Preparation of polymer electrolyte membrane with nanomatrix channel through sulfonation of natural rubber grafted with polystyrene

Abstract

The mechanism of proton transport of a polymer electrolyte membrane (PEM) with nanomatrix channel was investigated with respect to the activation energy of proton conductivity. The PEM with nanomatrix channel was prepared by graft-copolymerization of styrene onto deproteinized natural rubber (DPNR) followed by sulfonation with chlorosulfonic acid. The resulting sulfonated graft-copolymer (SDPNR-graft-PS) was characterized by FT-IR spectroscopy, solid-state 13C CP/MAS NMR spectroscopy, elemental analysis, transmission electron microscopy (TEM) and impedance analysis. The PEM was found to form completely continuous nanomatrix channel consisting of natural rubber particle of about 1μm in average diameter as a dispersoid and sulfonated polystyrene of about 60nm in thickness as a matrix. The value of the activation energy of proton conductivity estimated from the slope of Arrhenius plot was 12kJ/mol for SDPNR-graft-PS, suggesting that the proton transport occurred in a manner of Grotthuss mechanism.