Polyimidines. VIII. Condensation of 3,5-dibenzylidenepyromellitide-1,7-dithione with m-xylylenediamine

A new pyromellitimidine‐forming monomer, 3,5‐dibenzylidenepyromellitide‐1,7‐dithione, was synthesized by thionation of 3,5‐dibenzylidenepyromellitide using phosphorus pentasulfide in boiling chloro‐ or bromobenzene. Polymerization of this monomer with m‐xylylenediamine (MXDA) in chlorobenezene at 95°C afforded poly(dihydroxydibenzylpyromellitimidinethione) with inherent viscosities of 0.23–0.51 dL/g in yields from 73 to 84%. Subsequent dehydration was accomplished by thermal methods or in a polar aprotic solvent such as dimethylformamide (DMF) using acid catalyst. Hydrated and dehydrated polymers were soluble in N‐methyl‐2‐pyrrolidinone (NMP), m‐cresol, and dioxane, and partially soluble in chloroform. Very brittle films could be cast from NMP solution. Thermogravimetric analysis of the dehydrated polymer showed a 10% weight loss in nitrogen atmosphere at 460°C