Synthesis of Poly(diphenylacetylene) Membranes by Desilylation of Various Precursor Polymers and Their Properties

Diphenylacetylenes having various silyl groups (PhC≡CC6H4−SiRRR, SiR1R2R3 = p-SiMe3, p-SiMe2 i-Pr, p-SiEt3, p-SiMe2 n-C8H17, p-SiMe2 n-C18H37, m-SiMe3, m-SiMe2 t-Bu, 1a−g, respectively) were polymerized with TaCl5−n-Bu4Sn catalyst to provide high molecular weight polymers. The formed polymers (2a−g) afforded tough free-standing membranes by casting from toluene solution. Desilylation of these Si-containing polymer membranes was carried out with trifluoroacetic acid. Para-substituted polymers (2a−e) underwent desilylation completely, while meta-subustituted polymers (2f and 2g) did not. According to thermogravimetric analysis (TGA), both Si-containing and desilylated polymers exhibited high thermal stability, and all the desilylated polymers showed practically the same onset temperature (∼480 °C) of weight loss. The membranes of Si-containing polymers showed lower oxygen permeability as the silyl group became bulkier. The oxygen permeability coefficients (P(O2) 120−3300 barrers) of desilylated polymer membranes were quite different from each other irrespective of the same polymer structure. When bulkier silyl groups were removed, the oxygen permeability increased to larger extents. In ethanol/water pervaporation, both Si-containing and desilylated polymer membranes showed ethanol permselectivity, indicating that these membranes possess large excess free volumes.