Proton conductivity of smart membranes based on hydrocarbon polymers having phosphoric acid groups

New proton-conducting polymer electrolyte membranes having phosphoric acid groups have been systematically synthesized. These homopolymers and copolymers were prepared by a conventional radical polymerization and a copolymerization with acrylonitrile or styrene or similar materials. The phosphoric acid groups can be cross-linked by heat treatments at 100 8C, and hence their membranes showed excellent mechanical properties and chemical stability. Measurements of the water absorption and differential scanning calorimetry revealed that the copolymer membranes absorbed smaller amounts of water, which is freezing water under 90% RH, compared with the sulfonated polyelectrolyte membranes. The proton conductivity of the P-PHM membranes hydrated was measured to be 5.0!10K3 S cmK1 at 100 8C. This value was usually maintained up to 160 8C. Dried homopolymer membranes and copolymer membranes were also examined for the water absorption and proton conductivity. It was found that the copolymerization with acrylonitrile provided good film-forming properties, thermal stability, and useful control of the physical and electrochemical properties. q 2004 Elsevier B.V. All rights reserved.