A novel linear polyester with acid-labile beta-thiopropionate groups was synthesized via the direct lipase-catalyzed polycondensation of methyl 3-((2-hydroxyethyl)thio)propanoate (MHETP) using immobilized lipase B from Candida antarctica (CALB). The influences of reaction conditions such as polymerization temperature and time on the molecular weight of the poly(beta-thioether ester) (PTE) were studied. Ring-opening and condensation copolymerization of MHETP with epsilon-caprolactone (CL) led to the synthesis of novel poly(beta-thioether ester-co-epsilon-caprolactone) copolymers, poly(TE-co-CL), with well-defined composition and narrow polydispersity. The random copolymers were characterized by H-1 NMR, C-13 NMR, 2D NMR, GPC, TGA and DSC. The degradation of the poly(beta-thioether ester) under acidic conditions was investigated by GPC and H-1 NMR spectroscopy. (C) 2015 Elsevier Ltd. All rights reserved.