Stable crosslinked vinyl‐addition‐type polynorbornene graft copolymer proton‐exchange membranes

Abstract The graft copolymer poly(butoxymethylene norbornene‐ co ‐norbornenemethylene bromoisobutyrylate) [P(BN/NB)]‐ graft ‐poly(hydroxyethyl methacrylate) (PHEMA) was synthesized by the atom transfer radical polymerization of 2‐hydroxyethyl methacrylate from a copolymer prepared by two functional norbornene monomers via a vinyl addition mechanism. The graft copolymer P(BN/NB)‐ g ‐PHEMA was further crosslinked with 4,5‐imidazole dicarboxylic acid (IDA) and then doped with phosphoric acid (H 3 PO 4 ) to form imidazole–H 3 PO 4 complexes. The results show that the polynorbornene backbone and crosslinked micromorphology produced low methanol permeability in the membranes (from 1.5 × 10 −7 to 3.8 × 10 −6 cm 2 /s) and endowed the membranes with good mechanical properties (with elastic modulus values of 692.7 to 159.7 MPa, elongation at break values from 2.7 to 22.7%, and tensile strength at break values from 14.4 to 5.5 MPa) and excellent thermal stability (up to 280°C). Furthermore, the proton conductivities of the membranes increased with increasing temperature and increasing content of IDA/H 3 PO 4 in the membranes. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011