Synthesis and properties of novel donor–acceptor copolymers based on thiophene and squaraine moieties

Two novel donor–acceptor copolymers were synthesized by Sonogashira cross-coupling of alkyl/alkoxy thiophene and dibromo-substituted squaraine moieties. The structures and properties of these polymers were characterized using FT–IR, NMR, UV–Vis, gel permeation chromatography, and cyclic voltammetry. Both copolymers are readily soluble in common organic solvents. The polymer films exhibit broad absorption in the wavelength range from 300 to 1000 nm with the maximum peaks over 750 nm. Electrochemical studies reveal that the band gaps of the polymers range from 1.05 to 1.36 eV. Compared to the alkyl thiophene, the alkoxy thiophene units can effectively lower the band gap and result in significant red-shift absorption spectrum of the resulted polymer. The strong overlap of the solar spectrum and the extremely low band gaps of the polymers suggest that they may be promising candidates for solar cells.     

Synthesis and properties of nonlinear optical chromophores and polymers containing 6-nitroquinoline as π-electron acceptor

Summary Two nonlinear optical (NLO) methacrylate monomers, 2-methyl-acrylic acid 2-(ethyl-{4-[2-(6-nitro-quinolin-2-yl)-vinyl]-phenyl}-amino)-ethyl ester (5) and 2-methyl-acrylic acid 6-{3-[2-(6-nitro-quinolin-2-yl)-vinyl]-carbazol-9-yl}-hexyl ester (7) were newly synthesized and copolymerized with methylmethacrylate to give NLO polymers, P1 and P2. These polymers were well soluble in organic solvents and showed glass transition temperatures at 145 °C and 114 °C, respectively. The number average molecular weights (Mn) were 26,600 for P1 and 9,300 for P2. The SHG coefficients (d₃₃) of corona-poled films of P1 and P2 measured with 1.064 μm Nd-YAG laser were 32.2 pm/V and 17.6 pm/V, respectively. Received: 29 September 1998/Revised version: 7 December 1998/Accepted: 11 December 1998     

Synthesis and characterization of thiophene-based donor–acceptor type polyimide and polyazomethines for optical limiting applications

In this communication we describe the design and synthesis of four new conjugated polymers (P1–P4) based on 3,4-ditetradecyloxythiophene. The required diamine monomer was prepared by a unique catalyst-free reduction process using hydrazine hydrate. The structures of the intermediates and polymers were established by FTIR, ¹H NMR spectroscopy. Molecular weights of polymers were determined by gel permeation chromatographic (GPC) method. Their electrochemical properties were investigated by cyclic voltammetry and linear optical properties were determined by UV–Visible absorption and fluorescence emission spectroscopic techniques. Further, their nonlinear optical properties were evaluated by Z-scan technique using Nd:YAG laser. These polymers showed strong optical limiting behavior with two-photon absorption (2PA) coefficients of the order of 10^?10 m/W, which are comparable to that of good optical limiting materials reported in the literature. Also, it has been observed that the optical nonlinearity enhanced with the increase in donor–acceptor strength of the polymer backbone.     

Synthesis,characterization and third-order nonlinear optical properties of novel hyperbranched donor–acceptor polyfluorenes based on 1,3,6,8-tertsubstituted carbazole core

Two novel hyperbranched donor–acceptor polyfluorenes based on 1,3,6,8-tertsubstituted carbazole core (4BrCzP1 and 4BrCzP2) were synthesized and characterized. The third order nonlinear optical properties of the materials were studied using Z-scan technique with femtosecond Ti: sapphire laser with delivering pulses of 140 fs at 800 nm. The nonlinear optical refractive index was 9.29 × 10^?8 esu for 4BrCzP1 and 3.19 × 10^?7 esu for 4BrCzP2, respectively. While the third order nonlinear susceptibility was 1.29 × 10^?9 esu for 4BrCzP1 and 4.33 × 10^?9 esu for 4BrCzP2, respectively. The experimental results indicated that the hyperbranched polyfluorenes was a promising candidate in the application of third order nonlinear optical materials.     

Calix[4]arene–carbazole-containing polymers: Synthesis and properties

New highly fluorescent calix[4]arene-containing phenylene-alt-ethynylene-3,6- and 2,7-carbazolylene polymers (CALIX-PPE-CBZs) have been synthesized for the first time and their photophysical properties evaluated. Both polymers were obtained in good isolated yields (70–84%), having M_w ranging from 7660–26,700 g mol⁻¹. It was found that the diethynyl substitution (3,6- or 2,7-) pattern on the carbazole monomers markedly influences the degree of polymerization. The amorphous yellow polymers are freely soluble in several nonprotic organic solvents and have excellent film forming abilities. TG/DSC analysis evidences similar thermal behaviors for both polymers despite their quite different molecular weight distributions and main-chain connectivities (T_g in the range 83–95 °C and decomposition onsets around 270 °C).The different conjugation lengths attained by the two polymers dictates much of their photophysical properties. Thus, whereas the fully conjugated CALIX-PPE-2,7-CBZ has its emission maximum at 430 nm (E_g = 2.84 eV; Φ_F = 0.62, CHCl₃), the 3,6-linked counterpart (CALIX-PPE-3,6-CBZ) fluoresces at 403 nm with a significant lower quantum yield (E_g = 3.06 eV; Φ_F = 0.31, CHCl₃). The optical properties of both polymers are predominantly governed by the intrachain electronic properties of the conjugated backbones owing to the presence of calix[4]arenes along the polymer chain which disfavor significant interchain interactions, either in fluid- or solid-state.     

Highly π-extended polymers based on phenanthro-pyrazine: Synthesis,characterization, theoretical calculation and photovoltaic properties

Two novel narrow bandgap conjugated polymers containing phenanthro-pyrazine unit have been successfully synthesized by the Stille coupling reaction. Comparing to the common polymers containing dithiophen-quinoxaline or dithiophen-thieno[3,4-b]pyrazine moiety, the conjugation degree of these new polymers is extended through the direction perpendicular to the main chain by introducing phenanthrene-9,10-dione to maintain a rigid conjugated bridge. The obtained polymers exhibit solution-processing ability, high thermal stabilities, broad visible absorption bands and narrow optical bandgaps. Theoretical studies disclose that the P2 exhibits wholly coplanar conformation in 1-D and 2-D direction, and the PCE value is 6-folded higher than P1 under the same photovoltaic measurement condition.     

Synthesis and fluorescence properties of a waterborne polyurethane–acrylic hybrid polymeric dye

A waterborne polyurethane–acrylic hybrid polymeric dye was prepared depending on soap-free emulsion polymerization method. The resulting polymeric dye composed of methyl methacrylate (MMA) monomer which was polymerized into polymethyl methacrylate (PMMA) as cores and waterborne polyurethane-based dye was synthesized by anchoring dye monomers (6-amino-2-cyclohexyl-benz[de]isoquinone-1,3-dione) to polyurethane chains as shells. The average particle sizes of the hybrid polymeric dye emulsions were found to be increased with the increase in MMA contents for MMA monomers. Compared with dye monomers, the absorption intensities and fluorescence intensities of the hybrid polymeric dye were enhanced with the increase of particle sizes. This study revealed that enhanced fluorescence intensity of the hybrid polymeric dye was mainly attributed to the hindered formation of exciplexes among dye monomers and an augmented light absorption area. It was found that the fluorescence intensity of the hybrid polymeric dye was increased with increasing temperature and the trend first increased and then decreased with increase in concentration. Furthermore, the fluorescence of the hybrid polymeric dye emulsions was found to be very stable and not sensitive to the fluorescence quencher.     

Synthesis and properties of acrylate functionalized alkyds via a Diels–Alder reaction

The α-eleosterate pendent fatty acid of a tung oil based alkyd was functionalized via a Diels–Alder reaction with three different acrylate groups: (1) 2,2,2-trifluoroethyl methacrylate, (2) 3-methacryloxypropyl trimethoxysilane, and (3) triallyl ether acrylate. The modified alkyds were characterized by using ¹H NMR, ¹³C NMR, and gel permeation chromatography (GPC). The drying time was measured at ambient temperature. The viscoelastic properties of the alkyd-modified films were measured using dynamic mechanical thermal analysis. The viscoelastic and drying time results show that the alkyd modified with siloxane and triallyl group affords a faster drying time, higher crosslink density, and higher glass transition temperature compared to the unmodified alkyd, whereas the fluorinated alkyd possesses surface active properties, but suffers in terms of drying and crosslinking density.     

Synthesis and optical properties of π-conjugated polymers composed of diester-substituted bithiophene and dibenzothiophene or carbazole

Novel π-conjugated polymers composed of diester-subsituted bithiophene and dibenzothiophene (PDBT-DEBT) or N-alkyl carbazole (PCz-DEBT) were prepared via the Stille cross-coupling polymerization using Pd(0) catalyst. The structures of obtained polymers were confirmed by ¹H NMR and IR spectroscopies. Optical properties of the polymers were investigated by UV–vis and photoluminescence spectroscopies. The photoluminescence spectra of the polymers showed strong emission peaks in the green region.     

Synthesis and characterization of a new NLO-active donor–acceptor-type conjugated polymer derived from 3,4-diphenylthiophene

A new donor–acceptor-type conjugated polymer (P1) carrying 3,4-diphenylthiophene, 2,5-dihexyloxybenzene, and 1,3,4-oxadiazole units was synthesized through multistep reactions. The polymer was prepared using a polyhydrazide precursor route. The polymer has a well-defined structure and exhibits good thermal stability, with a decomposition onset temperature in nitrogen of 300 °C. Cyclic voltammetry experiments revealed that the polymer has low-lying LUMO (−3.68 eV) and high-lying HOMO (−5.78 eV) energy levels. The electrochemical band gap was found to be 2.10 eV. The UV-visible absorption spectrum of the polymer presented a maximum at 373 nm, and it displayed bluish-green fluorescence in dilute chloroform solution. The nonlinear optical properties of the new polymer were investigated at 532 nm using the Z-scan technique with nanosecond laser pulses. The polymer exhibited strong optical limiting behavior due to excited state absorption, which was phenomenologically similar to a three-photon absorption (3PA) process. The 3PA coefficient γ was found to be 7 × 10⁻²² m³/W². The studies show that the new polymer (P1) is a promising material for developing efficient photonic devices.     

Synthesis of liquid–crystalline benzoxazines containing a biphenyl group in the mesogenic moiety

In this work, we describe a process to synthesize novel liquid–crystalline (LC) benzoxazines from a LC phenol that contains biphenyl, ester and azomethine groups in the mesogenic moiety, various alkyl amines and formaldehyde. The LC behavior of the biphenyl-containing benzoxazines was investigated by differential scanning calorimetry and polarized optical microscopy and compared with analogous phenyl-containing LC benzoxazines containing phenyl, ester and azomethine groups in the mesogenic moiety. While the LC benzoxazines containing the phenyl groups only exhibited a nematic phase upon heating, the LC benzoxazines containing biphenyl groups exhibited a smectic phase as well as a nematic phase. Additionally, the LC-isotropic transition temperatures were over 100 °C higher than that for the phenyl-containing LC benzoxazines. A film obtained by curing the biphenyl-containing LC benzoxazine at 180 °C for 1 h exhibited birefringence. Finally, the thermal diffusivity of the cured LC benzoxazines was also investigated.     

Synthesis of well-defined norbornene–lactone-functionalized polymers via ATRP

Well-defined norbornene–lactone-functionalized polymers were synthesized by atom transfer radical polymerization (ATRP) of 5-methacryloxy-6-hydroxynorbornene-2-carboxylic-6-lactone (MNL) and 5-acryloxy-6-hydroxynorbornene-2-carboxylic-6-lactone (ANL) monomers. The ATRP of MNL initiated by ethyl 2-bromopropionate (EBrP), in both N,N-dimethylformamide (DMF) and o-dichlorobenzene (ODCB) solvents was successfully carried out in the presence of CuCl/CuBr and N,N,N′′,N′′,N′′-pentamethyltriethylenetetramine (PMDETA) at 70 °C. The CuCl/ODCB catalyst system gave rise to a lower M _w/M _n (≦1.20) than CuBr/DMF catalyst system. The ATRP of ANL was feasible in the presence of CuBr and PMDETA at 70 °C but showed lower reactivity than MNL. The resulting polymers were characterized by means of gel permeation chromatography (GPC) and ¹H NMR spectroscopy.     

Synthesis and characterization of new poly(ether–ester–imide)s as a generation of soluble and thermally stable polymers

A new-type of dicarboxylic acid 6 was synthesized from the reaction of 1,4-bis[4-aminophenoxy]butane 4 with trimellitic anhydride 5 in a solution of glacial acetic acid/pyridine (Py) at refluxing temperature. 1,4-Bis[4-nitrophenoxy]butane 3 was prepared by reaction of 4-nitrophenol 1 with 1,4-dibromo butane 2 in N,N-dimethylformamide (DMF) solution. Then dinitro 3 was reduced to 1,4-bis[4-aminophenoxy]butane 4 by using 10% Pd–C, ethanol, and hydrazine monohydrate. So six new thermally stable and organosoluble poly(ether–ester–imide)s (PEEIs) 8a–f with good inherent viscosities were synthesized by the direct polycondensation reaction of new 1,4-bis[4-(trimellitimido)phenoxy]butane 6 with several aromatic diols 7a–f through direct polycondensation using tosyl chloride (TsCl)/pyridine (Py)/DMF system as condensing agent. The resulted polymers were fully characterized by means of FTIR and ¹H NMR spectroscopy, elemental analyses, inherent viscosity, solubility tests, differential scanning calorimeter (DSC), thermogravimetric analysis (TGA), and derivative of thermogravimetric (DTG).     

Synthesis and properties of high-performance and good water-soluble melamine–formaldehyde resin

In this article, high-sulfonated melamine–formaldehyde (HSMF) resins were prepared with a sulfite/melamine (S/M1.5) molar ratio. During the sulfonation process, the reaction temperature and the added velocity of sodium bisulfite affecting the properties of the resin were studied. In the condensation stage, where the pH range is 6.0 and the temperature is about 25°C, the condensation time was prolonged above 24 h. The stability and water solubility of the resin was improved greatly. It is an effective superplasticizer at small dosages of admixture. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 3268–3271, 2001     

Synthesis and photovoltaic properties of alternative copolymers of benzo[1,2-b:4,5-b′]dithiophene and thiophene

Two conjugated polymers containing benzodithiophene (BDT) unit and the unit of thiophene or thieno[3,2-b]thiophene, P(BDT-T) and P(BDT-TT), were synthesized by Pd-catalyzed Stille coupling method. The UV–Vis absorption, thermal, and electrochemical properties of the two polymers were characterized. Photovoltaic properties of the polymers were studied by using the polymers as donor and PC₇₀BM as acceptor with a weight ratio of polymer: PC₇₀BM of 1:1.5. The power conversion efficiencies of the PSC devices based on P(BDT-T) reached 2.05% with an open-circuit voltage of 0.75 V, a short-circuit current of 4.5 mA cm⁻², and a fill factor of 0.61, under the illumination of AM1.5, 100 mW cm⁻².     

Synthesis,processing and properties of TaC–TaB2–C ceramics

Multi-phase ceramics in the TaC–TaB₂–C system were prepared from TaC and B₄C mixtures by reactive pressureless sintering at 1700–1900 °C. The pressureless densification was promoted by the use of nano-TaC and by the presence of active carbon in the reaction products. The presence of TaB₂ inhibited grain growth of TaC and increased the hardness compared to pure TaC. If a coarse TaC powder was used, the compositions did not densify. In contrast, pure nano-TaC was pressureless sintered at 1800 °C by the addition of 2 wt.% carbon introduced as carbon black or graphite. The introduction of carbon black resulted in fully dense TaC ceramics at temperatures as low as 1500 °C. The grain size of nominally pure TaC ceramics was a strong function of carbon stoichiometry. Enhanced grain size in sub-stoichiometric TaC, compared to stoichiometric TaC, was observed. Additional work is necessary to optimize processing parameters and evaluate the properties of ceramics in the TaC–TaB₂–C system.     

Synthesis and microwave absorption properties of Ni–Zn–Mn spinel ferrites

A series of Ni_0·5?xZn_0·3?xMn_0·2+2xFe₂O₄ ferrites was successfully prepared by the sol–gel autocombustion method. The structure and electromagnetic properties of the powders were characterised by X-ray diffraction, SEM and vector network analysis. The pure powders were formed by heating at 1200°C for 3 h in air, and grain sizes increased as the amount of substitution ranged from x?=?0·0 to x?=?0·25. For samples with x?=?0·1, a minimum reflection loss of ?27·57 dB was observed at 11·0 GHz with the less than ?10 dB absorption bandwidth at 8·0 GHz with 3·8 mm thickness. The results indicate that substitution with Mn and Zn ions can greatly improve the microwave absorption properties of NiFe₂O₄ ferrites.     

Preparation of π-conjugated polymers consisting of 2-decylbenzimidazole and thiophene units and chemical properties of the polymers

Polycondensation by Stille coupling of 2-decyl-4,7-dibromobenzimidazoles and N-methyl-2-decyl-4,7-dibromobenzimidazole with 2,5-bis(trimethylstannyl)thiophene and 5,5′-bis(trimethylstannyl)-2,2′-bithiophene gave the corresponding π-conjugated polymers, poly(2-decylbenzimidazole-4,7-diyl-thiophene-2,5-diyl) 1b, poly(2-decylbenzimidazole-4,7-diyl-bithiophene-2,5-diyl) 1c and poly(N-methyl-2-decylbenzimidazole-4,7-diyl-thiophene-2,5-diyl) 2b, in 98-99% yields. The polymers 1b and 2b were fully soluble in CF₃COOH, and partially soluble in DMF (about 60 and 40% for 1b and 2b, respectively) and NMP (about 70 and 40%, respectively). The NMP soluble part of 1b and DMF soluble part of 2b gave values of 0.36 and 0.24 dl g⁻¹ in NMP and DMF, respectively. The DMF soluble part of 1b, 1c and 2b showed absorption peaks at about 458, 465 and 388 nm, respectively, in DMF. In an alkaline medium the absorption peaks of 1b and 1c are shifted to a longer wavelength by 92-101 nm; the observed shifts in the acidic medium and alkaline medium were much larger than those observed with usual benzimidazoles with low molecular weights. Packing structures of 1b, 1c and 2b are discussed based on their XRD patterns.     

Synthesis of π-conjugated polymers bearing electronic and optical functionalities by organometallic polycondensations and their chemical properties

A wide variety of π-conjugated polymers have been synthesized by using organometallic polycondensations. For instance, Ni(0) complex-promoted dehalogenative polycondensation of dihaloaromatic compounds, X-Ar-X, affords poly(arylene)s, -(Ar)_n-. Pd-catalyzed polycondensation gives alternating copolymers, -(Ar-Ar′)_n-, and poly(arylene-ethynylene)s, -(Ar-CC-Ar′-CC)_n-. These polymers show distinguishing optical and electrochemical properties and functionalities. Their well-characterized linear structures lead to molecular assembly and packing of the polymer molecules in solutions and in the solid state. In this article, we describe the synthesis of π-conjugated polymers by the organometallic polycondensations, chemical properties of the synthesized polymers, and applications of the polymers for electronic and optical devices.     

Tensile,flexural and morphological properties of electron beam-crosslinked LDPE–EPDM blends

The effect of electron beam (EB) irradiation on the tensile, flexural and morphological properties of low-density polyethylene (LDPE)/ethylene-propylene diene elastomer (EPDM) blends had been studied in the absence and presence of crosslink promoters, such as trimethylolpropane triacrylate (TMPTA) and triallyl cyanurate (TAC). Blends were prepared by melt mixing of LDPE and EPDM followed by EB irradiation at various doses. The gel fraction (%) of irradiated blends was increased with an increase in EPDM content as well as EB irradiation dose and consequently the tensile and flexural properties of the blends increased. The incorporation of crosslinking promoters accelerated the gel formation and improved the properties upon irradiation more efficiently. The phase morphology of fractured surface displayed immiscibility with a rough appearance before irradiation. But after irradiation, the surface became fine, smooth and uniform, which went on increasing upon irradiation, supporting the steady increase in mechanical properties. Surface appeared even smoother in the presence of TMPTA and TAC.