Synthesis and Characterization of Polyimides Containing Benzimidazolyl Groups for Proton Exchange Membrane

• Main Authors: Bo-Yan Huang, 黃博彥
• Other Authors: Yaw-Terng Chern
• Format: Others
• Language: zh-TW
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/3vh5th

碩士 === 國立臺灣科技大學 === 化學工程系 === 106 === Reaction of 4,4-oxybis(benzoic acid) with 4-nitro-o-phenylenediamine in polyphosphoric acid gave bis(4-(2-(5-nitrobenzimidazolyl))phenyl)ether (O/IM/NO2), which was hydrogenated to give novel monomer of bis(4-(2-(5-aminobenzimidazolyl))phenyl)ether(O/IM/NH2). A series of copolyimides (PIs) containing main-chain and pendant benzimidazole groups were synthesized from 1,4,5,8-naphthalene tetracarboxylic dianhydride (NTDA), diamines which had benzimidazole such as O/IM/NH2, 2,2 ’-bis(2-benzimidazole)-4,4’- diaminobiphenyl (BP/IM/NH2), 1,3-diamino-5- (2- benzimidazole) benzene (m/IM/NH2) and other aromatic diamines. They had inherent viscosities in the range of 0.94~1.87 dL/g, and they could form tough and flexible films. The PIs exhibited high thermal stability with 10% decomposition temperature more than 500℃ in nitrogen, and their glass transition temperature is around 300℃. These films exhibited good mechanical properties with tensile stress exceeded 103 MPa. However, the mechanical properties of PI significantly decreased when phosphoric acid doping level increased. The mechanical properties of phosphoric acid doped PIs could be improved via crosslinking reaction of methyl group, cross-linked PI would form close packing, and it led to decrease of phosphoric acid doping level, but it could still maintain high proton conductivity and high mechanical properties. The tensile strength of C3-O6BPBI2PF1.7DMB0.3 in wet state enhanced from 8 to 15 MPa after crosslinking reaction. Almost all PIs exhibited higher on proton conductivities at 140℃ than m-PBI(52.7 mS/cm). For example, the proton conductivities of O7BPBI2PF1 and O6BPBI2F1DMB1 were 82.5 and 69.7 mS/cm, respectively. Thus, these polyimides (PIs) containing benzimidazole on main chain and on pendant could be the promising materials alternative to m-PBI membrane for medium-temperature fuel cells applications because of their high proton conductivity and good oxidative stability.