A novel class of crosslinkable poly(phthalazinone ether ketone)s with relative high molecularweight and good solubility were successfully synthesized by the copolymerization of bisphthalazinone containing monomer, 3,3'-diallyl-4,4-dihydroxybiphenyI and 4,4-difluorobenzophenone. The synthesized polymers with inherent viscosities in the range of 0.42 to 0.75 dL/g can form flexible and transparent membranes by casting from their solution. The crosslinking reaction of these polymers can be carried out by thermally curing of the virgin polymers in or without the presence of crosslinking agent. The experimental results demonstrated that the crosslinking reaction also occurred to some extent during the polymerization. The crosslinked polymers exhibited equivalent glass transition temperature (T-g) at lower crosslinking density, and showed higher T-g than virgin polymers at higher crosslinking density. The crosslinked high-temperature polymer can be used as the base material for high temperature adhesive, coating, enamel material, and composite matrices. (C) 2007 Wiley Periodicals, Inc.