THERMOREVERSIBLE MORPHOLOGY TRANSITION BETWEEN SPHERICAL AND CYLINDRICAL MICRODOMAINS OF BLOCK-COPOLYMERS

Thermoreversible morphological transition (MT) of a poly(styrene-block-isoprene) diblock copolymer was studied by small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). The cylindrical and spherical microdomains of polystyrene (PS) which are embedded in the polyisoprene matrix were thermoreversibly observed at 150 and 200-degrees-C, respectively. As far as we know, this work may be the first to show that the cylindrical and spherical morphologies can reversibly change with temperature. Using experimentally determined interaction parameters chi, we compared SAXS and TEM results with the theory in the weak segregation limit presented by Leibler, which predicts the thermoreversible MT between spheres and cylinders. Consequently, (chiN)t < (chiN)200-degrees-C < (chiN)s < (chiN)1 < (chiN)150-degrees-C was obtained, where (chiN)t, (chiN)s, and (chiN)1 denote the theoretical values of product chiN at the microphase separation transition (MST), at the spinodal point of the MST, and at the MT between spheres and cylinders, respectively, and N is the degree of polymerization of the copolymer.