Poly(aryl ether ketone)s with carboxylic acid groups: synthesis, sulfonation and crosslinking

Abstract

Carboxylic acid-containing poly(aryl ether ether ketone) (PFEEK–COOH) and poly(aryl ether ether ketone ketone) (PFEEKK–COOH) were synthesized from the monomer 9,9-bis(4-hydroxyphenyl)-fluoren-4-carboxylic acid. The latter polymer, PFEEKK–COOH, was post-sulfonated to yield SPFEEKK–COOH whereby the site and the degree of sulfonation (DS from 0 to 3) could be controlled. The reaction progress and structures of the resulting sulfonated polymers were identified by 1D and 2D NMR techniques. The carboxylic acid group was used as to crosslink SPFEEKK–COOH by reaction with poly(vinyl alcohol) (PVA) to prepare crosslinked membranes. The proton conductivity of a crosslinked SPFEEKK–COOH-1.6/PVA membrane was ∼0.15 S cm⁻¹ at 65 °C, while maintaining acceptable dimensional stability in water. Thermal stability, water uptake and proton conductivity of carboxylated, carboxylated/sulfonated, and crosslinked membranes were investigated.