Synthesis and Properties of Sulfonated Polyimides Containing Benzimidazole Groups
|School||Shanghai Jiaotong University|
|Keywords||Proton exchange membrane Imidazolyl - containing sulfonated polyimide Covalent crosslinking Radical oxidation resistance|
The polyimide has a high thermal stability, high mechanical strength and modulus, excellent electrical properties and good resistance to chemical stability, is widely used in industry. In recent years, studies show that the six membered ring sulfonated polyimide is a promising fuel cell proton exchange membrane materials. Have been reported a number of high proton conductivity, and hydrolytic stability of the sulfonated polyimide membrane. However, as in the film and many other sulfonated polymers, sulfonated polyimide membrane the radical oxidation resistance than the Nafion membrane lot worse, thus affecting the service life of the fuel cell. Has been previously reported crosslinked sulfonated polyphenylene benzimidazole having excellent anti-radical oxidation, Thus, the polymer structure is the introduction of an imidazole ring group, and the film is covalently crosslinked may be an increase anti-radical oxidation effective way. In this subject, by random copolymerization of the different structure of the main chain contains imidazolyl the sulfonated polyimide. 1,4,5,8 - naphthalene tetracarboxylic dianhydride (the NTDA), sulfonated diamine, an imidazolyl group-containing non-sulfonated diamine 5 - amino - (2 - p-aminophenyl) benzimidazole (Apabi) Ordinary non-sulfonated diamine 9,9 '- (4 - aminophenyl) fluorene (BAPF), m-cresol as solvent, is obtained in the presence of benzoic acid and triethylamine under 180 ℃ reaction 20h. Copolymerizable sulfonated diamines are: 2,2 '- benzidine disulphonic acid (BDSA), 4,4' - diaminodiphenylether -2,2 '- disulfonic acid (ODADS), 2,2' - (4 - sulfonatophenyl the group) benzidine (BSPOB), 4,4 '- two (4 - Amino-phenoxy) -3,3'-disulfonic acid (BAPBDS). The synthesis of the sulfonated polyimide having a good solubility in some organic solvents, such as m-cresol, DMSO. By a solution casting method have good mechanical properties (tensile strength of 30-120MPa) a film that successful synthesis of high molecular weight polymer. The proton exchange causes ionic crosslinking because the sulfonic acid group and imidazolyl, acid-base interactions. The film containing BAPF with polyphosphoric acid (PPA) at 180 ℃ processing covalently crosslinked. The covalent cross-linking is based on a condensation reaction between the phosphorus pentoxide (P2O5) catalysis in the sulfonic acid group and BAPF the 2,7 - position. Thermal decomposition temperature GT covalently crosslinked film and uncrosslinked films exhibit high thermal stability (a sulfonic acid group; 300 ° C). Because the cross-linking process a small part of the sulfonic acid group is consumed, the covalently cross-linked film of the ion exchange capacity (IEC) and the proton conductivity than the corresponding uncrosslinked film decreased slightly. The Fenton test (3% H2O2 3 ppm of FeSO4, 80 ° C) show that the imidazole group in the radical oxidation resistance plays an important role, but imidazolyl and covalently crosslinked synergy than a single factor of the film anti freedom yl oxidizing improve have greater significance. For instance, N-ODADS/BAPF/APABI (2/1/1) membrane, covalently crosslinked test 8h able to maintain the shape of the film, the ratio of the time under the same test conditions before crosslinking (3h) greatly extended. Excluding imidazolyl N-ODADS/BAPF (3/1), however, film, covalently crosslinked test 85min film after crush starts, slightly extended than the time under the same test conditions before crosslinking (60min). Successfully obtained having a high proton conductivity rate (>; 0.1S/cm, water) and an excellent anti-free radical oxidation (GT; 5H, 80 ° C Fenton test) of the sulfonated polyimide membrane.