The Mechanisms of Crystallization of Copolymers at Atmospheric and Elevated Pressures

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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. ***