MOLECULAR ENGINEERING OF LIQUID-CRYSTAL POLYMERS BY LIVING POLYMERIZATION .5. SYNTHESIS AND MESOMORPHIC BEHAVIOR OF POLY(2-[(4-CYANO-4'-BIPHENYL)OXY]ETHYL VINYL ETHER-CO-8-[(4-CYANO-4'-BIPHENYL)OXY]OCTYL VINYL ETHER)

The synthesis and characterization of poly{2-[(4-cyano-4'-biphenyl)oxy]ethyl vinyl ether} [poly(6-2)], poly{8-[(4-cyano-4'-biphenyl)oxy]octyl vinyl ether) [poly(6-8)] and of poly(6-2-co-6-8)X/Y (where X/Y is the molar ratio of the two monomeric structural units) with degrees of polymerization of about 10 and narrow molecular weight distribution are described. Both homopolymers and copolymers were prepared by the living cationic polymerization and copolymerization of 6-2 and 6-8. During the first heating scan poly(6-2) presents an inverse monotropic s(C) mesophase. During subsequent heating and cooling scans, this polymer is amorphous regardless of the thermal history of the sample. Poly(6-8) exhibits an enantiotropic s(A) mesophase. During both the first and subsequent heating and cooling scans, the phase diagram which plots the dependence of mesomorphic transition temperatures as a function of copolymer composition is continuous. In the case of poly(6-2-co-6-8) 3/7, which exhibits a triple point in its phase behaviour, the highest temperature mesophase changes from nematic to s(A). During the first heating scan, poly(6-2-co-6-8)X/Y with X/Y = 10/0 to 6/4 represents an inverse s(C) monotropic mesophase. Poly(6-2-co-6-8)X/Y with X/Y = 8/2 to 6/4 show in addition to the s(C) phase an enantiotropic nematic mesophase. Poly(6-2-co-6-8)5/5 exhibits only an enantiotropic nematic mesophase. while poly(6-2-co-6-8)4/6 displays both a nematic and a s(A) enantiotropic mesophase. Poly(6-2-co-6-8)X/Y with X/Y = 3/7 to 0/10 present an enantiotropic s(A) mesophase. The second and subsequent heating scans and first and subsequent cooling scans provide an identical phase behaviour with that obtained from the first heating scan, except that the s(C) mesophase is absent.