Syntheses of bisazo‐containing polymethacrylates using atom transfer radical polymerization and the photoalignment behavior

Three kinds of photoresponsive polymethacrylates containing different bisazo chromophores were prepared with atom transfer radical polymerization and characterized with proton nuclear magnetic resonance, gel permeation chromatography, and ultraviolet–visible spectra. These polymers had similar molecular weights, molecular weight distributions, glass‐transition temperatures, and absorption coefficients. The irradiation of these polymer films with a linearly polarized laser could induce birefringence because of the reorientation of the bisazo chromophores through trans–cis–trans isomerization cycles of double azo bonds, and the corresponding mechanism was also examined. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4237–4247, 2004     

Mechanistic study of trans⇆cis isomerization of the substituted azobenzene moiety bound on a liquid‐crystalline polymer

A mechanistic study of the trans?cis isomerization of the azobenzene moiety in a side‐chain liquid‐crystal polymer system was carried out with six liquid‐crystalline polymethacrylates in which different electron‐withdrawing substituents were attached to the para‐positions of the azobenzene chromophores. Compared to the non‐nitro‐substituted azo polymers, the nitro‐substituted azo polymers exhibited two quite different behaviors: an extraordinarily high reaction rate of the thermal cis–trans isomerization and an unexpected composition of cis–trans isomers obtained from the photochemical trans–cis isomerization process. A potential energy profile for the isomerization process was established on basis of the structures of the proposed transition states and was employed to elucidate the reaction mechanism. The results confirmed that the nitro‐substituted azo polymer system proceeded via a rotation mechanism in either direction of the trans?cis isomerization reaction, whereas the non‐nitro‐substituted species were more likely to follow an inversion mechanism. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2296–2307, 2001     

Hyperbranched photo responsive and liquid crystalline azo‐siloxane polymers synthesized by click chemistry

Three new types of hyperbranched photoactive liquid crystalline siloxane polymers containing azo moieties were synthesized using click chemistry methodology. The polymers were soluble in most of the polar solvents like chloroform, tetrahydrofuran, dimethylformamide, dimethyl sulphoxide and dichloromethane. The molecular weights of the polymers were in the range of 9000–12,000 g mol^?1. The trans‐cis photoisomerization of the polymer were studied both under UV radiation and dark. The isomerization rate constants were found to be in the range of 0.7–1.4 × 10^?2 sec^?1 and 7.0 × ?2.5 × 10^?5 sec^?1. The thermotropic behavior of the polymers was studied by using polarizing optical microscopy and differential scanning calorimetry, respectively. The polymers P1 and P2 showed liquid crystalline texture characteristic of nematic phase. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

A novel generation of photoactive comb‐shaped polyamides for the photoalignment of liquid crystals

A new approach to the synthesis of photoactive comb‐shaped homo‐ and copolyamides containing azobenzene, cinnamate, and coumarin side groups for photoalignment of liquid crystals was elaborated. Photooptical properties and photoorientational ability of these polymers with respect to liquid crystals were studied. It was shown that polarized UV irradiation of all spin‐coated polyamides leads to orientation of liquid crystalline molecules deposited on the polyamide thin films. The synthesized polymers containing cinnamate and coumarin side groups as well as azobenzene‐containing cyano‐ and nitro‐substituted polymers demonstrated good orientation ability in relation to liquid crystals displaying photoinduced planar orientation with high dichroism values within the range of 0.68–0.72. Contrary to the above‐mentioned polyamides, azobenzene‐containing fluorosubstituted polymers induced a homeotropic orientation of liquid crystals. It was shown that the synthesized photoactive polyamides can be considered as promising photoalignment materials for application in display technology, photonics, and other “smart” optical devices. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4031–4041     

Local forms of molecular mobility in copolymethacrylates containing side‐chain nonlinear optical chromophores

Local forms of molecular mobility of comb‐like random copolymethacrylates, containing side‐chain nonlinear optical chromophores and amyl‐ or octafluoroamyl‐groups, are studied. In the glassy state, two relaxation processes are found, which are due to reorientation of terminal polar groups (γ₂‐process) and rotation of chromophore groups about their long axes (β‐process). For octafluoroamyl‐containing copolymers, the γ₂‐process is superposition of the two molecular motions due to reorientation of terminal chromophore groups and ? CF₂H groups. The intensity and relaxation times in the range of the γ₂‐process depend on the chemical structure and concentration of chromophores in a copolymer. For the β‐process, the molecular mobility weakly depends on the chromophore structure, being mainly determined by the relative lengths of the rigid chromophore and flexible side chains. On the global spectrum of depolarization current it was observed the γ₁‐process due to reorientation of (CH₂)_n spacers between chromophore groups and copolymer backbone. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1488–1496, 2008     

Synthesis and characterization of bi‐functional photorefractive hyperbranched polyisophthalesters

A series of novel bi‐functional photorefractive (PR) hyperbranched polyisophthalesters (HPIPEs) with pendant end carbazolyl and azo groups, acting as photoconductors and electro‐optic (EO) chromophores, respectively, were synthesized by modifying the HPIPE with N‐hydroxyethyl carbazole and 4‐(p‐nitrophenylazo) (N‐ethoxyl‐N‐methyl)aniline. These obtained PR polymers were then characterized by UV‐vis and IR spectrum, ¹H‐NMR, elemental analysis, gel permeation chromatography (GPC) measurements and thermal analysis. As expected, due to their three‐dimension molecular structures, the lower glass transition temperatures (21–49°C) were obtained in the absence of plasticizers, which provide a necessary free volume for the EO chromophores reorientation. The acceptable thermal stability, as well as the degradation temperatures of 205–260°C, was also determined by thermogravimetric analysis (TGA). The two‐beam coupling experiments of HPIPE‐25Azo theoretically containing 25% azo end groups showed that a high gain coefficient of 59 cm^?1 was obtained at the applied electric field of 80 V μm^?1. Copyright © 2004 John Wiley & Sons, Ltd.     

Substituent effect on azobenzene‐based liquid‐crystalline organophosphorus polymers

An Erratum has been published for this article in Journal of Polymer Science Part A: Polymer Chemistry (2003) 41(23) 3862 A new series of combined‐type, azobenzene‐based organophosphorus liquid‐crystalline polymers were synthesized, and their photoisomerization properties were studied. The prepared polymers contained azobenzene units as both the main‐chain and side‐chain mesogens. Various groups were substituted in the terminal of the side‐chain azobenzene mesogen, and the effects of the substituents were investigated. All the polymers were prepared at the ambient temperature by solution polycondensation with various 4‐substituted phenylazo‐4′‐phenyloxyhexylphosphorodichloridates and 4,4′‐bis(6‐hydroxyhexyloxy) azobenzene. The polymers were characterized with gel permeation chromatography, Fourier transform infrared, and ¹H, ¹³C, and ³¹P NMR spectroscopy. Thermogravimetric analysis revealed that all the polymers had high char yields. The liquid‐crystalline behavior of the polymers was examined with hot‐stage optical polarizing microscopy, and all the polymers showed liquid‐crystalline properties. The formation of a mesophase was confirmed by differential scanning calorimetry (DSC). The DSC data suggested that mesophase stability was better for electron‐withdrawing substituents than for halogens and unsubstituted ones. Ultraviolet irradiation studies indicated that the time taken for the completion of photoisomerization depended on the dipolar moment, size, and donor–acceptor characteristics of the terminal substituents. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3188–3196, 2003     

Siloxane polymers containing azo moieties synthesized by click chemistry for photo responsive and liquid crystalline applications

Three new types of siloxane‐based photoactive liquid crystalline polymers containing azo side groups were synthesized through the click chemistry route. The polymers having molecular weight range of 14,000–34,000 g mol^?1 were soluble in most of the polar solvents like chloroform, tetrahydrofuran, dimethylformamide, dimethyl sulfoxide, and dichloromethane. The photoresponsive trans–cis photoisomerization under UV radiation and cis–trans relaxation process in dark for the polymers were studied. The isomerization rate constants were found to be 0.01–0.04 sec^?1 and 1.16*10^?4–4.67*10^?4 sec^?1, respectively. It has been noted that the polymers showed high intensity absorption for n‐π* in chloroform. Both trans and cis forms of azide monomers having azo moiety exhibited molar extinction coefficient ( ? _max) in the range of 22,000–33,000 L mol^?1 cm^?1. The thermotropic behavior of the polymers was studied by polarizing optical microscope (POM) and differential scanning calorimetry (DSC) experiments. Polymer P1 showed liquid crystalline textures of nematic droplets, whereas P2 showed smectic focal conic texture and nematic droplets. Polymer P1 was also studied for photomechanical bending on exposure to UV radiation. The polymers showed initial degradation temperature in the range of 210–275°C. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Postfunctionalization of poly(propargyl methacrylate) using copper catalyzed 1,3‐dipolar Huisgen cycloaddition: An easy route to electro‐optic materials

A one‐pot synthetic route based on copper‐catalyzed Huisgen reaction has been developed to functionalize a methacrylate propargylic polymer with azido‐substituted moieties. This procedure was used for the preparation of electro‐optic materials containing well‐known Disperse Red One (DR1) chromophores along with bulky adamantyl moieties (Adam). The postfunctionalization of the propargylic polymer was successfully achieved using different molar ratios of DR1/Adam. These novel polymers exhibit high glass transition temperature owing to the rigid structure of adamantyl units. Moreover, the second harmonic generation measurements demonstrated the effectiveness of adamantyl groups to act as insulating shield limiting thus the electrostatic interactions between chromophores. Indeed, higher optimal chromophore concentration (50 mol %) than in conventional DR1‐containing polymers (30 mol %) allowed us to increase the d₃₃ coefficient up to 92 pm/V. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5652–5660, 2009     

A Diels‐Alder/retro Diels‐Alder strategy to synthesize polymers bearing maleimide side chains

Polymers containing thiol‐reactive maleimide groups on their side chains have been synthesized by utilization of a novel methacrylate monomer containing a masked maleimide. Diels‐Alder reaction between furan and maleimide was adapted for the protection of the reactive maleimide double bond prior to polymerization. AIBN initiated free radical polymerization was utilized for synthesis of copolymers containing masked maleimide groups. No unmasking of the maleimide group was evident under the polymerization conditions. The maleimide groups in the side chain of the polymers were unmasked into their reactive form by utilization of retro Diels‐Alder reaction. This cycloreversion was monitored by thermo gravimetric analysis (TGA), differential scanning calorimetry (DSC), and ¹H and ¹³C NMR spectroscopy. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4545–4551, 2007     

Water‐soluble conjugated polymers: Synthesis and optical properties

Two sets of water‐soluble poly(phenylene vinylene)s were synthesized and their optical properties were studied. The aqueous solubility of all these polymers is rendered by pendant sulfonate groups. One set of polymers (polymer I series) contains, in addition to the sulfonate pendants, dimethoxy substituents, while the other (polymer II series) contains oligo(ethylene oxide) side chains. Within each set, polymers containing lithium (Ia and IIa), sodium (Ib and IIb), and potassium (Ic and IIc) counter ions were prepared. The two sets of polymers showed different properties from physical appearance (fiber vs film) to thermal properties and to optical properties. It was found that set I polymers, with shorter side chains, exhibit stronger aggregation in aqueous solutions than set II polymers, which led to their lower fluorescence quantum yields and lower polymer‐to‐MV²⁺ quenching efficiencies. Within each set, the effect of counter ions on optical properties was noted. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5123–5135, 2007     

Free‐radical crosslinking copolymerization of 2,2′‐azobis[N‐(2‐propenyl)‐2‐methylpropionamide] with vinyl benzoate resulting in polymeric azo initiators

2,2′‐Azobis[N‐(2‐propenyl)‐2‐methylpropionamide] (APMPA) with two carbon–carbon double bonds and an azo group was copolymerized with vinyl benzoate (VBz) at 60 °C, resulting in azo groups containing VBz/APMPA prepolymers and crosslinked polymers as soluble and insoluble polymeric azo initiators, respectively. The polymerization characteristics of APMPA as a novel diallyl monomer were clarified with the rate and degree of polymerization and the monomer reactivity ratios. The gelation behaviors in VBz/APMPA crosslinking copolymerizations were examined in detail with a comparison of the actual gel point and the theoretical gel point calculated according to Stockmayer's equation with the tentative assumption of equal reactivity for both vinyl groups belonging to VBz and APMPA. The effectiveness of the resulting branched or crosslinked poly(VBz‐co‐APMPA)s as soluble or insoluble polymeric azo initiators, respectively, at providing graft polymers through the cleavage of azo groups at an elevated temperature was examined by the polymerization of allyl benzoate at 120 °C. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 317–325, 2002     

Synthesis of azobenzene‐containing polythiophenes and photoinduced anisotropy

Three new polythiophenes containing an azobenzene moiety in the side‐chain were synthesized and characterized. Two of them, which are slightly soluble in tetrahydrofuran to allow the preparation of thin films from solution casting, were used to investigate the photoinduced anisotropy arising from the photoisomerization of azobenzene in this type of polymer. The results show that, unlike other amorphous azobenzene polymers, only an extremely small anisotropy can be induced on excitation with an Ar⁺ laser at 488 nm in these azobenzene‐containing polythiophenes, and that this photoinduced anisotropy is observable only by heating the polymer to some temperatures below glass transition temperature. It is suggested that the inability for azobenzene polythiophenes to display a significant photoinduced anisotropy may be caused by some structural constraints and/or a severe interference from conjugated thiophene chains that absorb strongly in the visible region. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3445–3455, 2004     

Effect of branched alkyl side chains on the performance of thin‐film transistors and photovoltaic cells fabricated with isoindigo‐based conjugated polymers

New isoindigo and di(thienyl)ethylene‐containing π‐extended conjugated polymers with different branched side chains were synthesized to investigate their physical properties and device performance in thin‐film transistors and photovoltaic cells. 11‐Butyltricosane (S3) and 11‐heptyltricosane (S6) groups were used as side‐chain moieties tethered to isoindigo units. The linking groups between the polymer backbone and bifurcation point in the branched side chain differ in the two polymers (i.e., PIDTE‐S3 and PIDTE‐S6 ). The polymers bearing S6 side chains showed much better charge transport behavior than those with S3 side chains. Thermally annealed PIDTE‐S6 film exhibited an outstanding hole mobility of 4.07 cm² V^?1 s^?1 under ambient conditions. Furthermore, bulk heterojunction organic photovoltaic cells made from a blend film of PIDTE‐S3 and (6,6)‐phenyl C61‐butyric acid methyl ester demonstrated promising device performance with a power conversion efficiency in the range of 4.9–5.0%. © 2015 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 2015 , 53, 1226–1234     

Nonlinear optical side‐chain polymers post‐functionalized with high‐β chromophores exhibiting large electro‐optic property

Electro‐optic side‐chain polymers have been synthesized by the post‐functionalization of methacrylate isocyanate polymers with novel phenyl vinylene thiophene vinylene bridge (FTC) nonlinear optical chromophores. For this application, FTC‐based chromophores were modified in their electronic donor structure, exhibiting much larger molecular hyperpolarizabilities compared with the benchmark FTC. Of these new chromophores, absorption spectra, hyper‐Rayleigh scattering experiment, and thermal analysis were carried out to confirm availability as effective nonlinear optical units for electro‐optic side‐chain polymers. The electro‐optic coefficients (r₃₃) of obtained polymers were investigated in the process of in situ poling by monitoring the temperature, current flow, poling field, and electro‐optic signal. Compared with the nonsubstituted analogue, benxyloxy modified FTC chromophore significantly achieved higher nonlinear optical property, exhibiting molecular hyperpolarizability at 1.9 μm of 4600 × 10^?30 esu and an r₃₃ value of 150 pm/V at the wavelength of 1.31 μm. Synthesized electro‐optic polymers showed high glass transition temperature (T_g), so that the temporal stability examination exhibited >78% of the electro‐optic intensity remaining at 85 °C over 500 h. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Pd‐initiated polymerization of diazo compounds bearing dialkoxyphosphinyl group and hydrolysis of the resulting polymers and oligomers to afford phosphonic acid‐containing products

Pd‐initiated polymerization and oligomerization of diazo compounds containing a dialkoxyphosphinyl group are described. Polymerization of 2‐dialkoxyphosphinylethyl diazoacetates with π‐allylPdCl‐based initiating systems afforded C? C main chain polymers bearing phosphonate on each main chain carbon atom. The quantitative transformation of the side chain phosphonate to phosphonic acid resulted in the formation of water soluble polymers having the acid groups accumulated around their main chains, although the carbonyl ester linkage in the side chain was cleaved via intramolecular acid‐assisted hydrolysis in water at 80 °C. Pd‐initiated oligomerization of diethyl diazomethylphosphonate yielded an oligomeric product bearing diethoxyphosphiny groups directly attached to its main chain carbons, with unexpected incorporation of azo group in the main chain framework. Hydrolysis of the phosphonate of the oligomer afforded a water‐soluble product, which was revealed to show higher proton conductivity than poly(vinylphosphonic acid) under certain conditions. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1742–1751     

Synthesis and characterization of hydrogen‐bonded thermotropic liquid crystalline aromatic‐aliphatic poly(ester–amide)s from amido diol

Fifteen highly regular hydrogen‐bonded, novel thermotropic, aromatic‐aliphatic poly(ester–amide)s (PEAs) were synthesized from aliphatic amido diols by melt polycondensation with dimethyl terephthalate and solution polycondensation with terephthaloyl chloride. Intermolecular hydrogen bonds more or less perpendicular to the main‐chain direction induce the formation and stabilization of liquid crystalline property for these PEAs. The structure of these polymers, even in the mesomorphic phase is dominated by hydrogen bonds between the amide–amide and amide–ester groups in adjacent chains. Aliphatic amido diols were synthesized by the aminolysis of γ‐butyrolactone, δ‐valerolactone and ε‐caprolactone with aliphatic diamines containing a number of methylene groups from two to six in isopropanol medium at room temperature. Effects of polarity of the solvent on solution polymerization and effect of catalyst on trans esterification were studied. These polymers were characterized by elemental analysis, FTIR, ¹H NMR, ¹³C NMR, solubility studies, inherent viscosity, DSC, X‐ray diffraction, polarized light microscopy, and TGA. All the melt/solution polycondensed PEAs showed multiple‐phase transitions on heating with second transitions identified as nematic/smectic/spherullitic texture. The mesomorphic properties were studied as a function of their chemical structure by changing alternatively m or n. Odd‐even effect on mesophase transition temperature, isotropization temperature, and crystallinity were studied. The effect of molecular weight and polydispersity on mesophase/isotropization temperature and thermal stability were investigated. It was observed that there exists a competition for crystallinity and liquid crystallinity in these PEAs © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2469–2486, 2000     

Synthesis,characterization, and photoresponsive behavior of new azobenzene‐containing polyethers

Two new polyethers, bearing azobenzene moiety in the side chain, were synthesized in excellent yields by means of anionic polymerization of 4‐glycidyloxyazobenzene and 4‐cyano‐4′‐glycidyloxyazobenzene (leading to azo‐P1 and azo‐P2 polymers, respectively) with the system polyiminophosphazene base t‐Bu‐P₄/3,5‐di‐tert‐butylphenol as initiator. The polymers were characterized with respect to their molecular weights, structure, and calorimetric features. The polyether bearing cyanoazobenzene group in the side chain was found to exhibit nematic phase up to 200 °C. E–Z isomerization of both polymers in tetrahydrofuran solution, after irradiating with UV light at 364 nm for 15 min, was investigated by means of UV–visible absorption spectroscopy. In the case of glycidylic monomers as well as the resulting polymers, E–Z isomerization was also investigated by means of ¹H NMR, by direct irradiation in the NMR probe in deuterated 1,1,2,2‐tetrachloroethane solution. By this technique, in the case of 4‐cyano‐4′‐glycidyloxyazobenzene, it was found that irradiation led to a photostationary state corresponding to an amount of Z isomer equal to 25%. For azo‐P1 polymer, Z–E or “reverse” isomerization was investigated at 60, 70, or 80 °C directly in the NMR probe; as expected, the process followed a first‐order rate law. The kinetic constants as well as the activation energy for the process were determined in this temperature range. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5426–5436, 2009     

Ferrocene‐based organophosphorus liquid–crystalline polymers: Synthesis and characterization

Ferrocene‐containing polyphosphate and phosphonate esters were synthesized by the solution polycondensation method. The structure of the polymers was confirmed using various spectroscopic techniques. The formation of two types of chain blocks was confirmed by ³¹P NMR spectroscopy. Hot stage optical polarized microscope (HOPM) analysis revealed that all the polymers have a liquid–crystalline property. The char yields of the synthesized similar polymers were much higher than those of nonphosphorus polymers already reported in the literature. DSC analysis confirmed our predictions over the liquid–crystalline property, glass‐transition temperature, isotropization temperature, and thermal stability of the polymers. The effects of substitution on the side chain, structure of the liquid‐–crystalline phase, and thermal stability of the polymers have also been discussed. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2396–2403, 2001     

Azobenzene‐Containing Block Copolymers as Light‐Induced Reworkable Adhesives: Effects of Molecular Weight,Composition, and Block Copolymer Architectures on the Adhesive Properties

We previously reported that ABA‐type triblock copolymers with azobenzene‐containing terminal blocks can be utilized as a light‐induced reworkable adhesive that enables repeatable bonding and debonding on demand. The reworkability was based on the photoisomerization of the azobenzene moiety and concomitant softening and hardening of the azo blocks. Our aim in this study is to investigate the effect of the composition, molecular weight, and block copolymer architectures on the reworkable adhesive properties. For this purpose, we prepared AB diblock, ABA triblock, and 4‐arm (AB)₄ star‐block copolymers consisting of polymethacrylates bearing an azobenzene moiety (A block) and 2‐ethylhexyl (B block) side chains and performed adhesion tests by using these block copolymers. As a result, among the ABA block copolymers with varied compositions and molecular weights, the ABA triblock copolymers with an azo block content of about 50 wt % and relatively low molecular weight could achieve an appropriate balance between high adhesion strength and low residual adhesion strength upon UV irradiation. Furthermore, the 4‐arm star‐block structure not only enhances the adhesion strength, but also maintains low residual adhesion strength when exposed to UV irradiation. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 806–813