LIQUID-CRYSTALLINE POLYMERS CONTAINING MACROCYCLIC POLYETHERS .2. SIDE-CHAIN LIQUID-CRYSTALLINE COPOLYSILOXANES CONTAINING MESOGENIC UNITS BASED ON 1,3-DIOXANE-2,5-DIYL AND BENZO[15]-CROWN-5

Abstract

Synthesis and characterization of a series of copolysiloxanes containing crown ether and trans-1,3-dioxane based mesogens are presented. The phase behaviour of the copolymers was studied using differential scanning calorimetry and optical polarizing microscopy and compared with the phase behaviour of the corresponding copolysiloxane-containing crown ether and biphenyl-based mesogens. Two copolysiloxanes containing trans-2-(benzo-[15]crown-5)-5-(omega-alkan-1-yloxy)-1,3-dioxane side groups present no liquid-crystalline behaviour. The other four copolysiloxanes exhibit a nematic mesophase and undergo side-chain crystallization at low temperature. Two of the four copolysiloxanes which contain a trans-1,3-dioxane-2,5-diyl group in the mesogenic unit present lower isotropization temperatures and narrower mesophase ranges than the other two. This result reveals that replacing a phenyl ring in the mesogenic unit of a liquid-crystalline polymer by a trans-1,3-dioxane ring will decrease the thermal stability of the mesophase exhibited by this polymer.