丙交酯-乙交酯共聚中的酯交换及共聚物结构和性质研究

以辛酸亚锡为催化剂 ,通过本体开环聚合合成了不同摩尔比的DL 丙交酯 乙交酯 (DL LA GA)共聚物 (PDL LGA) .1 H和1 3C NMR以及DSC结果表明 ,共聚物中GA结构单元的含量略高于按GA投料比计算的结果 ,聚合过程中存在二级酯交换反应 .当聚合温度为 16 0℃时 , GG 序列的平均长度 (lGG)随GA摩尔投料比增大而增长 ,而 LL 序列的平均长度 (lLL)则相反 .研究发现 ,随着GA摩尔投料比降低 , LL 单元的二级酯交换系数 (TⅡGLG])下降 ,至GA摩尔投料比达到为 5 0 %时最小 ,而后却逐渐增大 .L LA与GA在同样的条件下聚合 ,TⅡGLG]和lGG 都比DL LA与GA聚合的大 .聚合温度升高 ,TⅡGLG]增大 ,意味着二级酯交换反应加剧 ,但DL LA GA摩尔投料比较高 (75 2 5 )的共聚物的lGG 值有所下降 ,lLL值变化不大 ,而DL LA GA摩尔投料比较低 (5 0 5 0 )的共聚物的lGG值则变化不大 ,lLL值有所下降 ,说明聚合反应还受共聚单体的投料比和其它因素影响 .升高聚合温度比在较低温度下延长反应时间更有效改变共聚物的链结构 .在一定温度下聚合 ,共聚产物的Tg 随GA摩尔投料比增大而有规律降低和在氯仿中的溶解性下降 ;而DL LA GA摩尔投料比一定时 ,聚合温度对共聚物的Tg 的影响较为复杂 ,这与聚合温度对共聚物的链结构影响较大有关 .

STUDIES ON THE TRANSESTERIFICATION DURING COPOLYMERIZATION OF LACTIDE WITH GLYCOLIDE AND THE STRUCTURE AND PROPERTIES OF THE COPOLYMERS

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 (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/GA=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 GLG] 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.