Small-angle x-ray scattering studies on epoxidized butadiene-styrene block copolymers

Small-angle x-ray scattering (SAXS) and scanning electron microscopy (SEM) investigations for epoxidized butadiene-styrene (BS) block copolymers were performed. For unepoxidized copolymers, the SAXS curve exhibits a maximum which indicates that the copolymer has heterogeneity domain morphology. Using the standard theory for a two-phase system, mean distances between domains, the correlation length l _p , and the thickness of the phase boundary were calculated from the SAXS data. It was found that the epoxidation of BS copolymers decreases the ability of the copolymer to separate the individual components. As the content of the epoxide groups increases, the dimensions of the domains decrease until they disappear, the boundary between domains and the matrix becomes less and less definite, and the copolymer composes a homogeneous system. The disappearance of the two-phase structure of the BS copolymers indicates an increase in the compatibility of polystyrene and epoxidized polybutadiene. According to the method of Van Krevelen, the solubility parameters of polystyrene and epoxypolybutadiene were calculated. Small differences between these parameters support the conclusions drawn from the SAXS investigations