THERMOCHROMISM IN LIQUID-CRYSTALLINE POLYDIACETYLENES

The thermochromic behavior of diacetylene-containing hydrogen-bonding thermotropic Liquid crystalline monomers and a semirigid main chain th ermotropic poly(ester-diacetylene) were examined. These materials were successfully designed to undergo dramatic, first-order thermochromic transitions at the onset of their characteristic mesogenic transitions , as exhibited by changes in the shapes and locations of their polydia cetylene absorption bands and the corresponding visually observed colo r changes. Two different types of chromic response have been observed: one case, the diacid monomer 5,7-DODBA, in which the polydiacetylene chain responds to the liquid crystalline transitions of its host monom eric lattice, and two cases, the 10,12-DHDP monomer and 10,12-DHDP/TC polyester, in which the side chains covalently bonded to the polydiace tylene chain undergo mesogenic transitions that drive the thermochromi c transition. It was found that the thermochromic transition is not re versible beyond the melting points of the partially polymerized monome rs, whereas the poly(ester-diacetylene) exhibited partial reversibilit y above the polyester melting point. In all cases, a new absorption cu rve at higher energies represented the liquid crystalline phase above the mesogenic melt transition.