Polymerization of diphenylacetylenes with polar functional groups by the Grubbs-Hoveyda Ru carbene catalyst

Polymerization of various diphenylacetylene derivatives was investigated by using Grubbs-Hoveyda catalyst (1). Owing to excellent tolerance for polar functional groups, catalyst 1 polymerized diphenylacetylene (2) and diphenylacetylene derivatives bearing silyl (3), siloxy (4 and 5), ester (6 and 7), amide (8-10), and carbamate (11) groups. It is noteworthy that polymerization of monomers 6-11, which have polar functional groups, has been impossible until now due to the deactivation of well-known Ta catalysts. Although monomers having ester groups (6 and 7) hardly polymerized, their copolymerization with trimethylsilyl group-containing diphenylacetylene (3) afforded copolymers, which incorporated ester moieties more than the monomer feed ratio. While polymers with relatively nonpolar groups [poly(3)-poly(5)] were soluble in hydrocarbon solvents such as cyclohexane and hexane, polar group-bearing homo- and copolymers (poly(10), poly(11), etc.) dissolved in polar solvents (e.g., DMF and acetone). Polymerization of 1-(4-tert-butyldimethylsiloxy)phenyl-2-(4-fluoro-phenyl)acetylene (5) gave a high molecular weight polymer (M) over bar (n) = 178 000) suitable for membrane fabrication, and the membrane of this polymer showed higher gas permeability and permselectivity than that of the Ta-based polymer.