分子端基效应对聚(L-乳酸)球晶环带结构形成的影响

通过活性正离子开环聚合的方法,以苯甲醇或月桂胺引发L-丙交酯聚合合成了一系列分子量可控的聚(L-乳酸)(PLLA).研究发现,端基刚、柔性的变化,改变了PLLA环带球晶的生成条件和环带周期结构,因此可以通过改变端基的结构来调控PLLA所形成的环带结构.分子量相近而端基不同的PLLA,在相同温度下结晶时,刚性引发剂苯甲醇...

INFLUENCE OF END GROUP ON THE BANDED STRUCTURE OF PLLA SPHERULITES

pherulitic morphologies of a series of linear poly(L-lactide)s(PLLA),which was synthesized by ring opening polymerization(ROP) using initiators with different structures,i.e.the incoming end groups,were observed through direct melt-crystallization process by polarized optical microscopy(POM).It has been verified that the flexibility of the end group has a significant influence on the banded structure of PLLA spherulites.It was found that the spherulitic band spacing periodicity of PLLA initiated by rigid benzyl alcohol(B-PLLA) was much smaller than that of PLLA initiated by flexible lauryl amine(L-PLLA) with similar molecular weight at certain crystallization temperature.However,this end group effect was decreasing with increasing molecular weight.For B-PLLAs,the band spacing periodicity of spherulites increased with molecular weight increasing noticeably,for example,B-PLLA1 having a molecular weight of about 1700 yielded spherulites with band spacing periodicity being only several micrometers and spherulites of B-PLLA4 having a molecular weight of about 7000 had the band spacing periodicity more than 150 micrometers.Meanwhile,the temperature windows for the formation of regular banded spherulites of B-PLLAs shifted to higher region and became narrower with increasing molecular weight.Finally,a model was suggested to illustrate the effects of end group and molecular weight on the formation of twisting PLLA lamellae.