Nanoscale Phase Separation of Sulfonated Poly(arylene ether sulfone) / Poly(ether sulfone) Semi-IPNs for DMFC Membrane Applications

Unprecedented improvement in the selectivity (the ratio of proton conductivity to methanol permeability) of DMFC (direct methanol fuel cell) membranes has been demonstrated with a value roughly 16 times higher than that of Nafion117 having been achieved. The novel morphology of semi-interpenetrating polymer network (semi-IPN) membranes characterized by nanometer-sized domains as well as well-developed phase cocontinuity is a key factor in enabling such notable progress, which has not been seen in conventional microscale phase separation. The semi-IPN membranes (sIPN-100) consisted of a hydrophilic component acting as a proton conductor, that is, acrylate-terminated fully sulfonated poly(arylene ether sulfone) oligomers (acSPAES-100, degree of sulfonation = 100%), and a hydrophobic component functioning as a methanol barrier, that is, poly(ether sulfone) copolymers (RH-2000). We determined the nanoscale phase separation of sIPN-100 by deliberately controlling the kinetics (the change of solvent-evaporation...