Viscoelasticity of a butadiene–styrene block copolymer

Publisher Website
Google Scholar
Abstract
A commercial elastomeric block copolymer of butadiene (B) with styrene (A) is studied. A single chain of the material has the formula A‐B‐A. Differential thermal analysis studies show the presence of two transitions. The lower transformation temperature corresponds to the Tg of the butadiene chain segments, and the upper transformation temperature corresponds to the Tg of the styrene chain segments. The upper transition of the material is also studied by following the variation of the torsional modulus with temperature. This transition is found to be quite unusual. Our experiments show that the upper transformation of unstressed block copolymer samples is broad. The transition sharpens for samples which, prior to the modulus–temperature experiments, are stress‐relaxed at high elongations. These observations (and those of the literature) suggest that the styrene and butadiene chain segments in the block copolymer aggregate in the solid state and give rise to two distinct transition phenomena. Our studies of the upper transformation suggest that stretching of the bulk material enhances the aggregation of the styrene chain segments. Pure polystyrene (A) blocks of the material are recovered by selective cleavage and fractionation experiments. The Tg of the pure polystyrene blocks is found to be similar to the value of the upper transition temperature of the copolymer. The ABA blocks copolymer is found also to undergo a stress‐softening phenomenon analogous to that of reinforced rubber.

This publication has 8 references indexed in Scilit: