having two bulky groups, such as isobutyl and OTMS groups, on one side of the cage versus smaller groups, such as methyl groups, on the other side, vastly changes the thermal characteristics. The solid-to-liquid transition characteristics change from a sharp peak at 290 °C for the case with (Me)(OH) on one side to a broad peak around 145 °C where the functional groups are (iBu)(OTMS). The system's enthalpy drops as the size of the functional groups increases. To summarize, a series of compounds with the increasing bulkiness of the functional groups was synthesized. The initial series had a reactive silanol functional group present in the cages. This 89 functional group's presence affected the cages' thermal characteristics studies. To circumnavigate the silanol group's decomposition problem, the silanol group was protected with trimethylsilyl chloride. This protection helps to improve the thermal stability of the cage system and, at the same time, provides another system of compounds with a bulky side group leading to the formation of asymmetry in the cage. DSC analysis shows that bulky groups reduce the solid-to-liquid transition temperature from 290 °C to 145 °C. The enthalpy of the system also reduces with increasing size. Although the system shows solid-to-liquid transition temperatures lowering, the system still does not exhibit a glassy substance-like solid-to-liquid transition characteristic. A new class of modified DDSQ-like cage systems needs to be developed that will inherently modify the structure of the core cage rather than modifying the peripheral organic corona. The next chapter synthesized and explored a new series of DDSQ-like cage structures. 90 4.4 Experimental details 4.4.1 General Information All manipulations were done under a nitrogen atmosphere using standard Schlenk techniques except otherwise stated. All commercially available chemicals were used as received unless otherwise indicated. Methyldichlorosilane, methyl trichlorosilane, dimethyl dichlorosilane, methyl (propyl chloride) dichlorosilane, trimethylchlorosilane, isobutyl trichlorosilane deuterated chloroform with 1 vol % tetramethylsilane (CDCl3-1%TMS), were purchased from Sigma- Aldrich. Graphene nanoplatelet was obtained from XG Sciences. DDPh8T8(OH)4 was obtained from Hybrid Plastics. Triethylamine (Et3N) was purchased from Avantor and distilled over calcium hydride before use. Tetrahydrofuran (THF), dichloromethane (DCM), and methanol (MeOH) n-hexanes were purchased from Sigma-Aldrich. THF was distilled over benzophenone and sodium metal at 50 °C under nitrogen. The other solvents were used as purchased without further purification, and the glassware was oven dried. All 1H, 13C, and 29Si NMR were acquired on an Agilent DirectDrive2 500 MHz NMR spectrometer equipped with a OneProbe operating at 500 MHz for 1H NMR, 126 MHz for 13 C NMR, and 99 MHz for 29 Si NMR using CDCl3 and recorded at 25 ºC. 1H-NMR spectra were recorded with 8 scans, a relaxation delay of 1s, and a 13 pulse angle of 45° and referenced to the residual protonated solvent in CDCl3 (7.24 ppm). C- NMR spectra were collected with 254 scans, a relaxation delay of 0.1 s, and a pulse angle of 45°. 29 Si NMR spectra were recorded with either 256 scans, a relaxation delay of 25 s, and a pulse angle 45°. Column chromatography was performed on EMD Millipore silica gel 60 columns of 40– 63 Å silica, 230–400 mesh. Thin-layer chromatography (TLC) was performed on plates of EMD 250- µm silica 60-F254. 91 4.4.2 Synthesis of isomeric mixtures Scheme 4-6 : Reaction scheme for synthesis of 6 isomeric mixture To a 250 mL round bottom flask was added DDPh8T8(OH)4 (2.15 g, 0.002 mol, 1 equiv), methyl trichlorosilane (0.48 g, 0.002 mol, 1 equiv), dimethyldichlorosilane (0.40 g, 0.002 mol, 1 equiv) and a stir bar. The flask was placed under an N2 atmosphere, and freshly distilled DCM (~50 mL) was added. Et3N (0.815 g, 0.008 mol, 4 equiv) was added dropwise to this solution. Upon complete addition of the triethylamine, the white-colored reaction mixture turned colorless. The reaction mixture was stirred for 30 min. Dilute HCl solution (10 mL) was then added to the reaction flask, and the contents were stirred for 2 hours, after which the solvent was removed using a rotary evaporator. THF (~ 15 mL) was added to create a slurry. This slurry was filtered through a medium frit funnel to obtain the crude product. The products were isolated using silica column chromatography. A glass preparatory chromatography column, 60 cm in length 4 cm internal diameter, with a 500 mL round top reservoir, was packed with Si-gel, resulting in a packing height of about 75% of the total column height. DCM used as a mobile phase was flushed through the packed bed under pressure generated by a dry N2 stream. The mobile phase was passed through the column multiple times until no air bubbles or dry space was observed. 92 A concentrated solution of the product mixture with DCM was gently injected from the top of the wet Si-gel bed and pushed into the packed bed until no solution was observed above the packed bed. The column was then gently charged with 500 mL of DCM and flushed using the N2 stream. Fractions of 20 mL were collected at the bottom of the column until the DCM reached the top of the bed. Each fraction was seated on 5 cm TLC plates of Si-gel supported on aluminum. Fractions were eluted with DCM and then analyzed under a 245 nm UV lamp. Similar fractions were combined and dried. The asymmetrically capped DDSQ compound is eluted out as the second batch of fractions from the column. The yield is 48 %. 1 H NMR (500 MHz, Chloroform-d) δ 7.56 (ddt, J = 13.5, 8.1, 1.3 Hz, 8H), 7.44 (dq, J = 8.1, 1.5 Hz, 8H), 7.39 (tq, J = 7.8, 1.3 Hz, 4H), 7.36 – 7.29 (m, 4H), 7.25 (td, J =1.8 Hz, 8H), 7.22 – 7.14 29 (m, 9H), 2.65 (d, J = 1.7 Hz, 1H), 0.35 (d, J = 0.9 Hz, 3H), 0.31 (d, J = 1.0 Hz, 6H). Si{1H} NMR (99 MHz, Chloroform-d) δ -79.40, -79.28, -78.65, -78.49, -54.01, -16.36. 93 4.4.3 Synthesis of protected TMS cages Scheme 4-7 : Reaction scheme for synthesis of protected TMS cages To a 250 mL round bottom flask was added DDPh8T8(Me2)(MeOH) (1.05 g, 0.001 mol, 1 equiv), trichloromethyl silane (0.48 mL, 0.005 mol, 5 equiv), and a stir bar. The flask was placed under an N2 atmosphere, and freshly distilled DCM (~50 mL) was added. Et3N (0.102 g, 0.001 mol, 1.0 equiv) was added dropwise to this solution. Upon complete addition of the triethylamine, the white-colored reaction mixture turned colorless. The reaction mixture was stirred for 30 min, and the solvent was removed using a rotary evaporator. THF (~ 15 mL) was added to create a slurry. This slurry was filtered through a medium frit funnel to obtain the crude product. The products were isolated using silica column chromatography. The yield is 95 % 1 H NMR (500 MHz, Chloroform-d) δ 7.55 (td, J = 8.3, 1.4 Hz, 8H), 7.42 (dddd, J = 7.6, 4.6, 2.9, 1.4 Hz, 9H), 7.40 – 7.37 (m, 3H), 7.37 – 7.30 (m, 4H), 7.29 – 7.23 (m, 9H), 7.18 (q, J = 7.5 Hz, 8H), 0.30 (d, J = 1.6 Hz, 6H), 0.26 (s, 3H), 0.03 (s, 8H). 29Si{1H} NMR (99 MHz, Chloroform-d) δ -79.70, -79.50, -79.30, -78.65, -64.15, -16.59, 9.92. 94 REFERENCES (1) Agaskar, P. A. 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Polyhedron 2018, 155, 189–193. https://doi.org/10.1016/j.poly.2018.08.016. 96 APPENDIX Figure 4-3 : 1H-NMR (CDCl3, 500 MHz) 97 Figure 4-4 : 29Si{1H}-NMR (CDCl3, 99 MHz) 98 Figure 4-5 : 29Si{1H}-NMR (CDCl3, 99 MHz) 99 Figure 4-6 : 1H-NMR (CDCl3, 500 MHz) 100 Figure 4-7 : 29 Si{1H}-NMR (CDCl3, 99 MHz) 101 Figure 4-8 : 1H-NMR (CDCl3, 500 MHz) 102 Figure 4-9 : DSC data for heating cycles (R)DDSQ(MeOH). 103 Figure 4-10 : DSC data for heating cycles (R)DDSQ(MeOTMS). 104 Figure 4-11 : DSC data for heating cycles for (Me2)DDSQ(ROH) 105 Figure 4-12 : DSC data for heating cycles for (Me2)DDSQ(ROTMS) 106 Figure 4-13 : DSC data for heating cycle for (MeH)DDSQ(MeH) 107 Figure 4-14 : DSC data for heating cycle for (MeOH)DDSQ(MeOH) 108 Figure 4-15 : DSC data for heating cycle for (MeH)DDSQ(MeOH) 109 Figure 4-16 : Overlayed graph for the (MeR')DDSQ(MeR") isomeric system 110 5 SOLVENT EFFECT FOR CAPPING OF DDPh8T8(OH)4 111 5.1 Introduction Incompletely condensed phenyl double-decker-shaped silsesquioxane can be functionalized using difunctional dichlorosilanes or dialkoxysilanes. Although there is a vast potential for side-capped Scheme 5-1 : Reaction for capping of DDSQ tetrol using chlorosilanes DDSQs, significant research has not been performed on the synthesis of side-capped DDSQs.1 The most commonly used reaction scheme is in Scheme 5-1. Functionally capped SQs synthesized have a unique ability to be a part of the main chain or be a cross-linker between the polymer chains or act as pendants on the backbone of the polymer chain.2–6 The type of solvent used in the reaction plays a vital role in the rate of the reaction. Studies have suggested that depending on the type of reaction, changing the solvent from non-polar to polar solvent with either increase or decrease the rate of reaction.7 The specific interaction of solvent and the reactant molecules and the interaction between solvent and transition states dictate the solvent effect on reactivity in a homogeneous media.8–12 When the magnitude of solvent in elementary reaction changes, the reaction rate will also change. This chapter explicitly discusses the effect of good and poor solvents on the reactant DDSQ tetrol. Tetrahydrofuran (THF) acts as a good solvent for DDSQ tetrol, where the solubility of DDSQ in THF is 80 mg / mL, whereas 112 Dichloromethane (DCM) acts as a poor solvent where the solubility of DDSQ tetrol is approximately 0.2 – 0.3 mg / mL. The effect of solvent on the time required for completion of reaction in both the solvents has been reported. 5.2 DDSQ tetrol capping reaction using a good solvent The reaction scheme for capping of DDSQ tetrol using THF as reaction solvent is as shown in Scheme 5-2 Scheme 5-2 : Capping of DDSQ tetrol using THF as reaction solvent. 1, difunctional dichlorosilane and triethylamine are entirely soluble in THF. The solution is evident at the start of the reaction. As the reaction progresses, the chlorosilane reacts with the hydroxy groups, forming the product (2) and hydrochloric acid as a by-product. However, it has been found that the hydrochloric acid produced in the reaction can cause cleavage of the DDSQ cage. So, to neutralize the by-product, a base - triethylamine is used in the reaction. The neutralization reaction produces triethylammonium chloride salt, which is not soluble in THF, forming a white precipitate as the reaction progresses. A variety of symmetrically capped DDSQ products were synthesized via Scheme 5-2Scheme 5-2. The type of functional groups on dichlorosilanes used varied from MeHSiCl2, Me2SiCl2, and Ph2SiCl2. The reaction time was dependent on the size and type of chlorosilane used in the reaction. Bulkier chlorosilanes like Ph2SiCl2 have a reaction time closer to two hours for obtaining complete 113 conversion. Me2SiCl2 has a smaller size and leads to complete conversion within minutes. The progress of reactions can be monitored using NMR analysis. In another set of reactions, an equimolar mixture of two different chlorosilanes was used to synthesize asymmetrically capped DDSQ compounds, as seen in Scheme 5-3. This methodology helped to synthesize compounds with two different functional groups on either side of the cage structure. These asymmetrical structures are then used in various applications to cross-link the two Scheme 5-3 : Capping of DDSQ tetrol using equimolar chlorosilanes as capping reagents. polymeric chains to form a networked structure. Upon using an equimolar mixture of chlorosilanes as capping reagents, a mixture of 3 isomers of products was obtained. According to the probability distribution theory, if the dichlorosilanes have equal reactivity for the DDSQ tetrol, the ratio of isomers should be 25:50:25; that is, the yield of symmetrical products obtained from each chlorosilane should be 25%. In contrast, the ratio of the asymmetrical product should be 50% in the final product composition. However, the ratio of the isomers was not the same as expected from the statistical distribution. The symmetrical product obtained from less bulky chlorosilane has a higher yield than the one obtained from the bulkier chlorosilane. The time required to achieve complete conversion for various chlorosilanes was studied to determine the deviation in ratios from the statistical distribution. Two different types of chlorosilanes were selected for this study. Ph2SiCl2 and Me2SiCl2 were the chlorosilanes used to cap the DDSQ tetrol, as shown in Scheme 5-4. 114 Scheme 5-4 : Reaction scheme used to study the time required to achieve complete conversion to product. The capping reaction can be followed by using NMR analysis. An aliquot was removed from the reaction mixture and quenched with methanol to prepare the sample for NMR analysis. Post- quenching deuterated chloroform was added to the quenched product, and an NMR of the sample was taken. The phenyl region can be monitored to figure out the changes in the cage structure, as 24 hr 2 hr 10 min 0 sec Figure 5-1: Reaction progress monitoring using NMR analysis for DDSQ tetrol capping with Me2SiCl2 using THF as a solvent seen in Figure 5-1. As seen from the NMR analysis, there is no apparent change in the phenyl region after 1 min of the reaction time. The NMR sample taken after 2 hours almost matches the 115 NMR sample taken at 1 minute, indicating that the reaction reached complete conversion in that time. Similar studies were conducted using Ph2SiCl2 chlorosilanes. It was found that the reaction 24 hr 2 hr 40 min 10 min 1 min 0 sec Figure 5-2 : Reaction progress monitoring using NMR analysis for DDSQ tetrol capping with Ph2SiCl2 using THF as a solvent takes longer to reach completion. Figure 5-2 shows a zoomed-in picture of the phenyl region of DDSQ. As can be seen from the spectra, peaks at 6.97 ppm disappear as the reaction progresses. The peaks completely vanished in 2 hours—also, the peak position and intensities at 6.78 ppm changed as the reaction progressed. The doublet peak disappears, and a new singlet appears upfield to the original peaks. There was no change in the peak positions and intensities when the reaction was monitored from 2 to 24 hours, indicating reaction completion in 2 hours. This critical difference in the time required for the capping of the two chlorosilanes accounts for the differences in the ratio of the isomeric products. DCM was proposed as an alternative solvent for the capping 116 reaction to solve this issue and ensure the reaction time remains unchanged irrespective of the type of chlorosilanes used. 5.3 DDSQ tetrol capping reaction using a poor solvent Dichloromethane (DCM) acts as a poor solvent for DDSQ tetrol. The solubility of tetrol in DCM is approximately 0.2 mg / mL. This solubility is almost 400 times less than tetrol's solubility in THF (80 mg / mL). As a result, the starting reaction mixture is a suspension in DCM compared to being a clear solution in THF. Another essential difference between the two reactions is that the by-product triethylammonium salt formed during the reaction is soluble in DCM, which is insoluble in THF. The dichlorosilane used in the reaction total miscibility with the solvent. This fact helps to monitor the reaction visually. As the reaction progresses, the suspension turns into a clear solution. Adding a base to the suspended solution of DDSQ tetrol in DCM helps solubilize the DDSQ tetrol. It has been seen that the amount of base required to solubilize tetrol in DCM entirely is one equivalent per equivalent of the hydroxy group. Any lower amount of addition of base will not completely solubilize the tetrol. The reaction scheme for capping DDSQ tetrol with dichlorosilane is shown in Scheme 5-5 Scheme 5-5 : Reaction scheme for DDSQ tetrol capping using Ph2SiCl2 117 To verify the differences in the time required for the capping reaction for the Ph2SiCl2 reaction, aliquots were taken out at certain times, quenched with methanol, and then NMR analysis was done to motor the changes in the peaks. The NMR analysis is shown in Figure 5-3. 29Si NMR has been used to monitor the progress of the reaction. Spectra 1 depicts the NMR for the starting 9 min 3 min 30 sec 0 sec Figure 5-3 : Reaction progress monitoring using NMR analysis for DDSQ tetrol capping with Ph2SiCl2 using DCM as a solvent. material DDSQ tetrol; spectra 2 depicts the progress of the reaction after 30 seconds. The peak intensity at -69 ppm represents the silicon atom connected to the hydroxyl group. This peak will diminish in intensity as the product is formed. The peak at -78 ppm starts to increase in intensity, and this peak refers to the silicon atom that was previously connected to the hydroxy group, which is now connected with the silicon peak of the dichlorosilane. The peak -45 ppm also starts to appear, depicting the product's ‘D’ Silicon peak. Peaks at -38 ppm depict the silicon peaks obtained from quenched chlorosilane. Spectra 3 shows the progress of the reaction after 3 minutes. Spectra 4 shows the progress of the reaction after 9 minutes. 118 As seen from these spectra, the peak at -69 ppm completely vanishes, which leads to the conclusion that the reaction reaches completion within 3 minutes as opposed to the reaction done in THF, where the time required is 120 minutes. The difference in reactivity can be attributed to the difference in pKa of triethylamine in two different solvents. Triethylamine has a higher pKa value in DCM as compared to THF. This change in pKa results in a higher level of deprotonation of tetrol in the presence of DCM solvent than that in THF. Consequently, a higher reactant activity in DCM solvent than in THF solvent. As a result, we get a faster reaction in DCM as a solvent medium than in THF. Various chlorosilanes and mixtures of chlorosilanes were used to cap DDSQ tetrol using DCM solvent. Detailed information on the procedure and NMR spectra have been given in the SI. In conclusion, a new method for capping DDSQ tetrol with chlorosilanes has been proposed. The reaction time has been reduced to 5 minutes irrespective of the type of chlorosilane or mixture of chlorosilanes used in the reaction. The increased activity of the reactant in DCM can be attributed to the difference in pKa values of triethylamine in DCM vs. THF. 119 5.4 Experimental Details 5.4.1 General Information All manipulations were done under a nitrogen atmosphere using standard Schlenk techniques except otherwise stated. All commercially available chemicals were used as received unless otherwise indicated. Methyl trichlorosilane (MeSiCl3), dimethyl dichlorosilane (Me2SiCl2), diphenyl dichlorosilane(Ph2SiCl2), methyl cyanopropyl dichlorosilane Me(C3H6CN)SiCl2, deuterated chloroform with 1 vol % tetramethylsilane (CDCl3-1%TMS), were purchased from Sigma-Aldrich. Graphene nanoplatelet was obtained from XG Sciences. DDPh8T8(OH)4 was obtained from Hybrid Plastics. Triethylamine (Et3N) was purchased from Avantor and distilled over calcium hydride before use. Tetrahydrofuran (THF), dichloromethane (DCM), and methanol (MeOH) n-hexanes were purchased from Sigma-Aldrich. THF was distilled over benzophenone and sodium metal at 50 °C under nitrogen. Toluene was distilled over calcium hydride at a temperature of 120 °C. The other solvents were used as purchased without further purification, and the glassware was oven dried. All 1H, 13 C, and 29 Si NMR were acquired on an Agilent DirectDrive2 500 MHz NMR spectrometer equipped with a OneProbe operating at 500 MHz for 1 H NMR, 126 MHz for 13C NMR, and 99 MHz for 29Si NMR using CDCl3 and recorded at 25 ºC. 1 H-NMR spectra were recorded with 8 scans, a relaxation delay of 1s, and a pulse angle of 45° and 13 referenced to the residual protonated solvent in CDCl3 (7.24 ppm). C-NMR spectra were collected with 254 scans, a relaxation delay of 0.1 s, and a pulse angle of 45°. 29Si NMR spectra were recorded with either 256 scans, a relaxation delay of 25 s, and a pulse angle 45°. Column chromatography was performed on EMD Millipore silica gel 60 columns of 40– 63 Å silica, 230– 400 mesh. Thin-layer chromatography (TLC) was performed on plates of EMD 250-µm silica 60- F254. 120 5.4.2 Synthesis of 9,9,19,19-tetramethyl-1,3,5,7,11,13,15,17- octaphenyl-2,4,6,8,10,12,14,16,18,20,21,22,23,24-tetradecaoxa- 1,3,5,7,9,11,13,15,17,19- decasilapentacyclo[11.7.1.13,11.15,17.17,15]tetracosane Scheme 5-6 : Synthesis of capped DDSQ (Me)4 To a 100 mL round bottom flask were added DDPh8T8(OH)4 (2 g, 0.0018 mol, 1 equiv), dichlorodimethylsilane (0.50 mL, 0.0041 mol, 2.2 equiv), and a stir bar under N2 atmosphere. Freshly distilled THF (~30 mL) was then added. A clear solution was formed. Et 3N (1.05 mL, 0.0074 mol, 4 equiv) was added dropwise to this solution. Upon the addition of the triethylamine, the solution turned milky white. The reaction mixture was stirred for 120 min, after which a slurry was formed. This slurry was filtered through a medium frit funnel to obtain the crude product in the filtrate. The filtrate was concentrated to obtain white powder. This powder was washed with methanol (~60 mL) for 30 min. The slurry was again filtered through a medium frit funnel to obtain the product as a white powder (2.12 g, 96% yield). 1H NMR (500 MHz, Chloroform-d) δ 7.54 (d, J = 6.9 Hz, 8H), 7.40 (dd, J = 23.5, 7.2 Hz, 13H), 7.33 (t, J = 7.5 Hz, 5H), 7.24 (d, J = 7.5 Hz, 6H), 7.18 (t, J = 7.5 Hz, 9H), 0.30 (s, 12H). 13C{1H} NMR (126 MHz, Chloroform-d) δ 134.04, 133.92, 132.12, 131.07, 127.77, 127.62, 0.53. 29Si{1H} NMR (99 MHz, Chloroform-d) δ -16.55, -78.63, - 79.61. 121 5.4.3 Synthesis of 1,3,5,7,9,9,11,13,15,17,19,19-dodecaphenyl- 2,4,6,8,10,12,14,16,18,20,21,22,23,24-tetradecaoxa- 1,3,5,7,9,11,13,15,17,19- decasilapentacyclo[11.7.1.13,11.15,17.17,15]tetracosane Scheme 5-7 : Synthesis of capped DDSQ (Ph)4 To a 100 mL round bottom flask were added DDPh8T8(OH)4 (2 g, 0.0018 mol, 1 equiv), dichlorodiphenylsilane (0.79 mL, 0.0041 mol, 2.2 equiv), and a stir bar under N2 atmosphere. Freshly distilled THF (~30 mL) was then added. A clear solution was formed. Et 3N (1.05 mL, 0.0074 mol, 4 equiv) was added dropwise to this solution. Upon the addition of the triethylamine, the solution turned milky white. The reaction mixture was stirred for 120 min, after which a slurry was formed. This slurry was filtered through a medium frit funnel to obtain the crude product in the filtrate. The filtrate was concentrated to obtain crude white powder. The crude and purified by silica column chromatography (DCM mobile phase) to afford the desired product. 1H NMR (500 MHz, Chloroform-d) δ 7.71 – 7.65 (m, 8H), 7.54 – 7.51 (m, 8H), 7.40 – 7.35 (m, 8H), 7.31 – 7.27 (m, 4H), 7.22 (q, J = 7.5 Hz, 18H), 7.18 – 7.14 (m, 8H), 7.11 – 7.06 (m, 8H). 13C NMR (126 MHz, Chloroform-d) δ 127.40, 127.78, 127.82, 130.11, 130.19, 130.41, 130.49, 131.56, 134.03, 134.10, 134.27, 134.58. 29Si{1H} NMR (99 MHz, Chloroform-d) δ -79.40, -78.14, -45.47. 122 5.4.4 Synthesis of 4,4',4'',4'''-(1,3,5,7,11,13,15,17-octaphenyl- 2,4,6,8,10,12,14,16,18,20,21,22,23,24-tetradecaoxa- 1,3,5,7,9,11,13,15,17,19- decasilapentacyclo[11.7.1.13,11.15,17.17,15]tetracosane- 9,9,19,19-tetrayl)tetrabutanenitrile Scheme 5-8 : Synthesis of capped DDSQ (propylCN)4 To a 100 mL round bottom flask were added DDPh8T8(OH)4 (2 g, 0.0018 mol, 1 equiv), biscyanopropyldichlorosilane (0.83 mL, 0.0041 mol, 2.2 equiv), and a stir bar under N2 atmosphere. Freshly distilled DCM (~30 mL) was then added. A cloudy solution was formed. Et3N (1.05 mL, 0.0074 mol, 4 equiv) was added dropwise to this solution. Upon the addition of the triethylamine, the solution turned clear. The reaction mixture was stirred for 5 min, after which the solvent evaporated. Fresh THF (~50 mL) was added, and a slurry was formed. This slurry was filtered through a medium frit funnel to obtain the crude product in the filtrate. The filtrate was concentrated to obtain white powder. This powder was washed with methanol (~60 mL) for 30 min. The slurry was again filtered through a medium frit funnel to obtain the product as a white powder (2.45 g, 94% yield). 1 H NMR (500 MHz, Chloroform-d)δ 7.51 – 7.47 (m, 8H), 7.42 (qd, J = 9.3, 8.1, 4.8 Hz, 16H), 7.32 – 7.23 (m, 18H), 2.18 (t, J = 6.9 Hz, 8H), 1.80 – 1.67 (m, 9H), 0.96 – 0.81 (m, 8H). 13C NMR (126 MHz, Chloroform-d) δ 14.84, 19.20, 20.07, 119.19, 128.02, 128.13, 130.17, 130.89, 133.70, 133.86. 29Si{1H} NMR (99 MHz, Chloroform-d) δ -79.15, -78.19, -22.23. 123 5.4.5 Synthesis of 9,19-diallyl-1,3,5,7,11,13,15,17-octaphenyl- 2,4,6,8,10,12,14,16,18,20,21,22,23,24-tetradecaoxa- 1,3,5,7,9,11,13,15,17,19- decasilapentacyclo[11.7.1.13,11.15,17.17,15]tetracosane-9,19- diol Scheme 5-9 : Synthesis of capped DDSQ (allyl OH)2 To a 100 mL round bottom flask were added DDPh8T8(OH)4 (2 g, 0.0018 mol, 1 equiv), allyl trichlorosilane (0.57 mL, 0.0041 mol, 2.2 equiv), and a stir bar under N2 atmosphere. Freshly distilled DCM (~30 mL) was then added. A cloudy solution was formed. Et3N (1.05 mL, 0.0074 mol, 4 equiv) was added dropwise to this solution. Upon the addition of the triethylamine, the solution turned clear. The reaction mixture was stirred for 5 min, after which the solvent evaporated. Fresh THF (~50 mL) was added, and a slurry was formed. This slurry was filtered through a medium frit funnel to obtain the crude product in the filtrate. The filtrate was concentrated to obtain white powder. This powder was washed with methanol (~60 mL) for 30 min. The slurry was again filtered through a medium frit funnel to obtain the product as a white powder (2.45 g, 94% yield). 1 H NMR (500 MHz, Chloroform-d) δ 7.62 – 7.55 (m, 8H), 7.48 – 7.32 (m, 16H), 7.31 – 7.16 (m, 16H), 5.88 – 5.77 (m, 2H), 4.93 (dp, J = 17.0, 1.7 Hz, 2H), 4.79 (dq, J = 10.1, 1.9, 1.2 Hz, 2H), 3.75 – 3.71 (m, 2H), 1.87 – 1.78 (m, 6H). 29 Si{1H} NMR (99 MHz, Chloroform-d) δ -79.39, - 79.28, -79.16, -78.78, -60.76. 124 REFERENCES (1) Applications of Polyhedral Oligomeric Silsesquioxanes; Hartmann-Thompson, C., Ed.; Advances in Silicon Science; Springer Netherlands: Dordrecht, 2011; Vol. 3. https://doi.org/10.1007/978-90-481-3787-9. (2) Constable, G. S.; Lesser, A. J.; Coughlin, E. B. Morphological and Mechanical Evaluation of Hybrid Organic−Inorganic Thermoset Copolymers of Dicyclopentadiene and Mono- or Tris(Norbornenyl)-Substituted Polyhedral Oligomeric Silsesquioxanes. Macromolecules 2004, 37 (4), 1276–1282. https://doi.org/10.1021/ma034989w. (3) Fu, B. X.; Lee, A.; Haddad, T. S. Styrene−Butadiene−Styrene Triblock Copolymers Modified with Polyhedral Oligomeric Silsesquioxanes. Macromolecules 2004, 37 (14), 5211–5218. https://doi.org/10.1021/ma049753m. (4) Feher, F. J.; Budzichowski, T. A.; Rahimian, K.; Ziller, J. W. Reactions of Incompletely- Condensed Silsesquioxanes with Pentamethylantimony: A New Synthesis of Metallasilsesquioxanes with Important Implications for the Chemistry of Silica Surfaces. J. Am. Chem. Soc. 1992, 114 (10), 3859–3866. https://doi.org/10.1021/ja00036a038. (5) Gilman, J. W.; Schlitzer, D. S.; Lichtenhan, J. D. Low Earth Orbit Resistant Siloxane Copolymers. J. Appl. Polym. Sci. 1996, 60 (4), 591–596. https://doi.org/10.1002/(SICI)1097-4628(19960425)60:4<591::AID-APP12>3.0.CO;2-2. (6) Wright, M. E.; Schorzman, D. A.; Feher, F. J.; Jin, R.-Z. Synthesis and Thermal Curing of Aryl-Ethynyl-Terminated Co POSS Imide Oligomers: New Inorganic/Organic Hybrid Resins. Chem. Mater. 2003, 15 (1), 264–268. https://doi.org/10.1021/cm020238h. (7) Parker, A. J. Protic-Dipolar Aprotic Solvent Effects on Rates of Bimolecular Reactions. Chem. Rev. 1969, 69 (1), 1–32. https://doi.org/10.1021/cr60257a001. (8) Ghosh, K. K. Kinetic Solvent Effect on the Hydrolysis of N-Benzylbenzohydroxamic Acid in Some Binary Aqueous Solvent Mixtures. Journal of Molecular Liquids 1999, 81 (2), 135–145. https://doi.org/10.1016/S0167-7322(99)00062-8. (9) Schmeer, G.; Steinkirchner, J. Investigations on Substituent and Solvent Effects of Solvolysis Reactions. VIII. The Influence of Water and Nonaqueous Solvents on the Imidazolysis of 4-Nitrophenyl Acetate. (10) Seliverstova, T. S.; Kushner, M. A.; Matusevich, L. G. Kinetics and Mechanism of the Hydrolysis of Benzyl Ether Bonds in Aqueous–Organic Media. Russ. J. Phys. Chem. 2020, 94 (2), 310–316. https://doi.org/10.1134/S0036024420020302. (11) Habibi-Yangjeh, A.; Nooshyar, M. Prediction of Solvent Effects on Rate Constant of [2+2] Cycloaddition Reaction of Diethyl Azodicarboxylate with Ethyl Vinyl Ether Using Artificial Neural Networks. Bulletin of the Korean Chemical Society 2005, 26 (1), 139–145. https://doi.org/10.5012/BKCS.2005.26.1.139. 125 (12) Iglesias, E. Solvent Effects versus Concentration Effects in Determining Rates of Base- Catalyzed Keto-Enol Tautomerization. New J. Chem. 2005, 29 (4), 625. https://doi.org/10.1039/b415220d. 126 APPENDIX Figure 5-4 : 1H-NMR (CDCl3, 500 MHz) 127 Figure 5-5 : 13C-NMR (CDCl3, 126 MHz) 128 Figure 5-6 : 29Si{1H}-NMR (CDCl3, 99 MHz) 129 Figure 5-7 : 1H-NMR (CDCl3, 500 MHz) 130 Figure 5-8 : 13C-NMR (CDCl3, 126 MHz) 131 Figure 5-9 : 29Si{1H}-NMR (CDCl3, 99 MHz) 132 Figure 5-10 : 1H-NMR (CDCl3, 500 MHz) 133 Figure 5-11 : 13C-NMR (CDCl3, 126 MHz) 134 Figure 5-12 : 29Si{1H}-NMR (CDCl3, 99 MHz) 135 Figure 5-13 : 1H-NMR (CDCl3, 500 MHz) 136 Figure 5-14 : 29Si{1H}-NMR (CDCl3, 99 MHz) 137 6 INCOMPLETELY CONDENSED CAGE-LIKE SILSESQUIOXANES 138 6.1 Introduction Polyhedral oligomeric silsesquioxane (POSS) has been among the most promising hybrid organic- inorganic nanofillers in academic and industrial research due to its ease of functionalization, multifunctional nanostructure, and high thermal stability. The compounds’ thermal behavior and crystal packing structures have been studied in detail. Wang et al. synthesized a series of alkylated cage silsesquioxanes and found that the size of attached alkyl chains effectively tuned the intermolecular forces between the cage structures.1 Blanco et al. mono aryl halide substituted POSS cage structures and found an improvement in solubility and thermal properties of the synthesized POSS cage structures.2 Wang et al. extensively reviewed the enhancement of POSS’s thermal, mechanical, and optical properties modified using various corona groups.3 It was found that functionalizing the incompletely condensed octaphenyl double-decker silsesquioxane tetrasilanol, DDPh8T8(OH)4, with reactive dichlorosilanes forms a condensed, hybrid molecule with reactive organic groups on the opposite edge of the inorganic SiO1.5, SQ, core surrounded by phenyl moiety.4–12 Vogelsang et al. found that the cis/trans isomers formed during the capping of DDPh8T8(OH)4 can be isolated by using a combination of selective solvent fractional crystallization and liquid chromatography.13–17 On separation of the cis and trans isomers, it is found that trans isomers have higher melting temperatures than the cis isomers. Increasing the size of groups attached to the cage lowers the melting temperature. The cis-trans isomer mixture exhibits eutectic melting. On the contrary, a few studies on unsymmetrical/asymmetrical silsesquioxane or siloxane cages. This fact is mainly due to the difficulties in obtaining a perfect Janus cage using simple hydrolytic condensation techniques. Due to the unique physical and chemical properties related to the different types, quantities, and functionality of the organic groups present in the single molecule, 139 the synthesis of asymmetrical cage structures has become an essential subject in the field of silicon chemistry.18–23 So far, most of the studies and modifications on POSS/DDSQ cage have been on changing the corona groups of the system. This study focuses on tailoring the core Si-O-Si cage to study the Figure 6-1 : The structure of Side Open Ph8T8(OH)2 effects on thermal properties and the crystal packing of the system. To facilitate that, an asymmetrical closed cage silsesquioxane structure with one edge closed and silanol groups on the other end. 6.2 Synthesis of Incompletely Condensed Cage diol The starting material SOPh8T8(OH)2 was synthesized via base-mediated partial cage closure of DDPh8T8(OH)4. Allyl amine was used for the condensation reaction of tetra-silanol cages, as shown in Scheme 6-1 below. Scheme 6-1 : Reaction scheme for synthesis of SOPh8T8(OH)2 A per pass yield of 40% desired SOPh8T8(OH)2 compound was isolated from the condensation reaction shown above. The by-product of the reaction is a condensed silanol cage which can be separated using simple filtration techniques and is recycled to resynthesize DDPh8T8(OH)4 via 140 NaOH mediated route as shown by Barry et al. The uncondensed starting material can also be separated via filtration to be reused in the reaction. The synthesis does not require any complex work-up steps. The by-products produced in the reaction can be converted back to the starting material, thus making the synthesis an atom-efficient and green chemistry reaction. The condensation reaction synthesizing diol produces a partially or fully condensed cage. The amount of allyl amine used in the reaction must be optimized to get the desired cage's maximum yield, like diol. The conditions used for optimization have been illustrated in Table 6-1. Table 6-1 : Reaction optimization conditions for the synthesis of SOPh8T8(OH)2 mmol Time DDPh8T8(OH)4 SOPh8T8(OH)2 DDPh8T8 Compound [Weight (g)] hr Weight % Weight % Weight % DDPh8T8(OH)4 1.87 [2] A 2 0 1 99 Allylamine 1.34 [0.076] DDPh8T8(OH)4 1.87 [2] B 1 5 19 76 Allylamine 1.34 [0.076] DDPh8T8(OH)4 7.48 [8] C 1 21 37 42 Allylamine 1.34 [0.076] The best reaction conditions for optimum yield of the desired product are using 0.1 mL of allyl amine for every 8 g of DDPh8T8(OH)4 used in the reaction. Once the desired diol has been synthesized, the next step is capping the diol with different dichlorosilanes to obtain an analogous 141 series of compounds, as previously done by Vogelsang et al.13, which has been shown in Scheme 6-2 Scheme 6-2 : Capping of SOPh8T8(OH)2 using difunctional dichlorosilane Figure 6-2 : The series of compounds synthesized in this work The analogous series of compounds synthesized in this work has been shown in Figure 6-2 142 Si Si Si Si Si Figure 6-3 : 29Si NMR comparison between SOPh8T8(OH)2 and DDPh8T8(OH)4 To verify the synthesis of SOPh8T8(OH)2 and to study the behavior of the molecules in solution, Proton (1H), Carbon (13C), and Silicon (29Si), NMR analysis was performed. As seen in Figure 6-3, the silicon atoms for 2 can be classified into 3 different types, as depicted by the color of the silicon atoms. The 8 T-silicon atoms on the core cage are divided in the ratio 2:4:2 based on the bond connectivity and nuclear environment around these atoms. A noticeable difference can also be observed for the magnetic environment phenyl groups attached to these T-silicon atoms. Similarly, the silicon atoms for 1 can be classified into 2 different types as depicted by the color of the silicon atoms. The 8 T-silicon atoms on the core cage are divided in the ratio 1:1. The T-silicon atoms directly attached to the hydroxy groups (shown in black color) have a different magnetic environment than the silicon atoms internal to the cage(shown in orange color). The 1H NMR comparative analysis for 1 and 2 has been shown in 143 Figure 6-4. The splitting pattern of the phenyl protons for 1 was more uniform than that of 2, denoting more symmetry in the structure of 1 compared to 2. This change in splitting pattern can be attributed to the presence of 2 types of phenyl rings in 1 versus 3 types of phenyl rings in 2. Figure 6-4 : 1H NMR comparison between SOPh8T8(OH)2 and DDPh8T8(OH)4 The detailed synthesis procedures of the analogous series of compounds and the NMR data are provided in the chapter's supplementary information attached. For comparison, SOPh8T8Me2 and SOPh8T8Ph2 have been taken as model compounds, and their thermal properties have been studied. 6.3 Thermal properties of model compounds Detailed thermal studies have been performed to study the impact of the difference in the crystal packing and the consequence of cage structure variation on the isomers' thermal properties. The DSC analysis performed on the two isomers revealed a significant difference in their melting 144 points, as seen in Table 6-2. The DSC thermograms have been shown in SI. In the case of 4, ΔHm and ΔSm obtained from DSC are 29.8 kJ/mol and 60.4 J/mol K, respectively. However, in the case of SOPh8T8Me2, ΔHm and ΔSm values obtained are 58.5 kJ/mol and 107 J/mol K, respectively. Table 6-2 : Thermal Parameters for SOPh8T8Me2 and SOPh8T8Ph2 based on DSC analysis. SOPh8T8Me2 SOPh8T8Ph2 1st heating cycle Sharp melting peak (274 °C) Broad melting peak (267 °C) 1st cooling cycle Broad recrystallization at 236 No recrystallization peak was °C observed during cooling 2nd heating cycle Sharp melting peak like the first Cold recrystallization, as well heating cycle as a melting peak, was observed ΔHm (kJ/mol) 58.5 21 ΔSm* (J/ (mol K)) 107 38.9 A change in entropy of melting (ΔSm) is directly related to the ability to disrupt the intermolecular packing of the compounds. More significant the entropy changes at melting, the more compact the crystal packing. The cooling cycles also showed a significant difference in the recrystallization kinetics of the two isomers. A broad recrystallization peak was observed for SOPh8T8Me2. The enthalpy of recrystallization observed from the DSC thermogram was 46.3 kJ/mol. However, interestingly, SOPh8T8Ph2 did not exhibit any recrystallization peak even at low cooling rates (2 °C/min). A second heating cycle was performed on the isomers to verify the compounds’ thermal stability during the DSC runs. SOPh8T8Me2 exhibited a melting peak in the same temperature range as was obtained in the first heating cycle. SOPh8T8Ph2 exhibited an interesting thermogram in that a recrystallization peak was observed around 152 °C and a melting peak at the same temperature range as obtained in the first heating cycle. 145 6.4 Synthesis and Characterization of constitutional isomers Structural isomer (or constitutional isomer in the IUPAC nomenclature) is the most radical type of isomerism. Although two compounds have the same number of atoms, their chemical and physical properties are entirely different since they have logically distinct bonds. In this work, constitutional isomerism of cage-like silsesquioxanes has been investigated. Precisely, edge-open octaphenyl silsesquioxane diol condensed with tetramethyl dichlorosiloxane, 4, and double- decker-shaped silsesquioxane tetraol condensed with dimethyl dichlorosilanes, 5, form structural isomers. The characteristics of these two condensed derivatives were examined by Nuclear Magnetic Resonance (NMR) to confirm their structure. Physical and thermal characteristics were investigated using differential scanning calorimetry, thermogravimetric analysis, synchrotron X- ray, and rheometry. Scheme 6-3 : Synthesis of constitutional isomers To verify the synthesis and the purity of the two structural isomers 4 and 5 and to study the behavior of the molecules in solution, Proton (1H), Carbon (13C), and Silicon (29Si), NMR analysis was 146 performed. As seen in Figure 6-5, the silicon atoms for 4 can be classified into 4 different types, as depicted by the color of the silicon atoms. The methyl groups attached to D-silicon atoms (depicted by the marron color) have a similar magnetic environment. The 8 T-silicon atoms on the core cage are divided in the ratio 2:4:2 based on the bond connectivity and nuclear environment around these atoms. A noticeable difference can also be observed for the magnetic environment phenyl groups attached to these T-silicon atoms. Similarly, the silicon atoms for 5 can be classified into 3 different types as depicted by the color of the silicon atoms. The D-silicon atoms are located on either side of the cage as compared to 4, where the D-silicon atoms are on one side. Si Si Si Si Si Si Si Figure 6-5 : 29Si NMR comparison between isomers 4 and 5 The 8 T-silicon atoms on the core cage are divided in the ratio 1:1. The T-silicon atoms directly attached to the D-silicon atoms (shown in blue color) have a different magnetic environment than the silicon atoms internal to the cage(shown in red color). 147 Figure 6-6 : Comparative 1H NMR of the phenyl region for 4 and 5 Upon studying the comparative analysis of 1H NMR (Figure 6-6) for isomer 1 (4) and isomer 2 (5), it is evident that there are 12 protons for the four methyl groups attached to the D-Si atoms and 40 protons in the phenyl groups which are attached to T-Si atoms on the silsesquioxane cage. The chemical shift of the methyl group protons for 4 (0.23 ppm) was upshifted compared to that of 5 (0.30 ppm). The splitting pattern of the phenyl protons for 5 was more uniform than that of 4, denoting more symmetry in the structure of 5 compared to 4. This pattern can be attributed to 2 types of phenyl rings in 5 versus 3 in 4. 148 R1/R2/R3 Q1/Q2 R1/R2 P1/P2 S1/S2 Figure 6-7 : Comparative 13C NMR of the phenyl region for 4 and 5 The 13C NMR analysis of the isomers depicts the difference in the uniformity of cages between the isomers. The distribution of carbon atoms in phenyl rings for 4 and 5 are as labeled in Figure 6-7. The type of atoms connected to phenyl rings (or the silicon atoms) and the number of atoms are the same, but the chemical shifts of the carbon atoms are different. The phenyl rings’ steric position, shielding, and deshielding effects can explain the differences in the NMR spectra. The splitting pattern of carbon atoms in the phenyl region for 4 indicates the meta and ortho region carbon atoms in the ratio of 1:2:1, whereas that ratio is 1:1 for isomer 5. It can also be seen that the chemical shifts of ortho carbon > para carbon > meta carbon are due to the difference in electron densities. 29Si NMR shows the most discrepancies in the structure of the two isomers, as seen in Figure 6-5. The D-Si NMR peak for 4 (-18.64 ppm) is upshifted compared to 5 (-15.65 ppm). This shift indicates that the phenyl rings less effectively shield the D-Si atoms on the 149 silsesquioxane cage for 5. In the case of the T-Si region of the silsesquioxane cages for 5 exhibits only two peaks at -78.63 ppm, corresponding to four Si atoms attached to the D-Si atoms, and at - 79.61 ppm, corresponding to four interior cage Si atoms. For 4, this T-Si region has 3 peaks indicating the presence of 3 distinct types of Si atom environments and a more distorted cage structure. The peak at -77.13 ppm corresponds to two T-Si atoms connected to the D-Si atoms. The next peak denotes the interior four T-Si atoms at -78.88 ppm. The peak at -79.50 ppm corresponds to two T-Si atoms on the opposite end of the cage structure. Thus, it can be concluded that the phenyl rings have different angles of orientation on the silsesquioxane cage for the two constitutional isomers even in a solution, thus leading to a significant difference in the atomic packing structure of the cages. The crystal structure of each compound was obtained by X-ray diffraction from a solution-grown single crystal. The crystal packing structures of the two isomers are vastly different (Refer to Appendix for detailed crystal structure). Table 6-3 : Parameters for isomers from X-ray diffraction analysis Isomer 1 (4) Isomer 2 (5) Formula C52H52O14Si10 Formula C52H52O14Si10 CCDC # 2189474 CCDC # 1832148 Volume 5742.3 Å3 Volume 5852.3 Å3 Crystal System monoclinic Crystal System tetragonal Space Group P21/n Space Group P42/m Dcalc 1.37 g.cm-3 Dcalc 1.34 g.cm-3 a 10.9 Å a 14.9 Å b 21.3 Å b 14.9 Å c 24.6 Å c 26.2 Å α 90° α 90° Β 93.5° Β 90° γ 90° γ 90° 150 The parameters for the two isomer components from X-ray diffraction analysis have been shown in Table 6-3 It is evident from the analysis that 4 has a less symmetrical monoclinic crystal system, whereas 5 has a tetragonal crystal system. 4 has a volume (5742.3 Å3) lower than that of 5 (5852.3 Å3), but the density of 5 (1.34 g.cm3) was reported lower than that of 4 (1.37 g.cm3). This anomalous behavior can be attributed to the fact that 4 has a more distorted cage structure, thus effectively (A (B (C (D S Si S Si i3 i1 Si S S S S Si S i9 i8 i4 i2 i1 Si Si S S Si 10 i7 i5 S S Si Si i6 i2 Figure 6-8 : (A),(B) Crystal structure for isomers of tetramethyl capped Ph8T8 (C),(D) Analogous chemdraw structure for isomers of tetramethyl capped Ph8T8 helping it pack better in a crystal lattice than 5. From the analysis of the intramolecular configuration of the crystal structure of the isomers, the distances between various Si atoms (D-Si, T-Si) were extracted. The isomers have the same chemical formula yet different packing. For 4, the longest distance is between T-Si and D-Si atoms (Si(T) 9-Si(D) 2 - 7.69 Å). Since the cage is asymmetrically skewed, the distance between the second pair of T-Si and D-Si atoms (Si(T) 10 -Si(D) 1 - 7.69 Å) is slightly smaller. Similar findings can be seen in the case of two different pairs of T-Si - T-Si atoms. (Si(T) 9 - Si(T)10 – 3.06 Å; Si(T) 3 - Si(T) 6 – 5.69 Å). The distance between the pair of D-Si atoms (Si(D) 1-Si(D) 2) is almost three times smaller than that of the corresponding isomer. The findings in Figure 6-8 also suggest that the phenyl groups bonded to T-Si twist asymmetrically to accommodate the D-Si atoms affecting the overall crystallographic packing density. 151 For 5, three significant bond distances have been identified. The longest distance can be found between the two D-Si atoms (8.54 Å) on either side of the cage. The other notable distances between two T-Si atoms (4.55 Å) and D-Si – T-Si atoms (6.83 Å) have also been noted. Interestingly, the cage displays axial symmetry, and the bond distances remain the same across the similar atoms in the cage, as seen in Figure 6-8. 6.5 Thermal and Rheological Property of isomers: TGA, DSC, and Viscosity Detailed thermal studies have been performed to study the impact of the difference in crystal packing and the consequence of variation in cage structure on the thermal properties of the isomers. These thermal studies provide insights into the solid-liquid transition temperatures, thermal stability, and the phase behavior of these constitutional isomers. TGA analysis was performed on (A) (B) Figure 6-9 : TGA analysis for isomers 4 and 5. The solid red line indicates compound 4 whereas the dotted blue line indicates compound 5. (A) Weight loss vs temperature curves for the two isomers. (B) Derivatized weight loss curves for the two isomers two isomers to verify the vaporization behavior, as shown in Figure 6-9. The thermograms show that the onset of weight loss is almost identical. To further analyze the thermograms, derivatized weight loss versus temperature was plotted. The slope of the derivatized peak indicates the compounds’ evaporation rate. 152 The rate of evaporation for 4 is slower than the rate of evaporation for 5. This rate is indicated by the sharp slope of the derivative weight peak for 5. 4 indicated a secondary peak around 550 °C, whereas no secondary peak was observed for 5. This secondary indicates a more complex weight loss mechanism for 4 than 5. The final residual weight loss for 5 was higher than 4. 4 exhibited complete evaporation without residue in the TGA pan, whereas 5 left behind black solid mass residue (~ 10 wt. %). Although the number of Si atoms is the same for both isomers, there is a difference in the types of Si bonds. 4 exhibits a peculiar D-Si to D-Si bonding which is absent in 5. Also, the number of D-Si to T-Si bonds in 4 is half the number in 5. This difference in bonding can be a possible explanation for the complex weight loss mechanism exhibited by 4. 210.1 (A 277.57 °C ) (B 218.22 (C °C ) ) 272.57 °C Figure 6-10 : DSC analysis for isomers 4 and 5.(A) DSC heating and cooling curve for compound 5. (B) DSC heating and cooling curve for compound 4 (C) Comparative heating curves for compounds 4 and 5 The DSC analysis performed on the two isomers revealed a significant difference in their melting points, as seen in Table 6-4. Despite having the same number of bonds and atoms, a difference of 60 °C in the melting points of the compounds deserves to be investigated in further detail. Our group has demonstrated various examples of symmetrically capped DDSQPh8T8(OH)4 and the effect of various alkyl/cyclic/aromatic groups on the thermal properties of the compounds.13 We calculated the thermodynamic properties from the DSC thermogram, as seen in Table 6-4. The DSC thermograms have been shown in SI. In the case of 4, ΔHm and ΔSm obtained from DSC are 153 29.8 kJ/mol and 60.4 J/mol K, respectively. However, in the case of 5, ΔHm and ΔSm values obtained are 55.5 kJ/mol and 101 J/mol K, respectively. A change in entropy of melting (ΔSm) is directly related to the ability to disrupt the intermolecular packing of the compounds. It has been found that the more significant the entropy change at melting, the more compact the crystal packing for a given molecule. Considering this ΔSm value, we can conclude that 5 is more ordered and stable. Table 6-4 : Thermal Parameters for isomers 1 and 2 based on DSC analysis 5 4 1st heating cycle Sharp melting peak (276 °C) Broad melting peak (220 °C) 1st cooling cycle Rapid recrystallization at 225 No recrystallization peak was °C observed during cooling 2nd heating cycle Sharp melting peak like the Cold recrystallization, as well first heating cycle as a melting peak, was observed ΔHm (kJ/mol) 55.5 29.8 ΔSm* (J/ (mol K)) 101 60.4 The cooling cycles also showed a significant difference in the recrystallization kinetics of the two isomers. A rapid recrystallization peak with undercooling was observed for 5. The enthalpy of recrystallization observed from the DSC thermogram was 56.4 kJ/mol. However, interestingly, 4 did not exhibit any recrystallization peak even at low cooling rates (2 °C/min). A second heating cycle was performed on the isomers to verify the compounds’ thermal stability during the DSC runs. 5 exhibited a melting peak in the same temperature range as was obtained in the first heating cycle. 4 exhibited an interesting thermogram in that a recrystallization peak was observed around 140 °C, and a melting peak was observed at the same temperature range as obtained in the first heating cycle. 154 6.6 Rheological data Rheological data was calculated for compound 4. The effect of temperature on the viscosity of compound 4 was studied. The temperature range varied from 220 °C to 240 °C, and the corresponding viscosity of the compound was measured. It was found that the viscosity of the compound hard varied between 1 Pa.s to 4 Pa.s, as seen in Figure 6-11 below. The effect of shear rate versus viscosity was studied at constant temperature. The temperature was set at 230 °C, which was above the solid-to-liquid transition temperature of the compound. It was found that as the shear rate changed from 0.001 s-1 to 1 s-1, the viscosity of the compounds changed by two orders of magnitude, i.e., compound 4 exhibits shear thinning behavior. This behavior is unusual for isolated pure compounds. This behavior is usually seen in non-Newtonian materials. This behavior in compound 4 can be attributed to the molecule's shape. Due to the structure's non- symmetrical nature, the molecules' orientation significantly affects the compound's viscosity. 4 3 h (Pa.s) 2 Me4-DDSQ assymetric g× = 0.1 s-1 Temp. range = 220 C to 240 C 1 1.94 1.96 1.98 2.00 2.02 2.04 1000/T Figure 6-11 : Effect of temperature on viscosity of compound 4 155 102 Me4-DDSQ assymetric Temp. = 230 C h (Pa.s) 101 100 10-3 10-2 . 10-1 100 g (s )-1 Figure 6-12 : Effect of shear rate on viscosity with constant temperature at 230 °C To summarize, a novel strategy was developed to synthesize structural isomers to examine the effect of inorganic core on the thermal and crystal packing of cage-like silsesquioxane compounds. The synthesized isomers have the same number of atoms, the same types, and the number of bonds. 4 exhibits a 20 % faster weight loss rate and has a higher residual weight at 900 °C. The melting temperature of 5 (272 °C) was almost 60 °C higher than 4, and the heat of fusion for 4 was half that of 5. The entropy of melting for 5 was 40 % higher than that of 4. This value indicates a more compact and symmetrical packing for 5 over 4. Single crystal X-ray analysis indicates the symmetrical tetragonal crystal packing for 5, whereas 4 has more asymmetrical monoclinic crystal packing. It is interesting to note that although 5 has a lower asymmetry than 4, it has a higher density than 4. Although this work demonstrated that the inorganic core could affect properties, additional work is still needed to fully understand the effects of Si(T) vs. Si(D) atoms on the silsesquioxane cages. 156 6.7 Experimental Details 6.7.1 General Information All manipulations were done under a nitrogen atmosphere using standard Schlenk techniques except otherwise stated. All commercially available chemicals were used as received unless otherwise indicated. Allyl amine (C3H7N), dimethyl dichlorosilane (C2H6 Cl2Si), 1,3-dichloro- 1,1,3,3-tetramethyldisiloxane (C4H12Cl2OSi2), triethylamine (C6H15N) deuterated chloroform with 1 vol % tetramethylsilane (CDCl3-1%TMS), were purchased from Sigma-Aldrich. 1,3,5,7,9,11,14,17-octaphenyl-2,4,6,8,10,12,13,15,16,18-decaoxa-1,3,5,7,9,11,14,17- octasilatricyclo[7.3.3.33,7]octadecane-5,11,14,17-tetraol (DDPh8T8(OH)4) was obtained from Hybrid Plastics. Tetrahydrofuran (THF), dichloromethane (DCM), and methanol (MeOH) were purchased from Sigma-Aldrich. THF was distilled over benzophenone and sodium metal at 70 °C under nitrogen. Toluene was distilled over calcium hydride at a temperature of 120 °C. The other solvents were used as purchased without further purification, and the glassware was oven dried. All 1H, 13C, and 29Si NMR were acquired on an Agilent DirectDrive2 500 MHz NMR spectrometer equipped with a OneProbe operating at 500 MHz for 1H NMR, 126 MHz for 13C NMR, and 99 MHz for 29Si NMR using CDCl3 and recorded at 25 ºC. 1H-NMR spectra were recorded with 8 scans, a relaxation delay of 1s, and a pulse angle of 45° and referenced to the residual protonated solvent in CDCl3 (7.24 ppm). 13C-NMR spectra were collected with 254 scans, a relaxation delay 29 of 0.1 s, and a pulse angle of 45°. Si NMR spectra were recorded with either 256 scans, a relaxation delay of 25 s, and a pulse angle 45°. For crystallographic analysis, 0.5 g of each compound was dissolved in DCM and slowly evaporated for three days to get crystals. The crystal was kept at a temperature of 173 K during 157 data collection. The crystals obtained were mounted on a nylon loop with paratone oil and analyzed on a Bruker APEX-II CCD diffractometer. For differential scanning calorimetry (DSC) experiments, TA Instruments Q2000 equipped with a mechanical cooler was used. The temperature was equilibrated to 50 °C for 2 min, a constant heating rate of 10 K/min up to a determined temperature above melting. A second heating ramp with the same rate as the first was used to verify the reproducibility and possible thermal degradation that may occur during the first heating cycle. Cooling traces were obtained from the above complete melting at a constant cooling rate of 5 K/min up to 50 °C. No thermal degradation was observed. Thermogravimetric analysis was run in a TGA Q50 apparatus from TA instruments. A platinum pan was loaded with a sample weight of 8 mg ± 0.2 mg. The samples were equilibrated at 323.15 K and heated to 1073.15 K at a rate of 20 K/min. The experiment used a dry nitrogen stream at a 100 ml/min flow rate. Rheological measurements were performed on an Anton Paar MCR302 Rheometer with a CTD 600 oven. The temperature control accuracy was ± 0.1 K. Small amplitude oscillatory shear (SAOS) tests were performed on a pair of 4 mm diameter parallel plates at a temperature range from 373 K to 453 K. 158 6.7.2 Synthesis of 1,3,5,7,9,11,13,15-octaphenyl- 2,4,6,8,10,12,14,16,17,18,19-undecaoxa-1,3,5,7,9,11,13,15- octasilatetracyclo[9.5.1.13,9.15,15]nonadecane-7,13-diol Scheme 6-4 : Synthesis of SOPh8T8 (OH)2 To a 500 mL round bottom flask were added DDPh8T8(OH)4 (8 g, 0.0075 mol, 1 equiv), allylamine (0.1 mL, 0.0013 mol, 0.18 equiv), and a stir bar under N2 atmosphere. Freshly distilled DCM (200 mL) was then added. A clear solution was formed. The reaction mixture was stirred for 60 minutes, and a white slurry was observed. The solvent was evaporated, and THF (~ 200 mL) was added to recreate a slurry. This slurry was filtered through a medium frit funnel to obtain the crude product mixture in the filtrate. The filtrate was concentrated to obtain white powder. CHCl3 (2x200 mL) was added to recreate a slurry. This slurry was filtered through a medium frit funnel to obtain the product in the filtrate. The solvent was evaporated, and the product was obtained as a white powder (2.64 g, 33% yield). 1 H NMR (500 MHz, Chloroform-d) δ 7.74 – 7.70 (m, 4H), 7.60 (td, J = 8.3, 1.4 Hz, 12H), 7.46 – 7.33 (m, 14H), 7.28 (d, J = 7.6 Hz, 6H), 7.27 – 7.20 (m, 4H), 3.75 – 3.71 (m, 1H), 1.85 – 1.81 (m, 1H). 13C{1H} NMR (126 MHz, Chloroform-d) δ 127.76, 127.88, 130.20, 130.36, 130.64, 130.79, 130.87, 134.15, 134.18. 29Si{1H} NMR (99 MHz, Chloroform-d) δ -78.57, -78.32, -77.36, -69.27. 159 6.7.3 Synthesis of 17,17-dimethyl-1,3,5,7,9,11,13,15-octaphenyl- 2,4,6,8,10,12,14,16,18,19,20,21,22-tridecaoxa- 1,3,5,7,9,11,13,15,17- nonasilapentacyclo[9.7.1.13,9.15,15.17,13]docosane Scheme 6-5 : Synthesis of a capped SOPh8T8 (Me)2 To a 100 mL round bottom flask were added SOPh8T8(OH)2 (1 g, 0.95 mmol, 1 equiv), dimethyl dichlorosilane (0.13 mL, 1 mmol, 1.1 equiv), and a stir bar under N2 atmosphere. Freshly distilled THF (~30 mL) was then added. A clear solution was obtained. Et3N (0.26 mL, 0.0019 mol, 2.0 equiv) was added dropwise to this solution. The reaction mixture was stirred for 7 hr, after which the solvent was evaporated, and then fresh THF (~ 60 mL) was added to create a slurry. This slurry was filtered through a medium frit funnel to obtain the crude product in the filtrate. The filtrate was concentrated to obtain white powder. Methanol (~ 60 mL) was added to the reaction flask, stirring the slurry for 2 hours. The slurry was again filtered through a medium frit funnel to obtain the product as a white powder (0.89 g, 85% yield). 1H NMR (500 MHz, Chloroform-d) δ 7.74 – 7.69 (m, 5H), 7.60 (d, J = 6.9 Hz, 14H), 7.41 (d, J = 15.4 Hz, 4H), 7.37 – 7.23 (m, 20H), 0.31 (s, 6H). 13C{1H} NMR (126 MHz, Chloroform-d)δ 0.55, 127.75, 127.81, 127.84, 130.36, 130.55, 130.61, 130.73, 133.89, 134.11, 134.19. 29Si{1H} NMR (99 MHz, Chloroform-d) δ -79.31, -79.00, -77.48, -16.99. 160 6.7.4 Synthesis of 17,17-diethyl-1,3,5,7,9,11,13,15-octaphenyl- 2,4,6,8,10,12,14,16,18,19,20,21,22-tridecaoxa- 1,3,5,7,9,11,13,15,17- nonasilapentacyclo[9.7.1.13,9.15,15.17,13]docosane Scheme 6-6 : Synthesis of a capped SOPh8T8 (Et)2 To a 100 mL round bottom flask were added SOPh8T8(OH)2 (1 g, 0.95 mmol, 1 equiv), diethyl dichlorosilane (0.13 mL, 1 mmol, 1.1 equiv), and a stir bar under N2 atmosphere. Freshly distilled THF (~30 mL) was then added. A clear solution was obtained. Et3N (0.26 mL, 0.0019 mol, 2.0 equiv) was added dropwise to this solution. The reaction mixture was stirred for 7 hr, after which the solvent was evaporated, and then fresh THF (~ 60 mL) was added to create a slurry. This slurry was filtered through a medium frit funnel to obtain the crude product in the filtrate. The filtrate was concentrated to obtain white powder. Methanol (~ 60 mL) was added to the reaction flask, stirring the slurry for 2 hours. The slurry was again filtered through a medium frit funnel to obtain the product as a white powder (0.85 g, 80% yield). 1H NMR (500 MHz, Chloroform-d) δ 7.73 (d, J = 7.2 Hz, 5H), 7.60 (d, J = 7.2 Hz, 11H), 7.47 – 7.13 (m, 28H), 1.01 (q, J = 9.7, 8.7 Hz, 6H), 0.72 (q, J = 7.7 Hz, 4H). 13C{1H} NMR (126 MHz, Chloroform-d) δ 6.32, 6.92, 127.75, 127.80, 127.85, 130.32, 130.53, 130.67, 130.72, 133.88, 134.08, 134.19. 29Si{1H} NMR (99 MHz, Chloroform-d) δ -79.50, -78.98, -77.42, -17.22. 161 6.7.5 Synthesis of 17,17-diisopropyl-1,3,5,7,9,11,13,15-octaphenyl- 2,4,6,8,10,12,14,16,18,19,20,21,22-tridecaoxa- 1,3,5,7,9,11,13,15,17- nonasilapentacyclo[9.7.1.13,9.15,15.17,13]docosane Scheme 6-7 : Synthesis of a capped SOPh8T8 (iPr)2 To a 100 mL round bottom flask were added SOPh8T8(OH)2 (1 g, 0.95 mmol, 1 equiv), diisopropyl dichlorosilane (0.19 mL, 1 mmol, 1.1 equiv), and a stir bar under N2 atmosphere. Freshly distilled THF (~30 mL) was then added. A clear solution was obtained. Et3N (0.26 mL, 0.0019 mol, 2.0 equiv) was added dropwise to this solution. The reaction mixture was stirred for 1 hr, after which the solvent was evaporated, and then fresh THF (~ 60 mL) was added to create a slurry. This slurry was filtered through a medium frit funnel to obtain the crude product in the filtrate. The filtrate was concentrated to obtain white powder. Methanol (~ 60 mL) was added to the reaction flask, stirring the slurry for 2 hours. The slurry was again filtered through a medium frit funnel to obtain the product as a white powder (0.81 g, 74.3% yield). 1H NMR (500 MHz, Chloroform-d) δ 7.78 – 7.70 (m, 4H), 7.63 – 7.56 (m, 9H), 7.46 – 7.32 (m, 16H), 7.27 (m, 13H), 1.05 (m, 14H). 13C{1H} NMR (126 MHz, Chloroform-d) δ 12.89, 16.77, 127.79, 127.82, 127.89, 130.32, 130.43, 130.55, 130.72, 130.76, 132.13, 133.93, 134.10, 134.23. 29Si{1H} NMR (99 MHz, Chloroform-d) δ -80.07, -79.10, -77.48, -19.94. 162 6.7.6 Synthesis of 17,17-dibutyl-1,3,5,7,9,11,13,15-octaphenyl- 2,4,6,8,10,12,14,16,18,19,20,21,22-tridecaoxa- 1,3,5,7,9,11,13,15,17- nonasilapentacyclo[9.7.1.13,9.15,15.17,13]docosane Scheme 6-8 : Synthesis of a capped SOPh8T8 (nBu)2 To a 100 mL round bottom flask were added SOPh8T8(OH)2 (1 g, 0.95 mmol, 1 equiv), dibutyl dichlorosilane (0.22 mL, 1 mmol, 1.1 equiv), and a stir bar under N2 atmosphere. Freshly distilled THF (~30 mL) was then added. A clear solution was obtained. Et3N (0.26 mL, 0.0019 mol, 2.0 equiv) was added dropwise to this solution. The reaction mixture was stirred for 2 hr, after which the solvent was evaporated, and then fresh THF (~ 60 mL) was added to create a slurry. This slurry was filtered through a medium frit funnel to obtain the crude product in the filtrate. The filtrate was concentrated to obtain white powder. Methanol (~ 60 mL) was added to the reaction flask, stirring the slurry for 2 hours. The slurry was again filtered through a medium frit funnel to obtain the product as a white powder (0.68 g, 61% yield). 1H NMR (500 MHz, Chloroform-d) δ 7.77 – 7.70 (m, 4H), 7.63 – 7.57 (m, 9H), 7.46 – 7.32 (m, 12H), 7.32 – 7.19 (m, 12H), 1.47 – 1.37 (m, 4H), 1.29 (dt, J = 7.7, 7.3 Hz, 5H), 0.76 (s, 1H), 0.75 – 0.68 (m, 8H). 13C{1H} NMR (126 MHz, Chloroform-d) δ 15.41, 24.86, 26.09, 127.71, 127.77, 127.84, 130.28, 130.39, 130.52, 130.66, 130.71, 132.14, 133.89, 134.10, 134.19. 29Si{1H} NMR (99 MHz, Chloroform-d) δ -79.66, -78.98, -77.44, -18.61. 163 6.7.7 Synthesis of 17,17-dicyclopentyl-1,3,5,7,9,11,13,15-octaphenyl- 2,4,6,8,10,12,14,16,18,19,20,21,22-tridecaoxa- 1,3,5,7,9,11,13,15,17- nonasilapentacyclo[9.7.1.13,9.15,15.17,13]docosane Scheme 6-9 : Synthesis of a capped SOPh8T8 (cyP)2 To a 100 mL round bottom flask were added SOPh8T8(OH)2 (1 g, 0.95 mmol, 1 equiv), dicyclopentyl dichlorosilane (0.13 mL, 1 mmol, 1.1 equiv), and a stir bar under N2 atmosphere. Freshly distilled THF (~30 mL) was then added. A clear solution was obtained. Et3N (0.26 mL, 0.0019 mol, 2.0 equiv) was added dropwise to this solution. The reaction mixture was stirred for 7 hr, after which the solvent was evaporated, and then fresh THF (~ 60 mL) was added to create a slurry. This slurry was filtered through a medium frit funnel to obtain the crude product in the filtrate. The filtrate was concentrated to obtain white powder. Methanol (~ 60 mL) was added to the reaction flask, stirring the slurry for 2 hours. The slurry was again filtered through a medium frit funnel to obtain the product as a white powder (0.66 g, 58% yield). 1H NMR (500 MHz, Chloroform-d) δ 7.72 (d, J = 19.2 Hz, 5H), 7.66 – 7.51 (m, 9H), 7.51 – 7.31 (m, 14H), 7.31 – 6.85 (m, 14H), 1.76 (s, 4H), 1.48 (s, 11H), 1.00 (s, 2H). 13C{1H} NMR (126 MHz, Chloroform-d) δ 24.92, 27.02, 27.13, 127.72, 127.74, 127.85, 130.22, 130.41, 130.49, 130.71, 132.20, 133.84, 134.05, 134.19. 29Si{1H} NMR (99 MHz, Chloroform-d) δ -80.02, - 79.02, -77.43, -20.62. 164 6.7.8 Synthesis of 17,17-dicyclohexyl-1,3,5,7,9,11,13,15-octaphenyl- 2,4,6,8,10,12,14,16,18,19,20,21,22-tridecaoxa- 1,3,5,7,9,11,13,15,17- nonasilapentacyclo[9.7.1.13,9.15,15.17,13]docosane Scheme 6-10 : Synthesis of a capped SOPh8T8 (cyhex)2 To a 100 mL round bottom flask were added SOPh8T8(OH)2 (1 g, 0.95 mmol, 1 equiv), dicyclohexyl dichlorosilane (0.25 mL, 1 mmol, 1.1 equiv), and a stir bar under N2 atmosphere. Freshly distilled THF (~30 mL) was then added. A clear solution was obtained. Et3N (0.26 mL, 0.0019 mol, 2.0 equiv) was added dropwise to this solution. The reaction mixture was stirred for 7 hr, after which the solvent was evaporated, and then fresh THF (~ 60 mL) was added to create a slurry. This slurry was filtered through a medium frit funnel to obtain the crude product in the filtrate. The filtrate was concentrated to obtain white powder. Methanol (~ 60 mL) was added to the reaction flask, stirring the slurry for 2 hours. The slurry was again filtered through a medium frit funnel to obtain the product as a white powder (0.68 g, 59% yield). 1 H NMR (500 MHz, Chloroform-d) δ 7.78 – 7.69 (m, 4H), 7.59 (d, J = 7.7 Hz, 8H), 7.48 – 7.32 (m, 13H), 7.27 (q, J = 7.9 Hz, 14H), 1.79 (d, J = 7.8 Hz, 4H), 1.64 (d, J = 7.6 Hz, 6H), 1.30 (q, J = 12.0 Hz, 4H), 1.15 (d, J = 7.1 Hz, 6H), 0.85 (tt, J = 12.3, 3.0 Hz, 2H). 13C{1H} NMR (126 MHz, Chloroform-d) δ 24.80, 26.51, 26.82, 27.64, 127.72, 127.75, 127.85, 130.23, 130.50, 130.71, 132.18, 133.94, 134.07, 134.19. 29Si{1H} NMR (99 MHz, Chloroform-d) δ -80.08, -78.96, -77.43, -24.19. 165 6.7.9 Synthesis of 17,17-diphenyl-1,3,5,7,9,11,13,15-octaphenyl- 2,4,6,8,10,12,14,16,18,19,20,21,22-tridecaoxa- 1,3,5,7,9,11,13,15,17- nonasilapentacyclo[9.7.1.13,9.15,15.17,13]docosane Scheme 6-11 : Synthesis of a capped SOPh8T8Ph2 To a 100 mL round bottom flask were added SOPh8T8(OH)2 (1 g, 0.95 mmol, 1 equiv), diphenyl dichlorosilane (0.22 mL, 1 mmol, 1.1 equiv), and a stir bar under N2 atmosphere. Freshly distilled THF (~30 mL) was then added. A clear solution was obtained. Et3N (0.26 mL, 0.0019 mol, 2.0 equiv) was added dropwise to this solution. The reaction mixture was stirred for 7 hr, after which the solvent was evaporated, and then fresh THF (~ 60 mL) was added to create a slurry. This slurry was filtered through a medium frit funnel to obtain the crude product in the filtrate. The filtrate was concentrated to obtain white powder. Methanol (~ 60 mL) was added to the reaction flask, stirring the slurry for 2 hours. The slurry was again filtered through a medium frit funnel to obtain the product as a white powder (0.75 g, 65% yield). 1 H NMR (500 MHz, Chloroform-d) δ 7.95 – 7.63 (m, 7H), 7.57 (d, J = 7.3 Hz, 4H), 7.47 (d, J = 7.3 Hz, 6H), 7.39 (m, 13H), 7.31 – 6.69 (m, 20H). 13C{1H} NMR (126 MHz, Chloroform-d) δ 127.63, 127.80, 127.82, 127.85, 130.08, 130.28, 130.31, 130.45, 130.52, 130.75, 131.46, 134.02, 134.13, 134.18, 134.24. 29Si{1H} NMR (99 MHz, Chloroform-d) δ -78.81, -78.71, -77.35, - 45.95. 166 6.7.10 Synthesis of 9,9,19,19-tetramethyl-1,3,5,7,11,13,15,17- octaphenyl 2,4,6,8,10,12,14,16,18,20,21,22,23,24-tetradecaoxa- 1,3,5,7,9,11,13,15,17,19-decasilapentacyclo[11.7.1.13,11.15,17.17,15] tetracosane Scheme 6-12 : Synthesis of symmetrically capped DDSQ Me4 To a 100 mL round bottom flask were added DDPh8T8(OH)4 (2 g, 0.0018 mol, 1 equiv), dichloro dimethyl silane (0.50 mL, 0.0041 mol, 2.2 equiv), and a stir bar under N2 atmosphere. Freshly distilled DCM (~30 mL) was then added. A white-colored solution was formed. Et3N (1.05 mL, 0.0074 mol, 4 equiv) was added dropwise to this solution. Upon the addition of triethylamine, the solution turned colorless. The reaction mixture was stirred for 30 min, after which the solvent was evaporated, and THF (~ 60 mL) was added to create a slurry. This slurry was filtered through a medium frit funnel to obtain the crude product in the filtrate. The filtrate was concentrated to obtain white powder. This powder was washed with methanol (~60 mL) for 30 min. The slurry was again filtered through a medium frit funnel to obtain the product as a white powder (2.12 g, 96% yield). 1 H NMR (500 MHz, Chloroform-d) δ 7.54 (d, J = 6.9 Hz, 8H), 7.40 (dd, J = 23.5, 7.2 Hz, 13H), 13 7.33 (t, J = 7.5 Hz, 5H), 7.24 (d, J = 7.5 Hz, 6H), 7.18 (t, J = 7.5 Hz, 9H), 0.30 (s, 12H). C{1H} NMR (126 MHz, Chloroform-d) δ 134.04, 133.92, 132.12, 131.07, 127.77, 127.62, 0.53. 29Si{1H} NMR (99 MHz, Chloroform-d) δ -16.55, -78.63, -79.61. 167 6.7.11 Synthesis of 17,17,19,19-tetramethyl-1,3,5,7,9,11,13,15- octaphenyl-2,4,6,8,10,12,14,16,18,20,21,22,23,24-tetradecaoxa- 1,3,5,7,9,11,13,15,17,19- decasilapentacyclo[9.9.1.13,9.15,15.17,13]tetracosane Scheme 6-13 : Synthesis of SOPh8T8Me4 To a 100 mL round bottom flask were added SOPh8T8(OH)2 (2 g, 0.0019 mol, 1 equiv), 1,3- dichloro-1,1,3,3-tetramethyldisiloxane (0.41 mL, 0.002 mol, 1.1 equiv), and a stir bar under N2 atmosphere. Freshly distilled THF (~30 mL) was then added. A clear solution was obtained. Et3N (1.05 mL, 0.0074 mol, 2.0 equiv) was added dropwise to this solution. The reaction mixture was stirred for 7 hr, after which the solvent was evaporated, and then fresh THF (~ 60 mL) was added to create a slurry. This slurry was filtered through a medium frit funnel to obtain the crude product in the filtrate. The filtrate was concentrated to obtain white powder. Methanol (~ 60 mL) was added to the reaction flask, stirring the slurry for 2 hours. The slurry was again filtered through a medium frit funnel to obtain the product as a white powder (1.75 g, 78% yield). 1 H NMR (500 MHz, Chloroform-d) δ 7.71 (d, J = 7.0 Hz, 4H), 7.60 (d, J = 7.1 Hz, 4H), 7.49 (d, J = 7.2 Hz, 8H), 7.46 – 7.41 (m, 3H), 7.35 (t, J = 7.8 Hz, 11H), 7.27 (s, 2H), 7.22 (q, J = 7.5 Hz, 10H), 0.23 (s, 12H). 13 C{1H} NMR (126 MHz, Chloroform-d) δ 0.75, 127.65, 127.78, 127.89, 130.20, 130.40, 130.71, 130.73, 133.83, 134.04, 134.12. 29Si{1H} NMR (99 MHz, Chloroform-d) δ -79.50, -78.88, -77.13, -18.64. 168 REFERENCES (1) Wang, L.; Ishida, Y.; Maeda, R.; Tokita, M.; Hayakawa, T. Alkylated Cage Silsesquioxanes: A Comprehensive Study of Thermal Properties and Self-Assembled Structure. RSC Adv. 2014, 4 (66), 34981–34986. https://doi.org/10.1039/C4RA04987J. (2) Blanco, I.; Abate, L.; Bottino, F. A. 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J. 2019, 25 (7), 1683–1686. https://doi.org/10.1002/chem.201805200. 171 APPENDIX Figure 6-13 : 1H-NMR (CDCl3, 500 MHz) 172 Figure 6-14 : 13C-NMR (CDCl3, 126 MHz)) 173 Figure 6-15 : 29Si{1H}-NMR (CDCl3, 99 MHz) 174 Figure 6-16 : 1H-NMR (CDCl3, 500 MHz) 175 Figure 6-17 : 13C{1H}-NMR (CDCl3, 126 MHz) 176 Figure 6-18 : 29Si{1H}-NMR (CDCl3, 99 MHz) 177 Figure 6-19 : 1H-NMR (CDCl3, 500 MHz) 178 Figure 6-20 : 13C-NMR (CDCl3, 126 MHz) 179 Figure 6-21 : 29Si{1H}-NMR (CDCl3, 99 MHz) 180 Figure 6-22 : 1H-NMR (CDCl3, 500 MHz) 181 Figure 6-23 : 13C-NMR (CDCl3, 126 MHz) 182 Figure 6-24 : 29Si{1H}-NMR (CDCl3, 99 MHz) 183 Figure 6-25 : 1H-NMR (CDCl3, 500 MHz) 184 Figure 6-26 : 13C-NMR (CDCl3, 126 MHz) 185 Figure 6-27 : 29Si{1H}-NMR (CDCl3, 99 MHz) 186 Figure 6-28 : 1H-NMR (CDCl3, 500 MHz) 187 Figure 6-29 : 13C-NMR (CDCl3, 126 MHz) 188 Figure 6-30 : 29Si{1H}-NMR (CDCl3, 99 MHz) 189 Figure 6-31 : 1H-NMR (CDCl3, 500 MHz) 190 Figure 6-32 : 13C-NMR (CDCl3, 126 MHz) 191 Figure 6-33 : 29Si{1H}-NMR (CDCl3, 99 MHz) 192 Figure 6-34 : 1H-NMR (CDCl3, 500 MHz) 193 Figure 6-35 : 13C-NMR (CDCl3, 126 MHz) 194 Figure 6-36 : 29Si{1H}-NMR (CDCl3, 99 MHz) 195 Figure 6-37 : 1H-NMR (CDCl3, 500 MHz) of 4 196 Figure 6-38 : 13C{1H}-NMR (CDCl3, 126 MHz) 197 Figure 6-39 : 29Si{1H}-NMR (CDCl3, 99 MHz) 198 Figure 6-40 : 1H-NMR (CDCl3, 500 MHz) of 5 199 Figure 6-41 : 13C{1H}-NMR (CDCl3, 126 MHz) 200 Figure 6-42 : 29Si{1H}-NMR (CDCl3, 99 MHz) 201 Crystal structure data Table 6-5 : Crystal structure data for compound 4 Compound AL722A Formula C52H52O14Si10 CCDC 2189474 Dcalc./ g cm-3 1.367 m/mm-1 2.693 Formula Weight 1181.83 Color colorless Shape block-shaped Size/mm3 0.21×0.12×0.08 T/K 100.00(10) Crystal System monoclinic Space Group P21/n a/Å 10.93887(8) b/Å 21.34238(15) c/Å 24.64084(19) a/° 90 b/° 93.4495(7) g/° 90 V/Å3 5742.26(7) Z 4 Z' 1 Wavelength/Å 1.54184 Radiation type Cu Ka Qmin/° 2.741 Qmax/° 80.432 Measured Refl's. 98144 Indep't Refl's 12415 Refl's I≥2 s(I) 10850 Rint 0.0382 Parameters 899 Restraints 0 Largest Peak 0.744 Deepest Hole -1.010 GooF 1.032 wR2 (all data) 0.1260 wR2 0.1192 R1 (all data) 0.0575 R1 0.0499 202 Figure 6-43 : Crystal structure data for compound 4 203 Table 6-6 : Bond Angles for Compound 4 Atom Atom Atom Angle/° O1 Si1 O2 107.76(12) O1 Si1 C1 109.08(13) O1 Si1 C2 109.12(17) O2 Si1 C1 108.83(15) O2 Si1 C2 109.21(14) C1 Si1 C2 112.7(2) O1 Si2 O3 106.99(10) O1 Si2 C3 109.20(13) O1 Si2 C4 110.06(14) O3 Si2 C3 108.01(12) O3 Si2 C4 109.71(12) C4 Si2 C3 112.68(15) O2 Si3 O4 109.61(12) O2 Si3 O10 107.80(12) O2 Si3 C10A 109.21(16) O2 Si3 C10B 109.06(17) O4 Si3 O10 110.18(11) O4 Si3 C10A 102.76(14) O4 Si3 C10B 114.34(15) O10 Si3 C10A 117.09(17) O10 Si3 C10B 105.60(16) O4 Si4 O5 107.22(10) O4 Si4 O11 110.93(12) O4 Si4 C20 109.67(11) O5 Si4 O11 108.58(10) O5 Si4 C20 111.66(10) O11 Si4 C20 108.77(11) O5 Si5 O12 108.28(9) O5 Si5 C30A 116.81(13) O5 Si5 C30B 106.71(14) O6 Si5 O5 107.69(9) O6 Si5 O12 110.29(10) O6 Si5 C30A 102.82(12) O6 Si5 C30B 117.76(14) O12 Si5 C30A 110.73(13) O12 Si5 C30B 105.75(12) O3 Si6 O6 110.14(10) O3 Si6 O7 109.12(10) O3 Si6 C40A 109.61(15) O3 Si6 C40B 109.19(14) O6 Si6 C40A 118.43(15) O6 Si6 C40B 100.07(14) O7 Si6 O6 109.46(10) 204 Table 6-6 (cont’d) O7 Si6 C40A 99.36(17) O7 Si6 C40B 118.44(14) O7 Si7 O8 107.18(15) O7 Si7 O18 108.84(9) O7 Si7 C50A 116.1(2) O7 Si7 C50B 109.4(2) O8 Si7 C50A 108.1(2) O8 Si7 C50B 108.5(2) O18 Si7 O8 111.40(13) O18 Si7 C50A 105.3(2) O18 Si7 C50B 111.4(2) O8 Si8 O10 108.74(15) O8 Si8 C60A 106.58(16) O8 Si8 C60B 110.51(16) O9 Si8 O8 109.48(13) O9 Si8 O10 109.50(10) O9 Si8 C60A 119.95(16) O9 Si8 C60B 99.30(15) O10 Si8 C60A 101.99(16) O10 Si8 C60B 118.76(15) O9 Si9 O11 108.68(12) O9 Si9 O14 109.52(10) O9 Si9 C70A 99.55(14) O9 Si9 C70B 117.09(14) O11 Si9 C70A 109.26(14) O11 Si9 C70B 110.88(13) O14 Si9 O11 108.94(11) O14 Si9 C70A 120.16(15) O14 Si9 C70B 101.32(12) O12 Si10 C80A 111.1(2) O12 Si10 C80B 106.4(2) O14 Si10 O12 110.02(9) O14 Si10 C80A 107.6(2) O14 Si10 C80B 112.5(2) O18 Si10 O12 108.08(9) O18 Si10 O14 109.39(10) O18 Si10 C80A 110.6(2) O18 Si10 C80B 110.28(19) Si1 O1 Si2 152.53(14) Si3 O2 Si1 142.53(14) Si6 O3 Si2 148.41(12) Si4 O4 Si3 151.07(15) Si5 O5 Si4 150.36(11) Si5 O6 Si6 147.60(12) 205 Table 6-6 (cont’d) Si7 O7 Si6 153.01(13) Si7 O8 Si8 149.55(16) Si8 O9 Si9 157.30(15) Si8 O10 Si3 150.78(14) Si4 O11 Si9 141.73(12) Si5 O12 Si10 140.81(11) Si9 O14 Si10 141.40(13) Si7 O18 Si10 157.00(12) C11A C10A Si3 120.6(2) C11A C10A C15A 120.0 C15A C10A Si3 119.4(2) C12A C11A C10A 120.0 C11A C12A C13A 120.0 C14A C13A C12A 120.0 C13A C14A C15A 120.0 C14A C15A C10A 120.0 C11B C10B Si3 120.5(2) C11B C10B C15B 120.0 C15B C10B Si3 118.0(2) C12B C11B C10B 120.0 C11B C12B C13B 120.0 C14B C13B C12B 120.0 C13B C14B C15B 120.0 C14B C15B C10B 120.0 C21 C20 Si4 122.37(19) C21 C20 C25 118.0(2) C25 C20 Si4 119.6(2) C20 C21 C22 121.1(3) C23 C22 C21 119.4(3) C24 C23 C22 120.5(3) C23 C24 C25 119.6(3) C24 C25 C20 121.4(3) C35A C30A Si5 120.40(18) C35A C30A C31A 120.0 C31A C30A Si5 119.60(18) C30A C35A C34A 120.0 C33A C34A C35A 120.0 C32A C33A C34A 120.0 C33A C32A C31A 120.0 C32A C31A C30A 120.0 C35B C30B Si5 122.29(18) C35B C30B C31B 120.0 C31B C30B Si5 117.45(18) C30B C35B C34B 120.0 206 Table 6-6 (cont’d) C33B C34B C35B 120.0 C34B C33B C32B 120.0 C33B C32B C31B 120.0 C32B C31B C30B 120.0 C41A C40A Si6 120.2(2) C41A C40A C45A 120.0 C45A C40A Si6 119.8(2) C42A C41A C40A 120.0 C41A C42A C43A 120.0 C44A C43A C42A 120.0 C43A C44A C45A 120.0 C44A C45A C40A 120.0 C41B C40B Si6 123.3(2) C41B C40B C45B 120.0 C45B C40B Si6 116.5(2) C40B C41B C42B 120.0 C43B C42B C41B 120.0 C42B C43B C44B 120.0 C45B C44B C43B 120.0 C44B C45B C40B 120.0 C55A C50A Si7 119.7(4) C55A C50A C51A 120.0 C51A C50A Si7 120.2(4) C54A C55A C50A 120.0 C55A C54A C53A 120.0 C52A C53A C54A 120.0 C53A C52A C51A 120.0 C52A C51A C50A 120.0 C55B C50B Si7 118.2(4) C55B C50B C51B 120.0 C51B C50B Si7 121.6(4) C50B C55B C54B 120.0 C55B C54B C53B 120.0 C54B C53B C52B 120.0 C51B C52B C53B 120.0 C52B C51B C50B 120.0 C65A C60A Si8 122.4(3) C65A C60A C61A 120.0 C61A C60A Si8 117.1(3) C60A C65A C64A 120.0 C63A C64A C65A 120.0 C64A C63A C62A 120.0 C61A C62A C63A 120.0 C62A C61A C60A 120.0 207 Table 6-6 (cont’d) C61B C60B Si8 126.7(2) C61B C60B C65B 120.0 C65B C60B Si8 113.3(2) C62B C61B C60B 120.0 C61B C62B C63B 120.0 C64B C63B C62B 120.0 C65B C64B C63B 120.0 C64B C65B C60B 120.0 C75A C70A Si9 120.8(2) C75A C70A C71A 120.0 C71A C70A Si9 118.8(2) C70A C75A C74A 120.0 C73A C74A C75A 120.0 C72A C73A C74A 120.0 C73A C72A C71A 120.0 C72A C71A C70A 120.0 C75B C70B Si9 125.64(18) C75B C70B C71B 120.0 C71B C70B Si9 114.24(18) C70B C75B C74B 120.0 C73B C74B C75B 120.0 C74B C73B C72B 120.0 C73B C72B C71B 120.0 C72B C71B C70B 120.0 C81A C80A Si10 118.5(4) C81A C80A C85A 120.0 C85A C80A Si10 121.4(4) C82A C81A C80A 120.0 C83A C82A C81A 120.0 C84A C83A C82A 120.0 C83A C84A C85A 120.0 C84A C85A C80A 120.0 C81B C80B Si10 118.8(4) C81B C80B C85B 120.0 C85B C80B Si10 121.2(4) C80B C81B C82B 120.0 C83B C82B C81B 120.0 C82B C83B C84B 120.0 C85B C84B C83B 120.0 C84B C85B C80B 120.0 208 Table 6-7 : Bond lengths for compound 4 Atom Atom Length/Å Si1 O1 1.612(2) Si1 O2 1.628(2) Si1 C1 1.845(3) Si1 C2 1.852(4) Si2 O1 1.6149(19) Si2 O3 1.6310(18) Si2 C3 1.843(3) Si2 C4 1.841(3) Si3 O2 1.615(2) Si3 O4 1.6152(18) Si3 O10 1.617(2) Si3 C10A 1.894(3) Si3 C10B 1.838(3) Si4 O4 1.6072(19) Si4 O5 1.6187(16) Si4 O11 1.622(2) Si4 C20 1.841(2) Si5 O5 1.6186(16) Si5 O6 1.6065(16) Si5 O12 1.6194(16) Si5 C30A 1.872(2) Si5 C30B 1.855(2) Si6 O3 1.6049(18) Si6 O6 1.6183(17) Si6 O7 1.616(2) Si6 C40A 1.786(3) Si6 C40B 1.965(3) Si7 O7 1.602(2) Si7 O8 1.610(2) Si7 O18 1.6094(18) Si7 C50A 1.871(6) Si7 C50B 1.874(5) Si8 O8 1.612(2) Si8 O9 1.609(3) Si8 O10 1.614(2) Si8 C60A 1.828(3) Si8 C60B 1.965(3) Si9 O9 1.609(2) Si9 O11 1.624(2) Si9 O14 1.620(2) Si9 C70A 1.809(3) Si9 C70B 1.957(2) 209 Table 6-7 (cont’d) Si10 O12 1.6215(16) Si10 O14 1.6209(18) Si10 O18 1.6151(17) Si10 C80A 1.752(5) Si10 C80B 1.973(5) C10A C11A 1.3900 C10A C15A 1.3900 C11A C12A 1.3900 C12A C13A 1.3900 C13A C14A 1.3900 C14A C15A 1.3900 C10B C11B 1.3900 C10B C15B 1.3900 C11B C12B 1.3900 C12B C13B 1.3900 C13B C14B 1.3900 C14B C15B 1.3900 C20 C21 1.381(4) C20 C25 1.398(4) C21 C22 1.392(4) C22 C23 1.384(5) C23 C24 1.373(5) C24 C25 1.378(4) C30A C35A 1.3900 C30A C31A 1.3900 C35A C34A 1.3900 C34A C33A 1.3900 C33A C32A 1.3900 C32A C31A 1.3900 C30B C35B 1.3900 C30B C31B 1.3900 C35B C34B 1.3900 C34B C33B 1.3900 C33B C32B 1.3900 C32B C31B 1.3900 C40A C41A 1.3900 C40A C45A 1.3900 C41A C42A 1.3900 C42A C43A 1.3900 C43A C44A 1.3900 C44A C45A 1.3900 C40B C41B 1.3900 C40B C45B 1.3900 C41B C42B 1.3900 210 Table 6-7 (cont’d) C42B C43B 1.3900 C43B C44B 1.3900 C44B C45B 1.3900 C50A C55A 1.3900 C50A C51A 1.3900 C55A C54A 1.3900 C54A C53A 1.3900 C53A C52A 1.3900 C52A C51A 1.3900 C50B C55B 1.3900 C50B C51B 1.3900 C55B C54B 1.3900 C54B C53B 1.3900 C53B C52B 1.3900 C52B C51B 1.3900 C60A C65A 1.3900 C60A C61A 1.3900 C65A C64A 1.3900 C64A C63A 1.3900 C63A C62A 1.3900 C62A C61A 1.3900 C60B C61B 1.3900 C60B C65B 1.3900 C61B C62B 1.3900 C62B C63B 1.3900 C63B C64B 1.3900 C64B C65B 1.3900 C70A C75A 1.3900 C70A C71A 1.3900 C75A C74A 1.3900 C74A C73A 1.3900 C73A C72A 1.3900 C72A C71A 1.3900 C70B C75B 1.3900 C70B C71B 1.3900 C75B C74B 1.3900 C74B C73B 1.3900 C73B C72B 1.3900 C72B C71B 1.3900 C80A C81A 1.3900 C80A C85A 1.3900 C81A C82A 1.3900 C82A C83A 1.3900 C83A C84A 1.3900 211 C84A C85A 1.3900 C80B C81B 1.3900 C80B C85B 1.3900 C81B C82B 1.3900 C82B C83B 1.3900 C83B C84B 1.3900 C84B C85B 1.3900 212 Table 6-8 : Crystal structure data for compound 5 Compound AL722C Formula C50H48O14Si9 CCDC 2191689 Dcalc./ g cm-3 1.370 m/mm-1 2.602 Formula Weight 1125.69 Color colorless Shape irregular-shaped Size/mm3 0.32×0.15×0.14 T/K 100.00(10) Crystal System triclinic Space Group P-1 a/Å 13.9487(7) b/Å 14.6216(6) c/Å 15.1753(6) a/° 87.437(3) b/° 65.756(4) g/° 75.749(4) V/Å3 2729.7(2) Z 2 Z' 1 Wavelength/Å 1.54184 Radiation type Cu Ka Qmin/° 3.125 Qmax/° 89.674 Measured Refl's. 36882 Indep't Refl's 11537 Refl's I≥2 s(I) 8552 Rint 0.0530 Parameters 719 Restraints 31 Largest Peak 0.847 Deepest Hole -0.716 GooF 1.051 wR2 (all data) 0.2498 wR2 0.2294 R1 (all data) 0.1092 R1 0.0866 213 Figure 6-44 : Crystal structure data for compound 4 214 Table 6-9 : Bond lengths for compound 5 Atom Atom Length/Å i1 O1 1.580(4) Si1 O2 1.616(4) Si1 C1 1.867(9) Si1 C2 1.791(8) Si2 O1 1.592(4) Si2 O3 1.597(4) Si2 O6 1.607(4) Si2 C20 1.848(6) Si3 O3 1.615(4) Si3 O4 1.598(4) Si3 O7 1.603(3) Si3 C30 1.852(5) Si4 O4 1.614(4) Si4 O5 1.609(3) Si4 O8 1.616(3) Si4 C40 1.838(5) Si5 O2 1.589(4) Si5 O5 1.615(4) Si5 O9 1.600(3) Si5 C50 1.908(6) Si5 C50B 1.798(7) Si6 O6 1.609(3) Si6 O10 1.629(3) Si6 O13 1.611(4) Si6 C60 1.833(5) Si7 O7 1.617(3) Si7 O10 1.609(4) Si7 O11 1.609(4) Si7 C70 1.847(5) Si7 C70B 1.874(6) Si8 O8 1.611(3) Si8 O11 1.606(4) Si8 O12 1.615(4) Si8 C80 1.847(5) Si9 O9 1.602(3) Si9 O12 1.620(3) Si9 O13 1.596(4) Si9 C90 1.845(5) C20 C21 1.385(8) C20 C25 1.386(8) C21 C22 1.389(9) C22 C23 1.389(13) C23 C24 1.377(14) 215 Table 6-9 (cont’d) C24 C25 1.368(11) C30 C31 1.385(7) C30 C35 1.372(8) C31 C32 1.399(8) C32 C33 1.350(9) C33 C34 1.376(9) C34 C35 1.393(9) C40 C41 1.385(7) C40 C45 1.364(8) C41 C42 1.379(9) C42 C43 1.336(10) C43 C44 1.357(9) C44 C45 1.384(8) C50 C55 1.3900 C50 C51 1.3900 C55 C54 1.3900 C54 C53 1.3900 C53 C52 1.3900 C52 C51 1.3900 C50B C55B 1.3900 C50B C51B 1.3900 C55B C54B 1.3900 C54B C53B 1.3900 C53B C52B 1.3900 C52B C51B 1.3900 C60 C61 1.388(7) C60 C65 1.386(7) C61 C62 1.388(8) C62 C63 1.355(9) C63 C64 1.381(9) C64 C65 1.366(8) C70 C75 1.3900 C70 C71 1.3900 C75 C74 1.3900 C74 C73 1.3900 C73 C72 1.3900 C72 C71 1.3900 C70B C71B 1.3900 C70B C75B 1.3900 C71B C72B 1.3900 C72B C73B 1.3900 C73B C74B 1.3900 C74B C75B 1.3900 C80 C81 1.409(7) 216 Table 6-9 (cont’d) C80 C85 1.352(8) C81 C82 1.375(8) C82 C83 1.387(10) C83 C84 1.340(9) C84 C85 1.415(7) C90 C91 1.396(6) C90 C95 1.403(7) C91 C92 1.390(8) C92 C93 1.366(9) C93 C94 1.380(8) C94 C95 1.376(8) Table 6-10 : Bond Angles for Compound 5 Atom Atom Atom Angle/° O1 Si1 O2 110.8(2) O1 Si1 C1 106.6(4) O1 Si1 C2 111.6(4) O2 Si1 C1 103.4(3) O2 Si1 C2 111.8(3) C2 Si1 C1 112.2(5) O1 Si2 O3 109.5(2) O1 Si2 O6 109.2(2) O1 Si2 C20 109.3(2) O3 Si2 O6 109.75(19) O3 Si2 C20 109.1(3) O6 Si2 C20 110.0(2) O3 Si3 C30 110.3(2) O4 Si3 O3 108.3(2) O4 Si3 O7 110.1(2) O4 Si3 C30 110.4(2) O7 Si3 O3 109.4(2) O7 Si3 C30 108.4(2) O4 Si4 O8 109.19(19) O4 Si4 C40 110.0(2) O5 Si4 O4 107.6(2) O5 Si4 O8 110.25(18) O5 Si4 C40 110.1(2) O8 Si4 C40 109.6(2) O2 Si5 O5 109.8(2) O2 Si5 O9 109.2(2) O2 Si5 C50 110.3(3) O2 Si5 C50B 102.8(3) O5 Si5 C50 115.8(4) 217 Table 6-10 (cont’d) O5 Si5 C50B 107.6(4) O9 Si5 O5 108.15(18) O9 Si5 C50 103.2(3) O9 Si5 C50B 119.0(4) O6 Si6 O10 109.54(19) O6 Si6 O13 110.6(2) O6 Si6 C60 109.9(2) O10 Si6 C60 110.45(19) O13 Si6 O10 107.47(19) O13 Si6 C60 108.9(2) O7 Si7 C70 106.4(4) O7 Si7 C70B 114.7(4) O10 Si7 O7 108.68(19) O10 Si7 O11 110.12(19) O10 Si7 C70 117.6(3) O10 Si7 C70B 101.6(3) O11 Si7 O7 108.9(2) O11 Si7 C70 104.8(3) O11 Si7 C70B 112.5(4) O8 Si8 O12 109.28(19) O8 Si8 C80 110.2(2) O11 Si8 O8 109.27(19) O11 Si8 O12 108.6(2) O11 Si8 C80 109.9(2) O12 Si8 C80 109.6(2) O9 Si9 O12 109.8(2) O9 Si9 C90 108.86(19) O12 Si9 C90 109.81(19) O13 Si9 O9 109.0(2) O13 Si9 O12 108.3(2) O13 Si9 C90 111.0(2) Si1 O1 Si2 167.0(3) Si5 O2 Si1 143.3(2) Si2 O3 Si3 156.7(3) Si3 O4 Si4 152.4(3) Si4 O5 Si5 157.4(2) Si2 O6 Si6 157.5(3) Si3 O7 Si7 149.6(3) Si8 O8 Si4 147.8(2) Si5 O9 Si9 155.7(2) Si7 O10 Si6 143.5(2) Si8 O11 Si7 152.9(2) Si8 O12 Si9 145.0(2) Si9 O13 Si6 157.9(2) 218 Table 6-10 (cont’d) C21 C20 Si2 120.9(4) C21 C20 C25 118.3(6) C25 C20 Si2 120.7(5) C20 C21 C22 121.6(7) C23 C22 C21 118.8(8) C24 C23 C22 119.8(8) C25 C24 C23 120.9(9) C24 C25 C20 120.6(8) C31 C30 Si3 120.9(4) C35 C30 Si3 122.1(4) C35 C30 C31 117.0(5) C30 C31 C32 121.2(6) C33 C32 C31 120.5(6) C32 C33 C34 119.7(6) C33 C34 C35 119.6(7) C30 C35 C34 122.1(6) C41 C40 Si4 120.8(5) C45 C40 Si4 123.3(4) C45 C40 C41 115.9(5) C42 C41 C40 121.7(7) C43 C42 C41 120.8(6) C42 C43 C44 119.2(6) C43 C44 C45 120.2(6) C40 C45 C44 122.1(5) C55 C50 Si5 119.2(5) C55 C50 C51 120.0 C51 C50 Si5 120.8(5) C50 C55 C54 120.0 C53 C54 C55 120.0 C52 C53 C54 120.0 C53 C52 C51 120.0 C52 C51 C50 120.0 C55B C50B Si5 121.0(6) C55B C50B C51B 120.0 C51B C50B Si5 118.9(6) C50B C55B C54B 120.0 C53B C54B C55B 120.0 C54B C53B C52B 120.0 C53B C52B C51B 120.0 C52B C51B C50B 120.0 C61 C60 Si6 121.0(4) C65 C60 Si6 122.4(4) C65 C60 C61 116.6(5) C62 C61 C60 121.7(6) 219 Table 6-10 (cont’d) C63 C62 C61 119.7(6) C62 C63 C64 120.0(6) C65 C64 C63 119.9(6) C64 C65 C60 122.1(6) C75 C70 Si7 122.5(5) C75 C70 C71 120.0 C71 C70 Si7 117.4(5) C70 C75 C74 120.0 C73 C74 C75 120.0 C74 C73 C72 120.0 C73 C72 C71 120.0 C72 C71 C70 120.0 C71B C70B Si7 116.9(5) C71B C70B C75B 120.0 C75B C70B Si7 123.1(5) C70B C71B C72B 120.0 C73B C72B C71B 120.0 C72B C73B C74B 120.0 C75B C74B C73B 120.0 C74B C75B C70B 120.0 C81 C80 Si8 118.3(4) C85 C80 Si8 124.1(4) C85 C80 C81 117.6(5) C82 C81 C80 120.9(6) C81 C82 C83 119.5(6) C84 C83 C82 121.1(5) C83 C84 C85 118.8(6) C80 C85 C84 122.1(5) C91 C90 Si9 121.8(4) C91 C90 C95 117.2(5) C95 C90 Si9 121.0(4) C92 C91 C90 120.4(5) C93 C92 C91 121.3(5) C92 C93 C94 119.3(5) C95 C94 C93 120.2(6) C94 C95 C90 121.7(5) 220 Table 6-11 : Crystal structure data for SOPh8T8Et2 Compound AL722B Formula C52H50O13Si9 CCDC 2189783 Dcalc./ g cm-3 1.401 m/mm-1 2.629 Formula Weight 1135.73 Color colorless Shape block-shaped Size/mm3 0.15×0.08×0.05 T/K 100.00(10) Crystal System monoclinic Space Group P21/c a/Å 14.17342(8) b/Å 16.35769(10) c/Å 23.54541(15) a/° 90 b/° 99.4850(6) g/° 90 V/Å3 5384.24(6) Z 4 Z' 1 Wavelength/Å 1.54184 Radiation type Cu Ka Qmin/° 3.161 Qmax/° 80.286 Measured Refl's. 78522 Indep't Refl's 11693 Refl's I≥2 s(I) 10615 Rint 0.0334 Parameters 694 Restraints 0 Largest Peak 0.668 Deepest Hole -0.460 GooF 1.060 wR2 (all data) 0.1013 wR2 0.0989 R1 (all data) 0.0385 R1 0.0353 221 Figure 6-45 : Crystal structure data for SOPh8T8Et2 222 Table 6-12 : Bond lengths for compound 6 Atom Atom Length/Å Si1 O1 1.6269(13) Si1 O2 1.6404(13) Si1 C1 1.857(2) Si1 C3 1.8572(19) Si2 O1 1.6108(12) Si2 O3 1.6150(12) Si2 O6 1.6129(12) Si2 C10 1.8482(16) Si3 O3 1.6128(12) Si3 O4 1.6189(12) Si3 O7 1.6230(12) Si3 C20 1.8436(16) Si4 O4 1.6196(12) Si4 O5 1.6173(12) Si4 O8 1.6239(12) Si4 C30 1.8386(17) Si5 O5 1.6118(12) Si5 O6 1.6149(12) Si5 O9 1.6200(12) Si5 C40 1.8427(17) Si6 O2 1.6037(13) Si6 O10 1.6245(13) Si6 O13 1.6144(14) Si6 C50 1.8486(17) Si7 O7 1.6234(12) Si7 O10 1.6125(13) Si7 O11 1.6112(12) Si7 C60 1.8415(18) Si8 O8 1.6170(12) Si8 O11 1.6103(12) Si8 O12 1.6117(13) Si8 C70 1.8437(17) Si9 O9 1.6176(12) Si9 O12 1.6192(13) Si9 O13 1.6095(14) Si9 C80A 1.885(2) Si9 C80B 1.791(6) C1 C2 1.517(3) C3 C4 1.534(3) C10 C11 1.399(3) C10 C15 1.396(2) C11 C12 1.396(3) C12 C13 1.379(3) 223 Table 6-12 (cont’d) C13 C14 1.385(3) C14 C15 1.399(2) C20 C21 1.395(3) C20 C25 1.391(2) C21 C22 1.394(3) C22 C23 1.370(3) C23 C24 1.378(3) C24 C25 1.393(3) C30 C31 1.399(2) C30 C35 1.397(2) C31 C32 1.388(2) C32 C33 1.389(3) C33 C34 1.374(3) C34 C35 1.396(3) C40 C41 1.403(2) C40 C45 1.399(2) C41 C42 1.382(3) C42 C43 1.390(3) C43 C44 1.387(3) C44 C45 1.392(3) C50 C51 1.390(3) C50 C55 1.396(2) C51 C52 1.395(3) C52 C53 1.389(4) C53 C54 1.369(3) C54 C55 1.390(3) C60 C61 1.393(3) C60 C65 1.390(3) C61 C62 1.387(3) C62 C63 1.373(4) C63 C64 1.365(4) C64 C65 1.395(3) C70 C71 1.393(3) C70 C75 1.393(2) C71 C72 1.386(3) C72 C73 1.385(4) C73 C74 1.370(4) C74 C75 1.389(3) C80A C85A 1.3900 C80A C81A 1.3900 C85A C84A 1.3900 C84A C83A 1.3900 C83A C82A 1.3900 C82A C81A 1.3900 224 Table 6-12 (cont’d) C80B C85B 1.3900 C80B C81B 1.3900 C85B C84B 1.3900 C84B C83B 1.3900 C83B C82B 1.3900 C82B C81B 1.3900 Table 6-13 : Bond angles for compound 6 Atom Atom Atom Angle/° O1 Si1 O2 107.57(7) O1 Si1 C1 111.19(9) O1 Si1 C3 109.27(8) O2 Si1 C1 109.01(9) O2 Si1 C3 106.53(8) C1 Si1 C3 113.02(9) O1 Si2 O3 109.97(7) O1 Si2 O6 108.86(7) O1 Si2 C10 108.19(7) O3 Si2 C10 110.55(7) O6 Si2 O3 109.60(6) O6 Si2 C10 109.64(7) O3 Si3 O4 109.65(7) O3 Si3 O7 107.82(6) O3 Si3 C20 111.38(7) O4 Si3 O7 110.38(6) O4 Si3 C20 108.24(7) O7 Si3 C20 109.38(7) O4 Si4 O8 108.49(6) O4 Si4 C30 110.44(7) O5 Si4 O4 109.30(7) O5 Si4 O8 108.40(6) O5 Si4 C30 109.82(7) O8 Si4 C30 110.34(7) O5 Si5 O6 110.68(7) O5 Si5 O9 109.45(6) O5 Si5 C40 108.63(7) O6 Si5 O9 108.22(7) O6 Si5 C40 108.89(7) O9 Si5 C40 110.97(7) O2 Si6 O10 108.72(7) O2 Si6 O13 109.61(8) O2 Si6 C50 108.12(8) O10 Si6 C50 110.78(7) 225 Table 6-13 (cont’d) O13 Si6 O10 108.81(7) O13 Si6 C50 110.78(8) O7 Si7 C60 111.41(7) O10 Si7 O7 108.67(7) O10 Si7 C60 111.29(8) O11 Si7 O7 108.85(7) O11 Si7 O10 109.39(7) O11 Si7 C60 107.17(7) O8 Si8 C70 109.81(7) O11 Si8 O8 108.89(7) O11 Si8 O12 109.41(7) O11 Si8 C70 109.66(7) O12 Si8 O8 109.96(7) O12 Si8 C70 109.09(7) O9 Si9 O12 108.96(7) O9 Si9 C80A 111.0(2) O9 Si9 C80B 111.9(6) O12 Si9 C80A 105.28(15) O12 Si9 C80B 113.5(5) O13 Si9 O9 109.60(7) O13 Si9 O12 110.08(7) O13 Si9 C80A 111.85(15) O13 Si9 C80B 102.7(4) Si2 O1 Si1 160.22(9) Si6 O2 Si1 146.35(9) Si3 O3 Si2 161.71(9) Si3 O4 Si4 146.82(8) Si5 O5 Si4 157.22(9) Si2 O6 Si5 150.76(8) Si3 O7 Si7 141.96(8) Si8 O8 Si4 141.07(8) Si9 O9 Si5 148.05(8) Si7 O10 Si6 151.05(9) Si8 O11 Si7 153.44(9) Si8 O12 Si9 149.84(9) Si9 O13 Si6 158.85(10) C2 C1 Si1 117.80(14) C4 C3 Si1 114.48(14) C11 C10 Si2 120.51(14) C15 C10 Si2 121.31(13) C15 C10 C11 118.15(16) C12 C11 C10 120.60(19) C13 C12 C11 120.4(2) C12 C13 C14 120.10(17) 226 Table 6-13 (cont’d) C13 C14 C15 119.62(18) C10 C15 C14 121.13(17) C21 C20 Si3 120.13(13) C25 C20 Si3 121.67(13) C25 C20 C21 118.19(16) C22 C21 C20 120.70(19) C23 C22 C21 120.2(2) C22 C23 C24 119.94(17) C23 C24 C25 120.24(18) C20 C25 C24 120.70(18) C31 C30 Si4 120.50(13) C35 C30 Si4 121.56(14) C35 C30 C31 117.94(16) C32 C31 C30 121.44(17) C31 C32 C33 119.50(18) C34 C33 C32 120.09(17) C33 C34 C35 120.48(18) C34 C35 C30 120.52(18) C41 C40 Si5 120.16(13) C45 C40 Si5 121.82(13) C45 C40 C41 118.00(16) C42 C41 C40 121.31(17) C41 C42 C43 119.98(18) C44 C43 C42 119.74(17) C43 C44 C45 120.26(17) C44 C45 C40 120.70(17) C51 C50 Si6 121.04(14) C51 C50 C55 117.91(17) C55 C50 Si6 121.01(13) C50 C51 C52 121.0(2) C53 C52 C51 120.0(2) C54 C53 C52 119.63(18) C53 C54 C55 120.5(2) C54 C55 C50 120.99(18) C61 C60 Si7 119.95(14) C65 C60 Si7 122.25(15) C65 C60 C61 117.63(17) C62 C61 C60 121.0(2) C63 C62 C61 120.2(2) C64 C63 C62 120.2(2) C63 C64 C65 120.0(2) C60 C65 C64 121.1(2) C71 C70 Si8 120.36(14) C75 C70 Si8 121.53(14) 227 Table 6-13 (cont’d) C75 C70 C71 118.11(17) C72 C71 C70 121.2(2) C73 C72 C71 119.7(2) C74 C73 C72 119.93(19) C73 C74 C75 120.5(2) C74 C75 C70 120.6(2) C85A C80A Si9 120.2(2) C85A C80A C81A 120.0 C81A C80A Si9 119.7(2) C84A C85A C80A 120.0 C83A C84A C85A 120.0 C84A C83A C82A 120.0 C83A C82A C81A 120.0 C82A C81A C80A 120.0 C85B C80B Si9 120.0(6) C85B C80B C81B 120.0 C81B C80B Si9 119.9(6) C84B C85B C80B 120.0 C83B C84B C85B 120.0 C82B C83B C84B 120.0 C83B C82B C81B 120.0 C82B C81B C80B 120.0 228 7 SIGNIFICANCE AND PERSPECTIVE 229 7.1 Significance The works provide a window to significant applications of asymmetrically capped DDSQ. Some of the significant findings in this work are: • A simple, efficient way to disperse Graphene oxide into a polymeric matrix such as Derakene™ was developed. This methodology used simple magnetic stirring to disperse modified graphene oxide into polymeric resin compared to high-energy techniques such as sonicators. Asymmetrically capped DDSQ formed an amide bridge between the isocyanate group on the DDSQ and the hydroxyl groups on the Graphene oxide surface; the styrene group on DDSQ was polymerized with the Derakene network structure. The nanocomposites of Derakene/Graphene Oxide exhibit a significant improvement in strength and ductility compared to the neat sample. • Isomeric para/meta dichlorosilanes were synthesized using t-butyl lithium as a metalation reagent. This route yielded better results than the Grignard reagent route or the n-butyl lithium route. To improve the shelf life of chlorosilanes and yield, LiAlH4 is used as a reducing agent to convert chlorosilanes to silanes to improve the shelf life and yield. The silanes can be purified using column chromatography, which leads to better yields than sublimation/ distillation. An isomeric mixture of meta/para PEP DDSQ systems was synthesized, and the thermal and viscous properties show that the system can be tuned by changing the ratio of isomers to improve the processability of the system. • A series of compounds with increasing bulkiness of the functional groups were synthesized. The initial series had a reactive silanol functional group in the cages, which was later protected with trimethylsilyl chloride. DSC analysis shows that bulky groups reduce the solid-to-liquid transition temperature from 290 °C to 145 °C. The enthalpy of the system also reduces with 230 increasing size. The system does not exhibit glassy substances like solid-to-liquid transition characteristics. • A new method for capping DDSQ tetrol with chlorosilanes has been proposed using a poor solvent like DCM concerning DDSQ solubility. The reaction time for the capping has been reduced to 5 minutes, irrespective of the type of chlorosilane or mixture of chlorosilanes used in the capping reaction. The increased activity of the reactant in DCM can be attributed to the difference in pKa values of triethylamine in DCM vs. THF. • A novel strategy was developed to synthesize structural isomers to examine the effect of inorganic core on cage-like silsesquioxane compounds' thermal and crystal packing. A novel partially closed cage with one side open with two silanol groups was synthesized. This asymmetrical disilanol cage was capped with tetramethyl dichlorodisiloxane. The asymmetrically capped cage exhibits a 20 % faster weight loss rate and has a higher residual weight at 900 °C, and the melting temperature was almost 60 °C lower. Single crystal X-ray analysis indicates the novel asymmetrical cage has monoclinic crystal packing. 7.2 Perspectives • A universal system for using asymmetrically capped DDSQ as a nanoscale bridging material between carbonous materials and polymeric matrices needs to be developed. The carbonous material surface can be bonded to the DDSQ structure via Vander-Wall forces or hydrogen bonding. The DDSQ can be modified to suit the polymeric matrix via capping with a suitable functional group that can be polymerized with the matrix. Organic groups such as ureidopyrimidone can be capped onto a DDSQ cage containing four hydroxy groups. These groups can be bonded with the surface functional groups on graphene fibers or nanoplatelets. Other functional groups, such as the use of pyrene, can also be explored. 231 • The use of a poor solvent to change the reaction kinetics for the capping reaction of DDSQ needs to be investigated further. The effect of change in solubility and polarity needs to be explored further. Other solvents, such as 2-Methyl THF or a mixture of 50-50 THF and DCM, can be explored to see the effect of solubility on the capping reaction. Also, the base used in the capping reaction, triethyl amine, plays a role in changing the pKa value of the reaction system. Exploring different bases, such as pyridine or secondary amines, can help to understand this effect in further detail. • The novel asymmetrical silsesquioxane diol can prove a turning point to improve the processability of DDSQ-based polymeric matrices. The asymmetrical tetramethyl capped silsesquioxane system exhibits peculiar shear-thinning viscosity behavior, which was not found in mono molecular compounds. This behavior needs further investigation by changing the tetra functional groups capped on the silsesquioxane diol. The groups used for capping can be difunctional dichlorosilane groups or tetra-functional dichlorosilane groups. 232