Linear copolymeric poly(thia‐alkanedioates) by lipase‐catalyzed esterification and transesterification of 3,3′‐thiodipropionic acid and its dimethyl ester with α,ω‐alkanediols

Linear copolymeric polyesters (polyoxoesters) containing thioether functions [poly(3,3′‐thiodipropionic acid‐ co ‐α,ω‐alkanediols)] were formed in good yield by esterification of an equimolar mixture of 3,3′‐thiodipropionic acid (4‐thiaheptane‐1,7‐dioic acid) and 1,6‐hexanediol (weight average molecular mass, M W >600 Da: ∼81% after 6 h) or 1,12‐dodecanediol ( M W  > 900 Da: ∼90% after 6 h) catalyzed by immobilized lipase B from Candida antarctica (Novozym 435) for up to 336 h in moderate vacuo without a solvent or drying reagent in the reaction mixture. Poly (3,3′‐thiodipropionic acid‐ co ‐1,6‐hexanediol) and poly (3,3′‐thiodipropionic acid‐ co ‐1,12‐dodecanediol) were extracted from the reaction mixtures using tetrahydrofurane and precipitated from tetrahydrofurane— iso ‐hexane (1:1, v/v) at ∼0°C. The precipitate of poly(3,3′‐thiodipropionic acid‐ co ‐1,6‐hexanediol) showed a maximum molecular weight of 6 × 10 5 Da corresponding to a M W of ∼24,200 Da and a degree of polymerization of up to 2,150 monomer units. The precipitated poly(3,3′‐thiodipropionic acid‐ co ‐1,12‐dodecanediol) showed a maximum molecular weight of 8 × 10 5 Da corresponding to a M W of ∼27,200 Da and a maximum degree of polymerization of up to 2,200 monomer units. The chemical structures of both polyesters containing thioether functions were confirmed by chemical derivatization and NMR spectrometry. The chemical structures of various low‐molecular weight reaction intermediates of the esterification of 3,3′‐thiodipropionic acid with 1,6‐hexanediol were elucidated by GC–MS. Biotechnol. Bioeng. 2008;99: 1074–1084. © 2007 Wiley Periodicals, Inc.