开环聚合-固相缩聚法制备立体嵌段聚乳酸

首先，采用乳酸为引发剂，辛酸亚锡为催化剂，引发丙交酯开环聚合制得具有缩聚活性的L-聚乳酸和D-聚乳酸；然后，将两者熔融共混后进行固相缩聚，合成了一系列立体嵌段聚乳酸。采用核磁共振（NMR）、凝胶渗透色谱（GPC）及差示扫描量热仪（DSC）分析了产物的链结构、重均分子量、热性能，并探讨了均相晶体和立体复合晶体共存情况下的固相缩聚机理。结果表明，固相缩聚产物分子量增长的适宜反应条件为：反应时间30 h，较低的催化剂含量，L-聚乳酸质量分数为80%。L-聚乳酸和D-聚乳酸共混物较低的初始立体复合晶体结晶度有利于后续固相缩聚过程中产物分子量的增长；固相缩聚不仅发生在异链之间，而且也发生在同链之间。

Preparation of Stereoblock Poly(lactic acid) by Ring-Opening Polymerization-Solid State Polycondensation

L-poly(lactic acid)(PLLA) and D-poly(lactic acid)(PDLA) having reactivity for condensation polymerization were prepared using lactide as monomer,lactic acid and stannous octoate as initiator and catalyst respectively.A series of stereoblock poly(lactic acid)s were synthesized by the melt blend of PLLA and PDLA via Solid State Polycondensation(SSP).The chain structure,molecular weight and thermal properties of products were characterized by NMR,GPC and DSC respectively.The SSP mechanism was discussed when the homocrystal coexists with the stereocrystal in the same system.The results showed that the technological conditions suitable for the molecular weight increase of the SSP products is 30 h reaction time,relative low content of catalyst and 80% mass fraction of PLLA.Relative lower original stereo-crystallinity of the blend of PLLA and PDLA is beneficial to the molecular weight increase of the final products during the subsequent SSP progress.SSP was occured not only between different optical structure chains but also between the same optical structure chains.