An aromatic polyether contains within its chain the repeat units--Ph--CO--Ph-- I--[Ph--SO.sub.2 --Ph]n-- IIat a molar ratio I/II in the range 98:2 to 80:20 where Ph represents paraphenylene; the repeat units are linked through ether oxygen; and n is at least 1.1. pa It can be made by reacting together hydroxy and halogeno aromatic compounds corresponding to units I and II and to any minor units that are to be present. The reactants can be provided at least partly by a polymer containing an ether-linked succession of the units.