Poly(DL-lactide-co-glycolide) (PDL-LGA) copolymers with different DL-lactide／glycolide (DL-LA/GA) mole ratios were prepared by bulk ring-opening copolymerization of DL-LA with GA using tin octoate(Sn (Oct)2) as catalyst．Analytical results by 1H and 13C-NMR indicated that the mole fraction of glycolidyl units in the copolymers was a little higher than the feed mole fraction of GA

and the second mode of transesterification occurred during copolymerization．Copolymerization at 160℃

the average sequence length of glycolidyl (lGG) of the copolymers increased as the feed mole fraction of GA increased and the average sequence length of lactidyl (lLL) decreased. It was found that the transesterification coefficient of the second mode of lactidyl units (TⅡ[GLG]) decreased as the feed mole fraction of GA increased and reached to the least at a GA feed fraction of 50 mol％

after that

it increased gradually．In the case of copolymerization of L-LA with GA (L-LA／GA=75／25) at the same conditions

both the TⅡ [GLG] and lGG of the copolymer were higher than those of the corresponding PDLDL-LGA．As the copolymerization temperature increased

the TⅡ [GLG] increased

suggesting that the transesterification of the second mode became stronger；however

the value of lGG for the copolymer with higher DL-LA／GA feed mole ratio (75／25) was somewhat decreased and the lLL had no obvious change

whereas the copolymer with relatively lower DL-LA／GA feed mole ratio(50／50) behaved just conversely

i．e．

the value of lGG changed a little and lLL was somewhat decreased

indicating that the copolymerization was also affected by comonomers and other factors．Higher copolymerization temperature was more efficiently to change the microstructure of the copolymer chains than the prolonged copolymerization time at lower temperature．The glass transition temperature (Tg) and the solubility in chloroform of the copolymers synthesized at a given temperature decreased as the feed mole fraction of GA increased；however

the effect of polymerization temperature on the Tg of the copolymers with the same DL-LA／GA feed mole ratio became relatively complicated

indicating that the effect of polymerization temperature on the microstructure of the copolymers is more significant than that of the DL-LA／GA feed mole ratio.