The Mechanisms of Crystallization of Copolymers at Atmospheric and Elevated Pressures

在制造的加工和制造阶段，有许多变量影响结晶聚合物的物理和机械性能。其中最重要的四个是温度、压力、分子量和链的微观结构。这项研究的长期目标是了解所有这四个变量在确定具有商业重要性的聚合物结晶过程的基本物理细节时相互作用的方式。这些变量的协同效应将在几个精心选择的系统中进行研究，这样做将有助于本科生和研究生的教育。过去的工作主要集中在顺式聚异戊二烯、聚乙烯、聚丙烯和PET，以及它们与从晶体中分离出来的共聚单体的共聚物上，而最近的研究则增加了尼龙6,6的共聚物。后一组包括共聚物，其中共聚物并入均聚物的单元胞中。初步结果表明，这种共聚物的行为是完全出乎意料的，与所有其他共聚物不同。使用茂金属催化剂制备的新型乙烯和辛烯共聚物的研究已经开始，并表明它们与使用传统的Zeigler Natta型催化剂制备的类似共聚物的匹配部分有很大不同。本研究首次证明了另一个影响结晶行为的变量——共聚单体序列长度分布的重要性。建议扩大我们对无规乙烯-辛烯共聚物的研究，并在高压下研究它们。此外，聚丙烯中迷人的Y相在高压下形成的研究将继续进行，并扩展到已经在常压下研究的共聚物。共聚物在常压下显示出这一相，尽管根据均聚物的相图，它不应该存在。因此，它的形成的能量学似乎被一个可排除的单体的存在强烈地扰乱了。这项研究将有助于了解不同类别的商业重要共聚物在塑料工业成型操作中通常遇到的温度和压力条件下的结晶行为，同时为本科生和研究生提供宝贵的实验室经验。＊＊＊

9711986 Philllips There are many variables which influence the physical and mechanical properties of crystalline polymers through the processing and fabrication stages of manufacture. Four of the most important are temperature, pressure, molecular weight and chain microstructure. The long term objective of the research is to understand the ways in which all four of these variables interact in determining the details of the basic physics of the crystallization process in polymers of commercial importance. The synergistic effects of these variables will be investigated for several carefully chosen systems and in doing so will contribute to the education of undergraduate and graduate students. Whereas past work has concentrated on cis-polyisoprene, polyethylene, polypropylene and PET, and their copolymers with comonomers that are rejected from the crystals, recent research has added copolymers of nylon 6,6. This latter group includes a copolymer in which the comonomer is incorporated into the unit cell of the homopolymer. Preliminary results show the behavior of this copolymer to be quite unexpected and different from all others. Research already begun on the very important new copolymers of ethylene and octene made using metallocene catalysts is definitive and shows them to be very different from matched fractions of similar copolymers made using traditional Zeigler Natta type catalysts. For the first time, this research has demonstrated the importance of yet another variable on crystallization behavior, the comonomer sequence length distribution. It is proposed to expand our studies of the random ethylene-octene copolymers and to study them at elevated pressures. In addition studies of the formation of the fascinating Y phase in polypropylene at elevated pressures will be continued and extended to copolymers already studied at atmospheric pressure. Copolymers show this phase at atmospheric pressure despite the fact that it should not be there according to the phase diagram of the homopolymer. It therefore appears that the energetics of its formation are strongly perturbed by the presence of an excludable comonomer. %%% This research will contribute to the understanding of the crystallization behavior of different classes of commercially significant copolymers under conditions of temperature and pressure normally encountered in the molding operations of the plastics industry, whilst at the same time providing both undergraduate and graduate students with valuable laboratory experience. ***