Synthesis of aromatic polyetherketones in trifluoromethanesulphonic acid

Abstract

The superacid solvent trifluoromethanesulphonic acid ( H 0 = − 14.6) promotes rapid polycondensation of certain aromatic dicarboxylic acids with aromatic diethers at ambient temperature, to give linear polyketones of high molecular weight. Reactivity studies on a range of monomers and on model compounds indicate that the polymerization is inhibited by electron-withdrawing substituents on the same aromatic ring as the carboxylic acid function, and, in the ether component, by the transmission of electron-withdrawing effects between aromatic rings via the ether bridge. Monoacylation of diphenyl ether thus leads to very significant deactivation of the second, unsubstituted ring, so that this ether is not a satisfactory monomer for the present polyketone synthesis, whereas 1,4-diphenoxybenzene and 4,4′-diphenoxybiphenyl both undergo rapid diacylation, and hence polycondensation, at the terminal aromatic rings. Polymerizable one-component systems, designed for maximum self-reactivity, include (4-phenoxy)phenoxybenzoic acid and the previously unrecorded monomer 4-(4′-phenoxyphenyl)benzoic acid. Polymer characterization by 13C nuclear magnetic resonance and differential scanning calorimetry indicates that condensations proceed with very high para-selectivity, giving crystalline polyketones with melting points in the range 320–470°C.