Morphological Behavior of Sulfonated Styrene-Ethylene/Propylene-Styrene Triblock Copolymers

摘要

Sulfonated block copolymer ionomers possessing short (1K g/mol) styrene blocks and various rubber block lengths were synthesized via sequential anionic polymerization of styrene, isoprene, and styrene followed by hydrogenation and sulfonation. The ionomers were then characterized by small- angle x-ray scattering (SAXS) and atomic force microscopy (AFM). The SAXS data indicate the presence of microphase-separated sulfonated styrene domains within the rubber phase. The morphology of the phase separation in this system is not clear from SAXS due to the absence of higher order maxima. Increased Bragg spacing was observed as the rubber block molecular weights increased, but decreased upon neutralization of the sulfonic acid groups with sodium hydroxide. The intensity of the SAXS maxima increased for shorter rubber block segments. AFM images confirmed the presence of microphase-separated domains which appear spherical.