Synthesis and thermal and photoluminescence properties of liquid crystalline polyacetylenes containing 4-alkanyloxyphenyl trans-4-alkylcyclohexanoate side groups

Two series of polyacetylenes containing 4-alkanyloxyphenyl trans-4-n-alkylcyclohexanoate were synthesized using [Rh(nbd)Cl](2), MoCl5, and WCl6 as initiators. Polymers 1P-3P, which contain no flexible spacer, show no mesomorphic properties due to the rigid poly(phenylacetylene) backbone, Polymers 4P-9P, which contain three or four methylene units in their spacers, exhibit both SA and S, phases. X-ray diffraction diagrams reveal that the liquid crystalline polyacetylenes display an interdigitated bilayer structure for the smectic phases. Polymers 4P-9P are photoluminescent, and their emission wavelengths are about 500 rim. The photoluminescence intensity increased dramatically when a liquid crystalline polyacetylene was blended with poly(methyl methacrylate).