Effects of Molecular Weight Distribution on the Thermal Properties of Side-Chain Liquid Crystalline Poly(vinyl ether)s

Abstract

ABSTRACT:Three biphenyl-containing vinyl ether monomers: 2-(4-biphenyloxy)ethyl vinyl ether (I), 2-(4-biphenylcarboxyl)ethyl vinyl ether (II), and 2-(4'-methoxy-4-biphenyloxy)ethyl vinyl ether (III), were cationically polymerized with the hydrogen iodide/iodine (HI/Ii) initiator system to form living polymers with narrow molecular weight distributions. The thermal properties of the polymers were determined by DSC and by visual observations of samples placed on a hot stage on a polarizing microscope. Polymer I and Polymer II formed only isotropic melts, but Polymer III showed enantiotropic, liquid-crystalline (LC) behavior, and formed both smectic and nematic phases after one heating and cooling cycle. For comparison, polymers were also prepared with boron trifluoride etherate (BF3OEt2) as the initiator. Polymer III obtained with this initiator had a much broader molecular weight distribution and formed only a nematic phase. At approximately the same molecular weight, this sample also had a much higher isotropization temperature than the narrow distribution sample of Polymer III. KEY WORDSSide-Chain Liquid Crystalline Polymer / Poly(vinyl ether) / Cationic Living Polymerization / Biphenyl Group / 2-(4'-Methoxy-4-biphenyloxy)ethyl Vinyl Ether / Molecular Weight Distribution / Monodisperse Polymer / Hydrogen Iodide-Iodine Initiator / Liquid-crystalline polymers (LCP) can contain mesogenic units either in the main chain or in the side chain, and both types are of theoretical and practical interest. 1 In contrast to the main chain LCP, the liquid-crystalline order of side chain LCP is generally closely related to that of the monomer,2 so side chain LCP are of value for investigations on the relationship between mesogenic unit structure and mesophase type in polymers as compared to low molecular weight mesogens.Side-chain LCP can be prepared by three different routes including addition polymerization, condensation polymerization and post-reactions of polymers. 2 Among the three methods, the most convenient approach is to introduce the mesogenic unit beforehand into a reactive monomer capable of undergoing addition or chain-growth polymerization. 2 However, for the most part, the side chain LCP prepared by chain-growth polymerization have been limited to polymethacrylates,3 polyacrylates, 3 and polystyrene derivatives,4 and very few of these investigations were concerned with the control and effect of molecular weight distribution on the properties of the LCP. One example of such control is the preparation of polymethacrylates by group-transfer polymerization, 5 but the molecular weight distributions of these polymers * Permanent address:

Molecular engineering of side-chain liquid crystalline polymers by living polymerizations

“…22-50, pdi = 1.2), 147 Znl 2 as the catalyst in CH 2 Cl 2 at -5°C. 6-[(4' -n-Butoxyphenyl-4"-benzoate)hexyl]vinyl ether (DPn = 7.6-38, pdi = 1.10-1.15) was polymerized similarly using HI/1 2 , except that toluene was used as the solvent at -40°C.…”

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