EARLY STAGES OF SPHERULITE GROWTH IN MELT-CRYSTALLIZED POLYSTYRENE
EARLY STAGES OF SPHERULITE GROWTH IN MELT-CRYSTALLIZED POLYSTYRENE
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DOI：
10.1016/0032-3861(88)90301-1
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发表时间：
1988-08-01
期刊：
影响因子：
4.6
通讯作者：
BASSETT, DC
中科院分区：
文献类型：
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作者：
VAUGHAN, AS;BASSETT, DC
将全同立构聚苯乙烯样品从熔体中短时间结晶（即在190° C下1-10分钟，在220° C下17-81分钟），淬火并在高锰蚀刻和复制后通过透射电子显微镜检查。最长时间的结晶导致了由六边形薄片组成的结构的大量成核，这些薄片在边缘处彼此分开。这些物体类似于先前在温度高于200° C时结晶的聚苯乙烯中发现的物体。然而，随着结晶时间的缩短，所得到的结构变得更小、更简单，直到在最短的时间内，可以看到研究对象由一堆薄片组成，这些薄片通过中心线或核心连接在一起，其长度从1500埃到几微米不等。因此，提出在这些样品中，链折叠晶体的成核发生在主链周围，所述主链包括处于延伸构型的一些分子，可能在样品制备期间的某个时间引入必要的局部分子延伸，并且此后保持在适当位置，使得在结晶开始之前不能发生松弛，尽管加热到远高于聚合物的平衡熔点。降低熔体的分子量导致成核密度的急剧降低。然而，对足够小的物体的检查再次表明，它们由叠层组成，因此，成核过程在质量上没有随着分子质量的减少而改变。
Samples of isotactic polystyrene were crystallized from the melt for short times (ie 1–10 min at 190° C, 17–81 min at 220° C), quenched and examined by transmission electron microscopy following permanganic etching and replication. Crystallization for the longest times resulted in the profuse nucleation of structures composed of hexagonal lamellae which splayed apart from one another at the edges. Such objects were similar to those previously identified in polystyrene crystallized at temperatures greater than 200° C. As the crystallization time was reduced, however, so the resulting structures became smaller and simpler until at the shortest times studied objects could be seen which consisted of a stack of lamellae connected together by a central thread or core, the length of which ranged from∼ 500 A ̊ to several microns. It is therefore proposed that in these samples nucleation of chain folded crystals occurs about a backbone which includes some molecules in an extended configuration, the necessary local molecular extension being introduced, presumably, at some time during sample preparation and thereafter held in place such that relaxation is unable to occur prior to the onset of crystallization, despite heating to well above the polymer's equilibrium melting point. Reducing the molecular mass of the melt led to a dramatic reduction in the nucleation density. However, examination of sufficiently small objects again showed them to consist of stacks of lamellae, and as such, the nucleation process appeared qualitatively unchanged by the reduction in molecular mass.