PURPOSE: To obtain the titled polyimide having improved heat resistance and flame retardancy, by polycondensing a (tetracarboxy-10-phenylphenoxaphosphine-10- oxide)dianhydride which is a novel compound with a diamine.

CONSTITUTION: A ( tetracarboxy -10- phenylphenoxaphosphine-10-oxide )dianhydride of formula I is polycondensed with a diamine of the formula H2N-R-NH2 (R is bifunctional hydrocarbon group or bifunctional heterocyclic group) to form a polyamic acid consisting of repeating units expressed by formula II, which is, subsequently or after isolation, subjected to ring closure through dehydration to afford a novel polyimide consising of repeating units expressed by formula III. The polyconsensation is preferably carried out by isolating the polyamic acid prepared through solution polymerization at a low temperature, and heating the polyamic acid in a solvent at 100W200°C to carry out ring closure through dehydration in two stages. The compound of formula I is obtained by reacting a compound of formula IV with dichlorophenylphosphine, oxidizing the reaction product with a strong oxidizing agent, and subjecting the oxidation product to ring closure through dehydration.