Molecular Theories of Segmental Dynamics and Mechanical Response in Deeply Supercooled Polymer Melts and Glasses

We review recent progress in developing statistical mechanical theories for the slow activated segmental dynamics and mechanical response of deeply supercooled polymer melts and glasses. The focus is polymer-based predictive approaches and uniquely macromolecular aspects. We summarize the central concepts that underlie two prominent polymer theories in the molten state and critically discuss their key predictions and confrontation with experiment. The influence of anisotropic conformation and interchain packing on the emergence of activated glassy dynamics in oriented polymer liquid crystals and deformed rubber networks is discussed. In quenched nonequilibrium glass, the temperature dependence of segmental relaxation qualitatively changes, and physical aging commences. A very recent theory for the dramatic effects of external stress on polymer glasses is summarized, including acceleration of relaxation, yielding, plastic flow, and strain hardening. The review concludes with a discussion of some outstanding theoretical challenges.