Molecular engineering of liquid-crystalline polymers by living polymerization. Part 15.—Molecular design of re-entrant nematic mesophases in binary copolymers of 4′-(ω-vinyloxyalkoxy)biphenyl-4-yl cyanides

Abstract

The first examples of homopolymers and copolymers of 4′-(ω-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).