Aliphatic dithiol-diacid type polythioesters were first enzymatically prepared by the direct polycondensation of hexane-1,6-dithiol and diacid diesters using the immobilized lipase from Candida antarctica (lipase CA). As a typical example, diethyl sebacate and hexane-1,6-dithiol were polymerized using lipase CA in bulk in the presence of molecular sieves 4A to produce the corresponding polythioester with an M̄w of 10 200 in 90% yield. Both the melting and crystallization temperatures of the produced polythioesters were higher when compared to those of the corresponding polyoxyesters. A higher molecular weight polythioester was produced using lipase in a two-step procedure, i.e., cyclization with subsequent ring-opening polymerization.
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