Synthesis and characterization of azo‐based methacrylate polymers with methoxy and nitro end groups for nonlinear optical applications

One new and three already described azobased methacrylate monomers with methoxy and nitro end groups and spacer length 2 and 6 were synthesized. These monomers were copolymerized with methyl methacrylate and the monomers as well as copolymers were characterized by classical spectroscopy techniques (FTIR, NMR, and UV‐VIS), gel permeation chromatography (GPC), elemental analysis and thermal analysis (TGA and DSC). The glass transition temperature of the polymers was found to be above room temperature and thermal decomposition temperatures above 100°C. All the polymers were amorphous in nature and formed excellent homogeneous films with good optical transparency. The polymer films coated on indium tin oxide glass slides were poled and their order parameters were calculated to check the stability of oriented dipoles. Few samples were also studied for their second harmonic generation properties. Temporal stability, checked up to 120 h at room temperature, was found to be quite satisfactory. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 3497–3504, 2007     

Synthesis and characterization of accordion main‐chain azo‐dye polymers for second‐order optical non‐linearity

New type accordion polymers with azo‐dye chromophores as the major segments (up to 70% by weight) of the main chain for second optical non‐linearity (NLO) are designed and synthesized by the Knoevenagel polycondensation between bis(carboxaldehyde) containing azobenzene and bis(cyanoacetate) comonomers. Several important properties for NLO application, such as solubility and thermal stability, are investigated, and the effects of linkage groups on the physical properties of polymers are also discussed in some detail. Poled films of one of these polymers show a relatively high resonant d₃₃ value of 33 pm V⁻¹ by second harmonic generation (SHG) measurement, and their order parameter, which is determined to be 0.20 by UV–vis measurement, keep almost constant for 240 h at ambient temperature. © 2000 Society of Chemical Industry     

Synthesis and characterization of side‐chain polyimides for second‐order nonlinear optics via a post‐azo‐coupling reaction

A two‐step, generally applicable synthetic approach for nonlinear optical (NLO) side‐chain polyimides was developed. This included the preparation of a preimidized, organosoluble polyimide with benzene moiety pendant from main chains, followed by the covalent bonding of the NLO chromophores onto the polyimide backbone via a post‐azo‐coupling reaction. The degree of functionalization of polyimides was estimated by UV‐VIS spectroscopy. The glass transition temperature (T_g) of a polyimide decreased by only 10–20°C after the functionalization, which was much smaller than the decrease in T_g when the chromophores were chemically bonded to the polyimide main chains through an ether linkage using a post‐Mitsunobu condensation. The solubility and thermal stability of polyimides were also studied. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 290–295, 2000     

Thermally stable interpenetrating polymer networks for second‐order nonlinear optical materials

We report several kinds of interpenetrating polymer networks (IPNs) with nonlinear optical (NLO) properties. DMA spectra show that the two components of the IPNs have good compatibility with each other. The NLO materials have good optical transparency. The thermal stability of alignment was improved and the poled order remained very high. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 7–9, 1999     

Synthesis and photovoltaic device studies of azo‐linked low‐bandgap polymers

We report the synthesis of a series of new polymers containing azo linkage as a part of the main chain. The monomer 1,2‐bis(7‐bromo‐9,9‐dioctyl‐9H ‐fluoren‐2‐yl)diazene was synthesized using a precursor approach which avoids non‐selective bromination and was copolymerized with various donor or acceptor units. The homopolymer poly[1,2‐bis(9,9‐dioctyl‐9H ‐fluoren‐2‐yl)diazene] ( P1 ) as well as the copolymers poly[1‐(9,9‐dioctyl‐9H ‐fluoren‐2‐yl)‐2‐(9,9,9′,9′‐tetraoctyl‐9H ,9′H ‐[2,2′‐bifluoren]‐7‐yl)diazene] ( P2 ), poly[1‐(9,9‐dioctyl‐7‐(4‐octylthiophen‐2‐yl)‐9H ‐fluoren‐2‐yl)‐2‐(9,9‐dioctyl‐9H ‐fluoren‐2‐yl)diazene] ( P3 ) and poly[4‐(7‐((9,9‐dioctyl‐9H ‐fluoren‐2‐yl)diazenyl)‐9,9‐dioctyl‐9H ‐fluoren‐2‐yl)benzo[c ][1,2,5]thiadiazole] ( P4 ) were synthesized by Suzuki polymerization. The copolymers poly[1‐(7‐(4,4‐dioctyl‐4H ‐cyclopenta[1,2‐b :5,4‐b ′]dithiophen‐2‐yl)‐9,9‐dioctyl‐9H ‐fluoren‐2‐yl)‐2‐(9,9‐dioctyl‐9H ‐fluoren‐2‐yl)diazene] ( P5 ) and poly[4‐(5‐(7‐((9,9‐dioctyl‐9H ‐fluoren‐2‐yl)diazenyl)‐9,9‐dioctyl‐9H ‐fluoren‐2‐yl)‐4‐octylthiophen‐2‐yl)‐7‐(4‐octylthiophen‐2‐yl)benzo[c ][1,2,5]thiadiazole] ( P6 ) were synthesized by direct arylation polymerization reaction. Polymers synthesized using the direct arylation method show good molecular weight, with absorption maxima in the range 500 to 532 nm. P5 and P6 possess low optical bandgaps of 1.81 and 1.86 eV, respectively. A power conversion efficiency of 0.53% with open circuit voltage of 0.53 V, short circuit current density of 3.1 mA cm^?2 and fill factor of 29% has been achieved with C71‐PCBM as acceptor in bulk heterojunction solar cells fabricated with P5 as donor. © 2016 Society of Chemical Industry     

Synthesis and properties of novel crosslinkable second‐order nonlinear optical polymers based on 2,3,4,5,6‐pentafluorostyrene

Two crosslinkable second‐order nonlinear optical polymers were prepared by copolymerization of 2,3,4,5,6‐pentafluorostyrene, styrene (St), glycidyl methacrylate (GMA) and 1‐(4‐nitrophenyl)‐2‐(4‐{[2‐(methacryloyloxy) ethyl] ethylamino}‐phenyl) diazene (DR1M) via the sealed‐tube reaction technique. These polymers were characterized using ¹H, ¹³C and ¹⁹F NMR spectroscopy, gel permeation chromatography (GPC), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The crosslinkable polymers have high molecular weights, good organosolubility, excellent film‐forming properties and high glass transition (106–110 °C) and thermal decomposition temperatures (290–350 °C) after being crosslinked. Furthermore, the polymer films possess not only high values (12–16 pm V^?1) of electro‐optical coefficient (r₃₃) at 1.3 µm wavelength but also low optical loss (1.7 dB cm^?1) at 1.55 µm wavelength, which is of interest for applications in electro‐optical devices. Copyright © 2004 Society of Chemical Industry     

Development of polyurethanes with azo‐type chromophores for second‐order nonlinear optical applications

Active nonlinear optical nitro‐substituted thiazole, benzothiazole, and thiadiazole chromophores were prepared and condensed with tolylene‐2,4‐diisocyanate (TDI) and 4,4′‐methylenedi(phenyl isocyanate) (MDI) to yield a series of polyurethanes. The resulting polyurethanes were characterized with Fourier transform infrared, proton nuclear magnetic resonance, and ultraviolet–visible spectroscopy, differential scanning calorimetry, thermogravimetric analysis, and gel permeation chromatography. The weight‐average molecular weights of the polyurethanes ranged between 19,500 and 28,000 (weight‐average molecular weight/number‐average molecular weight = 1.71–2.15). All the polyurethanes exhibited excellent solubility in most common organic solvents, and this indicated that these polyurethanes offered good processability. The glass‐transition temperatures (T_g's) of the polyurethanes were in the range of 166–204°C. Among the polyurethanes, chromophores containing the nitrothiazole moiety exhibited lower T_g values in comparison with those of chromophores containing nitrobenzothiazole and nitrothiadiazole moieties. This was attributed to the small size of the nitrothiazole moiety in the polyurethane matrix. The polyurethanes containing a TDI backbone demonstrated relatively high T_g values in comparison with those of the polyurethanes containing an MDI backbone. This was a result of an enhancement of the rigidity caused by the incorporation of a toluene ring into the polyurethane backbone. The second harmonic generation (SHG) coefficients of the poled polyurethane films ranged from 67.29 to 105.45 pm/V at 1064 nm. High thermal endurance of the poled dipoles was observed for all the polyurethanes. This was attributed to the formation of extensive hydrogen bonds between urethane linkages. Furthermore, none of the developed polyurethanes showed SHG decay below 150°C, and this signified their acceptability for nonlinear optical devices. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Fumaryl chloride and maleic anhydride–derived crosslinked functional polymers for nonlinear optical waveguide applications

The synthesis, processing, and characterization of new crosslinked functional polymer thin films derived from fumaryl chloride and maleic anhydride is presented. Experimental data demonstrated that this is a versatile, convenient, and cost‐effective method of fabricating ultrastructure crosslinked and functional polymer thin films for potential nonlinear optical (NLO) or other applications where molecular orientation is required. The unsaturated and processable polyester thin films are capable of crosslinking in air to form a hardened lattice under a variety of conditions, including both thermal and photoinitiated crosslinking. The thermal stability of the second harmonic (SHG) signal for a crosslinked NLO thin film was stable at temperatures up to 150°C, which is in contrast to uncrosslinked polymers whose SHG signals typically decreased over 50% below 100°C. Because of the lack of NH/OH groups and their vibrational overtones in the polymer, these crosslinked polyester systems have a great potential for low optical loss applications at 1550 nm communication wavelength. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 317–322, 2004     

Synthesis and characterization of biodegradable and charged salen‐based polymers

The goal of this study was to synthesize novel biodegradable charged polymers for medical applications. The polymers synthesized were metal‐coordinated salicylidene‐based copolymers. The linear copolymers were prepared by polycondensation of the metal‐coordinated salicylidene monomer with acyl or aryl dichloride. Structure analysis was carried out by ¹H and ¹³C NMR, FTIR, and elemental analysis. Physicochemical evaluation was carried out using DSC and thermogravimetry. The surface properties were analyzed by contact angle measurements and the crystallinity was determined by polarizing microscopy and AFM. Finally, polymer electrical conductivity and biocompatibility were examined. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2568–2577, 2006     

Physiochemical,circular dichroism‐induced helical conformation and optical property of chitosan azo‐based amino methanesulfonate complex

We have demonstrated the efficient procedure for the preparation of chitosan azo‐based amino methanesulfonate complex in isopropyl alcohol under mild condition. The ionic complexation between chitosan and {4‐[(4‐nitrophenyl)azo]phenyl}amino methanesulfonate is confirmed by ultraviolet (UV) and Fourier transform infrared spectroscopy. The circular dichroism spectra of chitosan complex showed positive at λ = 298 nm band with 3.88 mdeg having UV absorbance maximum up to a narrow band at λ= 290 nm in dimethyl sulfoxide, indicating that the polymer adopted helical (right handed) secondary structure. Physical properties, thermal stability, and surface morphology were analyzed by X‐ray diffraction, thermogravimetric analysis, differential scanning calorimetry and scanning electron microscopy. Optical properties of chitosan complex are evaluated by photoluminescence spectroscopy that showed blue shift (λ_em) peak at 400 nm at excitation wavelength 325 nm. Overall, it may open new perspectives for the use of chitosan azo‐based biohybrid in biomedical applications. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis and characterization of novel diazenes bearing pyrrole, thiophene and thiazole heterocycles as efficient photochromic and nonlinear optical (NLO) materials

Two series of novel thermally stable second-order nonlinear optical (NLO) and photochromic chromophores have been designed and synthesized. The two series of compounds were based on different combinations of donor groups (pyrrole or thienylpyrrole) which act simultaneously as π-conjugated bridges, together with diazoaryl or diazothiazolyl as acceptor moieties. Their photochromic and electrochemical behavior were characterized, while hyper-Rayleigh scattering (HRS) was employed to evaluate their second-order nonlinear optical properties. The results of these studies have been critically analyzed together with two other related compounds reported earlier from our laboratories in which the thienylpyrrole system was used as the donor group keeping the functionalized diazoaryl as acceptor moiety. The measured molecular first hyperpolarizabilities and the observed photochromic behavior showed strong variations for the different donor systems used (pyrrole or thienylpyrrole) and were also sensitive to the acceptor strength of the diazenehetero(aryl) moiety.The thienylpyrrole based compounds endowed with extended π-conjugated bridges and stronger donor auxiliary effects in comparison to the pyrrole compounds, when coupled to the stronger acceptor diazo(hetero)aryl groups gave rise to significantly larger hyperpolarizabilities (β = 274-415 × 10⁻³⁰ esu) for an incident wavelength of 1064 nm. These compounds also displayed improved photochromic behavior with very fast response to the visible light stimulus (1.5 s) and fast thermal return to the original forms (2-3 s).     

Synthesis of a photo‐crosslinked stable nonlinear optical polymer and application to external electro‐optic measurement

A photo‐crosslinked side‐chain second‐order nonlinear optical polymer was synthesized with bis‐phenol‐A as the polymer backbone, p‐nitroaniline as the chromophore and cinnamyl group as the photo‐sensitizer. The characterization of the polymer was made by nuclear magnetic resonance, infrared, ultraviolet‐vis, and dynamic mechanical analysis methods. An electro‐optic film was obtained by spin coating of the polymer and corona poling then photo‐crosslinking reaction. An external electro‐optic measurement system was established based on the film and reflective light path configuration, and successfully applied to measure the electrical signals propagating on the under‐test circuits. The poled and crosslinked film showed high glass transition temperature (160°C) and improved chromophore orientation stability. The measuring principle was analyzed by electro‐optic tensor matrix and index ellipsoid methods. The results showed that the designed polymer film had the linear electro‐optic effect, the voltage sensitivity of the system was measured to be 5 mv/ at the condition of 1 kHz input signal. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1506–1512, 2000     

Synthesis and characterization of biodegradable lactic acid‐based polymers by chain extension

BACKGROUND: Poly(lactic acid) (PLA), coming from renewable resources, can be used to solve environmental problems. However, PLA has to have a relatively high molecular weight in order to have acceptable mechanical properties as required in many applications. Chain‐extension reaction is an effective method to raise the molecular weight of PLA. RESULTS: A high molecular weight biodegradable lactic acid polymer was successfully synthesized in two steps. First, the lactic acid monomer was oligomerized to low molecular weight hydroxyl‐terminated prepolymer; the molecular weight was then increased by chain extension using 1,6‐hexamethylene diisocyanate as the chain extender. The polymer was characterized using ¹H NMR analysis, gel permeation chromatography, differential scanning calorimetry and Fourier transform infrared spectroscopy. The results showed that the obtained polymer had a M_n of 27 500 g mol^?1 and a M_w of 116 900 g mol^?1 after 40 min of chain extension at 180 °C. The glass transition temperature (T_g) of the low molecular weight prepolymer was 47.8 °C. After chain extension, T_g increased to 53.2 °C. The mechanical and rheological properties of the obtained polymer were also investigated. CONCLUSION: The results suggest that high molecular weight PLA can be achieved by chain extension to meet conventional uses. Copyright © 2008 Society of Chemical Industry     

Synthesis, electrochemical and optical studies of new cyanopyridine based conjugated polymers as potential fluorescent materials

In this communication we describe the design and synthesis of four new conjugated polymers (P1-P4) carrying cyanopyridine in their backbone via Wittig condensation technique. Their structures were well established by FTIR, ¹H NMR, elemental analysis and gel permeation chromatographic techniques. They exhibited good thermal stability with the onset decomposition temperature around 300-350 °C in nitrogen atmosphere. Further, their electrochemical, linear and third-order non-linear optical properties have been investigated. The polymers showed low electrochemical band gaps in the range of 1.77-1.99 eV and displayed very good fluorescence emission property in various polar solvents. The fluorescence quantum yields of polymers P1-P4 in tetrahydrofuran (THF) were found to be 35, 42, 38 and 34%, respectively. The effective two-photon absorption coefficients (β) for the polymers were determined by Z-Scan technique and were found to be 1.34 × 10⁻¹¹, 1.24 × 10⁻¹¹, 3.04 × 10⁻¹¹ and 1.85 × 10⁻¹¹ m/W for polymers P1-P4, respectively.     

Third-order nonlinear optical properties and two-photon absorption in polymers doped with p-phenyl sydnone

We report the measurements of the third-order susceptibilities and two-photon absorption in three different polymers doped with p-phenyl sydnone moiety viz., 2-benzylhydrazono-5-(3-p-tolylsydnone-4-yl)1,3,4,-thiadiazine, which is recently synthesized and characterized, with the prospective of reaching a good compromise between processability and high nonlinear optical properties. The measurements were done using nano second Z-scan at 532nm. The Z-scan spectra reveal a large negative nonlinear refraction coefficient n₂ of the order 10⁻¹⁴ cm²/W and a two-photon absorption β, which is determined to be the order of cm/GW. The absorption cross section is 10⁻⁴⁶ cm⁴ s/photon. The molecular second-order hyperpolarizability in PMMA matrix was calculated to be 1.47 × 10⁻³¹ esu, comparable with stilbazolieum derivatives, a well-known class of optical materials for photonics and biophotonics applications. The chromophore shows its optical power limiting behavior in all the three polymer matrices. All these results suggest that this moiety has potential for the application of all-optical limiting and switching devices. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Organically modified inorganic sol‐gel materials for second‐order nonlinear optics

A series of the organically modified inorganic NLO sol‐gel materials based on the prepolymer of alkoxysilanes and an alkoxysilane dye (ASD) have been investigated. Optically clear samples exhibit large second‐order optical nonlinearity (d₃₃ = ∼10.8–54.0 pm/V at 1064 nm) after poling and curing at 220°C for 1 h. The thermal behavior of these NLO sol‐gel materials was studied by temperature‐dependent dielectric relaxation. The results indicate that the crosslinking density of cured NLO sol‐gel materials was increased with increasing alkoxysilane content. Subsequently, better temporal stabilities were obtained for the poled/cured NLO sol‐gel materials with a higher alkoxysilane content. Moreover, the structural influence of alkoxysilanes on the thermal behavior and second‐order nonlinearity was also studied for these NLO sol‐gel materials. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1852–1859, 2001     

Preparation of nano‐ and microparticles through self‐assembly of azobenzene‐pendent ionomers

The particle formation of azobenzene‐containing ionomers, through self‐assembly, in aqueous media (THF/H₂O solvent) was studied. The ionomers were synthesized by copolymerization between azobenzene‐pendent methacrylate and methacrylic acid. It was revealed by UV–vis spectra and light scattering measurements that the extent of H‐aggregation of the azobenzene units first decreased, and then increased with increasing volume fraction of H₂O of the solvent. The H₂O fraction at which the extent of H‐aggregation began to increase became lower, when the copolymers contained more azobenzene units. Colloidal particles were prepared by slow addition of various concentrations of aqueous NaOH to the copolymer THF solutions. The hydrodynamic diameters of the particles obtained by the procedures were several hundreds of nanometer. When the azobenzene unit content in the copolymer was smaller, the diameters of the particles became smaller. When the colloidal particles dispersions were cast on a carbon sheet and dried, the particles aggregated and formed larger spherical particles, with diameters of several micrometers. The size of the particles obtained by the drying process became smaller, when higher concentrations of aqueous NaOH solutions were used. Therefore, the particle sizes were controlled by the azobenzene units content in the copolymers and the concentration of aqueous NaOH solutions. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3913–3918, 2006     

Well-defined second-order nonlinear optical polymers by controlled radical polymerization,via multifunctional macromolecular chain transfer agent: Design,synthesis, and characterizations

To address the issue of the aggregation in second-order nonlinear optical (NLO) polymers we developed an approach based on the synthesis of a multifunctional macromolecular chain transfer agent. The controlled monomer insertion polymerization into the main chain by a ‘reversible addition-fragmentation chain transfer’ (RAFT) mechanism allows the spatial arrangement of the NLO chromophores along the polymeric chain in order to obtain sequence-ordered polymers. In a first step, a novel trithiocarbonate based macroinitiator containing the disperse red 19 (DR19) units in the main chain was synthesized by polycondensation; in a second step, this polymeric precursor was applied to the synthesis of a sequentially ordered polymer by controlled insertion radical polymerization of styrene. Size exclusion chromatography (SEC), nuclear magnetic resonance (NMR) data revealed that, (i) for the first time, polystyrenes (PS) bearing DR19 dyes covalently bounded were obtained, and (ii) both the insertion reaction and the length of the polystyrene segments were accurately controlled. Whatever the incorporated dye amount, all the copolymers were soluble in common solvents. Second-order optical nonlinearity in corona-poled thin films was evaluated, and second harmonic coefficients up to 80 pm/V were determined for loading ratio lower than 10 wt-% (DR19/PS). This approach opens up opportunities for the incorporation of more efficient chromophores even in apolar matrices.     

Photoactive polyamideimides synthesized by the polycondensation of azo‐dye diamines and rosin derivative

New rosin‐based photoactive polyamideimides (PAI‐a and PAI‐b) with a large second‐order nonlinear optical coefficient and photoinduced birefringence were synthesized by the polycondensation of rosin–maleic anhydride adduct (RMA) with azo‐dye diamines, 2‐(2‐{ethyl‐[4‐(4‐nitrophenylazo)phenyl]aminoethoxy)benzene‐1,4‐diamine (4a) or 2‐(2‐{ethyl‐[4‐(4‐methylsulfonylphenylazo)phenyl]amino}ethoxy)benzene‐1,4‐diamine (4b). Due to the bulky alicyclic structure of the rosin, these polymers were highly soluble in organic solvents and could easily be processed by spin‐coating into thin films of high optical quality. Fabricated polymer films were very smooth, tough, adhesive to the substrate, and optically clear. Second‐order nonlinear optical coefficients (d₃₃) of the corona‐poled PAI‐a and PAI‐b films were 83 and 54 pm/V, respectively, at the fundamental wavelength of 1064 nm. Birefringences as high as 0.072 for PAI‐a and 0.035 for PAI‐b could be induced and erased repeatedly by the irradiation of linearly polarized and circularly polarized 532‐nm light, respectively. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 687–695, 2001     

Synthesis,characterization and nonlinear optical properties of plasma‐prepared poly(4‐biphenylcarbonitrile) thin films

A novel conjugated polymer, poly(4‐biphenylcarbonitrile) (PBPCN), was prepared using a plasma polymerization technique. The effect of the discharge power on the chemical structure and surface compositions of PBPCN thin films was investigated using Fourier transform infrared, UV‐visible absorption and X‐ray photoelectron spectroscopies. A femtosecond time‐resolved optical Kerr effect technique was applied to investigate the third‐order nonlinearity of the obtained plasma PBPCN thin films. For the first time, a non‐resonant optical Kerr effect and ultrafast response for the PBPCN thin films were observed. Copyright © 2006 Society of Chemical Industry