MOLECULAR ENGINEERING OF LIQUID-CRYSTALLINE POLYMERS BY LIVING POLYMERIZATION .10. INFLUENCE OF MOLECULAR-WEIGHT ON THE PHASE-TRANSITIONS OF POLY(OMEGA-[(4-CYANO-4'-BIPHENYLYL)OXY]ALKYL VINYL ETHER)S WITH NONYL AND DECANYL ALKYL-GROUPS

The synthesis and living cationic polymerization of 9-[(4-cyano-4'-biphenyl)oxy]nonyl vinyl ether (6-9) and 10-[(4-cyano-4'-biphenylyl)oxy]decanyl vinyl ether (6-10) are described. The mesomorphic behavior of poly(6-9) and poly(6-10) with narrow molecular weight distributions and degrees of polymerization from 2 to 32 was discussed by comparison to that of 9-[(4-cyano-4'-biphenylyl)oxy]nonyl ethyl ether (8-9) and 10-[(4-cyano-4'-biphenylyl)oxy]decanyl ethyl ether (8-10), which are the model compounds of the monomeric structural units of poly(6-9) and poly(6-10). 8-9 exhibits monotropic nematic and monotropic s(A), while 8-10 exhibits monotropic smectic. A mesophases. Irrespective of the thermal history of the sample, over the entire range of molecular weights, poly(6-9) exhibits an enantiotropic s(A) mesophase. In the first heating scan, poly(6-10) exhibits a crystalline phase followed by an enantiotropic s(A) mesophase. In the second heating scan, poly(6-10)s with degrees of polymerization below 16 exhibit an enantiotropic s(A) mesophase, while polymers with higher degrees of polymerization display both s(A) and s(X) (unidentified) enantiotropic mesophases. Finally, the phase behavior of poly{omega-[(4-cyano-4'biphenylyl)oxy]alkyl vinyl ether}s with alkyl from ethyl to undecanyl will be discussed at four different degrees of polymerization: 30, 23, 13, and 4.