On the Form II of Syndiotactic Polypropylene
On the Form II of Syndiotactic Polypropylene
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DOI：
10.1021/ma980789m
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发表时间：
1998-09
期刊：
影响因子：
5.5
通讯作者：
C. Rosa;and Finizia Auriemma;Valeria Vinti
中科院分区：
文献类型：
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作者：
C. Rosa;and Finizia Auriemma;Valeria Vinti
描述了间同立构聚丙烯晶型II的结晶条件。通过X射线衍射和固态13 C NMR CPMAS光谱分析了用基于异戊二烯的催化剂以及用传统的齐格勒-纳塔钒基催化剂制备的具有不同立构规整度的不同间同立构聚丙烯样品的制备、熔融结晶和定向纤维样品。根据该分析，在具有低立构规整度的样品中有利于晶型II的结晶。实际上，高度有规立构的间同立构聚丙烯的制备和熔融结晶样品总是以I型结晶，而较少有规立构的样品存在少量的II型晶体和/或II型堆积模式作为I型堆积的主要模式中的缺陷出现。通过拉伸具有低立构规整性的样品的压缩成型试样，获得了纯的形式II，用金属嵌段共聚物制备。
The conditions for the crystallization of form II of syndiotactic polypropylene are described. As-prepared, melt-crystallized, and oriented-fiber specimens of different samples of syndiotactic polypropylene having different degrees of stereoregularity, prepared with a metallocene-based catalyst as well as with the traditional Ziegler−Natta vanadium-based catalyst, are analyzed by X-ray diffraction and solid-state 13C NMR CPMAS spectroscopy. According to this analysis, the crystallization of form II is favored in samples having a low degree of stereoregularity. Indeed, as-prepared and melt-crystallized samples of highly stereoregular syndiotactic polypropylene always crystallize in form I, whereas less stereoregular samples present small amounts of crystals of form II and/or a mode of packing of form II occurs as a defect in a prevailing mode of packing of form I. The pure form II has been obtained by stretching compression-molded specimens of samples having low stereoregularity, prepared with the metalloc...