MOLECULAR ENGINEERING OF LIQUID-CRYSTAL POLYMERS BY LIVING POLYMERIZATION .8. INFLUENCE OF MOLECULAR-WEIGHT ON THE PHASE-BEHAVIOR OF POLY (OMEGA-[(4-CYANO-4'-BIPHENYL)-OXY]ALKYL VINYL ETHER)S WITH ETHYL, PROPYL, AND BUTYL ALKYL-GROUPS

The synthesis and living cationic polymerization of 2-[4-cyano-4'-biphenyl)oxy]ethyl vinyl ether (6-2), 3-[4-cyano-4'-biphenyl)oxy]-propyl vinyl ether (6-3), and 4-[4-cyano-4'-biphenyl)oxy]butyl vinyl ether (6-4) are described. The mesomorphic behaviors of poly(6-2), poly(6-3), and poly(6-4) with different degrees of polymerization and narrow molecular weight distributions were compared to those of 6-2, 6-3, and 6-4 and of 2-[(4-cyano-4'-biphenyl)oxy]ethyl ethyl ether (8-2), 3-[(4-cyano-4'-biphenyl)oxy]propyl ethyl ether (8-3), and 4-[4-cyano-4'-biphenyl)oxy]butyl ethyl ether (8-4) which are model compounds of the monomeric structural units of poly(6-2), poly(6-3), and poly(6-4). In the first heating scan, all three polymers exhibit an x (unidentified) mesophase which overlaps the glass transition temperature, and an enantiotropic nematic mesophase. In the second and subsequent heating and cooling scans, poly(6-3) and poly(6-4) display only the enantiotropic nematic mesophase. Both in the first and subsequent scans, only poly(6-2) with degrees of polymerization lower than 4 exhibits an enantiotropic nematic mesophase.