Synthesis,characterization and fluorescence quenching of conjugated polymer containing triphenylamine group

Poly(triphenylamine-p-phenylenevinylene)s with two different end-groups were obtained through a Wittig polycondensation. The structures of two copolymers were characterized. Ultraviolet and visible spectroscopy (UV-Vis) and photoluminescence (PL) spectra show the end-capped polymer emits intensive green light in both solution and film state. Their applications in the detection of nitro compounds were investigated, and the results show high fluorescence quenching sensitivity of the end-capped polymer towards o-nitrotoluene (o-NT). When the concentration of o-NT was 21.5 × 10^-3 mol/L, the fluorescence quenching reached 96%. Additionally, after the exposure of polymer film in three different quenchers such as dinitrotoluene (DNT), p-nitrobenzoquinone (p-BQ) and p-nitrotoluene (p-NT) for 600 s, its fluorescence quenching reached 93.6%, 11.5% and 77.9%, respectively. This kind of polymer has great advantages in preparation and may find applications in the detection of nitro explosives.     

Selective oxidation of o-nitrotoluene to o-nitrobenzaldehyde with metalloporphyrins as biomimetic catalys

Selective oxidation of o-nitrotoluene to o-nitrobenzaldehyde with metalloporphyrins as biomimetic catalysts was studied. The peripheral substituent around porphyrin rings and various process parameters of NaOH concentration, reaction temperature, reaction time and oxygen pressure all affect the selectivity of o-nitrobenzaldehyde. Further, 82.0% selectivity of o-nitrobenzaldehyde was achieved under the optimum conditions: 1.0×10^t-5 mol · L⁻¹ of T(p-NO₂)PPFeCl catalyst, 2.5 mol · L⁻¹ of NaOH, 0.2 mol · L^t-1 of o-nitrotoluene, 45°C and 2.0 MPa for 6 h.     

Electrosynthesis of toluidines using thermally coated Ti/TiO2 electrodes

Cyclic voltammetric and preparative scale investigations on the electroreduction of (o-nitrotoluene (ONT), m-nitrotoluene (MNT), p-nitrotoluene (PNT) and 2,4-dinitrotoluene (DNT) to their corresponding toluidines in 1 m H₂SO₄ using thermally coated Ti/TiO₂ electrode are reported. In the cyclic voltammetric time scales inhibitive adsorption which decreased in the order i _p ONT > i _p MNT > i _p PNT > i _p DNT was noticed. The heterogeneous redox catalytic currents were also found to decrease in the same order. In preparative electrolysis, these inhibitive effects became unimportant. Yields around 90% were achieved for all four nitro compounds. The thermally coated Ti/TiO₂ electrode could be reused at least five times without any loss in yield and current efficiency.     

Thermal Degradation of Plasticized Poly(<Emphasis Type="Italic">para</Emphasis>-Methoxystyrene) in Solid Films

The thermal effect on the stability of poly(para-methoxystyrene) in solid films was studied within a temperature range of temperature range of 298–363 K. The fluorescence spectrum of poly(para-methoxystyrene) was found to be mainly excimeric emission at room temperature. However, this emission is quenched at higher temperatures. Added terephthalate and phthalate plasticizers to poly(para-methoxystyrene) caused a quenching of the excimer emission and enhanced exciplex emission. Thermal heating of the solid films of the plasticized and non-plasticized polymer was accompanied by quenching of fluorescence emission at low temperature and brought about a change in the structure of the fluorescence spectrum at high temperatures. This may indicate that thermodestruction of these polymers starts from a random chain scission. In addition to that the presence of the plasticizer in the polymer backbone was found to accelerate thermal degradation of the polymer. This was proved by the infrared spectra of the heated and unheated plasticized solid films of poly(para-methoxystyrene). The binding energy or excimer formation was calculated in solid film.     

Synthesis of a novel fluorene-based conjugated polymer with pendent bulky caged adamantane moieties and its application in the detection of trace DNT explosives

A novel fluorene-based conjugated polymer with phenylene spacers and steric bulky adamantane moieties in side chains has been synthesized by palladium-catalyzed Suzuki coupling reactions. This design strategy offers several advantages for the detection of trace 2,4-dinitrotoluene (DNT) vapor. The incorporation of the two groups into polymer side chains could retain an effective conjugation length and prevent the π-stacking of polymer chains. The detection of DNT vapor indicated that the polymer displayed higher fluorescence quenching sensitivity toward the explosives in films compared to reference polymers. The fluorescence quenching efficiency of the fluorescent polymer achieved 33.3% in 10 s and 71.1% in 60 s. The pathways or cavities generated by the two spacers are beneficial for the rapid diffusion of explosive vapor into the film interiors and increase the fluorescence quenching efficiency of the film.     

The oxidation of o-nitrotoluene to o-nitrobenzaldehyde with electrogenerated cobaltic sulphate

Indirect electrochemical oxidation ofo-nitrotoluene too-nitrobenzaldehyde by Co (III) has been studied. The highest aldehyde yield ( 80%) is obtained in dispersing a 70-fold excess ofo-nitrotoluene in a solution of CO₂(SO₄)3 in 60% H₂SO₄ at 12° C. The influence of acid concentration, excess of nitrotoluene and presence of catalyst are discussed and found to be compatible with a mechanism proposed by Bawn.     

Regioselective nitration of toluene to para-nitrotoluene with NO2 over dealumination Hβ zeolite: Comparison of organic and inorganic acids

This work presents a novel heterogeneous catalytic system for the preparation of para-nitrotoluene (p-NT) with nitrogen dioxide (NO₂) as a nitrating agent in the presence of oxygen (O₂). By applying dealuminated Hβ zeolite treated with oxalic acid (Hβ-Ox) as a catalyst, p-NT can be obtained with high conversion (90.5%) and selectivity (72.6%). In addition, it can be recycled at least five times without a significant decrease in catalytic activity. This result demonstrates that the catalyst has high efficiency, good stability, and regenerability. Meanwhile, the characteristics of pristine Hβ and different dealuminated Hβ zeolites modified with organic and inorganic acids were systematic contrastive studied using X-ray diffraction (XRD), nitrogen (N₂) adsorption-desorption, Fourier-transform infrared (FT-IR), scanning electron microscope (SEM), temperature-programed desorption of ammonia (NH₃-TPD), pyridine adsorption infrared (Py-FT-IR), and solid state ²⁷Al nuclear magnetic resonance (²⁷Al MAS-NMR). Finally, the higher conversion and para-selectivity over Hβ-Ox also give a reasonable explanation in this paper.     

Selectivity engineering in the nitration of chlorobenzene using eclectically engineered sulfated zirconia and carbon molecular sieve catalysts

Selective synthesis of the para‐nitro derivative from chlorobenzene by using nitric acid over an eclectically engineered sulfated zirconia carbon molecular sieve catalyst is reported. The p : o ratio in chlorobenzene nitration was found to be very high with eclectically engineered sulfated zirconia and carbon molecular sieve catalyst. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of some selective aromatic cosolutes on the main thermodynamic parameters of aqueous poly(n‐vinyl‐2‐pyrrolidone) solutions

Cloud‐point curves and theta temperatures have been determined for aqueous solutions of poly(N‐vinyl‐2‐pyrrolidone) at several concentrations for a variety of aromatic additives (benzoic acid, o‐ and p‐hydroxy benzoic acid, aniline, o‐ and p‐hydroxy aniline). The theta temperature of polymer is suppressed at lower temperatures depending on the chemical structure and the concentration of additives. The effectiveness, in decreasing order, of the cosolutes in reducing the temperature is: p‐hydroxy benzoic acid > o‐hydroxy benzoic acid > p‐hydroxy aniline > o‐hydroxy aniline ≈ benzoic acid > aniline. It is understood that changes in theta temperatures caused by the cosolute result from the changes taking place in the hydrophilic and hydrophobic interactions among polymer, solvent and polymer–solvent interactions from the added cosolute. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 507–510, 2000     

Solvent penetration and photoresist dissolution: A fluorescence quenching and interferometry study

A novel method, based upon fluorescence quenching measurements, is described for the study of the mechanistic details of solvent penetration into thin polymer films. Here poly(methyl methacrylate) (PMMA) labelled with phenanthrene (Phe) groups was coated as a film (0.8 μm thick) onto quartz disks. Diffusion of solvent (1 : 1 2-butanone/2-propanol) into the film was followed by a decrease in Phe fluorescence, while film dissolution was monitored simultaneously by laser interferometry. In the case of PMMA (M_w = 411,000, films annealed at 160°C) both processes occur at approximately the same rate and exhibit non-Fickian (relaxation-controlled) diffusion behavior. Correlating the results of these two experiments shows that, once the steady state is reached, the dissolution rate is controlled by the advance of the solvent front into the PMMA film. The “transition layer,” an important dissolution parameter, increases its thickness from 50 to 90 nm during the plasticization stage of solvent penetration and maintains its thickness until the solvent front reaches the quartz substrate.     

Graft copolymerization of styrene onto ethylene-vinyl p-nitrobenzoate copolymer by chain transfer reaction

The effect of steric hindrance on the attack of growing polymer radicals to the reaction sites on a trunk polymer was examined in the graft copolymerization of styrene onto a trunk polymer with pendant aromatic nitro groups by chain transfer reaction of growing polymer radicals to the pendant nitro groups. The nitro groups on ethylene-vinyl p-nitro benzoate copolymer (EVNB) are more effectively utilized in the graft copolymerization than those on the vinyl p-nitro benzoate homopolymer (PVNB) previously used as a trunk polymer, because the nitro groups are distributed less frequently on the trunk polymer in the former than in the latter. This was also confirmed by the higher chain transfer constant of growing polystyrene radicals to EVNB compared to that of PVNB.     

Effect of film thickness, blending and undercoating on optical detection of nitroaromatics using fluorescent polymer films

In this work, using a fluorescent poly(phenylene ethynylene) containing the rigid pentiptycene and large cholesteryl ester pendent groups, the fluorescence quenching properties of the polymer thin films in response to vapor of 2,4-dinitrotulene (DNT) have been investigated by varying the film thickness, applying an undercoating and blending with another polar polymer. A significant change in fluorescence intensity (51% in 60 s) in response to DNT vapor exposure at ambient temperature was achieved when the polymer film coated on glass plate was about 2 nm in thickness. In comparison with the film of polymer alone, the film undercoated with (3-aminopropyl)triethoxysilane and the film of polymer blend containing a non-fluorescent polymer showed additional 18.5% (in 20-s exposure) and 18.7% (in 5-min exposure) decrease in fluorescence intensity, respectively. The use of polymer or polymer blend coated on optic-fiber tip for detection of DNT vapor has also been demonstrated.     

The effect of catalyst film thickness on the magnitude of the electrochemical promotion of catalytic reactions

The effect of catalyst film thickness on the magnitude of the effect of electrochemical promotion was investigated for the model catalytic reaction of C₂H₄ oxidation on porous Pt paste catalyst-electrodes deposited on YSZ. It was found that the catalytic rate enhancement ρ is up to 400 for thinner (0.2 μm) Pt films (40,000% rate enhancement) and gradually decreases to 50 for thicker (1 μm) films. The Faradaic efficiency Λ was found to increase moderately with increasing film thickness and to be described semiquantitatively by the ratio 2Fr _o/I ₀, where r _o is the unpromoted rate and I ₀ is the exchange current of the catalyst–electrolyte interface. The results are in good qualitative agreement with model predictions describing the diffusion and reaction of the backspillover O^2- species, which causes electrochemical promotion.     

A thermoplastic polyurethane/rare earth composite film with adjustable fluorescence colors and optimal low-temperature flexibility

In this study, a unique series of luminous polymeric rare earth (RE) composite films was produced by loading RE ions into thermoplastic polyurethane (TPU) using solution blending. Compared to RE ions, luminous polymeric RE composites had greater luminescence intensity, indicating that the introduction of polymer polyurethane as the polymer matrix was advantageous for the luminescence intensity and efficiency of RE ions, with the polymer matrix's absorbed energy being transferred to the RE ions. Furthermore, the findings of the optical transmittance, UV–visible absorption and fluorescence emission spectra suggest that TPU-RE composite films possess exceptional fluorescence luminescence properties and optical transparency. Surprisingly, the fluorescence colors of TPU-RE fluorescent films could be adjusted between red and green by varying the ratios of Eu³⁺ and Tb³⁺ in the films and can be any mixture of red and green hues. In addition, the temperature at 5% weight loss (T_5%) for the TPU-RE composite film composition reached 250 °C. In addition, pure TPU and all TPU-RE hybrid films demonstrated a glass transition temperature (T_g) of about −30 °C. Simultaneously, the tensile strength of the TPU-T₀E₁₀ film reached its maximum (43.6 MPa). Consequently, the TPU-RE composite films will be utilized as photoluminescent functional materials. © 2022 Society of Industrial Chemistry.     

Oligomer of o-xylene as a heat stabilizer for isotactic polypropylene

Oligomers of o-xylene (molecular weight ～400) have been shown to be novel heat stabilizers for isotatic polypropylene film. In contrast to unstabilized films which failed after exposure of 5 hr in a 150°C air oven, a film containing 0.5 and 1.0 wt-% of the o-xylene oligomer survived 100 and 226 hr, respectively. Furthermore if 0.25% dilauryl thiodipropionate (DLTP) was also present, only 0.1 wt-% of the o-xylene oligomer was necessary to maintain a film intact up to 124 hr. In absence of DLTP, this low level of o-xylene oligomer was not effective. Oligomers of toluene, m-xylene, p-xylene, and 1,2,4-trimethyl benzene were found less effective.     

Polarographic behaviour of p-nitrotoluene and p-nitroaniline in water-alcohol mixtures

The polarographic behaviour at the dme of p-nitrotoluene and p-nitroaniline is investigated in water-methanol, water-ethanol and water-isopropanol, in presence of 0.1 M LiCl as indifferent electrolyte. In water-methanol solutions one wave is observed. In essentially aqueous solutions (> 80 wt-% H₂O) and essentially alcoholic solutions (> 80 wt-% alcohol) of water-ethanol and water-iso-propanol, one wave is also obtained. At moderate ethanol and iso-propanol concentrations, (20–80 wt-% alcohol) splitting into two waves takes place. The reduction mechanism of the nitro compounds and the nature of the waves are discussed.     

High Brightness Green Light-Emitting Diode Based on Silole-Containing Polyfluorenes

A novel silole-containing polyfuorene (PSFN) was successfully synthesized by palladium(0)-catalyzed Suziki coupling reactions. Optoelectronic properties of the copolymer were characterized by NMR, UV absorption, photoluminescence, and electroluminescence (EL). The film of the copolymer showed silole-dominant green emission. An EL device of the copolymer with a sandwich configuration of ITO/Polymer/Al displayed exclusive silole emission, which peaked at ~532 nm with the CIE coordinate of (0.33, 0.54). The polymer layer contained a conjugated silole-containing polyfluorene that emits green light, trimethylolpropane trimethacrylate, a low vapor pressure highly crosslinkable liquid, and lithium trifluoromethane sulfonate at a weight ratio of 20:5:1. A dynamic p–i–n junction was formed in thin films of light-emitting polymers admixed with an ionically conductive medium. The PLEC device was turned on at 8 V and the brightness reached up to 2000 cd/m² at 12 V.     

Effects of absorption overlap on the modulation of the polarized fluorescence of Eu(DBM)<Subscript>3</Subscript>Phen-doped azobenzene polymer films

Two azopolymers, poly(4-(4′-nitrophenylazo)phenoxy)hexyl methacrylate (PNAzoPOH) and poly(6-(N-methyl-N-(4-(4′-nitrophenylazo)phenyl)amino)hexyl methacrylate) (PNAzoPAH), bearing strong push–pull azobenzene chromophores, have been designed and synthesized. Azopolymer films doped with a europium complex, tris(dibenzoylmethanido)(o-phenanthroline)europium(III) (Eu(DBM)₃Phen), were prepared by a drop-casting method. UV-vis spectra indicated that the absorption peak of Eu(DBM)₃Phen at 365 nm overlaps with that of PNAzoPOH, rather than that of PNAzoPAH. Polarized fluorescence from both of the oriented films was observed to depend on the absorption overlap between the complex and the azopolymer. When excited by unpolarized light at 365 nm, the polarization ratio R of Eu(DBM)₃Phen-doped PNAzoPOH film shows an obvious decreasing trend with increasing irradiation time, and the ratio R of Eu(DBM)₃Phen-doped PNAzoPAH film has a relative stable value of about 1.47. When excited by polarized light at 365 nm, the florescence intensities from the two films show different dependences upon the angle between the direction of orientation of the film and the direction of polarization of the excitation light: for Eu(DBM)₃Phen-doped PNAzoPOH film, the strength of the polarized fluorescence depended on the direction of polarization of the excitation light; for Eu(DBM)₃Phen-doped PNAzoPAH film, no such dependence was observed. These different results arise due to differences between the azopolymers in terms of the allocation of energy between the oriented azobenzene groups and the complex.     

Adsorption of reaction species on raney nickel for slurry-phase hydrogenation of p-nitrotoluene

Adsorption of hydrogen, p-nitrotoluene, p-toluidine and water on Raney nickel from their methanol solutions has been investigated under catalytic conditions. The isotherms of reversible adsorption of hydrogen are linear and the estimated heat of adsorption is 28.9 kJ mol^?1. The amount of hydrogen held irreversibly on the catalyst is very large as compared to that adsorbed reversibly. The isotherms of adsorption of p-nitrotoluene, p-toluidine and water have different shapes (viz. types H3, S1 and L3 respectively). Among the reaction species, p-toluidine is not adsorbed on the catalyst at low concentrations (< 0.8 mmol cm^?3).     

Surface properties and chain structure of fluorinated acrylate copolymers prepared by emulsion polymerization

The fluorinated copolymer poly (MMA–co–FMA), composed of methyl methacrylate (MMA) and 2-perfluorooctylethyl methacrylate (FMA), was prepared by emulsion polymerization using a pre-emulsified monomer addition process. The results showed that the contact angle of water on its solvent-borne film increased dramatically and reached 118o when the FMA content in the copolymer was only 0.65 mol%, approaching that of poly(2-perfluorooctylethyl methacrylate) homopolymer. Unlike the copolymer prepared by solution polymerization, X-ray photoelectron spectroscopy (XPS), and sum frequency generation (SFG) vibrational spectroscopy analysis results indicated that the fluorinated moieties in this polymer were very easily segregated at the surface of the film. The interfacial structure and properties of this polymer in solution were investigated using SFG, surface tension, and dynamic laser light scattering (DLS). It was found that emulsion polymerization produced a chain structure of the fluorinated copolymer similar to that of FMA capped PMMA, thereby providing a possible way to produce fluorinated end-capped polymers using a popular polymerization method.