Regulation of micromorphology and proton conductivity of sulfonated polyimide/crosslinked PNIPAm semi‐interpenetrating networks by hydrogen bonding

Abstract

A series of novel sulfonated polyimide (SPI)/crosslinked poly(N‐isopropylacrylamide) (cPNIPAm) semi‐interpenetrating polymer networks (semi‐IPNs) were synthesized as the proton exchange membranes for direct methanol fuel cells via in situ polymerization. The micromorphology and properties of the semi‐IPN membranes were characterized. The results indicated that the hydrogen bonds between cPNIPAm and SPI in the semi‐IPN structure were a crucial factor for regulating the micromorphology, proton conductivity and other properties of the semi‐IPN membranes. A more uniform sulfonic ionic cluster distribution was observed in the membrane of SPI‐20‐cPNIPAm with equimolar ratio of sulfonic acid groups and amido bonds, which could provide effective proton transport channels. The SPI‐20‐cPNIPAm exhibited a maximum proton conductivity of 0.331 S cm−1 at 80 oC (relative humidity 100%), an optimal selectivity of 8.01 × 105 S s cm−3 and an improved fuel cell performance of 72 mW cm−2 compared with both pristine SPI and other semi‐IPN membranes. The SPI‐20‐cPNIPAm semi‐IPN membranes also retained good mechanical properties and thermal stabilities on the whole. © 2014 Society of Chemical Industry