SYNTHESIS AND CHARACTERIZATION OF NEW MESOGENIC DIACETYLENE MONOMERS AND THEIR POLYMERS

Three functionalized semirigid aromatic thermotropic diacetylene liquid crystals were prepared: an aromatic diacid containing tetramethylene spacers on either side of the diacetylene group (5,7DODBA) and aromatic diols with four and nine methylene spacers (5,7DHDP and 10,12DHDP). This paper addresses the design and synthesis of the monomers, their liquid crystalline behavior, and the reactivity of their diacetylene groups. 5,7DODBA and 5,7DHDP each exhibited smectic phases. For the 5,7DODBA diacid, in particular, hydrogen bonding is thought to play a significant role in the mesogenic behavior and the high stability of the mesophase, The mesogenic nature of 10,12DHDP was inconclusive; though a liquid crystalline phase-may exist within a narrow temperature range. Each of the monomers was photoreactive, producing deeply colored, conjugated poly(diacetylene) chains via-topchemical polymerization upon exposure to UV or electron beam irradiation. The degree of reactivity in the solid state was much greater for the 10,12DHDP monomer than for the 5,7 monomers due to the added flexibility of the longer methylene spacer. On the other hand, thermally induced liquid-state polymerization appeared to be much faster in 5,7-DKDP and 5,7-DODBA, due perhaps to the more rigid nature of these molecules in the melt. Polymers obtained from the liquid crystalline monomers are poly(diacetylenes) with functionalized mesogenic side chains. The partially polymerized diacetylene of 10,12DHDP monomer exhibited clear mesogenic melt behavior based on thermal analysis, optical microscopy, and wide-angle X-ray diffraction.