Methylated polyarylethersulfones have been prepared by conventional reactions of 4-chlorophenyl sulfone with methylhydroquinone, 2,3-dimethylhydroquinone, trimethylhydroquinone, durohydroquinone and mixtures of hydroquinone with durohydroquinone, in the presence of potassium carbonate. Polymer compositions were checked by H-1 n.m.r. spectroscopy. The effects of steric hindrance on the reactions are considered and glass transition temperatures for the polymers recorded. Several of the copolymers were sulfonated by dissolving them in sulfuric acid and the products analysed by H-1 n.m.r. after conversion to their tetramethylammonium salts. The bis-phenol residues in the homopolymers prepared using methylhydroquinone or its dimethyl analogue were monosulfonated completely, but with the homopolymer from trimethylhydroquinone this sulfonation was not complete and it appears that sulfonation of phenylene ether sulfone residues may also occur. Monosulfonation of copolymers prepared using mixtures of hydroquinone and durohydroquinone occurred as expected at the hydroquinone residues, but again some sulfonation of phenylene ether sulfone residues occurs and there may be other complications.