A series of poly(ether ketone) copolymers were prepared by nucleophilic aromatic polymerization reactions of the AB monomer 4-fluoro-4'-hydroxybenzophenone, 1, and the AB(2) monomer bis(4-fluorophenyl)-(4-hydroxyphenyl)phosphine oxide, 2, in the presence of 3 or 5 mol% of a highly reactive core molecule, tris(3,4,5-trifluorophenyl)phosphine oxide (B-3), 4. All of the copolymers prepared in the presence of a core molecule were sufficiently soluble in N-methylpyrrolidinone, NMP to allow the determination of their molecular weights and polydispersity indices, PDIs. Number-average molecular weights, M(n)s, of 3200-6800 Da were determined and the PDI values ranged from 1.41 to 4.07. The M-n Was controlled by the mol% of 4 present in the reaction mixture with higher molar percentages leading to lower M. values. Lower reaction temperatures and lower ratios of AB/AB(2) monomers afforded copolymers with lower PDI values. As expected, the crystallinity of the samples decreased with an increasing AB2 content or an increase in PDI The copolymers also exhibited excellent thermo-oxidative stability with a number of samples suffering 5% weight losses at temperatures, in air, well in excess of 450 degrees C. (c) 2008 Elsevier Ltd. All rights reserved.