Polyacetylenes bearing mesogenic side groups: Synthesis and properties, 2 - Biphenyl moieties with a short spacer and different tail lengths

We report on the synthesis of novel liquid crystalline polyacetylenes derived from monosubstituted acetylene monomers. In the monomers A10BP-Acn obtained from 3-bromo-1-propyne, the acetylenic moiety is linked through a very short spacer to a biphenyl mesogenic core. Several linear acyl groups of different length are introduced as tail groups. Most of the monomers show liquid crystalline behavior. Polymerizations are carried out in solution with typical metathesis catalysts based on Mo and W and yield polyacetylenes with fairly high molecular weight (MW), soluble in common organic solvents. Polymers PA10BP-Acn are fully characterized in terms of molecular structure, by GPC, FT-IR, NMR and UV/VIS techniques, and of thermal and morphological behaviour, by TGA, DSC, POM and X-ray diffraction experiments. THF solutions of the polymers show a quite relevant photoluminescence with a broadened maximum located around 450 nm.