The Influences of Chemical Microstructure and Pressure on the Mechanisms of Crystallization in Polymers

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Phillips There are many variables that 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 this research is to understand the ways in which all four of these variables interact in determining the details of the crystallization process. Building on past work, the synergistic effects of these variables will be investigated for several carefully chosen systems. Whereas much of past work has concentrated on cis-polyisoprene, polyethylene, and polypropylene, the proposed research will continue with polypropylene and its copolymers with ethylene. It will introduce copolymers of nylon- 6,6 as a new group. This latter group will permit a wider range of copolymer structures to be considered; in particular, there will be available a series of copolymers in which there is evidence for the comonomers being incorporated into the unit cell of the homopolymer. The research will permit a quantitative comparison to be made of crystallization theories and will enable us to look in a thorough manner at the existing theories of copolymer crystallization. The research will help us unravel some of the aforementioned complicated synergisms. In addition we will continue to investigate the details of the formation of the gamma phase in polypropylene at elevated pressures and the conditions governing its equilibrium with the alpha phase. It is also expected that this research will extend to the copolymers of polypropylene. The study of copolymers is one of the few methods available for the study of the critical secondary nucleus in polymers and many of the results will be applied to elucidating more information on this least explored of the important physical features of crystallization in polymers. %%% This research, by studying the crystallization behavior of important po lymers, will provide a more thorough understanding of how morphology influences observed bulk properties.