Hydrogen-bonding-mediated generation of side chain liquid crystalline polymers from complementary nonmesogenic precursors

Abstract

Liquid crystalline phases in macromolecular assemblies have been generated by utilizing complementary hydrogen-bonding interaction between functional vinyl polymers and rigid aromatic derivatives. While neither of the individual components is mesogenic, the resulting assemblies exhibited liquid crystalline behavior. Poly((2-dimethylamino)ethyl methacrylate) and poly(2-hydroxyethyl methacrylate) were chosen as the functional polymer backbone bearing proton-accepting and proton-donating groups, respectively. As rigid aromatic units, 4-hydroxybiphenyl, trans-4-hydroxystilbene, 4'-methoxy-4-hydroxyazobenzene, and 4-pyridylbenzoate were used. All the polymeric assemblies were obtained as transparent films and they exhibited liquid crystalline properties. Hydrogen-bonding in these assemblies was evident from their FTIR and ¹³C NMR spectra. The liquid crystalline behavior of these hydrogen-bonded polymeric assemblies was established by DSC, polarizing microscopy, and X-ray diffractometry. Phase diagrams of the mixtures revealed the dependence of the liquid crystalline transitions on the composition of such binary mixtures. Generation of liquid crysalline phases in these hydrogen-bonded polymeric assemblies derived from non-liquid crystalline precursors without the mediation of a flexible spacer is unprecedented. Furthermore, this approach offers a relatively simple route to prepare functional materials with controlled molecular architecture from readily accessible and simpler precursors.