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Biodegradable poly(L-lactide- r-trimethene carbonate) copolymers (P(LLA- co-TMC)) with different compositions were synthesized. The degradation of the copolymers was carried out in phosphate buffer saline solutions (pH = 7.4) at 37 °C. The compositions, structure and properties of the copolymers in degradation were characterized with H-NMR, DSC, XRD, GPC, and SEM. The weight loss of the P(LLA- co-TMC) 50/50 was much faster than that of P(LLA- co-TMC) 85/15 and PLLA homopolymer. Interestingly, though the molecular weight of the compolymers decreased greatly during degradation, the compositions were rarely varied. After long time degradation, the PLLA segments were induced to crystallize in the P(LLA- co-TMC) 85/15 copolymer. The SEM observation of the surface and cross-section of P(LLA- co-TMC) 85/15 copolymer films found it was similar to the bulk degradation of PLLA homopolymer. [ABSTRACT FROM AUTHOR]