Phase Transformations and Orientational Ordering in Chemically Disordered Polymers — a Modern Primer

Abstract

We review recent theoretical and experimental developments in the field of complex polymers that carry a chemical and topological disorder. The polymer classes discussed include chemically disordered crosslinked heteropolymers and liquid crystalline heteropolymers. Field theory and spin glass averaging methods are very useful to study complex disordered polymers. The field theory allows explicit account of chain conformation contributions to thermodynamical quantities and a faithful representation of experimentally observable order parameters. Spin glass averaging methods presented here are instrumental for averaging over chemical and topological disorders. The review centers on theory development, predictions for conformational and orientational ordering, phase diagram analysis and also comparison with experimental results when possible.

Random heteropolymers (RHPs) with physical crosslinks are shown to exhibit three globular phases: frozenglobular with micro-domain structure, random-globular and frozen-randomglobular. For RHPs with chemical crosslinks our theory predicts three frozen-globular phases, and one random-globular phase; the intra-frozen transitions are conformational transitions which do not require any re-entrant passages via the random-globular phase. The phase diagram of crosslinked RHPs is systematically explored in parameter and thermodynamic variable space, and physical explanations for the conformational organization and the order of the phase transitions is provided.

The second class of disordered polymers we review are manychain mesogen/flexible disordered copolymers (DLCP). A field theory and creation-annihilation summation rules are proposed to carry out coupled orientational and conformational averages of polymer chain conformations in these complex systems. Predictions for the effect of flexibility, stiffness and inter-segment alignment on orientational ordering, the nematic/isotropic density threshold and the segmental orientational ordering at the nematic/isotropic transition is discussed in close proximity to experimental studies.