Direct copolymerization of sulfonated poly(phthalazinone arylene ether)s for proton-exchange-membrane materials

Abstract

Sulfonated poly(phthalazinone ether ketone) (SPPEK) copolymers and sulfonated poly(phthalazinone ether sulfone) (SPPES) copolymers containing pendant sodium sulfonate groups were prepared by direct copolymerization. The reaction of disodium 3,3′-disulfonate-4,4′-difluorobenzophenone (SDFB-Na), 4,4′-difluorobenzophenone (DFB), and 4-(4-hydroxyphenyl)-1(2H)-phthalazinone (DHPZ) at 170 °C in N-methyl-2-pyrrolidione containing anhydrous potassium carbonate gave SPPEKs. SPPESs were similarly obtained with 3,3′-disulfonate-4,4′-difluorophenyl sulfone, 4-fluorophenyl sulfone (DFS), and DHPZ as monomers. The sulfonic acid groups, being on deactivated positions of the polymer backbone, were expected to be hydrolytically more stable than postsulfonated polymers. Fourier transform infrared and 1H NMR were used to characterize the structures and degrees of sulfonation of the sulfonated polymers. Membrane films of SPPEKs with SDFB-Na/DFB molar feed ratios of up to 60/40 and SPPESs with sulfonated 4-fluorophenyl sulfone/DFS molar feed ratios of up to 50/50 were cast from N,N-dimethylacetamide polymer solutions. Membrane films in acid form were then obtained by the treatment of the sodium-form membrane films in 2 N sulfuric acid at room temperature. An increase in the number of sulfonate groups in the copolymers resulted in an increased glass-transition temperature and enhanced membrane hydrophilicity. The sodium-form copolymers were thermally more stable than their acid forms. The proton conductivities of the acid-form copolymers with sulfonated monomer/unsulfonated monomer molar feed ratios of 0.5 and 0.6 were higher than 10−2 S/cm and increased with temperature; they were less temperature-dependent than those of the postsulfonated products. SPPESH-50 showed higher conductivity than the corresponding postsulfonated poly(phthalazinone ether sulfone). © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2731–2742, 2003