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Developing high-performance and low-cost polymer membranes for high-temperature proton exchange membrane fuel cells is a big challenge to the polymer design. Herein, high-temperature proton exchange membranes are prepared based on the low-cost thermoplastic resin of poly(vinyl chloride) (PVC). However, the methylimidazolium PVC exhibits significantly low phosphoric acid (PA) doping content and low conductivity due to the compact structure. Thus, the N-[3-(triethoxysilyl) propyl]-4,5-dihydroimidazole (SiIm) is employed as a dual functionalized reagent for PVC. On the one hand, SiIm is used to quaternize PVC through the SN2 nucleophilic substitution between chloride and imidazole. On the other hand, the crosslinked siloxane network is formed via the hydrolysis reaction of SiIm in a dilute sulfuric acid solution. The obtained polysilsesquioxane crosslinked membranes (PVC-x%SiIm) display good thermal stability, excellent PA doping ability, superior proton conductivity, and moderate tensile strength. For instance, the PVC-17%SiIm membrane achieves a high PA doping content of 243% after immersing in 85 wt% PA solution and exhibits the highest conductivity of 0.111 S·cm-1 at 180 °C without humidifying and tensile strength of 6.0 MPa at room temperature. [ABSTRACT FROM AUTHOR]

A novel copolymer of polybenzimidazoles was prepared by copolymerization of 3,3′‐diaminobenzidine tetrahydrochloride, 3,4‐diaminobenzoic acid and isophthalic acid in polyphosphoric acid at 200 °C. The polymerization could be performed within 90–110 min with the assistance of microwave irradiation. The solubility of the copolymer obtained in N,N‐dimethylacetamide (DMAc) was improved compared with those of poly[2,2′‐(m‐phenylene)‐5,5′‐bibenzimidazole] and poly(2,5‐benzimidazole). Thus copolymer membranes could be readily prepared by dissolving the copolymer powders in DMAc with refluxing under ambient pressure. The decomposition temperature of the copolymer was about 520 °C in air according to thermogravimetric analysis data. The proton conductivity and mechanical strength of the phosphoric acid‐doped copolymer membranes were investigated at elevated temperatures. A conductivity of 0.09 S cm−1at 180 °C and a tensile stress at break of 5.9 MPa at 120 °C were achieved for the acid‐doped copolymer membranes by doping acids in a 75 wt% H3PO4solution. Copyright © 2010 Society of Chemical Industry [ABSTRACT FROM AUTHOR]