Ring-opening copolymerization of L-lactide (LLA) and 1,3-trimethylene carbonate (TMC) blends with LLA/TMC feed ratios from 90/10 to 50/50 was realized at 110 or at 180 degrees C for various time periods, using low toxic zirconium (IV) acetylacetonate (Zr(Acac)(4)) as initiator. The resulting copolymers exhibit different chain microstructures. Copolymers obtained at 110 degrees C exhibit a gradient chain structure with the presence of lactidyl sequences next to very short ones, and are semicrystalline. In contrast, copolymers obtained at 180 degrees C are amorphous because of a more random chain microstructure with the presence of larger amounts of medium sequences. Degradation of the copolymers was carried out in pH 7.4 phosphate buffer at 37 degrees C. Analytical techniques such as H-1 NMR, DSC, GPC, and XRD were used to monitor the degradation. Initially amorphous copolymers can remain amorphous during degradation because of the highly random unit's distribution, and equivalent LLA and TMC contents. However; initially amorphous copolymers containing larger amounts of lactidyl units are able to crystallize during degradation because of the presence of relatively long LLA blocks. Insofar, as initially semicrystalline copolymers are concerned, degradation. occurs preferentially in the amorphous zones. Therefore, various degradation behaviors and degradation rates can be obtained by varying the chemical composition, chain microstructure, and morphology of PLLA-PTMC copolymers. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 38693879, 2009