Language：English   Publisher：WILEY-V C H VERLAG GMBH  

Liquid-crystalline polymers with photodeformable properties have been extensively studied due to their ability of wireless conversion of light energy into mechanical work. With the development of crosslinked liquid-crystalline polymers, various 3D motions, such as bending, twisting, oscillation, rotation, and translational motion have been successfully induced. Recent trends for developing soft robots and microrobots accelerate the progress of photomobile polymer materials. This review is focused on recent advances in the field of photomobile materials based on liquid-crystalline polymers. The structure-function relationship in photomobile polymer materials is overviewed, and the progress in recent years is detailed in terms of complex 3D deformation, continuous motions, self-regulation, and processability.

DOI： 10.1002/adom.201900380

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

We developed photomobile polymer materials with interpenetrating polymer network (IPN) structures composed of crosslinked liquid-crystalline azobenzene polymer (PAzo) and poly(dimethylsiloxane) (PDMS). By introducing PDMS into a PAzo template network, IPN was formed without disturbing the alignment of mesogens in the PAzo network. The films showed macroscopic bending behavior upon irradiation with UV and visible light. Although the IPN film showed a phase separated structure, the bending speed was significantly enhanced compared with the pristine film of PAzo, thanks to the soft nature of PDMS. The present method of preparing IPNs can be a promising approach to combine PAzo with various polymers and enhance the mechanical and photoresponsive properties.

DOI： 10.1039/c7sm01412k

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

We prepared a block copolymer composed of polythiophene (PT) with cinnamate groups and poly(ethylene oxide) (PEO), which are connected through a cleavable acetal bond, aiming at constructing donor/acceptor heterostructures through post deposition of acceptor molecules into donor template networks. The block copolymer films showed phase-separated structures with domain sizes of 10-100 nm. Irradiation with UV light afforded crosslinked films through [2+2] cyclodimerization of cinnamate groups. Then, PEO was removed by acidic cleavage of the acetal bond, yielding PT template networks. Taking advantage of the insoluble networks, a fullerene derivative was deposited into the PT templates through a spin-coating process to form donor/acceptor heterostructures. The introduction of the fullerene derivative was confirmed by UV-Vis absorption and fluorescence spectroscopy. This strategy of depositing acceptor molecules into donor template networks, instead of spin-coating from donor/acceptor blend solutions, could be applied to improve the phase-separated structures and power conversion efficiencies of polymer solar cells.

DOI： 10.1039/c6tc04409c

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

Incorporation of dynamic covalent bonds into photomobile liquid-crystalline elastomers with a polysiloxane backbone enables the alignment of mesogens and macroscopic shapes to be controlled through the rearrangement of the network topology, even after the formation of chemically crosslinked networks. The reshaped samples show various sophisticated 3D motions upon irradiation with UV and visible light, depending on their initial shapes.

DOI： 10.1002/adma.201602745

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

We developed interpenetrating polymer networks (IPNs) composed of a crosslinked azobenzene liquid-crystalline polymer (PAzo) and poly(alkyl methacrylate)s (PAMAs). When irradiated with UV and visible light, the IPN films showed reversible bending. The photo-responsive and mechanical properties of PAzo films were significantly enhanced by incorporation of the PAMA components.

DOI： 10.1039/c5tc01489a

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

Crosslinked liquid-crystalline polymer materials that macroscopically deform when irradiated with light have been extensively studied in the past decade because of their potential in various applications, such as microactuators and microfluidic devices. The basic motions of these materials are contraction-expansion and bending-unbending, which are observed mainly in polysiloxanes and polyacrylates that contain photochromic moieties. Other sophisticated motions such as twisting, oscillation, rotation, and translational motion have also been achieved. In recent years, efforts have been made to improve the photoresponsive and mechanical properties of this novel class of materials through the modification of molecular structures, development of new fabrication methods, and construction of composite structures. Herein, we review structures, functions, and working mechanisms of photomobile materials and recent advances in this field.

DOI： 10.1002/anie.201400513

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Single chain conformations during the stress relaxation process in uniaxially stretched poly(methyl methacrylate) (PMMA) films were observed in real space by scanning near-field optical microscopy (SNOM). The extension ratio at the molecular level was directly evaluated from the SNOM images and compared with the macroscopic stress relaxation. At the early stage of the relaxation process, the whole single chain retained the stretched conformation in spite of the decrease in, stress. This suggests that the fast relaxation in stress is caused by the local conformational change at the length scale much smaller than the entire chain length. The experimental data were successfully explained by the contraction of the primitive chain contour in the Doi-Edwards model. Furthermore, the distribution function of the chain dimension was found to retain its shape during the relaxation process, indicating that the conformational relaxation of polymer chain is rather homogeneous in the well-entangled system.

DOI： 10.1021/ma2004986

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCI LTD  

The conformation of single poly(methyl methacrylate) chain in the uniaxially stretched film was observed by the combination of the fluorescence labeling technique and scanning near-field optical microscopy (SNOM). The dimension of the individual probe chain (M-w = 1.99 x 10(6)) along the extension axis was evaluated from SNOM image. In the high molecular weight matrix (M-w = 1.89 x 10(6)) the average extension ratio at the single chain level coincided with the macroscopic extension ratio. The distribution of the chain conformation was in good agreement with that of the freely jointed chain followed by affine deformation. On the other hand, the probe chain embedded in the low molecular weight matrix (M-w = 1.76 x 10(5)) showed the smaller extension than that expected from the affine deformation. This suggests that the conformation of the probe chain is affected by the relaxation of the short surrounding chains through disentanglement. (C) 2009 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.polymer.2009.04.057

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCI LTD  

The conformation of the single polymer chain in uniaxially stretched poly(methyl methacrylate) (PMMA) films was studied by scanning near-field optical microscopy (SNOM), which enabled us to observe the elongated conformation of each polymer chain embedded in the film. The conformation of the individual PMMA chains was quantitatively evaluated from the fluorescence intensity distribution. Observation of films with different strains showed that the microscopic strain of the single chain was smaller than the macroscopic strain (6) of the film. Especially at the later stage of the deformation (epsilon > 1.5), the PMMA chain was not stretched with the increase in the macroscopic elongation of the film, suggesting the presence of slipping of polymer chain on the course of stretching. (c) 2007 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.polymer.2007.08.039

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Language：English   Publisher：NATURE PUBLISHING GROUP  

Crosslinked liquid-crystalline polymers (CLCPs) show macroscopic deformation along with a change in molecular order, which is triggered by various stimuli such as heat, electricity, and light. CLCPs containing photochromic moieties are realizable as photoresponsive soft actuators. This review focuses on recent developments in novel network structures of CLCPs: rearrangeable networks and interpenetrating polymer networks (IPNs). CLCPs with dynamic covalent bonds could be reshaped into 3D architectures through the rearrangement of the network topology, in contrast with conventional crosslinked polymers memorizing permanent shapes. The reshaped samples showed various photoinduced motions depending on their initial shapes. Furthermore, amorphous polymers were incorporated into conventional CLCP networks to control mechanical and photoresponsive properties. The sequential formation of CLCP and amorphous polymer networks resulted in IPN films with a homogeneous alignment of mesogens. The elastic moduli of IPN films were controlled through the selection of amorphous components. The incorporation of soft components such as poly(dodecyl methacrylate) and poly(dimethylsiloxane) (PDMS) significantly enhanced the rate of photoinduced bending. These strategies of controlling the network structures of CLCPs could enable the versatile design of photomobile polymer materials as soft actuators with desired architectures and functions.

DOI： 10.1038/s41428-019-0224-1

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：TAYLOR & FRANCIS LTD  

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.[GRAPHICS].

DOI： 10.1080/02678292.2018.1516822

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：TAYLOR & FRANCIS LTD  

Poly(4-vinylpyridine) (P4VP) brushes were grafted onto a substrate via Cu(0)-mediated atom transfer radical polymerization and 1-pyrenebutyric acid (PBA) was incorporated into the brushes through hydrogen bonding interactions with P4VP by immersing the resulting substrate in PBA solution. Fluorescence measurements performed on the substrate after immersion showed that PBA units formed excimers even after the substrate was rinsed with dichloromethane, which confirms the formation of hydrogen bonds between pyridyl groups in the P4VP brushes and carboxyl groups of PBAs.

DOI： 10.1080/15421406.2019.1595484

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：TAYLOR & FRANCIS LTD  

We prepared crosslinked azobenzene main-chain liquid-crystalline polymers (MCLCPs), in which the exchange of crosslinks can be brought about by transesterification reactions. The exchangeable crosslinks enable reshaping and self-healing of the MCLCPs upon heating. Furthermore, the stress generated by stretching the MCLCP film is completely relaxed at 180 degrees C through rearrangement of networks. The film after hot-drawing shows reversible bending behavior upon irradiation with UV and visible light.

DOI： 10.1080/15421406.2019.1595482

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：TAYLOR & FRANCIS LTD  

We prepared 2 types of crosslinked liquid-crystalline polymers (CLCPs) (polyacrylates) with the same side-chain length but a different position of an azobenzene moiety in the side chain. We evaluated photoinduced deformation behavior of the CLCP films and photoisomerization behavior of azobenzene in the films at cryogenic temperature. Azobenzene moieties in both CLCP films showed no trans-cis isomerization and neither film exhibited bending behavior upon irradiation with UV light in liquid nitrogen [77 K]. On the other hand, when the film included azobenzene with a long spacer and a short tail, cis-trans isomerization of azobenzene and photoinduced deformation were observed in liquid nitrogen.

DOI： 10.1080/15421406.2019.1595490

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：TAYLOR & FRANCIS LTD  

We developed a novel block copolymer composed of poly(ethylene oxide) (PEO) and polymethacrylate functionalized with liquid-cryst-alline oligothiophene by using the atom transfer radical polymerization (ATRP), aiming at application to organic photovoltaic (OPV) cells. Thermal investigation showed that the resultant polymer exhibits liquid-crystalline phases both on heating and cooling. Morphologies of the thin films of the block copolymer were investigated by atomic force microscopy (AFM). Microphase separation with a small size of almost 10nm (nano-phase-separated structures) was observed upon annealing.

DOI： 10.1080/15421406.2018.1466243

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：TAYLOR & FRANCIS LTD  

Crosslinked liquid-crystalline polymers (CLCPs) containing azobenzene moieties show reversible macroscopic deformation upon irradiation with light. The deformation of CLCPs strongly depends on alignment of mesogens. Therefore, it is desirable that the alignment of mesogens in CLCPs can be freely controlled even after crosslinking. We successfully realigned the mesogens in CLCPs with the aid of dynamic covalent bonds to accomplish this challenge. In this study, we prepared CLCP films containing dynamic covalent bonds and photoalignable azobenzene moieties. Photoalignment of the films was performed by irradiation with linearly polarized UV light at 120 degrees C. The films after photoalignment showed bending behavior along the direction in which the mesogens had been realigned by photoalignment when irradiated with unpolarized UV light. This result indicates that alignment of mesogens in the films changes before and after photoalignment even after crosslinking.

DOI： 10.1080/15421406.2018.1466242

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：TAYLOR & FRANCIS LTD  

We prepared crosslinked azotolane liquid-crystalline polymer (LCP) films doped with a stilbene derivative (two-photon chromophore) utilizing an interpenetrating polymer network (IPN) structure. The IPN films bend toward the light source upon irradiation with femtosecond laser pulses at 600nm, which can excite the stilbene derivative by two-photon absorption. The bending speed of the IPN films increases with the square of the laser pulse intensity, which is compelling evidence for the two-photon processes.

DOI： 10.1080/15421406.2018.1466241

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：TAYLOR & FRANCIS LTD  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：TAYLOR & FRANCIS LTD  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：TAYLOR & FRANCIS LTD  

Crosslinked liquid-crystalline polymers (CLCPs) show unique behavior of deforming macroscopically when stimulated with heat, electricity and light. However, they cannot be remolded and reshaped once prepared. Here, we designed crosslinked polysiloxane with side chain mesogens that contain exchangeable crosslinking points based on transesterification between phenyl benzoates and hydroxy groups. After the formation of a polymer network, a base catalyst was introduced into the CLCP. When heated at 80 degrees C, a piece of the CLCP was reshaped into a film and separate pieces of the CLCP were fused together, indicating that the CLCP is remoldable.

DOI： 10.1080/15421406.2015.1049910

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：TAYLOR & FRANCIS LTD  

We prepared photomobile polymer materials composed of crosslinked azobenzene liquid-crystalline polymers (LCPs) and methacrylates with interpenetrating polymer network (IPN) structures, and explored their photoresponsive behavior. The IPN films exhibited reversible bending upon photoirradiation. In addition, the durability of the IPN films was much higher than that of the pristine crosslinked azobenzene LCP films.

DOI： 10.1080/15421406.2014.940491

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Language：English   Publisher：NATURE PUBLISHING GROUP  

DOI： 10.1038/511300a

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：TAYLOR & FRANCIS LTD  

Various fabrication methods of photomobile polymer materials containing photochromic moieties have been developed to improve their photoresponsive and mechanical properties. Here, we newly prepared photomobile polymer materials with interpenetrating polymer network (IPN) structures. The IPN films, which are composed of azobenzene liquid crystalline polymer (LCP) and polymethacrylates, showed reversible bending behavior upon exposure to UV and visible light. Bending speed of the IPN films became higher with decreasing glass-transition temperature of polymethacrylate components. The IPN film containing poly(dodecyl methacrylate) showed faster bending than the pristine azobenzene LCP film.

DOI： 10.1080/15421406.2014.917479

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Language：English   Publishing type：Part of collection (book)   Publisher：Springer Japan  

An organic semiconductor is material that is capable of transporting a charge, that is, electrons and holes. By this characteristic, that is, the property to support a current flow, they can be used in various electronic devices. In the early 1970s, organic semiconductors have been put to their first practical use in the photosensitive drum of copy machines. Thereafter, it began to be used as a practical material for organic electroluminescent (EL) elements in the 1990s. In recent years, research and development has been actively aimed to practical use in organic solar cells and organic transistors.

DOI： 10.1007/978-4-431-54859-1_11

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

Photo-induced molecular motion in a liquid crystal polymer film including azobenzene was studied by the heterodyne transient grating method. The film was confined in a liquid crystal cell, where it is a photomobile film under free-standing conditions. By observation of the refractive index change induced by a laser pulse, contraction of the film was observed on the order of several hundreds of nanoseconds, and the subsequent reorientation and molecular rotation dynamics were observed from a few microseconds to a hundred milliseconds. Finally, the cis isomer of azobenzene was thermally returned back to the trans isomer in about ten seconds because the film could not be bent in the liquid crystal cell. Since the contraction, reorientation and molecular rotation took place before the cis to trans back-transformation, these processes correspond to the preliminary molecular motion preceding the macroscopic bending of the film.

DOI： 10.1039/c4cp00457d

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The conformation of poly(methyl methacrylate) (PMMA) chains in a thin film after the rubbing process was investigated through the direct observation of the single chains by scanning near-field optical microscopy (SNOM) and excitation polarization modulation microscopy (EPMM). The rubbing at room temperature hardly changed the dimension on the whole chain scale in spite of the increase in orientational order on the segmental scale. The increase in the chain dimension along the rubbing direction was observed in the film rubbed at the higher temperature, which showed a surface morphology with fine groove. The extension ratio of the whole chain in the rubbed film was much smaller than that in the uniaxially stretched film. This indicates that the rubbing process mainly induces the conformational change on the length scale of the monomer unit rather than for the whole chain.

DOI： 10.1021/la302513c

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

The conformational relaxation of single polymer chains in uniaxially elongated poly(methyl methacrylate) (PMMA) films were examined by direct observation using scanning near-field optical microscopy (SNOM) and excitation polarization modulation microscopy (EPMM). The relaxation behavior of the individual PMMA chains was investigated in the binary blend systems consisting of high and low molecular weight components. The whole chain dimension and the segmental orientation were evaluated for high molecular weight long chains from SNOM and EPMM images, respectively. At the early stage of the stress relaxation process, not only the segmental orientation but also the whole chain dimension of the long chain decreased faster in matrices with short chains. This indicates that the relaxation at the whole chain scale is accelerated by disentanglement, which is caused by the motion of the short surrounding chains. The fast relaxation in the whole chain dimension cannot be explained by the constraint release picture in the theoretical models, which assumes that the disentanglement only activates the local motion of the long chain.

DOI： 10.1039/c2sm25272d

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCI LTD  

The phase-separated structures in a thin-film conjugated polymer blend, poly(2-methoxy-5-(3,7-dimethyloctyloxy)-1,4-phenylenevinylene)/poly(methyl methacrylate) (MDMO-PPV/PMMA) was studied by scanning near-field optical microscopy (SNOM), which can probe both of the surface topography and the chemical composition at high spatial resolution. In thin films of MDMO-PPV/PMMA, the PMMA-rich phase with less fluorescent emission appeared as a raised structure while the MDMO-PPV-rich phase with highly fluorescent emission was present as a collapsed phase with a low height. Such the vertical structure of the phase separation was dependent on the solvent quality for each component. On the other hand, the lateral structure was determined by the surface property of the substrate. As the degree of hydrophobic character of the substrate increased, the PMMA domains tended to form a continuous form to a separated spherical form. This evolution arise from a change in affinity between the substrate surface and PMMA, which the hydrophilic substrate has higher affinity to PMMA for maintaining the continuous structures and the hydrophobic substrate with lower affinity to PMMA can not hold the structures continuously. (C) 2011 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.polymer.2011.10.043

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCI LTD  

Modern society is based on the production of energy, primarily, from fossil fuels; however, these resources are limited. Therefore we are now confronted with a difficult problem: producing energy without burning fossil fuels. Many countries have utilized nuclear power to generate electricity as an effective source of energy, such as the US, France, and Japan. However, the tragic disaster at the Fukushima nuclear power station has reminded us that nuclear power is a double-edged sword: it may be a useful energy source, but it can bare its fangs when we lose control. We have many natural energy sources that are present in unlimited quantities, and so are unlikely to be exhausted easily: namely, sunlight, water, and wind. It is thus timely to consider further developing these natural resources to replace nuclear power for the production of energy.

DOI： 10.1016/S1369-7021(11)70212-7

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Total pages：2冊   Responsible for pages：pp. 1244-1245   Language：Japanese  

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Total pages：xi, 517p   Responsible for pages：pp. 456-467   Language：Japanese  

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