Two series of novel copoly(arylene ether ketone) were successfully synthesized from hydroquinone or bisphenol A, bis(4‐fluorophenyl)ketone and 4‐(4‐hydroxyphenyl)‐2,3‐phthalazin‐1‐one with anhydrous potassium carbonate as the catalyst. The synthesized polymers exhibited high glass‐transition temperatures together with excellent thermooxidative stability. The chain structure of these polymers was studied by means of 13C‐nuclear magnetic resonance (NMR) spectroscopy, differential scanning calorimetry (DSC), and wide‐angle X‐ray diffraction (WAXD) techniques. The experimental results showed that these “as‐made” copolyaryleneketones containing hydroquinone moieties exhibited a multiblock chain structure with long segments that mainly consisted mainly of hydroquinone and bis(4‐fluorophenyl)ketone at the middle of the molecular chain. These long segments exhibited crystallites in the produced polymers. The synthesized copolyaryleneketone containing 90 mol % hydroquinone possessed a glass‐transition temperature higher than that of commercial PEEK. The synthesized polymers also exhibited either fair processability or solubility. The glass‐transition temperatures, solubility, and tensile strengths of the two series of copolyaryleneketones tended to increase with increasing phthalazinone moiety content. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2687–2695, 2001