Orientation-Induced Crystallization in Polymers

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The proposed research aims to explore several fundamental issues of orientation-induced crystallization in polymers. These issues include: (1) the mechanism of initial stages of crystallization in oriented chains, (2) the overall kinetics of crystallization from the system containing chains of varying degrees of orientation, (3) the effects of molecular weight, molecular weight distribution, chain architecture and chain branching on orientation-induced crystallization, (4) the influence of molecularly dispersed nanostructured molecules on the chain orientation, and (5) the resultant morphology consisting of oriented crystal, oriented mesomorphic and unoriented amorphous phases. To accomplish these goals, it is proposed to carry out four research projects including: (a) the weak shear-flow study under step-shear and steady-state shear conditions, (b) the strong elongation-flow study, (c) the study of the effect of molecularly dispersed nanostructured molecules in polymers, and (d) the study of crystallization in oriented polymers using supercritical carbon dioxide (CO2) as a mean to control molecular orientation. The planned experiments will include the use of combined methods of rheology, a high-pressure apparatus, in-situ optical (light scattering, birefringence and Raman spectroscopy) and x-ray (small- and wide-angle x-ray scattering with synchrotron radiation) techniques and ex-situ microscopic techniques.%%%The significance of the research lays in the fact that orientation-induced crystallization remains one of the most important problems in polymer processing today, and the subject is not fully understood. It is hoped that with the proposed study, an in-depth understanding about the subject can be obtained, increasing the ability to correlate the structure, morphology, process and property relationships for crystalline polymers, thus benefiting the polymer industry.