Synthesis of Imidazolium Salt-Containing Poly(diphenylacetylene)s and the Effect of Counter Anion on Gas Permeability

Poly(diphenylacetylene) with Br- as a counter anion [3(Br-)] was synthesized, and free-standing membranes were prepared by solvent-casting. Anion exchange reactions in the membranes of 3(Br-) were achieved using CH3CO2Na- and KF and membranes containing CH3CO2- [3(CH3CO2-)] and F- [3(F-)1 were obtained. The carbon dioxide permeability coefficient (P-CO2) and separation factor (P-CO2/P-N2) of 3(F-) were 4.5 barrer and 47, respectively. Compared with poly(diphenylacetylene)s having CF3CO2- [3(CF3CO2-)] and (CF3SO2)(2)N- [3(Tf2N-)] as counter anions, the permeability coefficients became larger in the order of 3(F-) < 3(Br-) < 3(CF3CO2-) < 3(Tf2N-). This may be due to the bulkiness of the counter anions that prevents polymer chain packing. On the other hand, 3(CH3CO2-) showed the lowest permeability in spite of the relatively bulky anion. This can be explained by the fact that the presence of CH3CO2- drastically decreased carbon dioxide diffusivity because of strong interaction of CH3CO2- with carbon dioxide.