Synthesis and Properties of Stereoregular Polyacetylenes Containing Cyano Groups, Poly[[4-[[[n-[(4‘-cyano-4-biphenylyl)- oxy]alkyl]oxy]carbonyl]phenyl]acetylenes

Abstract

We have succeeded in synthesizing soluble, stereoregular, and high molecular weight polyacetylenes containing polar cyano functional groups in high yields. Two new cyanoalkyne monomers, [4-[[[n-[(4‘-cyano-4-biphenylyl)oxy]alkyl]oxy]carbonyl]phenyl]acetylenes (1; n = 6, 12), are synthesized via multistep reactions. [Rh(nbd)Cl]2 effects the polymerization of 1, producing polymers (2) with high molecular weights (Mw up to 158 000) in high yields (up to 71%). Spectroscopic analysis reveals that the polymers possess alternating-double-bond backbones with high stereoregularity. The electronic and thermal transitions in 2 are sensitive to their stereostructures: The polymer with higher stereoregularity absorbs at longer wavelength and melts at higher temperature. The polymers prepared in DMF-based solvents are completely soluble in DMF, THF, and chloroform, although the dissolution takes quite a long time (up to a week) due to the high stereoregularity of the polyacetylene backbones and the strong electronic interaction among the push−pull mesogenic pendant groups. The polymers are thermally very stable (temperature for 5% weight loss: ca. 400 °C) and can be melt-processed in a moderate temperature range (ca. 100−150 °C).