Synthesis, characterization and properties of N‐maleimide side‐chain liquid crystalline copolymers

A homologous series of side-chain liquid crystalline (SCLC) poly{[N-[10-((4-(((4′-n-hexyloxy)benzoyl)oxy)phenoxy)carbonyl)-n-decyl]maleimide]-co-[N-(n-octadecyl)maleimide]} [(ME6)-co-(MI-18)] random copolymers with various MI-18 contents have been synthesized and their properties studied. The high content in threo-disyndiotactic sequences of the maleimide main chain seems responsible for the stability of the highly ordered smectic mesophase. The relationship between structure and composition on thermotropic mesophase was investigated by polarizing optical microscopy, differential scanning calorimetry, and X-ray diffraction. For copolymers with mesogenic unit contents less than ∼0.655 molar fraction the transition from (SA) texture to isotropic (I) is maintained, as shown by the TCl, ΔHCl and ΔSCl amounts and intermolecular spacing 4.42–4.53 A and intralayer correlation lengths of 44.2–45.2 A. The layer thickness does not appreciably depend on copolymer composition. However, copolymers with non-mesogenic comonomer MI-18 molar contents larger than >0.655 molar fraction X(M), are no longer liquid crystalline materials, despite its packing is preserved without any detectable appearance of birefringence. Thermodynamic boundaries of the liquid crystalline state have been established through a phase diagram. The properties of this n-hexyloxy pendant group-based series are compared to those of the analogous materials containing methoxy pendant groups (ME1), and differences are accounted for in terms of the local side-chain packing within the mesophase. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011