Preparation of phosphorus-containing polymers—XXIII: Phenoxaphosphine-containing polyimides

New phenoxaphosphine-containing polyimides were synthesized from 10-phenylphenoxaphosphine-2,3,7,8-tetracarboxylic dianhydride 10-oxide (IV) and diamines via polyamic acids in two steps. (IV) was prepared by dehydration of 10-phenylphenoxaphosphine-2,3,7,8-tetracarboxylic acid 10-oxide (III) derived from 2,3,7,8-tetramethyl-10-phenylphenoxaphosphine (I) or 2,3,7,8-tetramethyl-10-phenylphenoxaphosphine 10-oxide (II) by pyridine-permanganate oxidation. (I) was synthesized from bis(3,4-dimethylphenyl)ether and phenylphosphonous dichloride by the Friedel-Crafts reaction. The resulting polyimides had reduced viscosities of 0.13–0.84 di/g in cone H₂SO₄ at 30°. They were also soluble in dichloroacetic acid and some of them dissolved in DMA, DMSO. DMF and chloroform. Aromatic phenoxaphosphine-containing polyimides exhibited excellent thermal properties and hardly degraded below about 500°; the aliphatic polyimides decomposed at around 500. The aromatic polyimides had thermal stability similar or superior to aromatic polypyromellitimides and better heat resistance than linear open-chain phosphorus-containing polyimides. These polyimides showed retardance to inflammation.