分别以外消旋乳酸(D,L-LA)和左旋乳酸(L-LA)为原料,与乙醇酸(GA)直接熔融共聚,以0.5%氯化亚锡为催化剂,在165℃、70Pa下反应10h,合成了不同配比的系列生物降解高分子乳酸-乙醇酸共聚物(PLGA).用GPC、FTIR、1H NMR、DSC、X-射线衍射等进行表征,发现原料乳酸(LA)的构型对聚合物的Mw、Tg、结晶性、组成等产生影响.单体投料摩尔比LA/GA=50/50时,D,L-PLGA的[η]和Mw比L-型大.以D,L-LA为原料时,共聚物结构相对简单,共聚物性质易受GA链段控制.投料摩尔百分比LA(或GA)≥90%时,共聚物易于结晶,以L-LA为原料时更为明显.利用1HNMR数据计算共聚物组成,发现GA组分含量高于其投料值,且D,L-PLGA中GA的组成高于L-型产物.根据上述实验事实,提出D,L-LA、L-LA分别与GA共聚时,由于GA在共聚中反应速率比LA高,并且D,L-LA与L-LA存在反应速率差异,故有不同反应机理.
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