An aliphatic polythioester was enzymatically prepared by the direct polycondensation of mercaptoalkanoic acid using immobilized lipase of Candida antarctica (lipase CA) in bulk. The commercially available 11-mercaptoundecanoic acid was polymerized by lipase CA in bulk in the presence of molecular sieves 4A as a water absorbent at 110 degrees C for 48 h to produce poly(11-mercaptoundecanoate) with an M-w of 34 000 in high yield. The 104.5 degrees C melting temperature (T-m) of poly(11-mercaptoundecanoate) was about 20 degrees C higher than that of the corresponding polyoxyester, poly(11-hydroxyundecanoate). The polythioester was readily transformed by lipase into the corresponding cyclic oligomers mainly consisting of the dimer, which were readily repolymerized by the ring-opening polymerization using lipase as a sustainable chemical recycling.