The Microstructure of Block Copolymers Formed via Ionic Interaction

Abstract

The morphology produced by solution cast mixtures of telechelic polymers end capped with tertiary amine functionalities with telechelic polymers terminated with either sulfonate or carboxylate moieties closely resembles that seen in block copolymers formed by covalent bonding of two dissimilar chain segments. It has been found by temperature-dependent small-angle X-ray scattering and optical microscopic studies that the sulfonate/tertiary amine associations are more stable at elevated temperatures than the carboxylate analogs. These effective block copolymers undergo a classic order/disorder transition at elevated temperatures similar to that seen in covalently bonded block copolymers. However, due to the nature of the ionic associations, as the order/disorder is approached, the width of the interface between the two phases remains sharp. Finally, by increasing the molecular weight of the telechelic polymers at temperatures above the order/disorder transition temperature, the effects of an upper critical solution temperature are seen. Here, the telechelic polymers appear to phase separate in a spinodal manner. The phase diagrams for these systems are dictated by the relative positions of the microphase separation temperature of the effective block copolymers, the upper critical solution temperature of the dissociated telechelic polymers, the temperature at which the ionic aggregates dissociate, and the glass transition temperature. © 1988, American Chemical Society. All rights reserved.