High-molecular-weight poly(phthalazinone)s with very high glass-transition temperatures (T-g's) were synthesized via a novel N-C coupling reaction. New bisphthalazinone monomers (7a-e) were synthesized from 2-(4-chlorobenzoyl) phthalic acid in two steps. Poly(phthalazinone)s, having inherent viscosities in the range of 0.34-0.91 dL/g, were prepared by the reaction of the bis(phthalazinone) monomers with an activated aryl halide in a dipolar aprotic solvent in the presence of potassium carbonate. The poly(phthalazinone)s exhibited T-g's greater than 230 degreesC. polymer 8b synthesized from diphenyl biphenol and bis(4-flurophenyl) sulfone demonstrated the highest T-g of 297 degreesC. Thermal stabilities of the poly(phthalazinone)s were determined by thermogravimetric analysis. All the poly(phthalazinone)s showed a similar pattern of decomposition with no weight loss below 450 degreesC in nitrogen. The temperatures of 5% weight loss were observed to be about 500 degreesC. The poly(phthalazinone)s containing 4,4'-isopropylidenediphenol and 4,4'-(hexafluoroisopropylidene) diphenol and diphenyl ether linkage were soluble in chlorinated solvents such as chloroform. Other poly(phthalazinone)s were soluble in dipolar aprotic solvents such as N,N'-dimethylacetamide. The soluble poly(phthalazinone)s can be cast as flexible films from solution. (C) 2003 Wiley Periodicals, Inc.