STRESS-OPTICAL MANIFESTATIONS OF MOLECULAR AND MICROSTRUCTURAL DYNAMICS IN COMPLEX POLYMER MELTS

Experimental methods are presented for investigating molecular and mic rostructural aspects of the rheology of polymer melts. Measurements of stress, birefringence, and dichrcism are made simultaneously so that the connection between macroscopic viscoelasticity and the dynamics of the fluid microstructure can be established as directly and unambiguo usly as possible. We show how quantitative characterization of departu re from the stress-optic rule can expose distinct molecular and micros tructural dynamics in complex polymer melts. This general approach is applied (1) to resolve the contributions of distinct species to the ma croscopic stress, illustrated using a miscible polymer blend, (2) to d iscriminate between dynamical regimes that are controlled by conformat ional or microstructural relaxation, illustrated using an ordered bloc k copolymer, and (3) to distinguish the dynamics of topologically dist inct parts of a given molecule, illustrated using a side-group liquid- crystalline polymer.