Reprocessable Photodeformable Azobenzene Polymers

Photodeformable azobenzene (azo) polymers are a class of smart polymers that can efficiently convert light energy into mechanical power, holding great promise in various photoactuating applications. They are typically of crosslinked polymer networks with highly oriented azo mesogens embedded inside. Upon exposure to the light of appropriate wavelength, they experience dramatic order parameter change following the configuration change of the azo units. This could result in the generation and accumulation of the gradient microscopic photomechanical force in the crosslinked polymer networks, thus leading to their macroscopic deformation. So far, a great number of photodeformable azo polymers have been developed, including some unoriented ones showing photodeformation based on different mechanisms. Among them, photodeformable azo polymers with dynamic crosslinking networks (and some uncrosslinked ones) have aroused particular interest recently because of their obvious advantages over those with stable chemical crosslinking structures such as high recyclability and reprocessability. In this paper, I provide a detailed overview of the recent progress in such reprocessable photodeformable polymers. In addition, some challenges and perspectives are also presented.     

光响应液晶嵌段共聚物研究进展

光响应液晶嵌段共聚物综合了光响应性液晶和嵌段聚合物两类材料的优异特性,是一种多功能性的新型材料。其中以偶氮苯为代表的光响应基团作为液晶基元的嵌段共聚物是其目前研究的主体。本文对光响应液晶材料和嵌段聚合物分别做了简要介绍,阐述了它们各自的优势和特点。对于光响应液晶嵌段共聚物的光响应机理、相分离过程和有序化调控手段进行了重点探讨。在此基础上,介绍了其在光子学、有机纳米模板和聚合物胶束等方面的研究进展。     

Synthesis and properties of new ionic liquid crystals based on para-nitroazobenzene with substitution vinylimidazolium ion group

A new series of ionic liquid crystals (ILCs), 1-(4-(4-nitrophenylazo)phenyloxy) vinyl-3-methyl-1H-imidazol-3-ium bromide salts (C _n , n?=?6, 10) were synthesised. Their chemical structures were determined by ¹H NMR, ¹³C NMR, UV spectroscopy and elemental analysis. The liquid crystalline properties were investigated by differential scanning calorimetry, polarising optical microscopy, and powder X-ray diffraction. These measurements showed that C _n (n?=?6, 10) exhibit smectic liquid crystalline phases with focal-conic fan-shaped textures. The introduction of vinylimidazolium group onto the azobenzene enhances the thermal stability of the smectic state, which play an important role in forming the smectic layer structure.     

Synthesis of chiral azobenzene derivatives and the performance in photochemical control of blue phase liquid crystal

A series of chiral azobenzene compounds with branched terminal were synthesised, and the photosensitive performances were investigated accordingly. It was found that the photochemical properties were mainly affected by the trans–cis configuration of azobenzene and the linked position between the azobenzene and chiral centre. The para-type azobenzenes showed general photochemical decrease in helical twisting power (HTP), but the meta-type ones appeared interestingly showed photochemical increase in HTP. This work provided an effective method for designing molecules to control blue phase (BP) including adjusting colours, inducing BP and extending BP range, which was promising in the applications of optically addressable devices.     

Liquid‐crystalline azobenzene‐containing ferrocene‐based polymers: study on synthesis and properties of main‐chain ferrocene‐based polyesters with azobenzene in the side chain

Ferrocene‐based polymers are characterized by their electrochemical activity, good redox properties, thermal, photochemical stability, and liquid crystallinity, and thus they have various applications in different fields. A comprehensive investigation on the synthesis and properties of three novel main‐chain ferrocene‐based polyesters with azobenzene in the side chain (MFPAS) was carried out. The main‐chain ferrocene‐based polyester, poly(N‐phenyldiethanolamine 1,1′‐ferrocene dicarboxylate (PPFD), was synthesized via the solution polycondensation reaction of 1,1′‐ferrocenedicarbonyl chloride with phenyldiethanolamine (PDE). The novel MFPAS were synthesized via the post‐polymerization azo‐coupling reaction of PPFD with three different 4‐substituted anilines including 4‐nitroaniline, 4‐aminobenzoic acid, and 4‐aminobenzonitrile to produce 4‐nitrophenylazo‐functionalized‐PPFD (PPFD‐NT), 4‐carboxyphenylazo‐functionalized‐PPFD (PPFD‐CA), and 4‐cyanophenylazo‐functionalized‐PPFD (PPFD‐CN), respectively. All the synthesized polymers were characterized by ¹H NMR spectroscopy, Fourier transform infrared spectroscopy, and UV–visible spectroscopy. In addition, powder X‐ray diffraction patterns were measured for the synthesized polymers. The photoisomerization of the MFPAS was studied. The thermal properties of the MFPAS were studied using thermogravimetric analysis and differential scanning calorimetry. PPFD‐CA and PPFD‐CN were found to be more thermally stable than PPFD‐NT. Finally, the liquid‐crystalline properties of PPFD and the MFPAS were examined using polarized optical microscope. It was found that all the polymers possessed nematic phases and exhibited textures with schlieren disclinations. Copyright © 2012 John Wiley & Sons, Ltd.     

Recording medium based on a polymer azobenzene complex with cobalt for polarization holography

We have recorded holograms in films of a 4-methacroyloxy-(4′-carboxy-3′-hydroxy)-2-chloroazobenzene polycomplex with cobalt, for parallel and orthogonal orientation of the light beam polarization. The increase in the diffraction efficiency of the holograms and the decrease in their relaxation time in the case of orthogonal polarization compared with the case of parallel polarization of the recording light beams are connected with features of the structural rearrangement of the polymer matrix. We hypothesize that the information-related characteristics of the recording medium created can be controlled by external electric or magnetic fields, due to the presence of magnetic metal ions in the composition of the medium. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 45, No. 1, pp. 46–49, January–February, 2009.     

Water‐soluble triply‐responsive homopolymers of N,N‐dimethylaminoethyl methacrylate with a terminal azobenzene moiety

Novel water‐soluble triply‐responsive homopolymers of N,N‐dimethylaminoethyl methacrylate (DMAEMA) containing an azobenzene moiety as the terminal group were synthesized by atom transfer radical polymerization (ATRP) technique. The ATRP process of DMAEMA was initiated by an azobenzene derivative substituted with a 2‐bromoisobutyryl group (Azo‐Br) in the presence of CuCl/Me₆TREN in 1,4‐dioxane as a catalyst system. The molecular weights and their polydispersities of the resulting homopolymers (Azo‐PDMAEMA) were characterized by gel permeation chromatography (GPC). The homopolymers are soluble in aqueous solution and exhibit a lower critical solution temperature (LCST) that alternated reversibly in response to Ph and photoisomerization of the terminal azobenzene moiety. It was found that the LCST increased as pH decreased in the range of testing. Under UV light irradiation, the trans‐to‐cis photoisomerization of the azobenzene moiety resulted in a higher LCST, whereas it recovered under visible light irradiation. This kind of polymers should be particularly interesting for a variety of potential applications in some promising areas, such as drug controlled‐releasing carriers and intelligent materials because of the multistimuli responsive property. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2564–2570, 2010     

Photoresponsive poly(methyl methacrylate)2–(polystyrene)2 miktoarm star copolymer containing an azobenzene moiety at the core

We prepared a novel miktoarm star copolymer with an azobenzene unit at the core via combination of atom transfer radical polymerization (ATRP) and nitroxide‐mediated free radical polymerization (NMP) routes. For this purpose, first, mikto‐functional initiator, 3 , with tertiary bromide (for ATRP) and 2,2,6,6‐tetramethylpiperidin‐1‐yloxy (TEMPO) (for NMP) functionalities and an azobenzene moiety at the core was synthesized. The initiator 3 thus obtained was used in the subsequent living radical polymerization routes such as ATRP of MMA and NMP of St, respectively, to give A₂B₂ type miktoarm star copolymer, (PMMA)₂‐(PSt)₂ with an azobenzene unit at the core with controlled molecular weight and low polydispersity (M_w/M_n < 1.15). The photoresponsive properties of 3 and (PMMA)₂‐(PSt)₂ miktoarm star copolymer were investigated. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1396–1403, 2006     

光响应形变液晶聚合物的结构与应用

液晶聚合物能够在外界刺激下发生形状变化,是一类重要的柔性智能材料.其中液晶有序排列的改变诱导材料的宏观形变.光响应聚合物具有可远程操作、易于控制等特点,在刺激响应性聚合物的设计中受到了广泛关注.将具有光响应性的基团引入到液晶聚合物体系中,可以得到一系列具有重要应用前景的光致形变材料.本文综述了近年来光响应形变液晶聚合物...     

Reversed‐Phase High‐Performance Liquid Chromatographic Separation and Determination of 4‐Amino‐azobenzene‐4′,5‐disulfonic Acid and Related Products in Industrial Wastewater Effluents

A simple and rapid reversed‐phase high‐performance liquid chromatographic method for the separation and determination of 4‐amino‐azobenzene‐4′,5‐disulfonic acid (AABDS) and its process‐related impurities was developed. The separation was achieved on a μ‐Bondapak C₁₈ column using 0.15 M ammonium sulfate‐acetonitrile (55:45) (v/v) as eluent. A UV‐visible spectrophotometric detector fixed at 386 nm was used both for detection and quantitation. The method was used not only for quality assurance but also for process development and wastewater management of AABDS.