Poly (Arylether Ketone-Imidazole): Synthesis, Characterization And Film Prorerties

Poly (ether ether ketone) (PEEK), a high-temperature resistant thermoplastic resin, has been used in a lot of fields owing to its excellent properties. Sulfonated poly(ether ether ketone) (SPEEK) is widely investigated as candidate for Pronton Exchange Membrane (PEM) due to its high chemical and thermooxidative stability, good mechanical properties and lower cost. A series of unique PEEK, poly(ether ether ketone-x% benzimidazole)s (PEEK-x%BI), were synthesized by polycondensation of bisphenols and difluorobenzophenones in this work. The dielectric property and gas transport property of this polymer were discussed. Furthermore, SPEEKs containing benzimidazole units were synthesized. And the properties of resulted membranes were determined for estimating their potential application in DMFC.In the first part of this paper, poly(ether ether ketone-x% benzimidazole)s (PEEK-x%BI) was synthesized by polycondensation of difluorobenzophenones 5,5'-Bis[2-4(-hydroxyphenyl)-benzimidazole] (HPBI) and 2,2-Di-(4-hydroxyphenyl) -propane (BPA). The structures of polymer were confirmed by ¹H-NMR and FT-IR spectroscopies. Thermogravimetric analysis (TGA) showed that the introduction of benzimidazole into polymer main chain could improve the thermal stability of polymer effectively. Moreover, the glass transition temperature of PEEK-x%BI increased with the content of benzimidazole from 157 oC to 319 oC. The dielectric constants of all PEEK-x%BIs were higher than that of PEEK, but below 2.3. The gas permeation behavior of PEEK-x%BI casting film was tested. It was found that the gas permeation coefficients of O₂ and N₂ in PEEK-x%BI were quite close to that of commercial Ultem 1000 polyimides. The Scanning Electronic Microscopy (SEM) images of PEEK-alt-BI and SPEEK blend membranes showed a good compatibility between two polymers.In the second part, a novel copolymer of sulfonated poly(hexafluoropropane ether ether ketone-benzimidazole)s (SPEEK-AF-x%BI) was synthesized by polycondensation of HPBI, 2,2-Bis(4-hydroxyphenyl) hexafluoropropane (BPAF)and a mixture of sulfonated and non-sulfonated difluorobenzophenones. By varying the amount of two difluorobenzophenones, the content of sulfonic acid units was controlled straightforwardly. Furthermore, the imidazole content of could be adjusted of by varying the amount of HPBI and BPAF. The polymer structure was confirmed by ¹H-NMR and FT-IR spectroscopies. Two different methods of ion exchange capacity measurement supported a strong inter- and intra-molecular interaction between acid and base units, which resulted in an improved mechanical strength as well as avoiding phase separation. The water uptake and swelling ratio of 60SPEEK-AF-10%BI were much lower than that of 60SPEEK-AF. At the same time, the introduction of imidazole units could not only improve the thermal stability and chemical stability of polymer effectively, but also reduce the methanol permeability. At the temperature of 20 oC, the methanol permeability of 60SPEEK-AF-10%BI was 4.18×10^-7 cm2/s, lower than that of Nafion(?)117 membrane.