m 33‘: I!l%‘yé‘4ll“':l- 1 MW WI! ! IWHsW L W \ I w HUIlull1|lll|lllll|llllllllllllllllllllllll 3 1293 016871 This is to certify that the thesis entitled STUDIES ON SYTHESIS 0F COPOLYESTERTAMIDES presented by RHUTESH SHAH has been accepted towards fulfillment of the requirements for Master of Science degree infihfiminamgineering (”WM W Major professor eagle/39’ 0-7639 MS U is an Affirmative Action/Equal Opportunity Institution LIBRARY Michigan State Uhlverslty PLACE IN RETURN Box to remove this checkout from your record. To AVOID FINES return on or before date due. MAY BE RECALLED with earlier due date if requested. DATE DUE DATE DUE DATE DUE 1M WMpGS-pu STUDIES ON SYNTHESIS OF COPOLYESTER—AMIDES By Rhutesh Shah A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Chemical Engineering 1997 ABSTRACT STUDIES ON SYNTHESIS OF COPOLYESTER—AMIDES By Rhutesh Shah Copolyester-amides have been synthesized by two different methods : Copolymerization of s-caprolactone / e-caprolactam and ester-amide interchange reaction between Nylon 6 and polycaprolactone (PCL). Different catalysts for the copolymerization of e- caprolactone and e-caprolactam have been compared and a new catalyst system has been proposed for the rapid copolymerization of the two monomers. A study on the ester- amide interchange reaction between PCL and Nylon 6 has been done over different time periods. Initially, block copolymer is formed, but it gradually becomes random as the reaction time increases. Formation of copolymers was confirmed by DSC and FT-IR spectroscopy studies, while their composition was obtained by proton NMR spectroscopy. The results Show a 23% to 29% incorporation of Nylon 6 in the PCL chains. A brief treatise is also given on the various methods used for the synthesis of caprolactone. ACKNOWLEDGMENTS It has been a great pleasure to work on the synthesis of copolyester-amides. However such a work would not have been possible had I not received the guidance and facilities that I did receive. First and foremost, I am thankful to my advisor, Dr. Ramani Narayan, who has been the guiding light all through my work. I am grateful to the staff at Bioplastics Inc. and Michigan Biotech Institute (MBI) for providing me with all the facilities and an excellent working environment. Mike Rich and the staff at CMSC and the Department of Chemical Engineering also extended their fullest help and cooperation. And finally, a special thanks to all my friends for their assistance and encouragement. Chapter 1 Chapter 2 Chapter 3 Chapter 4 Table of Contents List of Tables List of Figures Introduction 1.1 Objective 1.2 Structure of the Thesis Background 2.1 Classification 2.2 Polymer Preparation 2.3 Copolymerization 2.4 Exchange Reactions Materials 3.1 Epsilon Caprolactone 3.2 Epsilon Caprolactam 3.3 Polycaprolactone 3.4 Polycaprolactam (Nylon 6) 3.5 Methanol 3.6 Catalyst 3.6.1 Catalysts for copolymerization 3.6.1.1 Triethyl Aluminum (TEA) 3.6.1.2 Triisobutyl Aluminum (TBA) 3.6.1.3 Sodium Caprolactam (Na-CL) 3.6.1.4 Sodium Hydride (NaH) 3.7 Activator (Co-catalyst) Synthesis of e-Caprolactone 4.1 Different methods for e-caprolactone synthesis V Page vii viii 15 15 17 19 21 23 23 23 24 26 27 29 30 32 32 4.2 Synthesis of e-caprolactone from e-caprolactam 4.2.1 Reaction 4.2.2 Experimetnal 4.2.3 Results Chapter 5 Copolymerization of e-caprolactone and e-caprolactam 5.1 Pretreatment of Materials 5.2 Reaction 5.2.1 Anionic copolymerization using Na—CL 5.2.2 Anionic copolymerization using Na-Cl and HMDI (co-catalyst) 5.3 Experimental Approach 5.3.1 Copolymerization using TEA as catalyst 5.3.2 Copolymerization using Na—CL as catalyst 5.3.3 Copolymerization using Na-CL and HMDI 5.4 Results Chapter 6 Ester-Amide Interchange Reaction 6.1 Synthesis of CPAEs 6.1.1 Pretreatment of materials 6.1.2 Ester-amide interchange reaction 6.1.3 Preparation of blends 6.4 Analysis 6.2.1 Differential Scanning Calorimetry (DSC) 6.2.2 Soxhlet Extraction 6.2.3 Fourier Transform Infrared Spectroscopy 6.2.4 Nuclear Magnetic Resonance Spectroscopy 6.3 Results and Discussion Chapter 7 Conclusions and Recommendations 7.1 Synthesis of e-Caprolactone 7.2 Synthesis of copolyamide esters Bibliography vi 35 36 36 36 40 40 41 41 42 43 43 45 45 46 49 49 49 50 50 52 52 52 53 54 54 65 65 66 68 List of Tables Page Table 3.1 Physical Properties of TONE® Monomer 16 Table 3.2 Physical Properties of a-Caprolactam 18 Table 3.3 Physical Properties of TONE® Polymer P-767 21 Table 3.4 Physical Properties of Nylon 6 22 Table 3.5 Physical properties of Methanol 23 Table 3.6 Properties of Triethyl Aluminum 25 Table 3.7 Properties of Triisobutyl Aluminum 26 Table 3.8 Physical Properties of Sodium Hydride 30 Table 3.9 Properties of Zinc Acetate 30 Table 3.10 Physical Properties of HDI 31 Table 5.1 Copolyester-amide yield by different catalysts over different 47 reaction times Table 6.1 Results of Soxhlet Extraction of Ester-Amide Interchange Reaction 57 vii Figure 3.1 Figure 4.1 Figure 4.2 Figure 5.1 Figure 5.2 Figure 5.3 Figure 6.1 Figure 6.2 Figure 6.3 Figure 6.4 Figure 6.5 Figure 6.6 Figure 6.7 Figure 6.8 Figure 6.9 Figure 6.10 List of Figures DSC plot of Sodium Caprolactam Gas Chromatogram of Caprolactone Synthesis Product (@ 290°C) Gas Chromatogram of Caprolactone Synthesis product (@ 310°C) Experimental Setup for Copolymerization reaction Copolymer yield with different catalysts for different reaction times IR spectra of the copolyester-amide Experimental Setup for Ester-Amide Interchange Reaction Experimental Setup for Soxhlet Extraction DSC plots of Nylon 6 and PCL DSC plots of Copolyester-amides and Nylon-PCL blend IR spectra of chloroform soluble phase of the reaction products Carbon-NMR spectra of 2h ester-amide interchange reaction product Carbon-NMR spectra of 4h ester-amide interchange reaction product Proton-NMR spectra of 2h ester-amide interchange reaction product Proton-NMR spectra of 4h ester-amide interchange reaction product Proton—NMR spectra of Nylon 6/PCL blend viii Page 28 38 39 44 47 48 51 53 55 56 59 62 63 64 Chapter 1 Introduction The biodegradation of synthetic polymers is of considerable interest to environmentalists, industrialists, academicians as well. as researchers. The study of biodegradation of polymers was initiated to prevent the polymers from attack by micro- organisms in the environment. However this study gained major impetus because of its ecological value [1]. As an important class of biodegradable polymers, aliphatic polyesters have been widely investigated [2,3]. Unfortunately the softening points (Tm) of synthetic aliphatic polyesters are too low to permit their use as a material in plastic applications. This restricts their applications to the biomedical area [2], adhesives and mold releasing. On the other hand, commercial aliphatic polyarnides as a class have a wide range of properties and therefore a wide range of applications. However most of them are non- biodegradable. The large concentration of hydrogen bonds and the high regularity of the polyamide structure are the possible reasons for the inertness of these nylons to biodegradation. On the basis of the above facts, copolyester-amides composed of esters and amides could potentially be a class of biodegradable polymers which would have better physical properties than polyesters [4,5]. Goodman et a1. [5], Ellis [7], and Korshak et a1. [8] studied the copolyesteramides synthesized from epsilon caprolactone (monomer for 2 PCL) and epsilon caprolactam (monomer for nylon-6). Tokiwa et al [4,6] and Chen [9] have shown that these copolyesteramides can be biodegraded by microbial activity or hydrolysis. 1.1 Objective The goal of this work was to synthesize copolyamide—esters (CPAES) which have a higher melting point as compared to aliphatic polyesters and at the same time are biodegradable. This would widen the applicability of biodegradable polymers to various fields. To attain this objective, studies were done on the copolymerization of caprolactone and caprolactam with different catalysts. A new catalytic system has been. proposed which results in the rapid copolymerization of the monomers. A study was also done on CPAE synthesis by ester-amide interchange reaction between nylon 6 and PCL. 1.2 Structure of the Thesis The following paragraphs give a brief outline of the contents in each chapter of this thesis : Chapter 2 gives a basic idea about polymers and the different mechanisms by which polymerization reactions proceed. The chapter also gives a brief idea about copolymerization, the conditions under which copolymers can be synthesized and the problems associated with copolymerization of ring structured monomers of different chemical nature. This is followed by a brief treatise on Exchange reactions. 3 Chapter 3 provides information on the constituent materials. The monomers, their nature and properties are discussed. It also includes a description of the various catalysts and co-catalyst employed for the cOpolymerization of e-caprolactone and s-caprolactam. Also included is a brief description of the polymers and catalysts involved in the ester- amide interchange reaction. Chapter 4 is concerned with the synthesis of e-caprolactone. Various present day methods used for the synthesis of a-caprolactone are discussed along with their advantages and disadvantages. A novel method for the synthesis of e-caprolactone from e-caprolactam has been described along with the results obtained. Chapter 5 deals with the copolymerization of e-caprolactone and e-caprolactam. Different catalysts employed for the copolymerization reactions has been discussed along with their mechanism. A new catalytic system comprising a catalyst and a co-catalyst has been proposed. The mechanism of copolymerization catalyzed by this system has been described in detail. This is followed by the experimental results obtained using different catalysts. An effort has been made to compare the copolymer yields obtained with different catalysts for different times. Chapter 6 covers the synthesis of CPAEs by esteramide interchange between Nylon 6 and PCL. The identification of the copolymer formed was done by IR and its composition was determined by NMR spectroscopy. The results were compared with those of a Nylon 6 - PCL blend. Chapter 7 presents the conclusions from the thesis and some recommendations for future work Chapter 2 Background High polymers are substances of very high molecular weight, which may be natural or synthetic in origin and which have at least some element of structural regularity. 2.1 Classification Polymers are classified by several classification schemes [10]. The most common classification is based on the polymer structure. Polymers in which the repeating units are linked together to form a straight chain are termed as linear polymers. X--[- M-M-M ..... -M-M -]--Y X and Y are end groups and they represent only a small fraction of the total weight of the polymer. Hence in most cases they can be ignored. The simplest linear polymers are those in which all structural units are identical. Such materials are called homopolymers, whilst polymers incorporating two or more chemically different types of structural unit into the chain are termed as copolymers. Copolymers may generally contain two or three different monomers and accordingly are termed binary or ternary copolymers. If the units are arranged in random sequence along the chain then such copolymers are random copolymers .' ........ AABAAABBAABABABBBAAB....... 5 If the chain consists of large groups of identical units then such copolymers are termed as block copolymers .' .......... AAAAAAABBBBBBBBBAAAAAAA...... Copolymers in which the units alternate along the chain are alternating copolymers : ......... ABABABABABABABABABW...” If all or some of the monomer molecules are trifunctional then the polymer may have a nonlinear structure. If the structural units of the side chain are identical to those of the main chain (or backbone) then the polymer is termed as branched polymer. If the side chains of a branched polymer are formed from structural units which are different from those of the backbone, the polymer is termed as graft copolymer. Within a polymer a trifunctional unit may react with another trifunctional unit which may cause the joining of the two chains and eventually the formation of a cross- linked polymer. Polymers are also classified based on it’s behavior at high temperatures. The term thermoplastic is applied to materials that soften and flow upon application of pressure and heat. Thus most thermoplastic materials can be remolded several times. The term ‘thennoset’ is applied to materials that, once heated, react irreversibly so that subsequent applications of heat and pressure do not cause them to soften and flow. In this case, a rejected or scrapped piece cannot be ground up and remolded. Another classification is based on the physical state. Polymer molecules may be partially crystalline or completely disordered. The disordered state may be glassy and 6 brittle, or it may be molten with the viscosity characteristic of a liquid or the elasticity we associate with a rubbery solid. 2.2 Polymer Preparation In principle, the main requirement for any molecule to be capable of acting as a structural unit of a polymer is that it should be difunctional. Broadly speaking difilnctionality can be achieved in three ways [11, 12] : 1. By opening a double bond (addition polymerization). 2. By using molecules bearing two reactive functional groups (condensation polymerization). 3. By opening a ring (Ring opening polymerization). The detailed discussion in this work will be restricted to addition polymerization and ring opening polymerization. However condensation polymerization will be covered briefly. 2.2.1 Addition Polymerization Substances of the general formula CH2=CRR’ are readily polymerized to yield high polymers which can be represented as : R —rCH2 —- c|2+n R These polymers have a repeat unit which is identical in composition to the monomer, and are formed without loss of any portion of the monomer molecules. Polymers of this type 7 are termed as addition polymers and the reactions producing them are called addition polymerizations. Addition polymerization of unsaturated monomers invariably proceed by a chain reaction mechanism. Initiation of the chain is usually achieved by addition of an active catalyst, which reacts with the monomer to produce an activated molecule by opening the double bond. Addition of further monomer molecules to those active centers then follows rapidly either until the active center is destroyed by some chemical reaction/ mpurity or until the supply of monomer is exhausted. The polymerization can thus be represented as follows : 1* + M , ===> IM* ------ Initiation IM* + M ===> IMM* or in general I-(M)n* + M ===> I-(M)n+1 * ------ Propagation I-(M)n* + ? ===> Inactive polymer ------ Termination The propagating centers in addition polymerization may be any of the following : 1. Free radicals (formed by homolytic opening of the double bond). 2. Anions (formed by heterolytic opening of the double bond). 3. Cations (formed by heterolytic opening of the double bond). 4. Complex coordination compounds. 8 The mechanism by which growing chains are terminated is dependent upon the nature of the active centers. Main features of addition polymerization are : 1. Growth occurs by rapid addition of monomer to a small number of active centers. 2. Monomer concentration decreases gradually during the reaction. 3. High molecular weight polymer is present at low conversions. 4. Polymer backbone usually consists exclusively of carbon atoms. As discussed before, addition polymerization may proceed by free radicals, co- ordinated catalysis, anionic or cationic mechanisms. The focus of this work will be on anionic polymerization systems. 2.2.1.1 Addition Polymerization by anionic mechanism The term ‘anionic polymerization’ is used whenever the active bears a negative charge. This does not necessarily imply the presence of a free anion on the growing polymer chain. The negative charge may be a free anion, or a component of an ion pair or a partially ionic bond. Generally all polymerizations initiated by organometallic compounds are referred as ‘anionic’. Initiation of anionic polymerization may take place by : 1. addition of an anion to the monomer 2. addition of an electron to produce an anion radical 9 The most common initiators of the first type are the alkyl and aryl derivatives of the alkali metals, although other substances such as the alkali metal amides, alkoxides, hydroxides and Grignard reagents also fall into this category. The polymerization then proceeds along by chain reaction mechanism, until the monomer is exhausted or the anion is destroyed by moisture or other impurities. The absence of a termination reaction allows block copolymers of known structure to be prepared by addition of a monomer B to a solution of a living polymer A. However such a reaction is feasible if and only if the living anion of monomer A is capable of initiating polymerization of the second monomer B. It is shown in chapter 5 how this concept has been used efficiently in the synthesis of block copolymers of e-caprolactone and e- caprolactam. . 2.2.2 Condensation Polymerization The term ‘condensation polymerization’ is used whenever two monomers polymerize with an elimination of water or another simple species. Difunctionality may be achieved by using a single monomer bearing two different functional groups, as for example in the polymerization of a hydroxy acid to yield a polyester : n n H0—6CH29x—COOH ————> H +0 —- (CH2)X— 0 —]—OH + (n-1) H20 Alternatively, the two functional groups may be present on different molecules, so that polyesters can also be produced by a diol. An example of this type is the reaction of ethylene glycol with sebacic acid. 10 n HO—(—CH2—)2—OH + n HOOC—(—CH2—)§—COOH O o II II _. HO—HCHmz—o—C—(CH2)8_C—o+n—H + (n-1)H20 Thus in a condensation polymerization, all of the molecules present are functionally capable of reaction at any time. Polymerization proceeds via stepwise condensation of a molecule with another molecule giving a dimer and then successively giving trimer, tetramer etc. Thus molecular weight increases gradually along with the conversion. The main features of condensation polymerization are : 1. Growth occurs by coupling of any two species (monomer or polymer). 2. Monomer disappears well before any high polymer is formed. 3. Polymer molecular weight increases continuously during polymerization. High polymer is present only at very high conversions. 4. Polymer repeat units are normally linked by oxygen and/ or nitrogen atoms. 2.2.3 Ring Opening Polymerization Polymerization of cyclic monomers to linear polymers by ring-opening mechanisms is a well established method of polymer preparation [12]. It is difficult to classify these reactions into either addition or condensation polymerization since their mechanisms are often typical polyadditions leading to products which are more ll conveniently considered as condensation polymers. e-caprolactone can be polymerized by ionic initiation [13]. bc=o (CH2)5 (I) Polymerization : _[__ C—(CH2)5 —O 4; H O This reaction behaves like a typical addition polymerization reaction; no water is eliminated and the structural unit is directly related to the monomer. However, the product is a linear polyester which would normally be considered as a condensation polymer. Ring opening polymerizations of some compounds may be even more complex, e.g. the polymerization of caprolactam to Nylon 6 [l4] : /\ 6:0 ’i (CH2)5 I Polymerization; + C—(CH2)5 _ N _l_ N — H (II) ” This reaction involves ring opening polyaddition in the presence of acidic or basic catalysts, but if water is present polymerization may occur in part or my hydrolysis of the monomer to caproic acid followed by polycondensation. In virtually all such reactions the monomer ring contains atleast one hetero-atom. The classes of structures that may be appropriate for ring opening polymerizations can be simplistically generalized as below [15] : A n (CH2)y X Z +(CH2)y—x4; ‘n’ i‘ (ll) X=O,S,NH,O—C, —N—C—’ —CH=CH— & y22 12 2.3 Copolymerization Nowadays copolymerization has grown to be of increasing importance in the industry because of it myriad applications. It is an efficient tool by which the desired properties of two monomers/polymers can be incorporated into one material. Mayo and Lewis did some pioneering work in the kinetic study of copolymerization reactions and proposed the “Copolymerization Equation” a/b = n = (Tux +1)/((1'2/X)+1) where, afb = the ratio of monomers in the initial polymers. x = A/B = ratio of monomers in the feed. r1 = K“ / Kab = ratio of the propagation constants. r2 = Kbb/ Kba = ratio of the propagation constants. Copolymerization reactions proceed most commonly by (a) Free radical mechanism. (b) Cationic mechanism. (c) Anionic mechanism. Block copolymers are readily prepared by the sequential addition of monomers to systems polymerizing under living ionic conditions. However this approach is limited in its applicability by the necessity of meeting two requirements : l3 1. The monomers involved must all be capable of clean polymerization by the selected propagating mechanism. This condition limits the combination of monomers which can be used to make copolymers since, for example, block copolymers of styrene (polymerized anionically) and THF (polymerized cationically) cannot be prepared in this way. 2. The order of monomer addition must be such that the polymer anion generated by the preceding monomer must be capable of initiating rapidly the polymerization of the succeeding monomer. This condition restricts the order in which sequences of the polymer segments can be synthesized. For example, living polystyrene can readily initiate the polymerization of ethylene oxide but the alcoholate ion of living polyethylene oxide cannot initiate styrene. Only a few examples of copolymerization of rings of different chemical nature are known, which is probably associated with the difficulty of running such reactions. The reactivity of ring structured monomers of different chemical nature can differ markedly, as a result of which not copolymers, but a mixture of homopolymers is formed when such monomers are copolymerized [8]. In these cases the task of synthesizing the copolymer reduces to finding such catalysts and such polymerization conditions that the polymerization rate of both monomers will be more or less the same. 14 2.4 Exchange Reactions In recent years considerable interest has arisen in the study of reactive blending of polymers and in the exchange reactions which may occur during the melt mixing processes [16, 17]. These reactions provide a facile route for the synthesis / manufacturing of block and random copolymers. The formation of copolyesters by this route is very popular [45,46]. Studies on the ester interchange reaction in polyethylene terepthalate (PET) has been extensively reported [18, 19]. Simplistically, an ester exchange reaction in polyesters (transesterification) to yield copolyesters is a result of two concurring processes : 1. The formation of copolymer from homopolymers - A-A-A-A- + -B-B-B-B- ===> ~A-A-A-A-B-B-B-B 2. The process in which the copolymer rearranges itself in another copolymer with a different sequence of A and B units along the copolymer chain. -A-A-A-A-B-B-B-B- =====> -A-B-B-A-A-B-B-A- Similar exchange reactions also occur in nylons (transamination reactions ) In this work, copolyamide-esters of Nylon 6 and PCL have been synthesized by an ester- amide interchange reaction (chapter 6). Chapter 3 Materials 3.1 Epsilon Caprolactone b c=o (CHzls | O e-Caprolactone is an important intermediate in organic synthesis. It is the most commonly manufactured by Baeyer - Villiger reaction between cyclohexanone and peracetic acid. Different variations of this prOcess are used for commercial production. A detailed description of these methods can be found in chapter 4. At present Union Carbide Corp. is the largest producer and supplier of e-caprolactone in the US. Epsilon caprolactone is an easy to handle, colorless, high boiling liquid that is expected to be a useful chemical intermediate for a wide variety of applications. In chemical synthesis, the molecule is characterized by its reactivity. Cleavage usually takes place at the carbonyl group. The e-caprolactone used for the co-polymerization reaction with e-caprolactam was provided by Union Carbide Corporation (Tone® monomer EC). ; Typical properties of the monomer used are listed in Table 3.1. 15 16 Table 3.1 Physical Properties of Tone® Monomer Molecular Weight : 114.07 Density (at 20 °C) : 1.0757 g/cc Boiling Point (at 760 mm Hg) : 235.3 °C Freezing Point : -1.5 °C Absolute Viscosity (at 20 °C) : 6.6 cP Water Solubility (25 °C) : Complete Epsilon caprolactone is also an excellent solvent for many polymers. It can solvate several hard to dissolve resins such as polyurethanes and polyvinylchloride. It differs in reactivity from its lower homologs, beta-propiolactone and gamma- butyrolactone. o It is much more prone to polymerize in the presence of active hydrogen compounds and the resulting polymers are not easily depolymerized. o It is much less prone to react by alkyl oxygen fission than either beta-propiolactone or gamma butyrolactone. Attack by an active hydrogen compound usually takes place at the carbonyl group in a-caprolactone. bozo (CH2)5 I Sigh—ta — 0-C-(CH2>5 — O 0 (Very low probability) ‘\ / C : O RING (CH2)5 2) bun—em — C-(CH2)5-O — ll 0 (High Probability) 0 Higher reaction temperatures are usually required for reactions with e-caprolactone than for analogous reactions with beta-propiolactone or gamma-butyrolactone. Since e-caprolactone tends to polymerize easily, it should not be brought into contact with such chemicals which promote its polymerization viz. mineral acids, alkalies, lewis acids, acidic or basic salts and water or water vapor. At elevated temperatures, their effect becomes more pronounced. Ultimately this may lead to gelation or serious reduction in purity. It is advisable to store caprolactone in and inert nitrogen atmosphere. 3.2 Epsilon Caprolactam /\CZO “2th l NW- \J H a-Caprolactam is the lactam form of amino caproic acid. It is the commonly used monomer for nylon 6. Caprolactam production in the US. rose to 1575 million pounds which was about 4% higher than in 1994 [25]. Caprolactone is manufactured from cyclohexanone oxime (Beckmann rearrangement) which is obtained by treating cyclohexanone with hydroxylamine. 18 p020 \ / V Another process starts with toluene which is oxidized to benzoic acid, hydrogenated to cyclohexane carboxylic acid and then treated with nitrosyl sulfuric acid to produce caprolactam. e-Caprolactam is available as highly hygroscopic white crystals which have a melting point of around 70 - 72 °C. Certain basic physical properties are summarized below. Table 3.2 Physical Properties of e-Caprolactam Molecular Weight : 113.16 Boiling Point : 136 °C at 10 mm Hg. 260 °C at 760 mm Hg. Melting Point : 69 - 72 °C Refractive Index (liquid) : 1.4797 Density (liquid) : 1.0212 Soluble in : Water, Methanol, Ethanol, Ether, DMF, Chlorinated hydrocarbons Chemically, caprolactam is capable of forming three series of derivatives, one resulting from substituents on the nitrogen, another from substituents on the carbon chain. It is also used as a solvent for high molecular weight polymers. l9 a-Caprolactam used for the synthesis of caprolactone as well as for the copolymerization with a-caprolactone was supplied by Aldrich. Taking into consideration its hygroscopic nature, it was constantly kept under N2 atmosphere. 3.3 Polycaprolactone ——[—— C-(CH2)5— O In O Polycaprolactone is a homopolymer of a-caprolactoneJt is a crystalline, low melting (55° C) polymer. It resembles medium density polyethylene in stiffness and has a waxy feel. Commercially available PCL was used for the copolymerization reaction with polycaprolactam (nylon 6). Carothers was the first to carryout the polymerization of e-caprolactone to PCL by the action of heat and catalysts. The polymerization can proceed by any of the following mechanisms : 1. Cationic polymerization [20] 2. Anionic polymerization [21] 3. Active hydrogen polymerization [22] 4. Zwitterionic polymerization [23] 5. Coordination polymerization [24] PCL holds a special advantage over other synthetic polymers : It is biodegradable. It has been shown that PCL resins degrade in environments hospitable to microbial growth. Soil burial tests of molded articles showed degradation, in terms of significant 20 property and weight loss. At the same time it exhibits broad miscibility or mechanical compatibility with many other plastics, including polyethylene, polypropylene, polystyrene, PVC, polycarbonate and PET. The strength, toughness, low melting point and biodegradability of PCL have been used to advantage in various unique applications : 0 Drug delivery system. Controlled release of pesticides, herbicides, fertilizers. Mulch films, Compost bags. Pigment dispersant. 0 Improving mold release. Adhesive applications. Orthopedic applications. PCL was used supplied by Union Carbide Corporation (TONE® Polymer P-767). This was prepared by initiation with a diol (HO-R-OH) and hence has the following SITUCIUI'C I HOR—G { c (CH2)5—O in 0 Typical physical properties of TONE® Polymer P-767 are listed below : 21 Table 3.3 Physical Properties of TONE® Polymer P-767 Specific Gravity : 1.1 Melting Point (Tm) : 59 °C Mn : 30,000 - 40,000 Mw : 45,000 - 60,000 3.4 Polycaprolactam (nylon 6) ——l— (“Z—(CH2)5—— NH —ln—— 0 Nylon 6 is a linear homopolymer of e-caprolactam. It is similar to nylon 66 however there are some basic differences as far as the molecular and crystalline structure is concerned. The fundamental difference lies in the odd number of methylene groups between the amide groups in nylon 6 compared to the even number in nylon 6,6. Lactam polymerization can proceed by any of the following mechanisms : 1. Cationic polymerization. 2. Anionic polymerization. 3. Hydrolytic polymerization [26]. 22 Pure dry caprolactam does not polymerize when heated for as long as 200 hours. Different catalysts are used for its polymerization and the nature of the catalysts dictates the mechanisms. Recent techniques involve the use of an activating agent (initiator) in addition to a catalyst. Mougin et a1 [27] talks about such activating agents in his work. Tilman Bartilla [28] was successful in carrying out the polymerization reaction in an extruder. Using hexamethylene diisocyanate as an activator, the reaction reached completion in about 4 - 5 minutes. Other instances of lactam polymerization in an extruder have also been noted [29]. Nylon 6 is white to yellow in color with a melting point of about 223 °C. It is immune to microbiological attack and hence high molecular weight nylon 6 does not biodegrade. It is resistant to most organic chemicals, but dissolved by phenol, cresol, and strong acids. Nylon 6 employed for the copolymerization reaction was supplied by Aldrich. Important physical properties of nylon 6 used are listed below : Table 3.4 : Physical Properties of Nylon 6 Specific Gravity : 1.084 Melting Point (Tm) : 233 °C Glass Transition Temperatue (Tm) : 40 °C Refractive Index : 1.53 Specific Heat : 1.6 J/(g. K) 23 Nylon 6 has got widespread applications in the manufacturing of tire cords, fishing lines, tow ropes, and woven fabrics. 3.5 Methanol Anhydrous methanol provided by Aldrich was used for the synthesis of caprolactone. The important physical properties of the methanol used are listed below: Table 3.5 : Physical Properties of Methanol Density (25 °C) : 0.78663 g/cc Boiling Point : 64.7 °C Freezing Point : -97.68 °C Viscosity (25 °C) : 0.541 cP Solubility in water : miscible Specific heat, liquid (25 °C) : 0.6054 cal/(hr. °C) 3.6 Catalysts 3.6.1 Catalysts for Copolymerization Different catalysts were employed to catalyze the e-caprolactam/a-caprolactone copolymerization reaction. Trialkyl aluminum has been known to be an efficient catalyst for the homopolymerization of lactams and lactones. For this reason, it has been used for the catalysis of the copolymerization reaction of these monomers. However these 24 catalysts are highly moisture sensitive and pyrophoric and hence they require special processing and handling techniques. On exposure to moisture, these react explosively to form aluminum hydroxide. R AIéR ,. 3H20 __. AI(OH)3 + 3R-H R They are freely soluble in and unreactive with aromatic and saturated aliphatic hydrocarbons. Because such solutions are less likely to ignite simultaneously on contact with air, large quantities are sold in hydrocarbon solution. Generally R3Al compounds exist as dimers through electron - deficient bonding. However if the R group is bulky, as in the case of isobutyl, the R3Al compound is monomeric. R. \ \ /R \ ,zR Al A. ' R/ \R/ \R Besides trialkyl aluminum, freshly prepared Na-caprolactam and NaH were also utilized for the anionic copolymerization of epsilon caprolactam and epsilon caprolactone. 3.6.1.1 Triethyl Aluminum (TEA) Al(C2H5)3 Triethyl aluminum is the most common of all trialkyl aluminums. Typical properties of TEA used are listed below. 25 Table 3.6 : Properties of Triethyl Aluminum State of Association : Dimer Melting Point : -58 °C Density (25 °C) : 0.835 g/cc Viscosity (25 °C) : 2.6 cP TEA is stable indefinately when stored under an inert atmosphere at ambient temperature. It begins to decompose slowly as shown below at temperatures around 100 °C. (CZH5)3A| —> C2H4 + (C2H5)2AIH (CzH5)2AIH —> 202H4 + Al + 3/2 H2 In this work, TEA provided by Aldrich (1.9 M solution in Toluene) was used. Typical present day applications of TEA include : -- Butadiene Polymerization Catalyst -- Isoprene Polymerization Catalyst. -- Propylene Polymerization Cocatalyst. 26 3.6.1.2 Tri isobutyl Aluminum (TBA) Al (CH2 - CH - CH3 )3 H3 TBA, a higher homolog of the same family differs somewhat from the other trialkyl aluminums because of its branched structure. Typical physical properties of TBA are listed below : Table 3.7 : Physical Properties of Triisobutyl Aluminum (TBA) Melting Point : 0 °C Density (25 °C) : 0.781 g/cc Viscosity (25 °C) : 1.9 cP Prolonged exposure to high temperatures may result in the decomposition of TBA. TBA utilized for the copolymerization reactions in this work was provided by Aldrich as a 1.0 M solution in toluene. Nowadays TBA is extensively used as a catalyst for several polymerization reactions. These include : -- Isoprene Polymerization (Ziggler Natta Catalyst) -- Butadiene Polymerization -- Oxetane Polymerization. 27 3.6.1.3 Na-Caprolactam (NaCL) bc=o (CH2)5 l Na+ Anionic co-polymerization is one of the facile ways for the ring opening copolymerization of caprolactam and caprolactone. The living copolymerization reaction requires initiation by an anionic species. Na-Caprolactam, a sodium salt of caprolactam, has been proved to be nucleophillic enough to initiate the lactam - lactone copolymerization reaction. The mechanism has been discussed in detail in chapter 5. Freshly prepared Na-caprolactam was used for catalytic purposes. It’s synthesis was carried out by two different methods. The basic reaction involved is : p020 bCZO (CH2)5 I + Na ——* (CHz)5 I + 1/2 H2 Methmfl; Caprolactam was melted at 80 °C in a nitrogen environment. Na metal lumps (under kerosene) were divided into fine particles of about 1 mm size. These were then continuously flushed with N2 for about 8 hrs to reduce the kerosene content to a minimum. Dried Na was added to molten caprolactam under agitation and was allowed to react/dissolve. The molten reaction mix was then cooled in a teflon tray under N2. A thermal analysis of the catalyst formed is shown in fig. 3.1. As seen, it shows a wide melting range from 150 - 240 °C. This can be attributed to the fact that the Na- 28 m uco oo E (CH2)5 I p“ p0 p““"“°“2’5‘°' ll 0 bc=o (Cl‘b)5 I b°=° N—c-(CHz)s—0' + x (Cl-E5 (I) II o b c=o (CHz)5 | ’ N_[—fi: —— (CHz)5—O-- —-C —— (CHz)5—O' XII p c=o (Cl-1215 I ”3+ b0: vN—[—fi:—(CH2)5—O— :c—5—O‘ + (CH2)5 I O _ /\ c=o ——> (CH2)5 l O Na+ x+1 \-/N—|}—|(|: -— (CH2)5—-O- —i\3 - (CH215—N' H 42 /\ C: o (CH2)5 0\ Na“ bizo N—— —IC— (CH2)5—O —-C — (CH2)5—N H + y (CH2)5 K/ _]x+1\\ . \JN—H O pC=O Na ——> (CH2)5 K/N_[— c—(CH2Is—o —] 1[—“ C—(CH2)5—-N —-]—c”:_(CH2)5—N'—H x+ y (I) H 5.2.2 Anionic copolymerization using Na-caprolactam as catalyst and HMDI as co catalyst. C/\c|:=o bc-zo bc=o Na" ( H.215 N' + (CHz)5 I —> (CHz)5 l O N—C— (CHz)5—O‘ Na+ (H) bc=o bc=o Cl-b I ( )5 N—CHZ—(CHzls—O‘ + x (CH2)5 (I) O bc=o ((311215 I —“’ pN—— —C—(CHz)5——O— C——-(CHz)5—O' I. “11 bc=o (CHz)5 I \\/N— —C-(CHz)5—O— — C—(CHzls—O' +O=C=N— 'o ‘1') /\C=o _. (Cl-b)5 l pN— —c— (CHzls—O c— hi—R II x+1 II 0 O 43 b C: 0 (011215 /\c= o pN—— IC——(CHz)5—O C— N—R + (Cl'b)5 N x+1]|) p H be. p H C=O —’ (CHz)5 I pN——O —|C—(CHz)5—O C— N —R + (CH2)5 I x+1|| Na+ O bc=o H I I N—c— (CH2)5— N' c— (CH2)5—o C— N— II II M II o o —-> (CH2)5 bc=o (CH2)5 l _ H bc=o N—c— (CH2)5—N +1i— (CH2)5—o —]-— c—— N—R + y (CH2)5 I x+10 ll ‘- 0 N H b C=O H -———> (CH2)5 N—C— (CH2)5— N —-[—| C— (CH2)5—N C— (CH2)5 -O C— lil— ll ”1” o o H 5.3 Experimental Approach 5.3.1 Copolymerization using Trialkylaluminum as catalyst : Dried Caprolactam (32.5 g) was taken in a 3 neck flask and melted in an oil bath maintained at 80 °C. TEA was then added (2.3 ml) to it followed by dried caprolactone (17.5 ml). The oil bath was then replaced by another oil bath maintained at 160 °C. The reaction mix was constantly agitated with a stirrer. Typical reaction setup is shown in figure 5.1. Reaction runs were taken for different reaction times. The products were then EVE—m iHZHS—M—HA—NH “ fin EDD—r.— HZ—a gamma.— xofi. Nz 1:0 Hsflafl dial—:— .7 _E g. I I“ . r A \ «05.2.1 L ”ES: ; 0.03.9.5... k mmozm loan—Hm..— EEOEHE H5255 m5 Nz “NEH—20:13:. 45 quenched at the end of a particular time period. Similar runs were taken using Triisobutyl aluminum (TBA) as catalyst. 5.3.2 Copolymerization using Na-caprolactam as catalyst Dried Caprolactam (32.5 g) was taken in a 3 neck flask and melted in an oil bath maintained at 80 °C. Dried a-caprolactone (17.5g) was then added to it and the mixture was allowed to equilibrate for a couple of minutes. 1.0 mole % of Na-caprolactam was added to it [5, 43] and subsequently the oil bath was replaced by another oil bath at 160 °C. The reaction mix was constantly agitated with a mechanical stirrer. Reaction runs were taken for different reaction times. The reaction was terminated by quenching the mix at the end of the stipulated period. 5.3.3 Copolymerization using Na-caprolactam and HMDI (co catalyst) Dried Caprolactone (17.5 g) was taken in a 3 neck flask and heated at 160 °C. 0.005 g of Na- caprolactam was added to it. The reaction mix was agitated for 5 minutes. Added 0.1 g of HMDI to it followed by molten caprolactam (32.5 g 160 °C). The anionic reaction was stalled by quenching the flask in an ice bath. Runs were taken for different reaction times. Purification The reaction products were then purified to obtain polyester-amides. For this a weighed quantity of the solid copolymer was dissolved in a mixture of Chloroform and 46 Trifluoroethanol (9 : 1). It was then added to diethyl ether, where the copolymer precipitates as a white solid. The copolymer were dried in a vacuum oven at 60 °C for 24 hours. 5.4 Results Comparison of the copolymer yields obtained using different catalysts for different times is shown in figure 5.2. The structure of the copolymer obtained was confirmed by FT-IR analysis (figure 5.3) which showed a C=O stretching vibration band at 1720 cm"l (ester), C=O stretching vibration band at 1640 cm'1 (amide) and N-H bending vibration band at 1550 cm"1 (amide). It can be seen that the caprolactam copolymerization proceeds slowly when complex coordinated catalysts (TEA and TBA) are used. A 1 hour reaction gave a 32% yield of copolymer with TEA and 50% with TBA. On the other hand Anionic copolymerization using Na-caprolactam yielded high yields of 67 % of copolymer in 30 minutes. The addition of an activator HMDI resulted in the rapid incorporation of caprolactam onto the polymer chains. This resulted in a phenomenal 52.5 % yield in 10 minutes and 86 % yield in 30 minutes. The resulting copolymers had very low crystallinity. 47 Copolymer yield (7.) Reaction Time (min) FIGURE 5.2 : TABLE 5.1 : COPOLYESTER-AMIDE YIELD BY DIFFERENT CATALYSTS COPOLYMER YIELD WITH DIFFERENT CATALSTS FOR DIFFERENT REACTION TIMES OVER DIFFERENT REACTION TIMES 10 (MIN) 20 (MIN) 30 (MIN) 45 (MIN) 60 (MIN) TEA - - 10.05 % 23.40 % 31.30 % TBA 21.30 % - 41.80 % - 50.30 % Na-CL 43.50 % 65.34 % 66.99 % - -- Na-CL + HDI 52.50 % 76.00 % 86.10 % - - 48 hazy—Oh H§<1¢EmH>AOAOU HE EC Ewan E u fin EU: 3%.. 8.: 8.2 3.: 8.2 8.2 8.: m cm: 8.: 8.2 8.2 2.2 8.8 22%. _ T n . 2 1: fl 2 T a 1 en . 3 4 3 i 9 1 an inn 13 1 no r 93 %T Chapter 6 Ester -Amide Interchange Reaction Till now, in this work, the focus for the synthesis of copolyamide - "esters (CPAEs) was from the monomers, epsilon caprolactone and epsilon caprolactam. The anionic polymerization of the monomers definitely provides a rapid route to CPAE synthesis. However, there are a sizable number of variables that need to be controlled. An alternate route was also employed for the CPAE synthesis which involved an amide - ester interchange reaction between polyamide and polyester (Nylon 6 and PCL). The structure of the polymer formed was then confirmed by IR and NMR spectroscopy. 6.1 Synthesis of CPAEs 6.1.1 Pretreatment of Materials Polycaprolactone (TONE ® 767, MW = 50000) were purchased from Union Carbide Corp. Nylon 6 (MW = 25000) was purchased from Aldrich Chemical Co. It is required that all materials used, be moisture free. For this purpose, Nylon 6 was dried in a vacuum oven at 70 ° C and 22 in. Hg for 24 hours and PCL was dried at 40° C for 24 hours. The materials were then stored and handled under nitrogen. 49 50 6.1.2 Esteramide Interchange Reaction -{-fi3- (CH2)5—0‘}— + —[—C- (CH2)5—N4— m n 0 i) H Zn-acetate; —{—c— (CH2)5—0 1T1?" (CH2)5—1'1 n, — (CH2)5—0+— “ u m" time H Block copolymer time ——> —[—C —- (CH2)5—O— C — (CH2)5—N—C — (CHz)5—-N ——C - (CHz)5—O — II H II II 0 0 H 0 H 0 Random copolymer m', m" < m and n', n" < n An equirnolar ratio of PCL and Nylon 6 were taken in a three neck round bottom flask in a nitrogen glove box. 0.5% of anhydrous zinc acetate was added as a catalyst. The mixture was then heated in a heating mantle, under nitrogen and was stirred when it began to melt after a few minutes. The temperature was then raised to 270 ° C and was maintained for a period of 2 hours and 4 hours. Typical experimental setup is shown in figure 6.1. As in the time course of a typical amide - ester interchange reaction, it was found that CPAEs with large blocks were formed in the first stage. The blocks got shortened along with time, and in the final stage random copolymer was formed. 6.1.3 Preparation of Blends Blends of polyamide and polyester were prepared similarly by stirring PCL and Nylon 6 at 270° C for 2 hours in the absence of a catalyst. Inspite of the absence of a catalyst, a small degree of ester-amide interchange may occur. 51 “H25 m<0 NZ 26—83mm HUZdeDfiE . ngmflhmm ZOE APE—m ASHZSHANH u a.» EOE Hz: games.— 653 N2. C . war—.722 02:24: “OBOE ”—335.50 .55. ”maul.— :EWNHE— 52 6.2 Analysis 6.2.1 Differential Scanning Calorimetry (DSC) DSC is an analytical technique in which the difference in heat flow between a sample and an inert reference is measured as a function of time and temperature as both are subjected to a controlled environment of time, temperature, atmosphere and pressure. DSC is used to measure temperatures and heat of transition, specific heat, rate and degree of crystallinity, purity, rate of reaction etc. Since the heating is controlled by a computer it is possible to follow a complex heating algorithm Thermal Analyst 2200 system (TA Instruments) was used to carryout DSC to observe the depression in the melting point (Tm) of the polymers, especially nylon 6. Conditions of DSC were as follows : Sample size : 9 - 11 mg Heating rate : 10° C / min. Mode : Standard, non-modulated. 6.2.2 Soxhlet extraction Soxhlet extraction was carried out to separate the nylon incorporated PCL from the PCL incorporated Nylon 6. The extraction apparatus consisted of an Allihn condenser, a soxhlet extractor, a 500 ml flat bottom single necked round flask and cellulose extraction thimbles (figure 6.2) and a hot plate frame. To extract PCL, chloroform was used since Nylon 6 is insoluble in chloroform. The solid sample was dried and powdered or finely cut. A weighed amount (about 10 g) 53 AllihnCondemOt 114,]; mm. 1 T——— Soxhlet Extraction Tube ‘Ihrm' ble Sample Flask FIGURE 6.2 : SETUP FOR SOXHLET EXTRACTION of this sample was placed in a cellulose thimble. About 300 ml of chloroform was taken in the dried flask and boiled with the help of a hotplate. The vapors condensed by the water running through the condenser, dripped down into the thimble dissolving PCL. When the solvent level reached a certain height within the extractor, it was automatically flushed back into the flask. Thus the solid wpolymer/blend was continuously refluxed with fresh solvent. Extraction was carried out for 48 hours. The thimble were then dried and weighed to give the weight of the residue as the difl’erential weight. 6.2.3 Fourier Transform Infrared Spectroscopy (FT-IR) The dissolved phase of extraction was then qualitatively analyzed using 8 FT- IR Spectrometer. A couple of drops of the solution in chloroform were taken on a Type 62 disposable IR cards and were allowed to dry. The cards were then placed in a Perkin Elmer System 2000 FT-IR The spectrum was recorded in the range of 1400 - 2000 cm”. 54 6.2.4 Nuclear Magnetic Resonance Spectroscopy (NMR) As a confirmatory test for the presence of amide linkages within the PCL chains dissolved in chloroform, a carbon NMR spectrum was collected. The chloroform solution phase from soxhlet extraction was dried in a rotavapor and then in a vacuum oven at 35°C for 24 hours. It was then dissolved in CDC13 (Duteriated Chloroform) and the solution was then analyzed in a 300 MHz Gemini NMR Spectrometer. A proton NMR spectrum was also collected to quantitate the amount of amide within the PCL chains. 6.3 Results and Discussion The process of the amide ester interchange reaction can be followed by DSC. Fusion peaks for Nylon 6 and PCL are shown in figure 6.3. Fusion peaks in heating, which revealed the reaction between nylon 6 and PCL (molar ratio 1:1) were as shown in figure 6.4. It can be seen that as the reaction proceeds the position of the fusion peaks shifted to lower temperatures, and their shape broadened gradually, possible indicating a decrease in crystallinity. When the reaction time was 240 minutes, the fusion peak due to PCL on the lower temperature side was not detected. Nylon 6 exhibits a clear depression in it’s melting point. The fusion peak shifted from 225 °C to 170 °C in 2 hours and to 145 °C in 4 hours. On the other hand, the nylon-PCL blend did not exhibit any major shift in fusion peaks. 55 2 PCL 1— o... O 3 \ 59.70 c E ‘v 07 2.J/- 5 E 8 - _ = 1 -2— -3 I l V I v 1 v I v v u v ‘ v -60 -60 -40 -20 . 0 20 40 60 80 100 1230:1312.qu 1.5 NYLON6 1.04 0.5— 3 ’— 0.0— 3 O a 8 i 210.54°c = -o.5— -1.0— ‘1.5 V 1 fi— I v 1 v I f 0 50 100 150 200 3:10 Tempulth’C) Figure 6.3 : DSC Plots for Nylon 6 and PCL 56 0.8 COPOLYESTER-AMDE (4 hr reaction tile) '00 3 E. £41.24 5 '01 0‘0 ab ' 160 F 150 3110 ' 180 ”mm 0.4 COPOLYESTER-AMIDE (2 hr reaction time) 0.2‘ 3 E 0.0-- 3.6.2. -0.4- 0.6“ 50 ‘00 100 T i no am Temper-8mm 0.0 NYLON-PCLBIEND 3 ’3' I 15~ i “a ab .86 ' 15'0 ' ado ' an Tel-pentlflm DSC plots of Copolyester - Amide. and Nylon-PCL blend 57 The results of Soxhlet extraction are shown Table 6.1. It is seen that as the reaction time increases the nylon chains get shorter and shorter and more and more of nylon gets incorporated in PCL. Table 6.1 : Results of Soxhlet Extraction of ester-amide interchange product. Sample wt Sample in Solid wt% sample wt % sample solution (g) Residue (g) in solution in residue Blend (A) 8.200 5.527 2.673 67.4 32.6 2 h Run (B) 9.880 7.191 2.689 72.8 27.2 4 h Run (C) 10.070 8.455 1.615 83.9 16.1 Furthermore, the formation of CPAE was confirmed by infrared analysis of the chloroform soluble fraction (PCL) after soxhlet extraction. Figure 6.5 shows the IR spectra of the product formed after a 4 hour ester-amide interchange reaction. It exhibits an absorption band at 1725 cm'1 due to PCL (non-conjugated C=O stretching vibration band). However it also reveals absorption bands due to Nylon 6 at 1640 cm'1 (C=O stretching vibration band in amides) and 1550 cm"1 (N -H bending vibration band). On the other hand, as shown in figure 6.5, the dissolved phase of the Nylon 6/PCL blend showed the presence of only PCL (1725 cm"'). To determine quantitatively the amount of amide linkages in PCL, NMR spectroscopy was used. As shown in figure 6.6 and 6.7, the carbon spectra displayed 5 CH2 peaks of the major component (PCL) and 5 CH2 peaks of the minor component (Nylon 6). The carbonyl carbon peak of PCL appeared at a shift of 170 ppm. However 58 the carbonyl carbon peak of Nylon 6 was not distinct, but appeared as a shoulder on the carbonyl carbon peak of PCL. The proton NMR on integration demonstrated a PCL to Nylon 6 ratio of 10 : 3 for the two hour ester-amide interchange reaction (figure 6.8) and 10 : 4 for the 4 hour reaction (figure 6.9). The proton NMR of the PCL - Nylon 6 blend displayed only 5 CH2 peaks corresponding to PCL (figure 6.10). The above results Show that copolyamide-ester was formed by the amide-ester interchange reaction between Nylon 6 and PCL. Another fact that draws attention is that the Nylon incorporation in PCL grew only from 10 : 3 to 10 : 4 when the reaction time was increased from 2 hours to 4 hours. This indicates that in the latter two hour period, the process of the formation of copolymer from homopolymer slows down. However during this period the copolymer rearranges itself into another copolymer with a different and more random sequence of PCL and Nylon 6 along the chain. 59 93.164 :7 — I 6 ' 91 J1” I l I l T N 2000 1900 1800 1700 1600 1500 ca" 1400 PCL-NYLON 6 BLEND u.”- If .I 73-“ i I I I r u r 2000 1900 1800 1700 1809 1800 1400 cr‘ 4 HR. ESTER-AMIDE INTERCHANGE REACTION PRODUCT FIGURE 6.5 : IR SPECTRA OF THE CHLOROFORM SOLUBLE PHASE OF THE REACTION PRODUCT 60 SODA—Cy: ZOE—.05 ”muggy—E ngmm—hmm— a N E .mO Ema—m flags—Om ECHOKOAIU REF NO (Em—mm £22 2030 u 06 EOE— iaa w om ov . om om co" ,om“ av" om« 3m“ . _ n p p . s p p . n . . :_‘Elai.xfil‘i’4gé .p _ .3441... ._. Hausa”: . _ ...-”1.1:. 3.1.2:. ifldduaia1u.%jii..iqa.laj_ifiin13.1313: ...: cow 61 EDA—O": ZOE—0(5— HUZEE HEN—awn.— E v E NO gm flags—Om SEQ—OMOx—HU E HO (Eu—hm g 2.620 n 66 EU: sum 0 cm O? on. cm can om“ own on“ em“ cow 62 EPA—Om.— 26515— .5ng figs—mama ..E a E .5 Ha.— ..Emaqom 2:98:35 n5. .5 sum ~22 2082: u 3 ago—...— 63 HUDQOmm 2°85 “calm—HZ— ngmamfl a v E MO Ema.— fldgflcm 529305 E hO gflmm g lacy—fl « a.» EU: film—Am 40m 3 ZOE HE .mO Ema.— HAgAOm EOHOMOANU E MO (EH45 g ZOBOHA u 3.9 g0: I-O a...“ ...~ ”an.“ ...» an... ...“. «.... )1! 1r. 4:} ..r. 1.. H N n v m o n 4 I. I -7- x V w x _ Chapter 7 Conclusions and Recommendations 7.1 Synthesis of Caprolactone Studies indicate that the Baeyer Villiger oxidation of cyclohexanone by molecular oxygen and an aldehyde in the presence of a catalyst is the most common method for the manufacturing of a-caprolactone. However because of the high cost of Benzaldehyde involved, the cost of the caprolactone manufactured remains high. An attempt was made for its synthesis from cheap and easily available material like e-caprolactam and methanol. However as shown in chapter 4, the method gives a very low yield of e-caprolactone. A closer observation of the gas Chromatogram indicates that the formation of other complex products from 8-caprolactarn is very high. Hence, even though the conversion of caprolactam is about 61%, the yield of e-caprolactone obtained is unacceptably low. Thus the use of a specific catalyst which may selectively increase the rate of 8- caprolactone formation and simultaneously inhibit other side reactions is required. The discovery of such a catalyst may lead to a commercially viable process for the production of e-caprolactone (S 1.9/ lb) from a—caprolactam ($ 0.90 / lb). 65 66 7.2 Synthesis of Copolyamide-esters Copolyamide-esters were synthesized by two methods : 1. Copolymerization of s-caprolactam and e-caprolactone. 2. Ester-amide interchange reaction between Nylon 6 and PCL. As seen in chapter 4, the copolymerization of a-caprolactone and a-caprolactam proceeds much faster with anionic catalysts than by complex coordinated catalysts. However the products formed had very low crystallinity which makes it difficult to measure its melting point. The formation of a copolyamide-ester was confirmed by IR studies. The use of an activator, HMDI along with the catalyst, Na-caprolactam gave a much higher yield of copolymer in a short time. The yield of 52.5 % in 10 minutes and 86% in 30 minutes is much higher than any of the other catalysts. However the molecular weight of the copolymers is very low. If it is possible to further reduce the reaction time, and also increase the molecular weight of the copolymer then it will be possible to carryout an extrusion polymerization in a twin screw extruder, provided proper dry conditions are maintained. The ester-amide interchange reaction provides a simpler alternative for the CPAE synthesis. The formation of CPAE was confirmed by FT-IR and NMR spectroscopy. The breaking of the polymer chains can be followed by the depression in melting point. Initially block copolymers are formed which gradually rearrange into a more random form as the reaction proceeds. It has been observed that highly random copolymers are more easily biodegraded than the block ones [5]. This is because the polymer chain in a 67 random copolymer, on degradation of PCL linkages will be reduced to monomers and oligomers of caprolactam which degrade easily. If required a single screw extruder with a pelletizer can be attached at the end of the reactor in which the esteramide reaction has taken place. Thus biodegradable resin pellets can be obtained for further processing like blown film extrusion, injection molding etc. Since the world is getting more and more environment conscious, such copolymers have a tremendous growth potential in tomorrow’s market. 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