A method for manufacture of PEEK-PEDEK copolymers is described herein, along with copolymers formed by the method and their use. The method includes a nucleophilic polycondensation of a mixture of dihydroxybenzene and dihydroxybiphenyl with 4,4′-dihalobenzophenone in a reaction mixture comprising sodium carbonate and potassium carbonate, in an aromatic sulfone solvent, at a reaction temperature rising to a temperature from 280° C. to 330° C. immediately prior to the addition of a reaction-stopping salt, such as LiCl or Li2SO4, to the reaction mixture. Further organic dihalide is subsequently added to the reaction mixture for end-capping of the copolymer. The resulting copolymer has reduced chain branching and reduced melt viscosity at low shear rate compared to prior art copolymer of comparable molecular mass.