Liquid Crystalline Polyacetylenes:  Synthesis and Properties of Poly{<i>n</i>-[((4‘-cyano-4-biphenylyl)oxy)carbonyl]-1-alkynes}

It is generally believed that cyano functionality is “toxic” to the classical MoCl5- and WCl6-based metathesis catalysts, but we here present such an example in which a group of cyano-containing acetylene monomers are polymerized by the “simple” metal halides. The WCl6(−Ph4Sn) catalysts in dioxane initiate the polymerizations of n-{[(4‘-cyano-4-biphenylyl)oxy]carbonyl}-1-alkynes (AnCN; n = 2, 3, 8), yielding polymers (PAnCNs) with relatively narrow molecular weight distributions (Mw/Mn down to 1.3). The same metal−halide mixtures in toluene, however, are generally ineffective in polymerizing AnCNs, suggesting that the tungsten−oxo complexes are involved in the active center formation. The differential scanning calorimetry, polarizing optical microscopy, and X-ray diffractometry analyses reveal that all the PAnCNs are mesomorphic, with the longer flexible spacer favoring the better ordering of the mesogenic groups. PA2CN shows monotropic nematicity, PA3CN exhibits enantiotropic nematicity, and PA8CN displays enantiotropic smecticity with an interdigitated molecular packing arrangement (sAd) over a wide temperature range (ca. 110 °C). In-domain banded structures within the sAd layers of PA8CN are observed during the transit of the bâtonnets to the focal-conic fan textures, and the formation of large scale band morphology is achieved by the application of shear force to PA8CN in its liquid crystalline state.