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摘要
Poly ( DL-lactide- co -glycolide) ( PDL-LCA) copolymers with different DL-lactide/glycolide ( DL-LA/ CA) 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 H-1 and C-13-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 160degreesC, the average sequence length of glycolidyl (l(GG)) of the copolymers increased as the feed mole fraction of GA increased and the average sequence length of lactidyl (l(LL)) decreased. It was found that the transesterification coefficient of the second mode of lactidyl units (T (II)[ 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/CA = 75/25) at the same conditions, both the T (II) [GLG] and l(GG) of the copolymer were higher than those of the corresponding PDL-LGA. As the copolymerization temperature increased, the T (II) [ GLC, I increased, suggesting that the transesterification of the second mode became stronger; however, the value of l (GG) for the copolymer with higher DL - LA/ GA feed mole ratio (75/25) was somewhat decreased and the l(LL) 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 l(GG) changed a little and l(LL) 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 (T-g) 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 T-g 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.
- 出版日期2003-12
- 单位中山大学
