Polymers from 4‐(4‐hydroxyphenyl)phthalazin‐1‐one

Abstract 2‐(4′‐Hydroxyphenylbenzoyl)benzoic acid is readily available from phenolphthalein by reaction with hydroxylamine. On treatment with hydrazine, 4‐(4‐hydroxyphenyl)phthalazin‐1‐one is formed in high yield. Under conditions conventionally used for the synthesis of poly(aryl ether)s the phthalazinone reacts with 4,4‐difluorobenzophenone or 4,4′‐difluorodiphenyl sulfone to yield high molecular weight linear polymers which are thermooxidatively stable and have Tg's approaching 300°C. The phthalazinone NH groups behave like phenolic OH groups and the resulting polymers contain O‐C and N‐C linkages. Phenyl‐substituted phenolphthaleins have also been synthesized and converted to the corresponding phthalazinone polymers.