A site-specific ESR spin-labeling study of molecular motion in microphase-separated polystyrene-block-poly(methyl acrylate) with lamellar morphology

Molecular motion at the specific sites of polystyrene-block-poly(methyl acrylate) (PS-block-PMA) forming a lamellar morphology was studied by electron spin resonance (ESR). PS-block-PMA's having nearly the same molecular weight and composition were selectively spin-labeled with stable nitroxide radicals at different specific sites (each free end, inside segments of each block, or the chemical junction point between the blocks). The molecular motion was analyzed from temperature-dependent ESR spectra of the spin-labels. Enhancement of molecular mobility of the chain end in comparison with that of the inside was detected. The enhanced molecular mobility of the both ends of the PS-block-PMA was more remarkable than those of the both homopolymers. This was brought from the much large free volume around the chain ends of the PS-block-PMA because of the local high concentration of the chain ends in the lamellar microdomains. The molecular mobilities of the PS-block-PMA and polystyrene-block-poly(ethyl acrylate) (PS-block-PEA) labeled at the junction points were related to thermal behavior and local environment of polymer chains in the interfacial region of the lamellar microdomains. This demonstrated that the structure in the interface was heterogeneous, although the both components were mixing compatibly in the interfacial region.