SYNTHESIS AND PROPERTIES OF SULFONATED POLY(ETHER SULFONE KETONE)S CONTAINING 3,5-DIMETHYL PHTHALAZINONE MOIETIES AS PROTON EXCHANGE MEMBRANE MATERIALS

A series of sulfonated poly(phthalazinone ether sulfone ketone) copolymers, SPPESK-DMs, with different degree of sulfonation (SD) were synthesized by polycondensation of 4-(3,5-dimethyl-4-hydroxyphenyl)-2,3-phthalazinone, 3,3'-disulfonate-4,4'-difluorobenzophenone and 4,4'-dichlorodiphenylsulfone, which were potentially utilized as membranes in proton exchange membrane fuel cells (PEMFC). The high molecular weight sulfonated polymers (SPPESK-DMs) with the inherent viscosity ranged from 1.36 dL/g to 6.04 dL/g were obtained when the sulfonation degree of samples varied from 0.2 to 1.0. The yellow transparent membranes cast from N-methyl-2-pyrrolidone solutions of SPPESK-DMs were obtained. The chemical structure of the sulfonated polymers was characterized by Frill and H-1-NMR, the thermobehavior of polymers was also investigated by TGA, and the properties of the membranes were investigated too. The results indicated that the decomposition temperatures of the sulfonic group and the main chain in the SPPESK-DMs copolymers were above 260 degrees C and 410 degrees C respectively, which demonstrated the copolymers had excellent thermal stability. The water uptake, swelling ratio, ion exchange capacity and proton conductivity increased with increasing of temperature and SD. The proton conductivity of the SPPESK-DM50 with the SD of 1.0 was 1.08 x 10(-2) S/cm at 85 degrees C, which was considerably lower than that of Nafion 117, but would meet the lowest requirement in PEMFC application. The methanol permeability values of SPPEK-DMs membranes were lower than that of Nafion117. The oxidative stability of the SPPESK-DMs membranes was better than that of SPPEK or SPPESK membranes, and the expended time that membranes started to break into pieces at 80 degrees C in Fenton's reagent was longer than 4.33 h.