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(t‐BuNSiMe2Flu)TiMe2 (1) activated with Me3Al‐free methylaluminoxane (dried MAO) which conducts vinyl addition polymerization of norbornene (N) with very high activity was applied for homopolymerization of N derivatives (i.e., 5‐vinyl‐2‐norbornene (5V2N), 5‐ethylidene‐2‐norbornene (5E2N), dicyclopentadiene (DCPD)) at 40 °C. The activities for the N derivatives were about two orders of magnitude lower than that for N and decreased in the following order: 5E2N ≫ 5V2N ≫ DCPD. Copolymerization of ethene (E) and 5E2N under an atmospheric pressure of E was then conducted by 1‐dried MAO. The copolymerization proceeded with better activity than the homopolymerization of 5E2N and gave poly(E‐co‐5E2N) with narrow molecular weight distribution. The content of the ethylidene group in poly(E‐co‐5E2N) was controlled by the feed ratio of 5E2N/E. The Tg value of the copolymer changed from 70 °C to 155 °C according to the 5E2N content from 27 mol % to 68 mol %. The addition of N as a third monomer to the E‐5E2N copolymerization improved the activity and raised the Tg values of the terpolymer above 200 °C. The content of 5E2N was controlled by the 5E2N/N ratio with keeping the high Tg values. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4581–4587, 2007 [ABSTRACT FROM AUTHOR]

Composite systems of liquid crystals (LCs) and polymers have been extensively studied in various forms such as polymer-dispersed LCs and polymer-stabilised LCs. Blending LCs and polymers is an effective approach to design functional materials with stimuli responsiveness and durability. Here, we show the development of a novel composite material with crosslinked azobenzene LC polymer (PAzo) and poly (dimethylsiloxane) (PDMS) aiming at the improvement of photomobile polymer materials in mechanical properties. The composite films were prepared by photopolymerisation of azobenzene monomers in PDMS elastomers. By forming phase separated structure, in which PAzo chains were dispersed in PDMS matrix, fracture strain of photomobile polymer materials was significantly enhanced. The composite film showed macroscopic bending upon irradiation with UV light. This result implies that PAzo domains in polymer matrix can work as microactuators to afford macroscopic deformation of the whole film. The further improvement of this system in photomechanical properties would be feasible through adequate control of composition and the alignment of mesogens. [ABSTRACT FROM AUTHOR]

A foreword to the journal "Molecular Crystals and Liquid Crystals," is presented.

The article discusses the mechanical properties of flexible films, such as surface strain of largely bending films, which are considered as key to design of stretchable electronic devices, wearable biointegrated devices, and soft microactuators or robots. It notes that the existing methods are mainly based on strain-gauge measurements that ask miniaturized array sensors, lead wires, and complicated calibrations.

A series of liquid-crystalline (LC) diblock copolymers with an azobenzene moiety in the side chain were prepared by atom transfer radical polymerization (ATRP). Using a bromo-terminated poly(methyl methacrylate) as a macroinitiator, the obtained diblock copolymers showed well-defined structures and narrow molecular-weight distributions. Microphase-separated nanostructures with mesogenic blocks in either continuous or separated phases were observed. Owing to varied content of mesogens in the block copolymers, they showed different behavior of photoinduced alignment and holographic recording. Block copolymers with azobenzenes in the majority phases exhibited a similar performance of photoinduced alignment and refractive-index modulation to the azobenzene-containing homopolymer, but their photoinduced mass transportation was partly suppressed by the microphase separation, leading to a lower surface relief than that of the homopolymer. The photoinduced mass transfer was greatly prohibited in the block copolymers with mesogenic groups in the minority phases, resulting in little surface relief. However, refractive-index gratings were still recorded upon local alignment, driven by the photoinduced alignment of azobenzenes or the phototriggered molecular cooperative motion between azobenzenes and nonphotosensitive cyanobiphenyl groups. Then the possible schematic illustrations of mesogens and microphase separation in the grating structures were proposed. [ABSTRACT FROM AUTHOR]

The synthesis and photopolymerization of alkaline-developable hyperbranched polyurethane (HBPUMA-COOH) were examined. The reaction of dicyclohexylmethane 4,4‘-diisocyanate (CMDI) and trimethylolpropane (TMP) in the presence of 2-methacryloyloxyethyl isocyanate (MOI) was carried out to give the soluble hyperbranched polyurethane (HBPUMA) with terminal methacryloyl groups in satisfactory yield. After that, HBPUMA-COOH was synthesized by the reaction of HBPUMA and cis-1,2,3,6-tetrahydrophthalic anhydride (THPA). The photoradical polymerization of HBPUMA-COOH was examined in the presence of 2-methyl-1-4-(methylthio)phenyl-2-morpholinopropan-2-one (Irgacure 907) as a photoinitiator in the film state upon UV irradiation to afford the corresponding cured film quantitatively. It was found that the tensile strength of the resulting cured film of HBPUMA-COOH was higher than those of the HBPUMA and linear one. The negative patterning property of HBPUMA-COOH also had 5 m line and space pattern resolution by UV irradiation with 150 mJ/cm2. Furthermore, it was cleared that the photocured HBPUMA and HBPUMA-COOH showed very low birefringence. [ABSTRACT FROM AUTHOR]

After being pre-treated upon irradiation of unpolarized light at 366 nm, an azobenzene-containing liquid-crystalline polymer film was photoinduced alignment by one linearly polarized laser beam at 488 nm, leading to a large birefringence of 0.21. Then holographic gratings were recorded in the pre-irradiated polymer films by interference of two coherent laser beams. Little surface relief was obtained by the holographic recording process, indicating that a refractive-index grating paid most of contributions to the diffraction efficiency. Because the cooperative motion of the azobenzene mesogens were eliminated in the cis-azobenzene-rich isotropic film by the pre-irradiation, multi-processes of the refractive-index gratings were successfully achieved. The obtained grating structures were clearly shown in the polarizing optical microscopic pictures, which were also verified by their diffraction patterns. The azobenzene-containing liquid-crystalline polymer used in this study has potential application in high-density information storage. [ABSTRACT FROM AUTHOR]

Three azobenzene acrylate monomers containing alkyl spacers of different length were synthesized. Thermodynamic and mesomorphic properties of the monomers were measured by differential scanning calorimetry and polarizing optical microscopy. A crosslinker with the undecyl spacer was also synthesized to prepare crosslinked liquid-crystalline polymer films by photopolymerization. Polarized UV spectra and polarizing optical micrographs demonstrated that the mesogens are aligned homogeneously in the films. Low glass transition temperature of the films enabled them to bend near room temperature upon UV irradiation. Besides, the films generally bent away from the light source before they at last bent towards the light irradiation. [ABSTRACT FROM AUTHOR]

Holographic gratings were formed in thick polymer films containing azobenzene and diphenylacetylene (tolane) moieties in the Bragg regime. Amorphous polymers containing various contents of the azobenzene moiety with photosensitivity and the tolane moiety with large birefringence in the side chain were synthesized, and optically transparent thick polymer films were prepared. The films were irradiated with a linearly polarized beam from an Arlaser (488 nm), and the transmittance of a He-Ne laser beam (633 nm) through a pair of crossed polarizers, with the film between them, was measured to estimate a photoinduced birefringence (n). The value of nincreased with an increase in the tolane moiety content in the polymer films. When two linearly polarized beams at 488 nm were interfered in the film, a diffraction beam was observed, and the maximum diffraction efficiency () increased with the tolane moiety content. In the film containing 70 mol% of the tolane moiety, the highest of 99% was achieved, and angular selectivity due to Bragg diffraction was clearly observed. We consider the cooperative molecular motion of the tolane moieties to be induced by the photoinduced change in alignment of the azobenzene moieties even if the polymers show no liquid-crystalline phase. When two orthogonal circularly polarized beams were allowed to interfere in the film, a Bragg-type polarization grating was formed. It was found that the value of reached 90% within 920 ms. [ABSTRACT FROM AUTHOR]

Optically transparent thick films of methacrylate copolymer containing donor-acceptor-type azobenzene and cyanobiphenyl moieties were prepared, and their optical properties were explored in terms of a photoinduced change in molecular alignment and the formation of Bragg gratings with angular and polarization multiplicity. Azobenzene moieties substituted with ethoxy, cyano, and nitro groups were employed, and their photoresponsive behavior was investigated. It was found by polarized UV-vis spectroscopy that the alignment of azobenzene moieties in the films was random in the initial state but became perpendicular to the direction of polarization of the writing beam after irradiation with a linearly polarized beam from an Arlaser at 514 nm. The film containing the cyanoazobenzene moieties showed the fastest formation of optical anisotropy due to an efficient change in molecular alignment. When two linearly polarized beams from the Arlaser were allowed to interfere in the films with a thickness of 200 m, the diffraction beam was observed immediately and reached 97% upon photoirradiation at 200 mW/cm2for 5 min. It was clearly observed that the response time became shorter with an increase in the light intensity of the writing beams, maintaining the high diffraction efficiency. Furthermore, it was clearly seen that the diffraction efficiency strongly depended on the direction of polarization of the reading beam. Holographic multiple data storage in a film was demonstrated, and 55 holograms with angular multiplicity were recorded successfully. In addition, multiple data storage using the polarization and angle selectivity simultaneously was first demonstrated. [ABSTRACT FROM AUTHOR]

The azobenzene liquid-crystalline gel (LCG) films with macroscopic uniaxial alignment were prepared to investigate photoresponsive behavior. By polarizing microscopy, fiber-like structures aligned in one direction were observed. Furthermore, with a confocal laser scanning microscope (CLSM), it was confirmed that the fiber-like structures were formed even in the bulk of the LCGs. When the LCG films were irradiated with UV light below Tg, changes in the microscopic surface morphology were observed, while no appreciable macroscopic change was observed. On the other hand, when the LCGs were plasticized by suspending in solvents or heating above Tg, the LCG films showed macroscopic changes (e.g. bending) upon UV light irradiation. The bending and unbending could be repeated just by changing the wavelength of the irradiation light. It was suggested that the bending is induced by an absorption gradient which produces a volume difference between the front surface area and the bulk of the gel films. [ABSTRACT FROM AUTHOR]