Morphology and transport properties of midblock-sulfonated triblock copolymers

Abstract

The morphology and transport properties of newly reported sulfonated triblock copolymers with varying degrees of sulfonation in the midblock and two different hydrophobic end block compositions were studied. The methacrylate-b-styrene-b-methacrylate triblock copolymers were grown from the center of the polymer chain by atom transfer radical polymerization using a difunctional initiator. It was found that the degree of sulfonation had a systematic effect on the block copolymer domain size as measured by small-angle X-ray scattering. Additionally, the degree of self-assembly of copolymers with hexyl methacrylate end blocks was greater than that of the samples with perfluorooctyl methacrylate end blocks as evidenced by higher order X-ray scattering peaks and transmission electron micrographs. The phase ordering of the materials appeared to be controlled by the solvent casting properties and glass transition temperature of the outer blocks. Increased order and high sulfonation levels led the poly(hexyl methacrylate)-b-sulfonated poly(styrene)-b-poly(hexyl methacrylate) materials to have greater conductivity than analogous samples with poly(perfluorooctyl methacrylate) end blocks.