The introduotion of the ether linkage into the main chain of an aromatio or hetorooyclic polymer may lead to an increase of the flexibility of the macremcleoule with an improvement of the processability of the polymer without any approciable loss of its thermal and thermal oxidative stability. Since sulfide is analogous to the ether linkage, the replacement of the ether linkage by a sulfide in the main chain may lead to the similar effect. 3, 3', 4, 4'-diphenyl sulfide tetracarboxylic aoid was synthesized by the condensation of N-pheny-4-chlorophthalimide a,nd sodium sulfide in a polar organic solvent and then through the hydrolysis of the product bis (sulfidephthalimide) with sodium hydroxide solution followed by acidification.A moldable poly (sulfide-imide) with excellent physioo-mechanical properties was synthesized from the tetra-acid thus obtained.