MOLECULAR ENGINEERING OF LIQUID-CRYSTAL POLYMERS BY LIVING POLYMERIZATION .9. LIVING CATIONIC POLYMERIZATION OF 5-[(4-CYANO-4'-BIPHENYL)OXY]PENTYL VINYL ETHER AND 7-[(4-CYANO-4'-BIPHENYL)OXY]HEPTYL VINYL ETHER, AND THE MESOMORPHIC BEHAVIOR OF THE RESULTING POLYMERS

The synthesis and living cationic polymerization of 5-[(4-cyano-4'-biphenyl)oxy]pentyl vinyl ether (6-5) and 7-[(4-cyano-4'-biphenyl)oxy]heptyl vinyl ether (6-7) are presented. The influence of molecular weight on the mesomorphic behaviour of poly(6-5) and poly(6-7) is discussed and compared to that of 5-[(4-cyano-4'-biphenyl)oxy]pentyl ethyl ether (8-5) and 7-[(4-cyano-4'-biphenyl)oxy]heptyl ethyl ether (8-7) which are models of the monomeric structural units of poly(6-5) and poly(6-7). Both (8-5) and (8-7) exhibit a monotropic nematic mesophase. Poly(6-5) with degrees of polymerization equal to and lower than six exhibit an enantiotropic nematic mesophase. Poly(6-5)s with higher degrees of polymerization display both smectic A and nematic enantiotropic mesophases. Poly(6-7) exhibits an enantiotropic smectic A mesophase over the entire range of molecular weights.