The proton conductivities of poly(vinylbenzyl phosphonic acid) (PVBPA) homopolymer and its statistical copolymers with 4-vinyl pyridine [poly(VBPA-stat-4VP)s] are comprehensively studied in this work. Temperature and composition-dependent "dry" proton conductivities of the copolymers have been determined and the self-condensation of phosphonic acid groups has been quantified. The results show that the intrinsic proton conductivities of poly(VBPA-stat-4VP)s and PVBPA are quite low at 150 °C and exhibit time-dependent changes due to anhydride formation at elevated temperatures. The effect of polymer composition on proton conduction shows a minimum at a 1:1 molar ratio of proton donor and acceptor groups and is discussed on the basis of the pK a values of the electrolyte species. A trace amount of water significantly increases conductivity probably due to additional hydronium ion diffusion and water bridging effects. Water content and proton conductivities of poly- (VBPA-stat-4VP)s are determined at different relative humidities. High amounts of water are absorbed at high humidities leading to high proton conductivities. © 2008 WILEY-VCH Verlag GmbH & Co. KGaA.
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