Thermoreversible Morphology Transition of Block Copolymers.

Abstract

Thermoreversible morphological transition of a poly(styrene-block-isoprene) (SI) block copolymer was studied by small-angle X-ray scattering and transmission electron microscopy (TEM). Although block copolymers are theoretically predicted to exhibit a reversible morphological change between lamellae and disordered state via cylinders and spheres with temperature, this thermoreversibility in morphology transition has not been experimentally confirmed yet. In order to study this thermoreversible transition, the SI diblock copolymer may have to have a biased composition and sufficient mobility. To meet these requirements, we used the SI with the weight fraction of polystyrene (PS) 0.16 and with a relative low number-average molecular weight 8.2×104. Heat treatments of the specimen were carefully conducted. Moreover, the ultrathin sectioning was performed by cryo-ultramicrotomy at -85°C for TEM studies. The cylindrical and spherical microdomains of PS which are embedded in the polyisoprene matrix were thermoreversibly observed at 150 and 200°C, respectively.