Abstract: Polyarylketones are made by electrophilic substitution using a dispersant for the polymer. The dispersant comprises a polymer having first pendent groups which are substantially compatible with the reaction mixture but are substantially incompatible with the polymer and second pendent groups which comprise Lewis bases. Preferred dispersants are copolymers of aliphatic vinyl compounds and N-vinyl pyrollidone, particularly of 1-eicosene (CH.sub.3 (CH.sub.2).sub.17 CH.dbd.CH.sub.2) and N-vinyl pyrollidone in which the ratio of first groups to second groups is in the range 1.5:1 to 0.5:1, and more preferably is 1:1.