Structure/property relationships in polystyrene-polyisobutylene-polystyrene block copolymers

Structure/property relationships of polystyrene-polyisobutylene-polystyrene (PS-PIB-PS) triblock copolymer made by different processes were studied using dynamic mechanical analysis (DMA). The PS-PIB-PS films were composed of approximately 30% polystyrene end-blocks. Small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) confirm that a self-assembled, segregated cylindrical morphology forms in the copolymer. DMA was used as a tool to investigate the structure-property relationships in these polymers. Modified PS-PIB-PS copolymers were also characterized. Modifications of the copolymers were carded out by conversion of approximately 20 mol% of the polystyrene end-blocks to styrene sulfonic acid. The modified copolymers exhibited distinctly different thermal characteristics than the unmodified copolymers, which were most notable in the storage modulus and tan δ data. The presence of sulfonic acid groups disrupted the morphology and solvent sorption characteristics of the copolymers. Dynamic mechanical behavior is discussed as it relates to the morphology of the PS-PIB-PS copolymers formed via different processing methods and chemical modification.