Blue-light emitting diodes and flat display based on poly(p-phenylenevinylene) copolymers

Copolymers containing alternating flexible aliphatic blocks and rigid poly(p-phenylenevinylene) (PPV) blocks were synthesized and characterized. It was found that the fluorescent intensity increases with increasing length of the flexible blocks. Bright blue-light emitting diodes were fabricated using PPV copolymers as electroluminescent layers. The devices show 190 cd/m(2) light-emitting brightness at 460 nm and 15 V rum-on voltage. The effects of oxadiazole derivative PBD and tris(8-hydroxyquinoline) aluminum Alq(3) electron-transporting layers on the luminance and stability of the devices are discussed.

Novel morphology in ring-banded spherulites from single-phase mixtures of poly(epsilon-caprolactone) with poly(styrene-co-acrylonitrile)

Novel morphology of ring-banded spherulites in the surface of poly(epsilon-caprolactone)/poly(styrene-co-acrylonitrile) (PCL/SAN) blends was discovered and studied by SEM and TEM. The ring-banded spherulites separate into those exhibiting a very dark contrast, of relatively regular bundles of lamellae and others appearing with a much brighter intensity, of a coarse and irregular aggregates of lamellae. The origin of the novel morphology is not due to different crystalline structures as in the case of isotactic polypropylene because only one crystal structure exists in PCL/SAN blends. The formation may reflect whether spherulites in PCL/SAN blends are nucleated at the bottom surface or at the top (free) surface.

Cure processing modeling and cure cycle simulation of epoxy-terminated poly(phenylene ether ketone). V: Estimation of temperature distribution during cure process

A numerical method to estimate temperature distribution during the cure of epoxy-terminated poly(phenylene ether ketone) (E-PEK)-based composite is suggested. The effect of the temperature distribution on the selection of cure cycle is evaluated using a suggested alternation criterion. The effect of varying heating rate and thickness on the temperature distribution, viscosity distribution and distribution of the extent of cure reaction are discussed based on the combination of the here-established temperature distribution model and the previously established curing kinetics model and chemorheological model. It is found that, for a thin composite (<=10mm) and low heating rate (<=2.5K/min), the effect of temperature distribution on cure cycle and on the processing window for pressure application can be neglected. Low heating rate is of benefit to reduce the temperature gradient. The processing window for pressure application becomes narrower with increasing thicknesses of composite sheets. The validity of the temperature distribution model and the modified processing window is evaluated through the characterization of mechanical and physical properties of E-PEK-based composite fabricated according to different temperature distribution conditions.

Studies on fracture morphology of short carbon fiber reinforced poly(phenylene ether ketone)(SCF/PEK-C) composites

The shear fracture morphology of SCF/PEK-C composite with carbon fibers treated for different times was studied carefully by SEM. The result shows that the adhesion between fiber and matrix was improved and fractured model also changed from interface fracture to brittle fracture with increasing treatment time of carbon fiber. The fracture mechanism was discussed preliminary.

Morphology and structure of poly(aryl ether ketone ketone) containing isophthaloyl moieties crystallized from dilute solution

Spherulites and lamellar single crystals of poly(aryl ether ketone ketone) containing isophthaloyl moieties (PEKK(I)) were obtained from dilute alpha-chloronaphthalene solution. The morphology and structure of the spherulites and single crystals were studied by electron microscopy and electron diffraction. The spherulites were found to consist of elongated lamellar branches that grow with the b crystallographic axis in the radial direction. Single crystals possess a similar habit, with b parallel to the long axis, a transverse, and c perpendicular to the lamellae plane. High-resolution images of the PEKK(I) crystals which show the perfection of and defects in the crystals, were obtained, and many defects or dislocations a,ere observed. (C) 1997 Elsevier Science Ltd.

Synthesis and high efficiency green light-emitting diode of a soluble polymer

A soluble polymer emitting green color with high efficiency was synthesized. Bright green electroluminescence devices, both single layer and multilayer, were fabricated. The luminous efficiency was improved dramatically. Carrier injection from the electrodes to the emissive layer and concomitant green electroluminescence from the emissive layer were observed. A luminance of 920 cd/m(2) and luminous efficiency of 5.35 1m/W were achieved at a drive voltage of 15 V for the multilayer device. (C) 1997 Elsevier Science S.A.

Bright blue electroluminescent devices utilizing poly (N-vinylcarbazole) doped with fluorescent dye

Bright blue electroluminescent devices have been fabricated using poly (N-vinylcarbazole) (PVK) doped with perylene as the emissive layer, poly(p-phenylenevinylene) (PPV) as the hole-transporting layer, 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD), tris(8-hydroxyquinoline)aluminum (Alq(3)) as the electron-transporting layer, and Al as the cathode. A luminance of 700 cd/m(2) and a luminescent efficiency of 0.8% are achieved at a drive voltage of 36 V. In the experiment, it is found that the introduction of electron-transporting layer PBD has a great effect on the emissive color of the electroluminescent devices prepared by PVK doped with perylene. Yellow-green emission is observed from the device structure of glass substrate/indium-tin-oxide/PVK:perylene/Al. The possible emissive mechanisms are given. The effect of the transporting layer on the electroluminescence is also discussed. (C) 1997 Elsevier Science S.A.

Isothermal melt and cold crystallization kinetics of poly(aryl ether ether ketone ketone) (PEEKK)

Isothermal melt and cold crystallization kinetics of PEEKK have been investigated by differential scanning calorimetry in two temperature regions. During the primary crystallization process, the relative crystallinity develops with a time dependence described by the Avrami equation, with exponent n = 2 for both melt and cold crystallization. The activation energies are -544.5 and 466.7 kJ/mol for crystallization from the melt and amorphous glassy state, respectively. The equilibrium melting point T-m(o) is estimated to be 371 degrees C by using the Hoffman-Weeks approach. The lateral and end surface free energies derived from the Lauritzen-Hoffman spherulitic growth rate equation are sigma=10 erg/cm(2) and sigma(e) = 60 erg/cm(2), respectively. The work of chain folding q is determined as 3.98 kcal/mol. These observed crystallization kinetic characteristics of PEEKK are compared with those of PEEK. (C) 1997 Elsevier Science Ltd.

Synthesis and characterization of soluble polyimides from 1,1-bis(4-aminophenyl)cyclohexane derivatives

A series of novel aromatic diamines (1-3) containing kinked cyclohexylidene moieties was synthesized by a reaction of excess aniline and corresponding methyl-substituted cyclohexanone derivatives. The structures of (1-3) were identifield by H-1 NMR, C-13 NMR, and FT-IR. The polymers were synthesized from the obtained diamines and various aromatic dianhydrides by the conventional polycondensation reaction followed by chemical imidization as well as high-temperature one-step polymerization. The inherent viscosities and weight-average molecular weights of the resulting polyimides were in the ranges of 0.55-1.58 dL/g and (7.4-15.2) x 10(4) g/mol, respectively. The prepared polyimides showed excellent thermal stabilities and good solubility. All polymers were readily soluble in common organic solvents such as tetrahydrofuran, chloroform, tetrachloroethane, etc., and the glass transition temperatures were observed at 290-372 degrees C.

Study of molecular order in organo-soluble polyimide thin films

The changes in refractive indices (n(TE) and n(TM)) in a direction normal to the plane of thin films of an organo-soluble polyimide based on 1,4-bis(3,4-dicarboxyphenoxy) benzene dianhydride and 2,2'-dimethyl-4,4'-methylene dianiline were measured by a prism coupler. The results implied that the molecules near the substrate-polyimide interface were much ordered, while those near the polyimide-air interface were less ordered, judging from the variation in the level of negative birefringence with the depth of the films. The molecules are more condensed near the substrate surface, as seen by the average refractive index increasing from the polyimide-air interface to the substrate-polyimide interface, which implies that the condensed states of polyimide molecules change gradually in the depth direction. (C) 1997 Elsevier Science B.V.

Red color filter in an organo-soluble polyamide matrix for liquid crystal displays

A red color filter was laminated from a solution of red color pigment and an organo-soluble polyamide, based on 1,4-bis(3,4-dicarboxyphenoxy) benzene dianhydride (HQDPA) and 2,2'-dimethyl-4,4'-methylene dianiline (DMMDA). The red color filter in a polyamide matrix with negative birefringence plays an important role in twisted nematic liquid crystal displays (TN-LCDs). The red color filter, and also compensation films, extend the viewing angle of LCDs. (C) 1997 Elsevier Science S.A.

The miscibility of homopolymer random copolymer blends .3. Blends of SAA with polymethacrylates and polyesters

The miscibility of blends of poly(styrene-co-allyl alcohol) (SAA) with poly(methyl methacrylate) (PMMA), poly(ethyl methacrylate) (PEMA), poly(n-butyl methacrylate) (PnBMA), poly-epsilon-caprolactone (PCL) or polycarbonate (PC) has been studied by means of NMR, FT-IR and DSC techniques. It was found that SAA and PMMA, PEMA or PCL form miscible blends and SAA is only partially miscible with PC or PnBMA. Both phenyl groups and hydroxyl groups in SAA are involved in the intermolecular interactions between SAA and PMMA, PEMA or PCL. Also the hydroxyl-carbonyl hydrogen bonds existing in all the miscible blends studied are formed partially at the expense of the disruption of self-association of hydroxyl groups in pure SAA. (C) 1997 Elsevier Science Ltd. All rights reserved.

The synthesis of a 1,1'-bi-2-naphthol-based bis(ether anhydride) and aromatic polyimides derived therefrom

2,2'-Bis(3,4-dicarboxyphenoxy)-1,1'-binaphthyl dianhydride was used as a new monomer with various aromatic diamines to obtain polyimides by the usual two-step method. The bis(ether anhydride) was prepared by a nucleophilic substitution of I,1'-bi-2-naphthol with N-phenyl-4-chlorophthalimide, N-methyl-4-nitrophthalimide or 4-nitrophthalonitrile in aprotic polar solvent, and subsequent hydrolysis of the resulting bis(ether imide)s or bis(ether dinitrile), and then dehydration of the corresponding tetracarboxylic acid to afford the dianhydride. Most of the obtained polyimides were soluble in chloroform, pyridine, DMF, etc. The polyimide prepared from p-phenylene diamine was partial crystalline, whereas the others showed amorphous patterns in a WAXD study. These polymers have glass transition temperatures between 255-294 degrees C and 5% weight loss temperatures in the range of 502-541 degrees C in nitrogen and 473-537 degrees C in air. (C) 1997 Elsevier Science Ltd.

An effective etching technique for polycarbonate/core-shell poly(butyl acrylate) poly(methyl methacrylate) blend

Two etching techniques are used to reveal the morphology of PC/PBA-cs-PMMA blend. One is based on acetic acid (CH3COOH) solutions, whereas the other uses CCl4/ C2H5OH (3/1 v/v). The latter approach shows to be more appropriate and successful for revealing the morphology of PC/PBA-cs-PMMA blend.

Crystallization behavior of a novel poly(aryl ether ketone): PEDEKmK

Isothermal melt and cold crystallization kinetics of PEDEKmK linked by meta-phenyl and biphenyl were investigated by differential scanning calorimetry in two temperature regions. Avrami analysis is used to describe the primary stages of the melt and cold crystallization, with exponent n = 2 and n = 4, respectively. The activation energies are -118 kJ/mol and 510 kJ/mol for crystallization from the melt and the glassy states, respectively. The equilibrium melting point T-m(0) is estimated to be 309 degrees C by using the Hoffman-Weeks approach, which compares favorably with determination from the Thomson-Gibbs method. The lateral and end surface free energies derived from the Lauritzen-Hoffman spherulitic growth rate equation are sigma = 8.45 erg/cm(2) and sigma(e) = 45.17 erg/cm(2), respectively. The work of chain folding q is determined as 3.06 kcal/mol. These observed crystallization characteristics of PEDEKmK are compared with those of the other members of poly(aryl ether ketone) family. (C) 1997 John Wiley & Sons, Inc.