1993 рік

Oxidative polymerization of aniline in aqueous dispersion stabilized by poly(vinyl alcohol coacetate) was studied in situ by electron absorption spectroscopy. A mechanism is proposed, accounting for the dependence of the main polymerization steps (oxidation and reduction) on both the pH of the medium and the oxidation state of the chain

Детальніше...  

Novel copoly(isocyanurate-urea)s have been produced by reaction injection moulding (RIM). The materials were formed from -,~ 2:1 weight ratio of polyisocyanate to polyoxypropylene polyamine in the presence of an organic trimerization catalyst. In some cases an aromatic diamine chain extender was also used. The effects of the polyether polyamine functionality and the incorporation of aromatic diamine chain extenders on the morphology and properties of the copoly(isocyanurate-urea)s were studied using the SAXS, TEM, d.m.t.a, and tensile stress-strain techniques. The RIM materials were stiff plastics with room-temperature Young's moduli between 1.5 and 0.7 GPa, depending on the morphology. Development of morphology is a result of competition between polymerization kinetics, chemical gelation and (micro)phase separation. Materials with an isotropic, co-continuous morphology with a size-scale of ~ 100,~ had higher moduli than materials containing isolated glassy particles of ~ l #m in size. Correlations between morphology and dynamic mechanical-thermal and tensile stress-strain properties of a systematic series of copoly(isocyanurate-urea)s have been established

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Novel, reactively terminated, polysulphone thermoplastics have been used as particulate interlaminar toughening agents in epoxy, bismaleimide, and cyanate ester resin based composites. These particles dissolved completely into each thermoset resin matrix during cure, resulting in two separate toughening mechanisms. A crack front pinning type toughening was observed at low particle areal densities in the interlaminar regions ( < 3 x 103 particles cm-2), whilst a toughened film interleaf effect was produced at high particle areal densities (> 6 x 103 particles cm-2). The fracture toughness, Glc, of one epoxy composite was improved from 0.51_ 0.07 kJ m-2 to 0.77 + 0.10 kJ m-2, with no drop in interlaminar shear strength. Compression after impact testing of the cyanate ester composite at 6.67 x 103 J m- 1 revealed a decrease in delamination area from 28.2+3.0cm 2 to 11.6+1.5cm 2 with interlaminar toughening. Compression resistance rose accordingly from 223.4+0.7MPa to 268.9+ 15.9MPa. This was achieved for a laminate weight increase of only 1.1%

Детальніше...  

Chemical oxidative polymerization of aniline in aqueous dispersion stabilized by poly(vinyl alcohol coacetate) in initially neutral and alkaline media was studied by electron absorption spectroscopy and in situ pH measurements. It was shown that polyaniline could be obtained only under conditions when the initial stage of polymerization (formation of oxidized dimer) results in a decrease of pH to values lower than about 2.

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The morphology, crystallization kinetics and melting behaviour of the blends of poly(ether ether ketone) (PEEK) with poly(ether sulfone with cardo side group) (PES-C) prepared by casting from solution were studied using optical microscopy, scanning electron microscopy, wide-angle X-ray scattering and differential scanning calorimetry. The amorphous PES-C was shown to be trapped interfibrillarly or interlamellarly in the spherulites of PEEK at a relatively low crystallization temperature. Its addition causes dilution of the nuclei in PEEK and a great depression in the spherulitic growth rate and overall crystallization rate of PEEK. Also, melting point and crystallinity of PEEK are lowered by PES-C. Besides composition, crystallization temperature was shown to have an influence on the morphology, crystallization kinetics and melting behaviour of the blends.

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The feasibility of introducing a second thermotropic liquid crystalline polymer (TLCP) as a compatibilizer, or coupling agent, in order to improve the adhesion and dispersion between components of incompatible TLCP/thermoplastic blends was investigated. Two TLCP blends of a wholly aromatic copolyester (K 161) with poly(ethylene terephthalate) (PET) and polycarbonate (PC) were prepared by a two-step melt-blending process, using an aliphatic containing TLCP, PET/60% poly(hydroxybenzoate) (PHB60), as the coupling phase. Preliminary morphological evidence indicated that the K161 reinforcing phase in the ternary systems exhibited improved adhesion and dispersion in a much finer scale than in binary blends of K 161/PET and K161/PC prepared under the same processing conditions. It was found that the adhesion between the reinforcing K161 and the matrix PET phases depended on both the concentration of the coupling PET/PHB60 phase and the relative composition of the two TLCPs. The improved adhesion between K161 and PC matrix with the inclusion of PET/PHB60 phase was further delineated by comparing the phase morphology and mechanical properties of the ternary blends after a cold-drawing process with those of the binary systems. While the binary systems remained practically unaffected by the cold-drawing process, the ternary blends exhibited a well aligned and elongated K161 fibrillar phase with a diameter of around 1 pm or less. An increase of both initial modulus and breaking strength suggests that the enhanced adhesion between K161 and PC facilitates a better stress transfer for the deformation of the dispersed K161 particles into oriented, ellipsoidal domains. Other characterizations, including both differential scanning calorimetry and dynamic mechanical analysis, were conducted to elucidate the nature of the interactions between the components.

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A series of model compounds has been synthesized from 4-benzoylnaphthalic anhydride and oxydianiline in various solvents (aprotic, protic), with or without catalyst at 180°C. A mechanism of the reaction is proposed.

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Polybenzimidazole (PBI) is known to absorb 15 wt % water at equilibrium. This sorbed water greatly affects the mechanical properties of this polymer. Both FTi.r. and broadline n.m.r, have been used to study the interaction between water and PBI. The results clearly show that the water in PBI is mobile and therefore does not hydrogen bond to the polymer chain.

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The divinyl ether of diallylbisphenol A (VEABA) was investigated as a candidate for advanced composite matrix resin. VEABA was readily prepared in over 90% yield from a condensation reaction between diallyl bisphenol A and chloroethyl vinyl ether using a phase transfer catalyst. Since vinyl ethers are electron-rich monomers, they are polymerized by cationic initiators. The VEABA polymer possesses properties comparable to polymers produced from epoxy resins based on the diglycidyl ether of bisphenol A, except for much lower moisture absorption and a slightly lower glass transition temperature. Since the VEABA monomer is a low viscosity liquid, it is a good candidate for filament winding, resin transfer moulding and pultrusion fabrications for advanced composites.

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Both the internal and external porous structure of poly(p-phenylene) films, synthesized electrochemically via oxidation of benzene in concentrated H2SO4, was shown to be highly regular, possessing two characteristic ranges of pore radii, up to 2.5 and 80-200 nm.

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