Vinyl-addition type norbornene copolymers containing flexible spacers and sulfonated pendant groups for proton exchange membranes

Novel sulfonated poly(2-butoxymethylenenorbornene-co-2-(6-phenoxy-hexyloxymethylene)-5-norbornene [sP(BN/PhHN)] were prepared successfully through vinyl-addition type polymerization and then sulfonated with concentrated sulfuric acid (98%) as sulfonating agent in a component solvent. The sP(BN/PhHN)-40 with the maximal degree of sulfonation of 40% can be obtained by controlling the sulfonating reaction time from 8 to 20 h, and a proton conductivity of 3.35 x 103 S/cm was achieved at 70 degrees C. The methanol permeabilities of these membranes were in the range from 0.26 to 6.58 x 107 cm2/s, which were remarkably lower than Nafion (2.36 x 106 cm2/s). TEM analysis revealed that these side-chain type membranes have a microphase separated structure composed of hydrophilic side-chain domains and hydrophobic polynorbornene main chain domains. Sulfonated polynorbornene containing soft spacers displayed better properties, such as lower water uptake, high thermal properties, mechanical properties, and low methanol permeability. (c) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013