Synthesis And Characterization Of Novel Linear And Hyperbranched Polybenzimidazoles

A novel sulfonated polybenzimidazole, sulfonatedpoly[2,2'-(p-oxydiphenylene)-5,5'-bibenzimidazole] (SOPBI), were successfully prepared by post-sulfonation reaction of the parent polymer, poly[2,2'-(p-oxydiphenylene)-5,5'-bibenzimidazole] (OPBI), using concentrated or fuming sulfuric acid as the sulfonating reagent at 80 ℃, and the degree of sulfonation (DS) could be regulated by controlling the reaction conditions. No significant polymer degradation was observed in the post-sulfonation processes. Direct polymerization of 4,4'-dicarboxydiphenyl ether-2,2'-disulfonic acid disodium salt (DCDPEDS) and 3,3'-diaminobenzidine (DABz), however, resulted in insoluble gels either in polyphosphoric acid (PPA) or in phosphorus pentoxide/methanesulfonic acid in the ratio of 1:10 by weight (PPMA) reaction medium. The SOPBIs prepared by the post-sulfonation method showed good solubility in dimethyl sulfoxide (DMSO), high thermal stability, good film forming ability and excellent mechanical properties. OPBI and the SOPBI (DS = 60%) exhibited much better radical oxidative stability than the commercial PBI. The SOPBI membrane with high DS (154%) displayed high proton conductivity (0.18 S/cm) in liquid water at 60 ℃.A series of hyperbranched polybenzimidazoles (HBPBIs) were successfully synthesized by condensation polymerization of 1,3,5—benzenetricarboxylic acid (BTA) and 3,3'—diaminobenzidine (DAB) in polyphosphoric acid (PPA) at 190 ℃. Different monomer addition manners and molar ratios resulted in different polymers, i.e., simultaneous addition of BTA and DAB with the molar ratio of 1:1 (manner 1) gave carboxyl-terminated HBPBI (HBPBI-1), whereas the addition of BTA portion-wise to DAB solution in PPA with the molar ratio of DAB:BTA = 2:1 (manner 2) yielded amine-terminated HBPBI (HBPBI-2). The free carboxyl and amino groups of HBPBI-1 and HBPBI-2 could further react with o—diaminobenzene and benzoic acid, respectively, to form the chemically modified polymers (HBPBI-3 and HBPBI-4). Except HBPBI-2, all the HBPBIs showed good solubility in some organic solvents (e.g. dimethyl sulfoxide and N,N-dimethylacetamide) and strong acids. Thermogravimetric analysis measurement...