We newly prepared liquid crystalline (LC) polymer brushes containing an azobenzene (Az) mesogenic moiety on a quartz or silicon substrate by surface-initiated atom transfer radical polymerization (ATRP). The grafted chain length was controlled by polymerization time and initial monomer concentration. The grafted chain film adopted a smectec LC phase and the molecular orientation of Az mesogens in the grafted chain was nearly parallel to the substrate plane. The in-plane photo-orientation behavior of LC polymer brushes was evaluated by polarized UV-vis absorption spectoscopy and grazing incidence X-ray diffraction measurements. Highly ordered in-plane photoalignment of Az mesogens in the grafted chain was readily provided by the irradiation with linearly polarized visible light due to the effective light absorption of the Az mesogens aligned parallel to the substrate. The highest degree of in-plane orientation was generated at a temperature slightly above T g of the polymer. As a result, monodomain LC polymer films were readily obtained by the linearly polarized light irradiation.

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 4-((E)-4-butylstyryl)phenoxy groups as the mesogens units gave the highly ordered hexagonal nanocylinder structures in the 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.

Liquid crystalline (LC) polymer brushes containing a mesogenic azobenzene (Az) moiety are synthesized on a quartz or silicon substrate by surface-initiated atom transfer radical polymerization. The molecular orientation of the Az units and the LC properties in the grafted chains are evaluated by UV-vis spectroscopy, polarized optical microscopy, and grazing incidence X-ray diffraction measurements. The Az side chains of the grafted chains exhibited a smectic LC phase in which the smectic layers are oriented perpendicular to the substrate with a parallel orientation of the mesogens. In contrast, a spincast film of the identical LC polymer without grafting to the surface shows layer structures parallel to the substrate. A drastic effect of tethering one end to the substrate on the LC orientation is demonstrated.

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