A series of sulfonated fluorine containing polybenzimidazoles (sPBI) with controlled sulfonation degree (SD) were synthesized from 3,3'-diaminobenzidine, 5-sulfoisophthalic acid monosodium salt and 2,2-bis(4-carboxyphenyl)hexafluoropropane by solution copolycondensation in poly(phosphoric acid). The resulting polymers were characterized mainly by means of FT-IR, ¹H NMR, GPC and TGA. The number-average molecular weights of the obtained samples are 61300～86000, and the polydispersity indices are 1.96～2.34. The sPBI samples present good film processing properties and excellent thermal stabilities. The temperatures of 5% and 10% weight loss increase with increasing SD of the samples, and are equal to 549 and 576 ℃ respectively for sample I_e (SD, 70%). This kind of sPBI is promising for application to proton exchange membrane.

Key words: polybenzimidazole, sulfonation, poly(phosphoric acid), proton exchange membrane