Liquid crystalline poly(vinyl ether)s and block copoly(vinyl ether)s by living cationic polymerization

A series of liquid crystalline (LC) poly(vinyl ether)s 1 was prepared by living cationic polymerization of a mesogenic vinyl ether monomer, 4-butoxyphenyl 4-((6-vinylhexyl)oxy)benzoate (11), in the presence of the HI/I₂ (1/1 mol/mol) initiating system. The number average molar mass of polymers 1 increased linearly with the initial monomer to initiator molar ratio (M_⊙ = 3000-15 000 g mol^-1, DP_⊙ ≈ 5-50), according to the living character of the polymerization, and their molar mass distribution was rather narrow (MJM_⊙ = 1.10-1.15). Furthermore, two sets of AB diblock copoly(vinyl ether)s 2 and 3 were prepared by sequential polymerization of vinyl ether 11 and isobutyl vinyl ether (12) and chiral (S)-2-methylbutyl vinyl ether (13) respectively, by using the same HI/I₂ system. While the average degree of polymerization of the LC block was kept constant (DP_⊙ ≈ 10), the length of the non-LC block was varied (DP_⊙ ≈ 2-25), according to the chosen feed conditions. An X-ray investigation proved that polymers 1 gave rise to a sequence of ordered smectic (F or I), smectic C, and nematic mesophases with increasing temperature. Their transition temperatures and entropies followed slightly different molar mass dependence, but each of them reached a saturation value at M_⊙ ≈ 6000 g mol^-1. The same basic mesophase polymorphism was also observed for the LC block copolymers 2 and 3, thus suggesting that the chemically different blocks were microphase separated within the solid and LC phases.