Raman spectroscopic and gas transport study of a pentablock ionomer complexed with metal ions and its relationship to physical properties

A series of poly(b-(t-butyl styrene)-b-(ethylene-co-propylene)-b-(styrene-co-styrene sulfonate)-b-(ethylene-co-propylene)-b-(t-butyl styrene)) ionomers were complexed with a series of metal ions. Raman sulfonate group symmetric ν s(SO3 −) and asymmetric ν as(SO3 −) stretching modes at 1031 and 1127 cm−1 were proportional to ion-exchange capacity. Mono and divalent counter-ions of Li+, Na+, K+, and Ca2+ affected the stretching modes of ν(SO3 −) due to ion size and charge. The gas permeability P and diffusivity D of O2, CO2, N2, and CH4 decreased with increasing complexation strength between sulfonate group and metal ion. Solubility S was a maximum for ionomers complexed with K+ and CO2, but small changes were observed for other metal ions. Overall, these results suggest that ionomers coordinated with different metal ions influence network physical properties, chain mobility, and gas transport.