Enzyme‐catalyzed preparation of polymers offers several potentially valuable advantages over the usual polymerization procedures and has been studied for several years. A significant limitation on the polyesters prepared to date has been the low molecular weights achieved. The present studies have established that, in the polycondensation of bis(2,2,2‐trifluoroethyl) glutarate with 1,4‐butanediol using porcine pancreatic lipase as the catalyst, this limitation arises from at least two sources: hydrolysis of activated ester end groups by water introduced along with the enzyme and the polymerization's reaching equilibrium despite using the poorly nucleophilic 2,2,2‐trifluoroethanol as the leaving group. Evidence is also developed that the presence of trifluoroethanol accelerates the release of the enzyme‐bound water which hydrolyzes the activated ester end groups. The hydrolysis could be avoided by choosing a relatively high‐boiling solvent, such as bis(2‐ethoxyethyl) ether, then removing the trifluoroethanol by placing the reaction mixture under vacuum periodically or by drying the enzyme rigorously. The vacuum method also removed the limitation on molecular weight resulting from the reaction's reaching equilibrium. A further improvement in the molecular weight to nearly 40,000 daltons, well within the range that is technically interesting, was achieved by using 1,2‐dimethoxybenzene or 1,3‐dimethoxybenzene as the polymerization solvent. © 1995 John Wiley & Sons, Inc.

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Enzyme-catalyzed preparation of polymers offers several potentially valuable advantages over the usual polymerization procedures. This paper summarizes our successful use of lipase-catalyzed polycondensations to prepare both a series of achiral [AA-BB]x polyesters from bis(2,2,2- trichloroethyl) alkanedioates and diols and of an optically active, epoxy-substituted polyester having a stereochemical purity estimated to be greater than 96%, from racemic bis(2,2,2-trichloroethyl) trans-3,4-epoxyhexanedioate and 1,4-butanediol. All of the reactions were carried out at ambient temperature in anhydrous, low to intermediate polarity, organic solvents such as ether, THF, 2-ethoxyethyl ether, dibenzyl ether, o-dichlorobenzene, or methylene choride, using porcine pancreatic lipase (PPL) as the catalyst. The molecular weight achieved by the polycondensation is limited by accumulation of the trihaloethanol that forms as the reaction progresses, probably because it frees enzyme-bound water permitting hydrolysis of the polymer to occur. This problem has been alleviated by using a high boiling solvent and removing the alcohol by placing the re'action mixture under vacuum.

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