This invention relates to copolymers which consist essentially of [-ether-phenyl-ether-phenyl-carbonyl-phenyl-]and [ether-phenyl-phenyl-ether-phenyl-carbonyl-phenyl-] repeat units, as well as end units, which have reduced melting temperature (Tm) compared to prior art copolymers including such repeat units. The copolymers of the invention exhibit crystallinity and have similar glass transition temperatures to the prior art polymers.