Copolymers transesterification

Higher alkyl acrylates and alkyl-functional esters are important in copolymer products, in conventional emulsion appHcations for coatings and adhesives, and as reactants in radiation-cured coatings and inks. In general, they are produced in direct or transesterification batch processes (17,101,102) because of their relatively low volume. 

Polycarbonates are prepared commercially by two processes Schotten-Baumaim reaction of phosgene (qv) and an aromatic diol in an amine-cataly2ed interfacial condensation reaction or via base-cataly2ed transesterification of a bisphenol with a monomeric carbonate. Important products are also based on polycarbonate in blends with other materials, copolymers, branched resins, flame-retardant compositions, foams (qv), and other materials (see Flame retardants). Polycarbonate is produced globally by several companies. Total manufacture is over 1 million tons aimuaHy. Polycarbonate is also the object of academic research studies, owing to its widespread utiUty and unusual properties. Interest in polycarbonates has steadily increased since 1984. Over 4500 pubflcations and over 9000 patents have appeared on polycarbonate. Japan has issued 5654 polycarbonate patents since 1984 Europe, 1348 United States, 777 Germany, 623 France, 30 and other countries, 231. 

Structurally the difference between PEN and PET is in the double (naphthenic) ring of the former compared to the single (benzene) ring of the latter. This leads to a stiffer chain so that both and are higher for PEN than for PET (Tg is 124°C for PEN, 75°C for PET is 270-273°C for PEN and 256-265°C for PET). Although PEN crystallises at a slower rate than PET, crystallization is (as with PET) enhanced by biaxial orientation and the barrier properties are much superior to PET with up to a fivefold enhancement in some cases. (As with many crystalline polymers the maximum rate of crystallisation occurs at temperatures about midway between Tg and in the case of both PEN and PET). At the present time PEN is significantly more expensive than PET partly due to the economies of scale and partly due to the fact that the transesterification route used with PEN is inherently more expensive than the direct acid routes now used with PET. This has led to the availability of copolymers and of blends which have intermediate properties. 

A porphinatoaluminum alkoxide is reported to be a superior initiator of c-caprolactone polymerization (44,45). A living polymer with a narrow molecular weight distribution (M /Mjj = 1.08) is ob-tmned under conditions of high conversion, in part because steric hindrance at the catalyst site reduces intra- and intermolecular transesterification. Treatment with alcohols does not quench the catalytic activity although methanol serves as a coinitiator in the presence of the aluminum species. The immortal nature of the system has been demonstrated by preparation of an AB block copolymer with ethylene oxide. The order of reactivity is e-lactone > p-lactone. 

FIGURE 5 Stepwise synthesis of a triblock copolymer (PCL-PLA-PCL) of PCL and polylactic acid using aluminum coordination catalysts to minimize randomization of the block structure by transesterification. (From Ref. 43.)... 

Ester-thioester copolymers were enzymatically synthesized (Scheme 7). ° The lipase CA-catalyzed copolymerization of e-caprolactone with 11-mercaptoundecanoic acid or 3-mercaptopropionic acid under reduced pressure produced the polymer with molecular weight higher than 2 x 10". The thioester unit of the resulting polymer was lower than the feed ratio. The transesterification between poly(8-caprolactone) and 11-mercaptoundecanoic acid or 3-mercaptopropionic acid also took place by lipase CA catalyst. Recently, aliphatic polythioesters were synthesized by lipase CA-catalyzed polycondensation of diesters with 1,6-hexanedithiol. ... 

The copolymerization of lactones took place through enzyme catalysis [92]. The copolymerization of e-CL with d-VL catalyzed by lipase PF affords the corresponding copolymer having a molecular weight of several thousand. From 13C NMR analysis, the copolymer was found to be of random structure having both units, suggesting the frequent occurrence of transesterifications between the polyesters. In the copolymerization of 8-OL with e-CL or DDL, random copolyesters were also formed [84], whereas the copolymer from e-CL and PDL was not statistically random [88]. 

Early studies using calcium oxide, carbonate, and carboxylates reported low activities for the polymerization of LA, even in bulk at 120-180 °C.827,828 PolyGA and copolymers of GA with CL and L-LA have been prepared using Ca(acac)2, but again high temperatures (150-200 °C) are required.829 Under these conditions transesterification occurs, although to a lesser extent than in analogous Sn(Oct)2-initiated polymerizations. 

Ethylene carbonate, 10 640, 665 in lithium cells, 3 459 molecular formula, 6 305t physical properties, 6 306t transesterification of, 13 651-652 Ethylene-carbon monoxide (ethylene-CO) copolymers, 5 9 10 197 Ethylene chlorohydrin process, 10 640 Ethylene-chlorotrifluoroethylene (E-CTFE) alternating copolymer (ECTFE), 15 248... 

It was previously mentioned was that a large number of minor copolymers of PET have been developed over the past 50 years, with the intent of modifying textile fiber properties and processability [2, 3], Of broader interest is that some of these textile modifications, such as PET copolymers with metal salts of 5-sulfoisophthalic acid (SIPA), have their own rich chemistries when the extent of polymer modification is increased beyond textile levels. An example of such a modification is that changing the counterions associated with SIPA can significantly effect the kinetics of polyester transesterification reactions (the... 

Studies have shown that this reaction is a result of transesterification between PBT and PC. Transesterification is influenced by many factors, including PBT end groups and catalyst residues. While a little copolymer formation is not a bad thing for the performance of the blend, uncontrolled reaction is unacceptable since the same material could never be made twice. Fortunately, methods to control this chemistry were developed. Generally, addition of certain phosphites is used to quench the transesterification and related reactions [45, 46], Since phosphites are also used as antioxidants and color stabilizers, the quencher was often... 

Smith et al. [64] prepared a series of PET/PTT copolyesters, and found that addition of the other component suppressed the melting point of the respective homopolymer. Between 37 and 60 % PTT content, the copolymers became amorphous and did not show any melting endotherms in the differential thermal analyzer scans. A similar behavior was observed by Balakrishnan and coworkers [102] in PET/PTT copolyesters prepared by the transesterification of PET with PDO, and by the copolymerization of EG and PDO with DMT [103, 104], The non-crystallizing behavior of copolymers with intermediate contents of the respective component is similar to that of a eutectic mixture, indicating formation of random copolyesters. The 7 g and solubility temperature of the copolyesters were, however, continuous and went through minima with increasing PTT content [64],... 

On the other hand, when sCL is copolymerized with dilactones such as GA [38] and (D- andD,L-)LA [39], tapered or pseudoblock copolymers are obtained with a reactivity ratio much in favor of the dilactone. As an example, the reactivity ratios in the copolymerization of eCL and D,L-LA in toluene at 70 °C are r = 0.92 (e-CL) and r2=26.5 (D,L-LA). Very similar reactivity ratios were calculated for copolymerization between eCL and L-LA, other experimental conditions being kept unchanged. However the control over the polymerization is lost due to transesterification side reactions perturbing the propagation step. Such a behav-... 

Fig. 11 Copolymerization of CL with aliphatic co-mercapto carboxylic acids (top) and transesterification of pCL with aliphatic co-mercapto carboxylic acids (bottom) to give random copolymers with thioester linkages [30]...

In a related approach, Padovani et al. prepared copolymers of styrene and a styrene derivative containing two pendant ester bonds using free-radical polymerization (Scheme 15) [108], Transesterification reactions were conducted with Novozym 435 as the catalyst and benzyl alcohol or (rac)-l-phenylethanol as the nucleophile. Interestingly, the ester bond closest to the polymer backbone (position A in Scheme 15) remained unaffected, whereas ester bond B reacted in up to 98% to the corresponding benzyl ester. The transesterification was not only highly chemoselective but also enantioselective. Conversion of (rac)-l-phenylethanol in the transesterification reaction amounted to a maximum conversion of 47.9% of the (/ )-alcohol, and only at the ester position B. 

The potential for rapid randomizing processes in the copolyesters at elevated temperatures has been demonstrated conclusively by heating a mixture of the two homopolymers of PHBA and PHNA at 450 °C at a pressure of around several hundred psi [40]. Within a few seconds a viscous melt was observed to extrude from the cracks in the mold. Analysis of this material showed a structure consistent with the random 50/50 copolymer of HBA/HNA (see Figs. 18 and 19). We estimate that at this very high temperature the rate of interchain transesterification reactions corresponds to 1000 ester interchanges/chain/10 s. 

In the saponification of an EVA copolymer, usually an alkali catalyst is used. The alkali catalyst acts as a catalyst for the transesterification between EVA and an alcohol. It is known that in a process where saponification proceeds mainly with this transesterification, when water is present in the reaction system, the alkali catalyst is consumed, and the reaction rate of the saponification decreases. 

With one exception [447], only sulphonated resins were used as catalysts in kinetic studies of esterification and transesterification, the resins being almost exclusively styrene—divinylbenzene copolymers in one case, a sulphonated phenol—formaldehyde resin was also used [433]. The main factors determining the catalytic activity are (i) the concentration of functional groups in protonated form (— S03H groups) and (ii) the degree of crosslinking of the copolymer (characterised by the divinylbenzene content). 

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