EFFECT OF UNIDIRECTIONAL SHEAR ON THE STRUCTURE OF TRIBLOCK COPOLYMERS .2. POLYSTYRENE POLYISOPRENE POLYSTYRENE

Rheological and small-angle X-ray scattering (SAXS) measurements on a polystyrene- polyisoprene-polystyrene block copolymer indicate that high-strain, high-stress unidirectional shear flow in the microphase-separated regime produces a well-oriented, microdomain structure with cylindrical microdomains. Experiments in low-stress, high-strain flow produced little orientation. The material studied is a high molecular weight copolymer with 24 vol % polystyrene and a cylindrical microdomain morphology as indicated by SAXS. Flow above the microphase-separation temperature (TMST) determined by linear- viscoelastic measurements resulted in no microdomain orientation. The linear-viscoelastic results show that materials sheared near 7MST do not recover to a well-microphase-separated morphology after high-strain shear flow. A flow mechanism for microphase-separated block copolymers proposed previously is compatible with the results obtained here. © 1990, American Chemical Society. All rights reserved.