Competition in Crystallization between Different Components and Formation of Concentric Double Spherulites in Block Copolymers

聚（epsilon-己内酯）-嵌段-聚（乙二醇）-嵌段-聚（epsilon-己内酯）（PCL- peg -PCL）三嵌段共聚物ABA-2和ABA-3 （PCL成分分别为66%和60%）具有独特的球粒形态，即同心圆状双球粒。同心球晶的内、外球晶分别为PCL和PEG。在同心圆球晶的形成过程中，PCL组分的球晶首先必然产生并生长，然后从PCL球晶的生长前沿发育为PEG球晶。聚乙二醇球晶的任何成核先于PCL未被观察到。在三嵌段共聚物ABA-1和ABA-4中，PCL含量分别为83%和34%，没有观察到同心球晶，而是形成了通常的单一球晶；ABA-1只形成PCL球晶，ABA-4只形成PEG球晶。ABA-2和ABA-3出现了两个熔化峰，其中出现了同心球晶。由于ABA-2和ABA-3的晶片和非晶层交替结构，SAXS曲线也出现了两种峰。从峰值位置估计出的较长的间距表明，在晶片之间存在非晶态的反晶链。

A unique morphology of spherulites, namely double spherulites like concentric circles, was observed for poly(epsilon-caprolactone)-block-poly(ethylene glycol)-block-poly(epsilon-caprolactone) (PCL-PEG-PCL) triblock copolymers, ABA-2 and ABA-3, with PCL compositions of 66 and 60 wt%, respectively. The inside and outside spherulites in the concentric spherulites were those of PCL and PEG, respectively. In formation of the conceniric spherulites, the spherulites of the PCL component first occurred necessarily and grew, and then the PEG spherulite developed from the growth front of the PCL spherulite. Any nucleation of the PEG spherulite prior to that of PCL was not observed. In the triblock copolymers, ABA-1 and ABA-4, with PCL compositions of 83 and 34 wt%, respectively, no concentric spherulites were observed but a usual single spherulite was formed ; in ABA-1 only PCL spherulites was formed while only PEG spherulite was observed in ABA-4. Two melting peaks appeared for ABA-2 and ABA-3 in which the concentric spherulites was observed. The SAXS curves also had two kinds of peaks due to alternating structure of the crystal lamella and amorphous layer for both ABA-2 and ABA-3. The long spacing estimated from the peak position suggested that the amorphous chains of the counter component existed between the crystal lamella.