White electroluminescence from polyfluorene chemically doped with 1,8-napthalimide moieties

An efficient white light-emitting polymer was developed with blue polyfluorene (PFO) chemically doped with orange fluorescent 1, 8-naphthalimide moieties. The emission spectrum can be easily tuned by varying the content of 1, 8-naphthalimide moieties. A white polymeric light-emitting diode (WPLED) with a structure of indium tin oxide (ITO)/the complex of (3,4-ethylenedioxythiophene) and polystyrene sulfonic acid (PEDOT)/polymer/Ca/Al showed a current efficiency of 5.3 cd/A and a power efficiency of 2.8 Lm/W at 6 V with the Commission Internationale de L'Eclairage (CIE) coordinates at (0.25,0.35). Moreover, the WPLED from the copolymer showed a very stable white light emission at different driving voltage and brightness. The CIE coordinates of the WPLED were (0.25, 0.35), (0.26, O.36), and (0.26, 0.36) under driving voltages of 6, 8, and 10 V, corresponding to the brightness of 82, 3555, and 7530 cd/m(2), respectively. This approach for realization of white light emission is promising over the polymer blending system in terms of both efficiency and color stability.

Microphase separation induced in the melt of Pluronic copolymers by blending with a hydrogen bonding urea–urethane end-capped supramolecular polymer

Blending with a hydrogen-bonding supramolecular polymer is shown to be a successful novel strategy to induce microphase-separation in the melt of a Pluronic polyether block copolymer. The supramolecular polymer is a polybutadiene derivative with urea–urethane end caps. Microphase separation is analysed using small-angle X-ray scattering and its influence on the macroscopic rheological properties is analysed. FTIR spectroscopy provides a detailed picture of the inter-molecular interactions between the polymer chains that induces conformational changes leading to microphase separation.

Influence of kaolinite particle size on cross-link density, microstructure and mechanical properties of latex blending styrene butadiene rubber composites

Cross-link density, microstructure and mechanical properties of styrene butadiene rubber (SBR) composites filled with different particle sized kaolinites are investigated. With the increase of kaolinite particle size, the cross-link density of the filled SBR composites, the dispersibility and orientation degree of kaolinite particles gradually decrease. Some big cracks in filled rubber composites are distributed along the fringe of kaolinite aggregates, and the absorbance of all the absorption bands of kaolinites gradually increase with the increase of kaolinite particle size. All mechanical property indexes of kaolinite filled SBR composites decrease due to the decrease of cross-linking and reduction of interface interaction between filler and rubber matrix.

Spectral, thermal and electrical properties of poly(o- and m-toluidine) PVC blends prepared by solution blending

Poly(o-toluidine) (POT) and poly(m-toluidine) (PMT) blends with polyvinylchloride (PVC) of five different compositions have been prepared by solution blending. The POT-PVC and PMT-PVC blends were prepared using THF as a solvent in which POT-HNO3, PMT-HNO3 bases and PVC are soluble. The blends have been characterized by spectral, thermal and electrical measurements. The results indicate the formation of blends at all the compositions presently studied. The thermal stability of the POT-PVC and PMT-PVC blends is higher than that of POT-HNO3 and PMT-HNO3 salts, respectively. Using the present method, POT/PMT can conveniently be blended with 30% wt/wt of PVC without significant loss in its conductivity. (C) 1998 Elsevier Science Ltd. All rights reserved.

Narrow band gap conjugated polymer for improving the photovoltaic performance of P3HT:PCBM ternary blend bulk heterojunction solar cells

A new D-A structured conjugated polymer (PBDO-T-TDP) based on electron-rich benzo 1,2-b:4,5-b'] difuran (BDO) containing conjugated alkylthiophene side chains with an electron-deficient diketopyrrolopyrrole (DPP) derivative is designed and synthesized. The polymer shows a narrow band gap with broad UV-Visible absorption spectra, which is in contrast to that of the P3HT:PCBM binary blend. Furthermore, its energy levels can meet the energetic requirement of the cascaded energy levels of P3HT and PCBM. Therefore, PBDO-T-TDP is used as a sensitizer in P3HT: PCBM based BHJ solar cells and its effect on their photovoltaic properties was investigated by blending them together at various weight ratios. It is observed that the resulting ternary blend system exhibited a significant improvement in the device performance (similar to 3.10%) as compared with their binary ones (similar to 2.15%). Such an enhancement in the ternary blend system is ascribed to their balanced hole and electron mobility along with uniform distribution of PBDO-T-TDP in the blend system, as revealed by organic field effect transistors and AFM studies.

Improvement of amplified spontaneous emission performance by doping tris(8-hydroxyquinoline) aluminum (Alq3) in dye-doped polymer thin films

A well-known red fluorescent dye 4-(dicy-anomethylene)-2-t-butyl-6(1,1,7,7-tetramethyljulolidyl-9-enyl)4H-pyran (DCJTB) was codoped with an electron transport organic molecule tris(8-hydroxyquinohne) aluminum (Alq3) in a host matrix of polystyrene (PS), and the amplified spontaneous emission (ASE) was studied by optically pumping. It was found that the ASE performance was significantly improved by the introduction of Alq3. The Alq3:DCJTB:PS blending thin films showed a low threshold (2.4 mu J/pulse) and a high net gain coefficient (109.95 cm(-1)) compared with the pure DCJTB:PS system (threshold of 15.2 mu J/pulse and gain of 35.94 cm(-1)). The improvement of the ASE performance was considered to be attributable to the effective Foster energy transfer from Alq(3) to DCJTB. Our results demonstrate that the Alq(3):DCJTB could be a promising candidate as gain medium for red organic diode lasers.

Reactive blending of modified polypropylene and polyamide 12: Effects of compatibilizer content on crystallization and blend morphology

The crystallization behavior and morphology of nonreactive and reactive melt-mixed blends of polypropylene (PP) and polyamide (PA12; as the dispersed phase) were investigated. It Was found that the crystallization behavior and the size of the PA12 particles were dependent on the content of the compatibilizer (maleic anhydride-modified polypropylene) because an in situ reaction occurred between the maleic anhydride groups of the compatibilizer and the amide end groups of PA12. When the amount of compatibilizer was more than 4%, the PA12 did not crystallize at temperatures typical for bulk crystallization. These finely dispersed PA12 particles crystallized co-incidently with the 1313 phase. The changes in domain size with compatibilizer content were consistent with Wu's theory. These investigations showed that crystallization of the dispersed phase Could not be explained solely by the size of the dispersion. The interfacial tension between the polymeric components in the blends may yield information on the fractionation of crystallization.

A wide-bandgap semiconducting polymer for ultraviolet and blue light emitting diodes

A novel wide-bandgap conjugated polymer (PDHFSCHD) consisting of alternating dihexylfluorene and rigidly twisted biphenyl units has been synthesized. The new fluorene-based copolymer composed of rigid twisting segments in the main-chain exhibits an optical bandgap of as high as 3.26 eV, and a highly efficient ultraviolet emission with peaks at 368 nm and 386 nm. An electroluminescence device from PDHFSCHD neat film as an active layer shows UV emission which peaks at 395 nm with a turn on voltage below 8 V By optimizing the device conditions, a peak EL quantum efficiency of 0.054% and brightness of 10 cd.m(-2) was obtained. Furthermore, blending a poly(dihexylfluorene) in the PDHFSCHD host gave pure blue emission peaking at 417 nm, and 440 nm without long wavelength emission from aggregated species. Efficient energy transfer from PDHFSCHD to PDHF was demonstrated in these blended systems. Depressed chain-aggregation of PDHF in the PDHFSCHD host can correspond to pure blue emission behaviors.

Reactive reinforcement of the interface of high performance polymer blends by PMR-POI

The effect of PMR-polyimide(POI) as the interfacial agent on the interface characteristics, morphology features and crystallization of poly (ether sulfone) /poly (phenylene sulfide) (PES/PPS) and poly(ether ether ketone)/poly (ether sulfone) (PEEK/PES) partly miscible blends were investigated by means of the scanning electron microscopy, WAXD and XPS surface analysis. It is found that the interfacial adhesion was enhanced remarkably, the size of the dispersed phase particles was reduced significantly and the miscibility was improved by the addition of POI. During melt blending cross-link and/or grafting reaction of POI with PES, PEEK and PPS homopolymers was detected, however the reaction activity of POI with PPS was much higher than that of PES and PEEK. It was also found that POI was an effective nucleation agent of the crystallization of PPS.

Reactive blending of polyamide 6,6 and Vectra A

In this paper, blends of Nylon 6,6 with the liquid crystal polymer Vectra A950 are considered; specifically we focused our attention on Nylon 6,6 modifications by interchange reactions that can occur in the melt, as a function of mixing conditions and blend compositions. Two matrix samples have been used, characterised by a slightly different relative amount of amine and carboxylic end groups, being the latter predominant in both cases. The dried polymers Nylon 6,6/Vectra, combined in weight ratios between 95/5 and 50/50, were subjected to reactive blending with different methods (single-screw extruder, Brabender, pyrex reactor). Pure Nylon samples have been also investigated as reference materials. The soluble Nylon 6,6-rich fraction of each blend was separated from the insoluble Vectra-rich one and used for molecular and spectroscopic characterisations. Thermal and morphological analyses, as well as testing of tensile properties, were carried out on the blends. Evidences of the occurrence of interchange reactions are given and the most probable ones are suggested. (C) 2001 Elsevier Science Ltd. All rights reserved.

Luminescence enhancement by blending PVK with blue PPV copolymer

The PL and EL properties of the polymer blends of PVK and blue PPV copolymer were studied. Considerable enhancement of both the photoluminescent and the electroluminescent intensity were observed by using the polymer blends as emission layer in the LED devices. The energy transfer process and the formation of exciplex in the polymer blends were also discussed.

Liquid crystalline polymer as a processing agent in blends of poly(ether-ketone)/LCP70

Blends of a liquid crystalline thermotropic copolyester (LCP70) and an amorphous phenolphthalein based poly(ether-ketone)(PEK-C) with two viscosities were prepared by melt blending. The blends' morphology, rheological and mechanical properties were investigated by DSC, SEM, mechanical and rheological tests. It was observed that the optimum composition of the PEK-C/LCP70 blend was 10 wt% LCP for both mechanical and rheological properties. When the LCP content was less than 10%, the LCP phase existed as finely dispersed fibrous domains with a diameter of about 1 mu m in the matrix, and both tensile and flexural properties were improved. In contrast, when the LCP content reached 20% or more, the LCP domains coalesced to ellipsoidal particles with a diameter of about 5 mu m, and the mechanical properties decreased as a result. It is demonstrated that pure PEK-C with a high viscosity which was difficult to process by melt extrusion, could be extruded conveniently when 10% LCP70 was incorporated. It is emphasized that LCP not only can be used as a reinforcing phase but also an effective processing agent for engineering thermoplastics, especially for those with high viscosity and narrow processing window. (C) 1997 Elsevier Science Ltd.

Thermal, mechanical and ionic conductive behaviour of gamma-radiation induced PEO/PVDF(SIN)-LiClO4 polymer electrolyte system

An effort has been made to modify the mechanical behaviour of our previously reported gel-type gamma-radiation crosslinked polyethylene oxide (PEO)-LiClO4 polymer electrolyte. A highly polar and gamma-radiation crosslinkable crystalline polymer, polyvinylidene fluoride (PVDF), was selected to blend with PEO and then subjected to gamma-irradiation in order to make an simultaneous interpenetrating network (SIN), which was used as a polymer host to impart stiffness to the plasticized system. Experimental results have shown that the presence of PVDF in the system, through gamma-radiation induced SIN formation, could not only give a rather high mechanical modulus of 10(7) Pa at ambient temperature, but also maintain the room temperature ionic conductivity at a high level (greater than 10(-4) S/cm). DSC, DMA and conductivity measurement techniques were used to examine the effects of blending, gamma-irradiation and plasticization on the variations of glass transition and melting endotherm, on the appearance of high elastic plateau and on the temperature dependence of ionic conductivity: In addition, it was found that, in contrast with the unplasticized system, the ionic conductivity mechanism of this gel-type electrolyte seems to conform to the Arrhenius model, suggesting that, as a result of the high degree of plasticization, the polymer chains act mainly as the skeleton of the networks or polymer cages to immobilize the liquid electrolyte solution, whereas the ionic species migrate as if they were in a liquid medium. (C) 1997 Elsevier Science Ltd.

Electrical and dynamic mechanical behavior of carbon black filled polymer composites

The effect of processing conditions on the electrical and dynamic behavior of carbon black (CB) filled ethylene/ethylacrylate copolymer (EEA) composites was investigated. The compounds were prepared by two methods, solution blending and mechanical mixing. Compared with the solution counterpart, the mechanical composites have a strong positive temperature coefficient (PTC) effect and a high dynamic elastic modulus, which results from the good dispersion state of carbon black in EEA, i.e. the strong interaction between carbon black and EEA. It can be concluded that the strong interaction between polymer and carbon black is essential for composites to have a high PTC intensity, good electrical reproducibility and high dynamic elastic modulus. Copyright (C) 1996 Published by Elsevier Science Ltd.

Enhanced glass fiber-reinforced phenolphthalein poly(ether ketone) composites by blending poly(phenylene sulfide)

The mechanical properties of glass fiber-reinforced phenolphthalein poly(ether ketone)/poly(phenylene sulfide) (PEK-C/PPS) composites have been studied. The morphologies of fracture surfaces were observed by scanning electron microscope. Blending a semicrystalline component, PPS, can improve markedly the mechanical properties of glass fiber-reinforced PEK-C composites. These results can be attributed to the improvement of fiber/matrix interfacial adhesion and higher fiber aspect ratio. (C) 1996 John Wiley & Sons, Inc.