Preparation and electro‐optic properties of novel Y‐type polyimides with highly enhanced thermal stability of second harmonic generation

BACKGROUND: In the development of nonlinear optical (NLO) polymers for electro‐optic device applications, stabilization of electrically induced dipole alignment is one of the important criteria. Polyimides for NLO applications have attracted attention because of their high T_g values and high thermal stability. In this work we designed and synthesized a new type of NLO polyimide, in which the pendant NLO chromophores are parts of the polymer backbone. These mid‐type NLO polymers are expected to have the merits of both main‐chain and side‐chain NLO polymers: stabilization of dipole alignment and good solubility. RESULTS: 3,4‐Bis‐(3,4‐dicarboxyphenylcarboxyethoxy)‐4′‐nitrostilbene dianhydride was prepared and reacted with the corresponding aromatic diamine to yield unprecedented Y‐type polyimides containing 3,4‐dioxynitrostilbenyl groups as NLO chromophores, which constituted parts of the polymer backbones. The resulting polyimides are soluble in polar solvents such as dimethylformamide and dimethylsulfoxide. These polymers showed a thermal stability up to 320 °C in thermogravimetric thermograms with T_g values obtained from differential scanning calorimetry thermograms in the range 143–164 °C. The second harmonic generation (SHG) coefficients (d₃₃) of poled polymer films at the 1064 nm^?1 fundamental wavelength were around 9.45 × 10^?18 C. CONCLUSION: The dipole alignment exhibited exceptionally high thermal stability even at 30 °C higher than T_g. There was no SHG decay below 180–190 °C because of the partial main‐chain character of the polymer structure, which is acceptable for NLO device applications. Copyright © 2007 Society of Chemical Industry     

Synthesis and nonlinear optical properties of novel Y‐type polyurethane containing nitrothiazolylazoresorcinoxy groups with highly enhanced thermal stability of second harmonic generation

Novel Y‐type polyurethane 4 containing 4‐(5‐nitro‐2‐thiazolylazo)resorcinoxy groups as nonlinear optical (NLO) chromophores, which are parts of the polymer main chains, was prepared and characterized. Polyurethane 4 is soluble in common organic solvents such as N,N‐dimethylformamide and dimethylsulfoxide. It shows thermal stability up to 280 °C as determined from thermogravimetric analysis with a glass transition temperature obtained from differential scanning calorimetry of about 126 °C. The second harmonic generation (SHG) coefficient (d₃₃) of poled polymer film at 1064 nm fundamental wavelength is 3.78 pm V^?1. Polymer 4 exhibits thermal stability even at 4 °C higher than glass transition temperature, and no significant SHG decay is observed below 130 °C, which is acceptable for NLO device applications. © 2016 Society of Chemical Industry     

Synthesis and nonlinear optical properties of a novel X‐type polyester containing dicyanovinylnitroresorcinoxy groups with enhanced thermal stability of dipole alignment

A novel X‐type polyester (5) containing 4‐(2′,2′‐dicyanovinyl)‐6‐nitroresorcinoxy groups as nonlinear optical (NLO) chromophores, which constitute parts of the polymer backbone, was prepared and characterized. Polyester 5 is soluble in common organic solvents such as N,N‐dimethylformamide and acetone. Polyester 5 shows thermal stability up to 300 °C from thermogravimetric analysis with a glass transition temperature obtained from differential scanning calorimetry of near 108 °C. The second harmonic generation (SHG) coefficient (d₃₃) of poled polymer films at the 1064 nm fundamental wavelength is 2.99 pm V^?1. The dipole alignment exhibits thermal stability even at 7 °C above the glass transition temperature, and no significant SHG decay is observed below 115 °C due to the partial main‐chain character of the polymer structure, which is acceptable for NLO device applications. © 2013 Society of Chemical Industry     

Molecular design,synthesis, and electro‐optic properties of novel Y‐type polyesters with high thermal stability of second harmonic generation

3,4‐Di‐(2′‐hydroxyethoxy)‐4′‐nitrostilbene was prepared and condensed with terephthaloyl chloride, adipoyl chloride, and sebacoyl chloride to yield novel Y‐type polyesters containing NLO‐chromophore dioxynitrostilbenyl groups, which constituted parts of the polymer backbone. Polymers were found soluble in common organic solvents such as acetone and N,N‐dimethylformamide. They showed thermal stability up to 300 °C in thermogravimetric analysis with glass‐transition temperatures obtained from differential scanning calorimetry in the range 110–152 °C. The second harmonic generation (SHG) coefficients (d₃₃) of poled polymer films at a 1064 cm^?1 fundamental wavelength were around 3.51 × 10^?8 esu. The dipole alignment exhibited high thermal stability even at 10 °C higher than the glass‐transition temperature, and there was no SHG decay below 120 °C for one of these polymers due to the partial main‐chain character of polymer structure, which was acceptable for NLO device applications. Copyright © 2005 Society of Chemical Industry     

Synthesis and electro‐optical properties of novel Y‐type polyurethanes containing dioxynitrostilbene

3,4‐Di‐(2′‐hydroxyethoxy)‐4′‐nitrostilbene (2) was prepared by the reaction of 2‐iodoethanol with 3,4‐dihydroxy‐4′‐nitrostilbene. Diol 2 was condensed with 2,4‐toluenediisocyanate, 3,3′‐dimethoxy‐4,4′‐biphenylenediisocyanate and 1,6‐hexamethylenediisocyanate to yield novel Y‐type polyurethanes 3–5 containing dioxynitrostilbene as a non‐linear optical (NLO)‐chromophore. Polymers 3–5 were soluble in common organic solvents, such as acetone and DMF. These polymers showed thermal stability up to 280 °C in TGA thermograms with T_g values in the range of 100–143 °C in DSC thermograms. The approximate lengths of aligned NLO‐chromophores of the polymers estimated from AFM images were around 2 nm. The SHG coefficients (d₃₃) of poled polymer films were around 4.5 × 10^?8 esu. Poled polymer films had improved temporal and long‐term thermal stability owing to the hydrogen bonding of urethane linkage and the main‐chain character of the polymer structure, which are acceptable for NLO device applications. Copyright © 2004 Society of Chemical Industry     

Synthesis and electro‐optic properties of novel polyurethane containing the nitrophenylazoresorcinoxy group

A novel Y‐type polyurethane (polyurethane 3) containing 4‐(4‐nitrophenylazo)resorcinoxy groups as nonlinear optical (NLO) chromophores, which constitute part of the polymer backbone, was prepared and characterized. Polyurethane 3 is soluble in common organic solvents such as acetone and N,N‐dimethylformamide. It shows thermal stability up to 270 °C from thermogravimetric analysis with a glass transition temperature obtained from differential scanning calorimetry of 102 °C. The second harmonic generation (SHG) coefficient (d₃₃) of the poled polymer film at 1064 nm fundamental wavelength is 2.06 pm V^?1. Polymer 3 exhibits thermal stability up to T_g, and no significant SHG decay is observed below 100 °C, which is acceptable for nonlinear optical device applications. Copyright © 2012 Society of Chemical Industry     

Synthesis of novel T-type nonlinear optical polyester with enhanced thermal stability of second harmonic generation for electro-optic applications

2,5-Di-(2′-hydroxyethoxy)benzylidenemalononitrile (3) was prepared and condensed with terephthaloyl chloride to yield novel T-type polyester (4) containing 2,5-dioxybenzylidenemalononitrile groups as NLO-chromophores, which are parts of the polymer backbones. The resulting polymer 4 was soluble in common organic solvents such as acetone and DMF and showed thermal stability up to 280 °C with T _g of 83 °C. The second harmonic generation (SHG) coefficient (d ₃₃) of poled polymer film at the 1,064 nm fundamental wavelength was around 4.46 × 10⁻⁹ esu. The dipole alignment exhibited high thermal stability even at 10 °C higher than T _g, and there was no SHG decay below 95 °C due to the partial main-chain character of polymer structure, which was acceptable for NLO device applications.     

Synthesis of novel poly(vinyl ether)s containing the oxybenzylidenemalononitrile group as a nonlinear optical chromophore,and their electro‐optic properties

2,4‐Di‐(2′,2′‐dicyanovinyl)‐1‐(2′‐vinyloxyethoxy)benzene and 2,4‐di‐(2′‐carbomethoxy‐2′‐cyanovinyl)‐1‐(2′‐vinyloxyethoxy)benzene were prepared by condensation of 4‐(2′‐vinyloxyethoxy)isophthaldehyde with malononitrile and methyl cyanoacetate, respectively. The two vinyl monomers were polymerized with boron trifluoride etherate as a cationic initiator to yield poly(vinyl ether)s containing two oxybenzylidenemalononitrile and oxybenzylidenecyanoacetate groups, which are effective chromophores for second‐order nonlinear optical applications. These polymers were soluble in common organic solvents such as acetone and dimethyl sulforide. They showed thermal stabilities up to 300 °C from thermogravimetric analysis (TGA), with differential scanning calorimeter (DSC) thermograms giving T_g values in the range 73–87 °C. The second harmonic generation (SHG) coefficients (d₃₃) of poled polymer films were around 1.8 × 10^?9 esu, and these polymers showed good long‐term thermal stability for 60 days at room temperature, which is acceptable for nonlinear optical (NLO) device applications. Copyright © 2004 Society of Chemical Industry     

Enhancement of nonlinear optical and thermal properties of polyurethanes by modifying the chromophores with fused heterocyclic and pyrimidine rings

This article describes the synthesis of substituted triazolo[3,4‐b]‐thiadiazole heterocycles based nonlinear optical (NLO) responsive chromophores. To enhance the NLO properties of the chromophores, the pyrimidine ring was introduced with an appropriate π‐bonding. With these chromophores, different series of polyurethanes were prepared by condensation with tolylene‐2,4‐diisocyanate and 3,3′‐dimethoxy‐4,4′‐biphenylene diisocyanate. The structure of the resulting chromophores and polyurethanes was confirmed using Fourier transform infrared, proton nuclear magnetic resonance, and Carbon Hydrogen Nitrogen (CHN) analyzer. The inherent viscosities (η_inh) of the polyurethanes measured by Ubbelohde viscometer were in the range of 0.2324–0.2760 dl/g. Thermal behavior of the polyurethanes was investigated using differential scanning calorimetry and thermogravimetric analysis. The molecular orientation in polyurethane films was induced by a corona poling, and this was ascertained using ultraviolet‐visible spectrophotometer and atomic force microscope. The thicknesses and refractive indices of thin films were determined by an Ellipsometer. Polyurethanes exhibited excellent solubility in most of the common organic solvents. The second harmonic generation (SHG) coefficients (d₃₃) of the poled polyurethanes ranged from 63.20 and 95.32 pm/V at 532 nm. None of the polyurethanes showed SHG decay below 100°C, and retained 95% of the signal even up to 500 h. The resulting enhanced NLO efficiency and longer temporal stability make these polyurethanes as promising candidates for photonic devices. POLYM. ENG. SCI., 59:500–509, 2019. © 2018 Society of Plastics Engineers     

Synthesis and properties of novel X-type polyurethane containing dicyanovinylnitrocatechol of enhanced SHG thermal stability for electro-optic applications

Novel X-type polyurethane 5 containing 4-(2′,2′-dicyanovinyl)-5-nitrocatecholic groups as nonlinear optical chromophores, which constitute parts of the polymer backbone, was prepared and characterized. Polyurethane 5 is soluble in common organic solvents such as acetone and N,N-dimethylformamide. It shows thermal stability up to 270 °C from thermogravimetric analysis with a glass-transition temperature obtained from differential scanning calorimetry thermogram of around 113 °C. The second harmonic generation (SHG) coefficient (d ₃₃) of poled polymer film at 1,064 nm fundamental wavelength is around 5.72 × 10^?9 esu. The dipole alignment exhibits a thermal stability even at 7 °C higher than glass-transition temperature, and there was no SHG decay below 120 °C due to the partial main-chain character of the polymer structure, which is acceptable for nonlinear optical device applications.     

Preparation of novel polyimides with high thermal stability of dipole alignment for electro-optic applications

3,4-Bis-(3,4-dicarboxyphenylcarboxyethoxy)-1-(2,2-dicyanovinyl)benzene dianhydride (4) was prepared and reacted with 1,4-phenylenediamine and 4,4’-oxydianiline to yield novel Y-type polyimides 5-6 containing 3,4-dioxybenzylidenemalononitrile groups as NLO-chromophores, which constitute parts of the polymer backbones. The resulting polyimides 5-6 were soluble in polar solvents such as acetone and N,N-dimethylformamide. Polymers 5-6 showed a thermal stability up to 330 °C in thermogravimetric analysis thermograms with T _g values obtained from differential scanning calorimetry thermograms in the range of 181–190 °C. The second harmonic generation (SHG) coefficients (d ₃₃) of poled polymer films at the 1064 nm fundamental wavelength were around 4.73×10^-9 esu. The dipole alignment exhibited a thermal stability even at 20 °C higher than the glass-transition temperatures, there was no SHG decay below 200 °C because of the partial main chain character of polymer structure, which was acceptable for nonlinear optical device applications.     

Synthesis of novel polyurethanes containing dioxybenzylidenecyanoacetate,as non‐linear optical chromophores and their properties

Methyl 3,4‐di‐(2′‐hydroxyethoxy)benzylidenecyanoacetate (3) was prepared by hydrolysis of methyl 3,4‐di‐(2′‐vinyloxyethoxy)benzylidenecyanoacetate (2). Diol 3 was condensed with 2,4‐toluenediisocyanate, 3,3′‐dimethoxy‐4,4′‐biphenylenediisocyanate, and 1,6‐hexamethylenediisocyanate to yield polyurethanes 4, 5 and 6 containing the non‐linear optical (NLO) chromophore 3,4‐dioxybenzylidenecyanoacetate. The resulting polyurethanes 4–6 were soluble in common organic solvents such as acetone and DMF. T_g values of the polymers obtained from DSC thermograms were in the range 80–102 °C. Polymers 4–6 showed thermal stability up to 300 °C in TGA thermograms, and electro‐optic coefficients (r₃₃) of the poled polymer films were in the range 10–12 pm V^?1 at 633 nm, which are acceptable for NLO device applications. © 2002 Society of Chemical Industry     

Synthesis of novel polyimide with highly enhanced thermal stability of second harmonic generation for electro-optic applications

2,3-Bis-(3,4-dicarboxyphenylcarboxyethoxy)-1-(2,2-dicyanovinyl)benzene dianhydride (4) was prepared and reacted with 1,4-phenylenediamine to yield novel Y-type polyimide 5 containing 2,3-dioxybenzylidenemalononitrile group as NLO-chromophores, which constitute parts of the polymer backbones. The resulting polyimide 5 was soluble in polar solvents such as acetone and N,N-dimethylformamide. Polymer 5 showed a thermal stability up to 330 °C in thermogravimetric analysis thermogram with T _g value obtained from differential scanning calorimetry thermogram near 190 °C. The second harmonic generation (SHG) coefficient (d ₃₃) of poled polymer films at the 1064 nm fundamental wavelength was around 3.15×10^-9 esu. The dipole alignment exhibited a thermal stability even at 20 °C higher than the glass-transition temperature, and there was no SHG decay below 210 °C because of the partial main chain character of polymer structure, which was acceptable for nonlinear optical device applications.     

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 main‐chain,second‐order,nonlinear optical polyurethanes with isolation moieties and zigzag structures

In this study, two main‐chain second‐order nonlinear optical (NLO) polyurethanes were successfully prepared with indole‐based chromophores. The introduced phenyl isolation group and the continuous zigzag polymer backbone were found to be helpful for effectively decreasing the intermolecular dipole–dipole interactions and enhancing the NLO properties of the resulting polymers. The studied polymers exhibited good optical transparency, high thermal stability, and excellent NLO effects; this indicated that the nonlinearity–stability trade‐off and nonlinearity–transparency trade‐off could be alleviated by this newly designed polymer system. Poly{4‐anilinocarbonyl[N‐ethoxyl‐5‐phenyl‐3‐azo(2′‐oxyethylene‐4′‐nitrobenzene)indole]carbonylimino} with a zigzag backbone showed a large second harmonic generation coefficient (d₃₃) value of 88.4 pm/V. However, poly{5‐naphthyliminocarbonyl[N‐ethoxyl‐5‐phenyl‐3‐azo(2′‐oxyethylene‐4′‐nitrobenzene)indole]carbonylimino} (PUAZN) with a continuous zigzag structure exhibited a higher d₃₃ value of 116.2 pm/V, which was attributed to the unique rigid and zigzag linkage of 1,5‐naphthalene as the isolation spacer. The enhanced NLO efficiency and relatively longer term temporal stability made PUAZN as a promising candidate for practical applications in photonic devices. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42974.     

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     

Synthesis and characterization of nonlinear optical side-chain polyimides containing the thiadiazole chromophores

Thermally stable second-order nonlinear optical (NLO) polyimides were synthesized using a standard condensation polymerization technique. The polyimides were prepared from 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and pyromellitic dianhydride (PMDA) with two aromatic azo- and diazo-diamine derivatives as the NLO chromophores. The resulting polyimides were characterized by FTIR, ¹H-NMR, UV-vis spectroscopies, differential scanning calorimetry, thermogravimetric analysis, and gel permeation chromatography. The weight-average molecular weights of polyimides determined by gel permeation chromatography (GPC) were in the range of 32,100 to 39,300 (M_w/M_n = 1.58–1.74). All the polyimides exhibited an excellent solubility in many of the aprotic polar organic solvents, manifesting that these polyimides offer good processability. The glass transition temperature for the resulting polyimides was in the range of 152 to 194°C and most of them showed high thermal stability. Particularly, the polyimides containing diazo group and PMDA backbone showed an enhanced thermal stability and glass transition temperature. The second harmonic generation (SHG) coefficients (d₃₃) of the poled polyimide films range from 43.71 to 80.49 pm/V at 532 nm. Further, it is noticed that there was no SHG decay below 180°C because of the partial main-chain character of the polyimide structure, which is acceptable for nonlinear optical device applications. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

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     

Synthesis of polyurethanes containing dioxynitrostilbene as a NLO-chromophore and their properties

Summary 3,4-Di-(2'-hydroxyethoxy)-4'-nitrostilbene (2) were prepared by the reaction of 2-iodoethanol with 3,4-dihydroxy-4'-nitrostilbene (1). Diol 2 was condensed with 2,4-toluenediisocyanate and 3,3'-dimethoxy-4,4'-biphenylenediisocynate to yield polyurethanes 3 and 4 containing the NLO-chromophore 3,4-dioxy-4'-nitrostilbene. Polymers 3 and 4 were soluble in common organic solvents such as acetone and DMSO. T _g value of the resulting polymers was in the range of 109–114°C. Electrooptic coefficient (r₃₃) of the poled polymer films were in the range of 20–25 pm/V at 633 nm. Polymers 3 and 4 showed a thermal stability up to 300°C in TGA thermograms, which is acceptable for NLO device applications. Received: 29 September 1999/Revised version: 19 November 1999/Accepted: 25 November 1999     

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