Vinyl-addition type norbornene copolymer containing sulfonated biphenyl pendant groups for proton exchange membranes

Abstract

The vinyl addition type copolymer poly(butoxymethylene norbornene-co- biphenyl oxyhexamethyleneoxymethylene norbornene) (P(BN/BphN)) was synthesized by using bis-(β-ketonaphthylimino)nickel(II)/B(C 6F 5) 3 catalytic system. P(BN/BphN) was sulfonated to give sulfonated P(BN/BphN) (SP(BN/BphN)) with concentrated sulfuric acid (98%) as sulfonating agent in a component solvent. The ion exchange capacity (IEC), degree of sulfonation (DS), water uptake, and methanol permeability of the SP(BN/BphN)s were increased with the sulfonated time. The methanol permeability of the SP(BN/BphN) membranes was in the range of 1.8 × 10 -7 to 7.5 × 10 -7 cm 2/s, which were lower than the value 1.3 × 10 -6 cm 2/s of Nafion®115. The proton conductivity of SP(BN/BphN) membranes increased with the increase of IEC values, temperature, and water uptake. Water uptake of the SP(BN/BphN) membranes was lower than that of Nafion® 115 and leads to low proton conduction. Microscopic phase separation occurred in SP(BN/BphN) membrane and domains containing sulfonic acid groups were investigated by SEM and TEM. SP(BN/BphN) membranes had good mechanical properties, high thermal stability, and excellent oxidative stability. © 2012 Wiley Periodicals, Inc.