Tailoring Thermotropic Liquid Crystalline Properties of Random Copolymers Based on Vinyl Monomers with Laterally Attached Mesogenic and Nonmesogenic Substituents via No Spacer

Abstract

Vinyl copolymers comprising mesogenic 2,5-bis((4-methoxyphenyl)oxycarbonyl)styrene (MPCS) and nonmesogenic 2,5-di(n-butoxycarbonyl)styrene (BCS) were synthesized via free radical polymerization. The random nature of the copolymers was characterized by the single glass transition and the reactivity ratios of the comonomers (rMPCS ) 1.51, rBCS ) 0.42 by 1 H NMR). In contrast to the copolymers based on MPCS and other nonmesogenic monomers such as styrene (St) and methyl methacrylate (MMA), which display no mesophase when the content of St or MMA exceeds a certain amount, all the copolymers obtained in this study showed quite stable liquid crystalline properties regardless of the copolymer compositions. A combination of differential scanning calorimetry, polarized light optical microscopy, and one-dimensional and two-dimensional wide-angle X-ray diffraction analyses demonstrated that the liquid crystalline phase structures of this series of copolymers were strongly composition dependent. When the molar fraction of MPCS in feed (MMPCS) was above 0.5, a hexatic columnar nematic (…HN I ) phase was formed with a constant d spacing value of 1.58 nm. When MMPCS was below 0.1, a hexagonal columnar (…H) phase was observed, and the corresponding d spacing was about 1.44 nm. In between 0.1 < MMPCS < 0.5, another hexatic columnar nematic (…HN II ) phase could be recognized with tunable d spacing relying on the copolymer compositions.