MOLECULAR ENGINEERING OF LIQUID-CRYSTALLINE POLYMERS BY LIVING POLYMERIZATION .15. MOLECULAR DESIGN OF REENTRANT NEMATIC MESOPHASES IN BINARY COPOLYMERS OF 4'-(OMEGA-VINYLOXYALKOXY)BIPHENYL-4-YL CYANIDES

The first examples of homopolymers and copolymers of 4'-(omega-vinyloxyalkoxy)biphenyl-4-yl cyanides which exhibit the I-N-S(Ad)-N(re) sequence of phase transitions have been described. All previously reported polymers exhibiting an N(re) phase were based on a polyacrylate backbone. Poly{1-[5-(4'-cyanobiphenyl-4-yloxy)pentyloxy]ethylene} [i.e. poly(6-5), where 5 represents the number of methylenic units in the spacer] displays an N(re) phase over a large range of degrees of polymerization (DP = 10-30). Systematic binary copolymerization experiments have demonstrated that N(re) mesophases are exhibited by copolymers generated from structural units, one of which belongs to a homopolymer leading to an S(A) phase, and the other to N or glassy phases. The following copolymer compositions were shown to display the I-N-S(Ad)-N(re) sequence: poly{1-[11-(4'-cyanobiphenyl-4-yloxy)undecanyloxy]ethylene-co-1-[5-(4'-cyanobiphenyl-4-yloxy)pentyloxy]ethylene}X/Y {poly[(6-11)-co-(6-5)]X/Y}, where X/Y represents the molar ratio of the two structural units i.e., poly[(6-11)-co-(6-5)]1/9 (DP = 20), poly[(6-11)-co-(6-3)]3/7 (DP = 20), poly[(6-8)-co-(6-2)]6/4 (DP = 10), poly[(6-11)-co-(6-2)]4/6 (DP = 15).