Polyacetylenes Bearing Mesogenic Side Groups: Synthesis and Properties, 2 a Biphenyl Moieties with a Short Spacer and Different Tail Lengths Paola Stagnaro, 1 Lucia Conzatti, 1 Giovanna Costa,* 1 Bernard Gallot, 2 Cinzia Tavani, 3 Barbara Valenti 3 1 CNR, Istituto per lo Studio delle Macromolecole ISMAC, Sezione di Genova, via De Marini 6, 16149 Genova, Italy Fax: þ39 010 6475 880; E-mail: costa@ge.ismac.cnr.it 2 CNRS, Laboratoire des Mate ´riaux Organiques a ` Proprie ´te ´es Spe ´cifiques, BP 24, 69390 Vernaison, France 3 Universita ` di Genova, Dipartimento di Chimica e Chimica Industriale, via Dodecaneso 31, 16146 Genova, Italy Keywords: liquid crystalline polyacetylenes; metathesis catalyst; phase behavior; photoluminescence; X-ray Introduction The introduction of orientable pendant mesogenic moieties onto a polyacetylene backbone might increase the conjuga- tion in the main chain and yield polymers with a perma- nent coupling between electro-active properties and order. Recently, the use of a rigid polymer backbone, such as a polyene chain, to prepare side-chain liquid crystalline poly- mers has been considered with growing interest by various research groups. [1–15] Most of the monomers used to this purpose are monosubstituted acetylenes, and their poly- merization is generally performed by using Mo, W, or other transition metal-based catalysts. [1–18] In a previous work we investigated the influence of the rigid pendant group on the thermal behavior of novel poly- acetylenes. [1] These compounds were obtained from mono- mers bearing different mesogenic substituents linked to the polyene backbone through a short flexible spacer. It is well Full Paper: We report on the synthesis of novel liquid crys- talline polyacetylenes derived from monosubstituted acety- lene monomers. In the monomers A1OBP-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 PA1OBP- Acn are fully characterized in terms of molecular structure, by GPC, FT-IR, NMR and UV/VIS techniques, and of thermal and morphological behavior, by TGA, DSC, POM and X-ray diffraction experiments. THF solutions of the polymers show a quite relevant photoluminescence with a broadened maxi- mum located around 450 nm. POM analysis on monomer A1OBP-Ac6: crystal transfor- mation on heating at 76 8C. 714 Macromol. Chem. Phys. 2003, 204, 714–724 Macromol. Chem. Phys. 2003, 204, No. 4 ß WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim, 2003 1022-1352/2003/0403–714$17.50þ.50/0 a Part 1: cf. ref. [1]