The synthesis and characterization of the novel poly(aryl ether ketone)s with liquid crystallinity

The novel poly(aryl ether ketone)s with liquid crystallinity were synthesized by nucleophilic substitution reactions of 4,4'-biphenol and substituted hydroquinone with 4,4'-difluorobenzophenone and their thermotropic liquid crystalline properties were characterized by DSC, PLM and WAXD, The copolymers containing 70% biphenol formed nematic phase while the copolymer containing 50% biphenol exhibited smectic texture, The banded textures were formed after shearing the sample in the nematic liquid crystalline state. The identification of the structures in each mesogenic phase has been carried out by combining WAXD with PLM and DSC.

Influence of annealing on structure of poly(aryl ether ether ketone ketone) revealed by SAXS

Structural studies of poly(aryl ether ether ketone ketone) (PEEKK) using small-angle X-ray scattering and one-dimensional electron density correlation function methods revealed that its aggregated state structure was significantly influenced by the annealing temperature. The long period L, the average thickness of the lamellae d, the electron density difference between the crystalline and amorphous regions eta(c) - eta(a), and the invariant Q increased with increasing annealing temperature, but it was opposite to the case of the specific inner surfaces O-s. A transition zone existed between the traditional "two phases" with a dimension about 0.5 nm for semicrystalline PEEKK. (C) 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 1829-1835, 1998.

Sodium sulfonate-functionalized poly(ether ether ketone)s

A new monomer, sodium 5,5'-carbonylbis(2-fluorobenzenesulfonate) (1), was synthesized by sulfonation of 4,4'-difluorobenzophenone (2) with fuming sulfuric acid. Poly(ether ether ketone)s containing sodium sulfonate groups were synthesized directly via aromatic nucleophilic substitution from the sodium sulfonate-functionalized monomer 1 and Bisphenol A (3) in the presence of potassium carbonate in dimethyl sulfoxide. The polycondensation proceeds without any side reactions. The differential scanning calorimetry measurement indicated that the polymers are amorphous and the glass transition temperatures increase with the content of sodium sulfonate groups in the polymer chain. The degree of substitution with sodium sulfonate groups has strong influence on their thermal stability and solubility.

Novel poly(aryl ether ketone)s exhibiting liquid crystallinity

Novel poly(aryl ether ketone)s were synthesized by nucleophilic substitution reactions of difluoromonomer with 4,4'-biphenol and substituted hydroquinone. The results showed that the novel polymers exhibited multiple phase transitions and formed optical birefringence textures above their melting transitions.

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.

The synthesis and thermotropic liquid crystalline behaviour of novel main chain poly(aryl ether ketone)s containing a lateral phenyl group

Novel main chain poly(aryl ether ketone)s containing a lateral phenyl group were synthesized by nucleophilic substitution reactions of 4,4'-biphenol and phenylhydroquinone with either 4,4'-difluorobenzophenone or 1,4-bis(4-fluorobenzoyl)benzene and their thermotropic liquid crystalline properties were characterized by a variety of experimental techniques. Thermotropic liquid crystalline behaviour was observed in the copolymers containing 50 and 70mol% biphenol. Melting (T-m) and isotropization (T-i) transitions both appeared on the DSC thermograms. A banded texture was formed after shearing the sample in the liquid crystalline nematic state. As expected, each of the copolymers had a relatively lower melting transition than the biphenol-based homopoly(aryl ether ketone)s because of the copolymerization effect of the crystal-disrupting monomer phenylhydroquinone.

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

Nonisothermal melt crystallization kinetics of PEDEKmK linked by meta-phenyl and biphenyl was investigated by differential scanning calorimetry (DSC). A convenient and reasonable kinetic approach was used to describe the nonisothermal melt crystallization behavior, and its applicability was verified when the modified Avrami analysis by the Jeziorny and Ozawa equation were applied to the crystallization process. The crystallization activation energy was estimated to be -219 kJ/mol by Kissinger method while crystallizing from the PEDEKmK melt nonisothermally. These observed crystallization characteristics were compared to those of the other members of poly(aryl ether ketone) family. (C) 1998 John Wiley & Sons, Inc.

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.

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.

Cure processing modeling and cure cycle simulation of epoxy-terminated poly(phenylene ether ketone) .3. Determination of the time of pressure application

The curing temperature, pressure, and curing time have significant influence on finished thermosetting composite products. The time of pressure application is one of the most important processing parameters in the manufacture of a thermosetting composite. The determination of the time of pressure application relies on analysis of the viscosity variation of the polymer, associated with curing temperature and curing time. To determine it, the influence of the time of pressure application on the physical properties of epoxy-terminated poly(phenylene ether ketone) (E-PEK)-based continuous carbon fiber composite was studied. It was found that a stepwise temperature cure cycle is more suitable for manufacture of this composite. There are two viscosity valleys, in the case of the E-PEK system, associated with temperature during a stepwise cure cycle. The analysis on the effects of reinforcement fraction and defect content on the composite sheet quality indicates that the width-adjustable second viscosity valley provides a suitable pressing window. The viscosity, ranging from 400 to 1200 Pa . s at the second viscosity valley, is the optimal viscosity range for applying pressure to ensure appropriate resin flow during curing process, which enables one to get a finished composite with optimal fiber volume fraction and low void content. (C) 1997 John Wiley & Sons, Inc.

Cure processing modeling and cure cycle simulation of epoxy-terminated poly(phenylene ether ketone) .4. Cure cycle simulation

Epoxy-terminated poly(phenylene ether ketone) (E-PEK) developed in this Institute is a candidate matrix resin for polymer composites as structural materials. Cure cycles for this reaction system were simulated according to the previously established processing model. It is found that for the E-PEK system, the curing process is best completed by a stepwise cure cycle comprising two isothermal processes at different temperatures, T-1 and T-2. The cure cycles over a wide range of processing parameters simulated, based on the established processing model, indicate that the processing window is width-adjustable. Analysis of the mechanical properties of the composite sheets showed that the simulated cure cycles are acceptable and reliable. (C) 1997 John Wiley & Sons, Inc.

Cure processing modeling and cure cycle simulation of epoxy-terminated poly(phenylene ether ketone) .1. DSC characterization of curing reaction

The curing reaction process of epoxy-terminated poly(phenylene ether ketone) (E-PEK) with 4,4'-diaminodiphenyl sulfone (DDS) and hexahydrophthalic acid anhydride (Nadic) as curing agents was investigated using isothermal differential scanning calorimetry (IDSC) and nonisothermal differential scanning calorimetry (DDSC) techniques. It was found that the curing reactions of E-PEK/DDS and E-PEK/Nadic are nth-order reactions but not autoaccelerating. The experimental results revealed that the curing reaction kinetics parameters measured from IDSC and DDSC are not equivalent. This means that, in the curing reaction kinetics model for our E-PEK system, both isothermal and nonisothermal reaction kinetics parameters are needed to describe isothermal and nonisothermal curing processes, The isothermal and nonisothermal curing processes were successfully simulated using this model. A new extrapolation method was suggested. On the basis of this method the maximum extent of the curing reaction (A(ult)) that is able to reach a certain temperature can be predicted. The A(ult) for the E-PEK system estimated by the new method agrees well with the results obtained from another procedure reported in the literature. (C) 1997 John Wiley & Sons, Inc.