A new monomer, 1,4-bis(4-phenoxybenzoyl)naphthalene (BPOBN), was conveniently synthesized via a simple synthetic procedure from readily available materials. A series of novel copolymers of poly(ether ketone ether ketone ketone) and poly(ether ketone ketone ether ketone ketone) containing 1,4-naphthylene moieties were prepared by the Friedel-Crafts acylation solution copolycondensation of terephthaloyl chloride (TPC) with a mixture of BPOBN and 4,4'-diphenoxybenzophenone (DPOBPN), over a wide range of BPOBN/DPOBPN molar ratios, in the presence of anhydrous AlCl3 and N-methylpyrrolidone in 1,2-dichloroethane. The copolymers with 10-40% BPOBN are semicrystalline and had remarkably increased T(g)s over the conventional PEEK and PEKK due to the incorporation of 1,4-naphthylene moieties in the main chains. The copolymers with 30-40 mol% BPOBN had not only high T(g)s of 176-177 degrees C, but also moderate T(m)s of 332-338 degrees C, which are suitable for the melt processing. These polymers had tensile strengths of 101.5-104.7 MPa, Young's moduli of 2.49-2.65 GPa, and elongations at break of 13.3-15.7% and exhibited high thermal stability and excellent resistance to organic solvents. (C) 2016 Society of Plastics Engineers