Side-Chain Liquid Crystalline Alternating Copolymers of Mesogenic Monomers: Synthesis and Properties

Seven new vinyl ether and fumarate monomers containing different mesogenic groups were synthesized and copolymerized to obtain three series of side-chain liquid crystalline copolymers. The freeradical copolymerization of the monomers led to copolymers with nearly alternating structures, although a preferential incorporation of fumarate units was always observed. Alternating tendency and composition behavior of the copolymers were interpreted in terms of a penultimate unit effect model. By appropriately adjusting the stoichiometry of the feed mixture, copolymers with a random distribution of mesogenic groups were also prepared. Comparison of the nematic-to-isotropic transition temperature and entropy (T_NI, ΔS_NI) of alternating copolymers revealed that the randomization of mesogenic groups produces a moderate but definite increase in both the stability (T_NI) and degree of order (ΔS_NI) of the nematic mesophase.