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

The hydrogen bond interaction between cPNIPAm and SPI in the semi-IPN structure is a crucial factor for regulating the micromorphology and properties of the semi-IPN proton exchange membranes. 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 0.331Scm^-1 at 80 ^oC (relative humidity 100%), an optimal selectivity of 8.01×10⁵Sscm^-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.