Azo Polymer Research Articles

Lignin derived Si@C composite as a high performance anode material for lithium ion batteries

Carbon coated 50 nm Si NPs using alkali lignin (AL) or alkali lignin-derived azo polymer (AL-azo-NO2) as the low cost carbon precursors were synthesized. The Si@C composites were facilely prepared by evaporating solvent THF of the Si NPs/carbon precursor dispersion solutions followed by carbonization in nitrogen. The resulting Si@C composites showed a vesical-like morphology with integrated carbon coating on Si NPs. When used as the anode materials for Li-ion batteries, the nitrogen-doped carbon coated Si NPs (Si@C-AL-azo-NO2) stemmed from the use of AL-azo-NO2 showed superior electrochemical performance. As the results, Si@C-AL-azo-NO2 exhibited a high reversible specific capacity of 882 mAh/g at a current of 200 mA/g over 150 cycles and a high coulombic efficiency (99%), paving the way for promising application of lignin in high performance Si@C anode materials for Li-ion batteries.

On stress – strain responses and photoinduced properties of some azo polymers

Mechanical properties of two amorphous azo polymers were characterized in tensile measurements and correlated with photoinduced behaviour of the materials observed upon irradiation with blue light of moderate intensity. Side-chain azobenzene poly(amide imide)s capable of forming high-quality free-standing layers of a large area and thickness of a few micrometers were chosen for the investigations. High Young's modulus of ca. 2 GPa and yield stress of the order of 30 MPa were found for the materials. Photoinduced birefringence measurements evidenced efficient chromophore orientation in both polymers, while polymer mass transport upon illumination with interference pattern was hardly observed. Nevertheless, subtle periodic changes in the surface topography of the films after irradiation with right- and left-handed circularly polarized beams suggested that opto-mechanical stress reached the value of a few tens of MPa, i.e., the minimum value needed for inducing plastic deformations in the studied azo polymers.

Dielectric Properties of Azo Polymers: Effect of the Push-Pull Azo Chromophores

The relationship between the structure and the dielectric properties of the azo polymers was studied. Four azo polymers were synthesized through the azo-coupling reaction between the same precursor (PAZ) and diazonium salts of 4-aminobenzoic acid ethyl ester, 4-aminobenzonitrile, 4-nitroaniline, and 2-amino-5-nitrothiazole, respectively. The precursor and azo polymers were characterized by 1H NMR, FT-IR, UV-vis, GPC, and DSC. The dielectric constant and dielectric loss of the samples were measured in the frequency range of 100 Hz–200 kHz. Due to the existence of the azo chromophores, the dielectric constant of the azo polymers increases compared with that of the precursor. In addition, the dielectric constant of the azo polymers increases with the increase of the polarity of the azo chromophores. A random copolymer (PAZ-NT-PAZ) composed of the azo polymer PAZ-NT and the precursor PAZ was also prepared to investigate the content of the azo chromophores on the dielectric properties of the azo polymers. It showed that the dielectric constant increases with the increase of the azo chromophores. The results show that the dielectric constant of this kind of azo polymers can be controlled by changing the structures and contents of azo chromophores during the preparation process.

Organic Nanoprobes for Fluorescence and 19F Magnetic Resonance Dual‐Modality Imaging

Multimodal imaging techniques have been demonstrated to be greatly advantageous in achieving accurate diagnosis and gained increasing attention in recent decades. Herein, we present a new strategy to integrate the complementary modalities of 19F magnetic resonance imaging (19F MRI) and fluorescence imaging (FI) into a polymer nanoprobe composed of hydrophobic fluorescent organic core and hydrophilic fluorinated polymer shell. The alkyne‐terminated fluorinated copolymer (Pn) of 2,2,2‐trifluoroethyl acrylate (TFEA) and poly(ethylene glycol) methyl ether acrylate (PEGA) was first prepared via atom transfer radical polymerization (ATRP). The PEGA plays an important role in both improving 19F signal and modulating the hydrophilicity of Pn. The alkynyl tail in Pn is readily conjugated with azide modified tetra‐phenylethylene (TPE) through click chemistry to form azo polymer (TPE‐azo‐Pn). The core‐shell nanoprobes (TPE‐P3N) with an average particle size of 57.2 ± 8.8 nm are obtained via self‐assembly with ultrasonication in aqueous solution. These nanoprobes demonstrate high water stability, good biocompatibility, strong fluorescence and good 19F MRI performance, which present great potentials for simultaneous fluorescence imaging and 19F–MR imaging.

Fabrication of chromophore molecule-linked azo polymer as waveguide material of polymeric thermo-optic digital optical switch

A chromophore molecule-linked azo polymer as waveguide material (MCAP) of polymeric thermo-optic digital optical switch (DOS) was prepared with a chromophore molecule (ABFA), a polyether polyol and isophorone diisocyanate (IPDI). The chemical structures of ABFA monomer and azo polymer MCAP were characterized by FT-IR and UV–Visible spectroscopy. The thermal and mechanical properties of the MCAP film were investigated. The refractive index and transmission loss of MCAP film were measured at different temperatures and different laser wavelengths by an attenuated total reflection (ATR) technique and CCD digital imaging devices. A polymeric thermo-optic DOS based on the thermo-optic effect of the MCAP was designed and the performance of the switch was simulated by using the finite difference beam propagation method (FD-BPM). The experimental results showed that the power consumption of the polymeric thermo-optic switch could be only 0.64[Formula: see text]mW, while the response time of the switch could be as short as 3.0[Formula: see text]ms.

Light-Triggered Formation of Surface Topographies in Azo Polymers

Properties such as friction, wettability and visual impact of polymer coatings are influenced by the surface topography. Therefore, control of the surface structure is of eminent importance to tuning its function. Photochromic azobenzene-containing polymers are an appealing class of coatings of which the surface topography is controllable by light. The topographies form without the use of a solvent, and can be designed to remain static or have dynamic properties, that is, be capable of reversibly switching between different states. The topographical changes can be induced by using linear azo polymers to produce surface-relief gratings. With the ability to address specific regions, interference patterns can imprint a variety of structures. These topographies can be used for nanopatterning, lithography or diffractive optics. For cross-linked polymer networks containing azobenzene moieties, the coatings can form topographies that disappear as soon as the light trigger is switched off. This allows the use of topography-forming coatings in a wide range of applications, ranging from optics to self-cleaning, robotics or haptics.

Polymer complexes. LXVII: electrical conductivity and thermal properties of polymer complexes of quinoline azo dye

A novel series of divalent transition metals (Cu2+, Co2+ and Ni2+) polymer complexes of azo ligand named 5-(2,3-dimethyl-1-phenylpyrazol-5-one azo)-8-hydroxyquinoline (Q) have been synthesized. The azo quinoline ligand (Q) and polymer complexes are characterized by various physicochemical techniques. The thermal properties of the ligand and its isolated polymer complexes are studied using thermogravimetric analysis. The physicochemical investigations elucidate that the azo ligand acts as a neutral bis(bidentate) ligand. The polymer complexes are found to be octahedral geometry. The change in the ac electrical conductivity, loss tangent and dielectric properties are studied upon heating in temperature region 298–550 K and frequency ranging from 0.1 to 100 kHz, moreover, the mechanism of conduction is determined. The electrical conductivity studies indicate that the ligand (Q) and polymer complexes have the semiconducting behavior. The correlated barrier hopping is the dominant conduction mechanism for all samples.

Photodeformable Microspheres from Methacrylate‐Based Azo Homopolymers

In this study, two methacrylate‐based azo homopolymers are synthesized and used to fabricate photodeformable microspheres through a self‐assembling approach. The methacrylate‐based azo homopolymer with the narrow molecular weight distribution is synthesized by reversible addition fragmentation chain transfer polymerization, while the other with the relatively broad molecular weight distribution is synthesized by conventional radical polymerization. The azo polymers are characterized by proton nuclear magnetic resonance (1H‐NMR), Fourier transform infrared spectroscopy (FT‐IR), differential scanning calorimetry (DSC), thermal gravimetric analysis TGA, gel permeation chromatography GPC, and ultraviolet‐visible spectroscopy (UV–vis) m. The colloidal spheres are obtained by gradually adding deionized water into the solutions of the azo polymers in N,N‐dimethylformamide. Laser light scattering analysis and transmission electron microscopy observations show that although both azo polymers can form uniform colloidal spheres in the dispersions, the molecular weight and its distribution show significant effects on the colloid formation process and the sizes of the colloidal spheres formed in the process. Upon irradiation with a linearly polarized Ar+ laser beam for a period of time, the azo polymer microspheres show the elongated deformation along the polarization direction of the actinic light. image

Study the nonlinear optical property of pull/push type azo dye-doped polymer using 633nm He–Ne laser

Azo dyes with different pull/push substituents are selected as photosensitive molecules. Guest–host amorphous azo polymer samples are prepared by doping these azo dyes directly in poly(methyl methacrylate) polymeric matrices. Nonlinear optical properties of these pull/push type azo dye-doped polymers are investigated using the Z-scan experiment. The influence of the pull/push substituents and the azo dye concentration on the nonlinear optical property is studied.

Temperature dependent characteristics of photo-induced birefringence in different types of azo materials

At different temperatures, a semiconductor laser with a wavelength of 650 nm is used as probe light, and an Nd:YAG continuous laser with a wavelength of 532 nm is selected as pump light. The azo samples are placed between a pair of orthogonal polarizers with the vertical direction clockwise and counterclockwise 45 degrees, respectively. The polarization direction of the pump light is set to be the vertical direction. In order to reduce the effect of the stray light, a chopper is placed in the optical path of the probe light. The signal of photo-induced birefringence is recorded by a phase-locked amplifier (NF-LI5640). The photo-induced birefringences of the doped azo material, the azo polymer and the azo liquid crystal polymer are measured respectively, and the dynamic processes of photo-induced birefringence are fitted by a double e-index model. The experimental results show that with the influence of the pump light, photo-induced birefringences of the three types of azo materials rise rapidly at first and then gradually tend to reach their own saturation state because of the photo-induced cis and trans isomerism and the photo-induced molecular orientation properties of azo molecules. The photo-induced birefringence shows a tendency to increase at first and then decrease with the temperature increasing, which can be understood as a competitive mechanism. The photo-induced birefringence depends on the photo-induced orientation and irregular thermal motions of azo groups. In the range below the glass transition temperature of the samples, the increase of the temperature of samples contributes to the rearrangement of the azo molecules due to the influence of the pump light. When the temperature of the samples is higher than the glass transition temperature, molecular chains begin to move. The irregular thermal motions of azo components and polymer molecules are aggravated. This destroys the orientations of the polymer molecules and results in the drop of the photo-induced birefringence. Comparing the doped azo material with the azo polymer sample, the azo liquid crystal polymer sample exhibits not only a larger photo-birefringence, but also the photo-induced birefringence that does not change obviously after the pump light has been turned off, which means that the azo liquid crystal polymer sample has long optical storage properties. This shows that the azo liquid crystal polymer material is an ideal polarization-sensitive optical recording medium, which is expected to be used in the fields of optical storage, polarization holography and optical information processing.

Janus second-order nonlinear optical dendrimers: their controllable molecular topology and corresponding largely enhanced performance.

A new type of Janus dendrimers, consisting of two different side dendrons with the dipole orientation of the second-order nonlinear optical (NLO) chromophore moieties partially in a non-centrosymmetric direction, was intelligently designed and synthesized in order to enhance the macroscopic NLO performance and break through the limitation of NLO efficiency in the current molecular topological structure of azo chromophore-based polymers. This kind of Janus dendritic structure was constructed by the combination of convergent and divergent methods, with the utilization of a powerful "click chemistry reaction". The obtained three dendrimers, D-13N, D-17N and D-21N, show very high NLO performance, especially the dramatically enhanced NLO coefficient of 299 pm V-1 for D-13N, which is the highest value ever reported for polymers containing a simple azo chromophore. The new dendrimers provide a clear structure-properties relationship between high NLO efficiency and the controllable molecular topology with the non-centrosymmetrical alignment of dipole orientation, thus opening up a new avenue for the further development of NLO dendrimers with high performance and more importantly providing some clues for the rational design of functional dendrimers with controllable molecular topology.

Induction of supramolecular chirality by chiral solvation in achiral Azo polymers with different spacer lengths and push–pull electronic substituents: where will chiral induction appear?

Effects of achiral azobenzene polymers with different spacer lengths and push–pull electronic substituents on supramolecular chirality induced by chiral limonene are reported in detail.

Исследование локальной подвижности азо-полимеров по колебательным спектрам хромофоров

Исследование локальной подвижности азо-полимеров по колебательным спектрам хромофоров

Azo‐Polymer Janus Particles Assembled by Solvent‐Induced Microphase Separation and Their Photoresponsive Behavior

We report the successful fabrication of photoresponsive Janus particles (JPs) composed of an epoxy-based azo polymer and poly(methyl methacrylate) (PMMA). Two representative azo polymers, of which one polymer (BP-AZ-CN) has cyano groups as electron-withdrawing substituents on the azobenzene moieties and the other polymer (BP-AZ-CA) has carboxyl groups as the electron-withdrawing substituents, were adopted for the investigation. The nanoscaled JPs, with a narrow size distribution and different azo polymer/PMMA ratios, were fabricated through self-assembly in solution and as dispersions. Upon irradiation with linearly polarized light (λ=488 nm), two types of photoresponsive behavior were observed for JPs in the solid state. For JPs composed of BP-AZ-CN and PMMA, the light irradiation caused the azo-polymer component to be stretched along the light polarization direction. Conversely, for JPs composed of BP-AZ-CA and PMMA, the azo-polymer component became separated from PMMA component under the same irradiation conditions. These observations are valuable for a deeper understanding of the nature of self-assembly and photoinduced mass-transport at the nanometer scale.

Azo Polymer Janus Particles Possessing Photodeformable and Magnetic-Field-Responsive Dual Functions.

It is of great fundamental and practical significance to endow Janus particles with various field-responsive properties. In this study, a new strategy with a wide range of application possibilities is developed to fabricate JPs composed of a methacrylate-based azo polymer, polystyrene, and Fe3 O4 nanoparticles. The JPs are obtained through microphase separation in a confined volume of the dispersed droplets. The azo polymer and PS are incorporated in JPs in a core-compartmentalized manner, and Fe3 O4 are proved to exist in the azo polymer phase. The JPs show responsive movement in the magnetic field and can be easily oriented with the help of the field. By variation of the intersection angle between the particle symmetrical axis and the polarization direction of the linearly polarized laser beam, different deformation modes are feasibly achieved for the JPs. By exploiting the dual-responsive properties, JPs with designed shapes can be fabricated by exposing the JPs to linearly polarized light.

Synthesis and Characterization of Photoprocessable Lignin-Based Azo Polymer

Lignin-based azo polymer-bearing pseudo-stilbene-type azo chromophores have been synthesized by a post-azo coupling reaction between the modified alkali lignin and diazonium salts of 4-aminobenzoic acid in DMF with high yield. The polymer synthesized was characterized by using spectroscopic methods. Significant dichroism and surface relief patterns could be photoinscribed on the prepared azo polymer films by using appropriate laser beams. Self-assembly of the lignin-based polymer in selective solvents (THF/H2O) can give uniform colloidal spheres, which can be elongated along the polarization direction of the irradiation light. This novel synthesized lignin-based azo polymer could potentially be used for applications such as reversible optical data storage, photoswitching, sensors, and other photo-driven devices, which provide a simple strategy for value-added utilization of lignin biomass resources.

Fabrication of fluorescent surface relief patterns using AIE polymer through a soft lithographic approach

A new aggregation-induced emission (AIE) active polymer (PS-TPE) with high tetraphenylethene (TPE) loading density was synthesized. The synthesized polymer showed significant AIE properties, good solubility and high thermal stability. Soft-lithographic contact printing process by using photoinduced surface relief structures on azo polymer film as masters and duplicated PDMS elastomer as stamps was used to fabricate fluorescent PS-TPE patterns. Various fluorescent structures with high contrast including surface relief gratings, periodically dotted patterns, and quasi-crystal structures can be easily fabricated through this approach. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 1838–1845

Hollow lignin azo colloids encapsulated avermectin with high anti-photolysis and controlled release performance

Lignin-based azo polymer (AL-azo-H) was prepared from alkali lignin (AL) and then used to prepare uniform colloids via self-assembly. Due to the unique UV-blocking performance, AL-azo-H colloids were applied to encapsulate photosensitive pesticide avermectin (AVM). The self-assembled structure of AL-azo-H colloids and their controlled release and anti-photolysis performances for AVM were investigated by dynamic light scattering (DLS), static light scattering (SLS), transmission electron microscopy (TEM) and high performance liquid chromatography (HPLC). Results show that AL-azo-H colloids are hollow spheres. Hollow AL-azo-H colloidal spheres have remarkable AVM encapsulation efficiency as high as 61.49% (w/w). The cumulative release amount of AVM encapsulated by AL-azo-H (AL-azo-H@AVM) after 120h was 84% and the release was still going on. The decomposition rate of AL-azo-H@AVM was less than 41% even after 72h of UV irradiation. Hollow AL-azo-H colloidal spheres showed excellent UV-blocking and controlled release performance for AVM.

Azo Polymer Janus Particles and Their Photoinduced, Symmetry-Breaking Deformation.

We report the successful fabrication of photoresponsive Janus particles (JPs) composed of a methacrylate-based azo polymer (PAZO-ADMA) and poly(methyl methacrylate) (PMMA). The JPs are obtained through microphase separation in a confined volume of the dispersed droplets, which incorporates the azo polymer and PMMA into one single particle in a core-compartmentalized manner. It is observed that several unique types of symmetry-breaking deformations are induced upon irradiation with a linearly polarized laser beam at 488 nm. The JPs with such properties are valuable for fundamental understanding and smart photofabrication in micrometer scale.

Optical tweezing by photomigration.

Photomigration in azo polymers is an area of research that witnessed intensive studies owing to its potential in optical manipulation, e.g., optical tweezing, the physical mechanism of which remains unsolved since its discovery about two decades ago. In this paper, a detailed theoretical study that reproduces the phenomena associated with photomigration is presented, including the physical models and the associated master equations. Polarization effects are discussed and analytical solutions are given to describe the steady-state and the dynamics of photomigration. Such a theory leads to new theoretical experiments relating material properties to light action. A photoisomerization force which is described by a spring-type model is introduced. This force is derived from a harmonic light potential that moves the azo polymer. This force is parenting to optical tweezers, but it is quite different in the sense that it requires photoisomerization to occur. The azo polymer's motion is governed by four competing forces: the photoisomerization force, and the restoring optical gradient and elastic forces, as well as the random forces due to spontaneous diffusion.