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 × 10 −3 S/cm was achieved at 70°C. The methanol permeabilities of these membranes were in the range from 0.26 to 6.58 × 10 −7 cm 2 /s, which were remarkably lower than Nafion (2.36 × 10 −6 cm 2 /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. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013