Synthesis and Characterization of New Mesogenic Diacetylene Monomers and theirPolymers

摘要

A series of three functionalized semi-rigid aromatic thermotropic diacetyleneliquid crystals were prepared: an aromatic diacid containing tetramethylene spacers on either side of the diacetylene group (5,7 DODBA), and aromatic diols with four and nine methylene spacers (5,7 DHDP and l0,12 DHDP). This paper addresses the design and synthesis of the monomers, their liquid crystalline behavior, and the reactivity of their diacetylene groups. 5,7 DODBA and 5,7 DHDP each exhibited smectic phases. For the 5,7 DODBA 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 10,12 DHDP was inconclusive, though a liquid crystalline phase may exist within a narrow temperature range. Each of the monomers was photo-reactive, producing deeply colored, conjugated polydiacetylene chains via topochemical polymerization upon exposure to UV or electron beam irradiation. The degree of reactivity in the solid state was much greater for the 10,12 DHDP 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 DHDP and DODBA, due perhaps to the more rigid nature of these molecules in the melt. Polymers obtained from the liquid crystalline monomers are polydiacetylenes with functionalized mesogenic side chains. The partially polymerized diacetylene of 10,12 DHDP monomer exhibited clear mesogenic melt behavior based on thermal analysis, optical microscopy, and wide angle X-ray diffraction. Liquid crystalline polymers, Diacetylene polymers, Mesogenic polymers, Characterization, Synthesis.