Cooperative Molecular Motions in Glassy Polymers

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Strong correlations exist between secondary mechanical relaxations in glassy polymers and their mechanical properties. Previous dynamic mechanical studies have not yielded precise information on the nature and origin of the mechanical relaxations. Advanced NMR techniques have provided detailed information on certain molecular motions, but these motions are not necessarily representative of those detected by DMS. Molecular motions most directly relatable to mechanical deformations are likely to be highly cooperative. Cooperative molecular motions in copolymers of polycarbonates will be studed by systematically varying sequences of mobile and less mobile repeat units. The in-chain correlation distance will be determined using dynamic-mechanical measurements. By measuring dynamic bulk relaxation, one can assess the extent of intermolecular interaction associated with these cooperative motions. By measuring the yield stress and post yield cold drawing dependence on temperature and strain rate, one can establish correlations between molecular architecture, molecular cooperativity, and mechanical properties. This research could ultimately lead to polymers with improved mechanical properties by relating those propertes with the structure of the polymers and their molecular motions.