Synthesis and properties of poly(diphenylacetylenes) containing siloxy and halogen/methyl groups and their desilylated membranes

Diphenylacetylenes containing both siloxy groups and halogen or methyl substituents (p-tert-BuMe2SiOC6H4CCC6H3R2, R = m,p-Cl,Cl; m,m-Cl,Cl; m,p-Br,Br; m,m-Br,Br; m,p-Me,Me; m,m-Me,Me, 1a–f, respectively) were polymerized with TaCl5–n-Bu4Sn catalyst to give high molecular weight polymers (2a–f) in good yields. Free-standing membranes were fabricated by casting from toluene solution. Desilylation of these siloxy group-containing polymer membranes with trifluoroacetic acid (TFA) afforded poly(diphenylacetylene) membranes having hydroxy groups (3a–f). Polymers 2a–f were soluble in low polar solvents such as toluene and CHCl3, while 3a–f were insoluble in these solvents. According to thermogravimetric analysis (TGA), 2a–f and 3a–f exhibited high thermal stability (T0 ∼340 and ∼390 °C, respectively). The gas permeability of the halogen-containing polymer membranes was higher than that of methyl group-containing ones. The PCO2/PN2 permselectivity ratios of polymer membranes 3a–f were in the range of 14–49. The points of 3a–f in the PCO2 vs PCO2/PN2 plot were located obviously above Robesonʹs upper bound.