Normally Oriented Cylindrical Nanostructures in Amphiphilic PEO-LC Diblock Copolymers Films

The amphiphilic diblock copolymers consist of poly(ethylene oxide) (PEO) and poly(methacrylate) (PMA) having azobenzenes as mesogen units in the side chain afford highly ordered phase-segregated nanostructures, in which PEO cylindrical domains are hexagonally arranged and normally oriented in PMA matrix in the thin films. The liquid crystalline ordering in the strongly segregated block copolymers plays one of the most important roles to attain such an excellent arrangement of the nanostructure potentially leading to practical use. In order to elucidate the role of the mesogen units in the side chain of the PMA segment, a new series of amphiphilic liquid crystalline diblock copolymers were synthesized to tune molecular interaction between mesogen units in liquid crystalline segments by using azobenzene, benzylideneaniline, and stilbene as mesogen cores. All the side-chain liquid crystalline diblock copolymers exhibited smectic phase and gave hexagonally arranged cylindrical nanostructures in the bulk pellets. The block copolymers having 4-(4-butylphenylazo)phenoxy, 4-((E)-(4-butylphenylimino)methyl)Phenoxy, or 44(E)-4-butylstyryl)phenoxy groups as the mesogens units gave the highly ordered hexagonal nanocylinder structures in thin film, while the copolymers having (E)-4-(4-butylbenzylideneamino)phenoxy mesogen group afforded less ordered nanostructures. The former three kinds of copolymers showed obvious hypsochromic shifts and large hypochromic effects on the UV-vis spectra of annealed film, implying the formation of the strongly H-aggregated and homeotropic alignment of mesogen moieties in the PMA matrix.