1994 рік

Silicone rubber was functionalized with acrylamide (AM) to effect interaction with sulfonated EPDM. I.r. spectroscopic studies confirm the dipole-dipole interactions between this graft copolymer (AM-9-silicone) and sulfonated EPDM (S-EPDM) through the splitting of the carbonyl stretching and N H stretching peaks. Physical property measurements show that the functionalized blend has a higher tensile strength, modulus and swelling resistance and lower elongation at break. The thermal stability and ageing behaviour of the new blends are improved owing to an increase in the activation energy of degradation. Finally, dynamic measurements show that the transition temperatures are all increased by 8 10°C and the storage modulus in the temperature range 25-125°C is higher, owing to strong interspecies interactions between the components in the functionalized blends

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High-temperature thermoset polyimide resins were prepared using p-phenylenediamine and a 1:3 mixture of 1,1,1,3,3,3-hexafluoro-2,2-bis(3,4-dicarboxyphenyl)propane dianhydride (6FDA) and 3,3',4,4'-tetracarboxybiphenyl dianhydride (BPDA) for the imide backbone, and diarylacetylene derivatives as reactive capping agents. The thermo-oxidative stability at 370°C of the cured resins was evaluated in comparison with control samples based on several known reactive capping agents. The polyimide resin end-capped with 4-(phenylethynyl)phthalic anhydride exhibited the best thermo-oxidative stability.

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A l:2 complex of MgCI 2 and tetrahydrofuran (THF) was prepared by a simple Grignard decomposition reaction using Mg metal and 1,2-dichloroethane in THF as diluent. The MgC12.2THF complex formed a homogeneous solution with titanium-n-butoxide in xylene at 60°C. The soluble Mg-Ti complex in xylene polymerized ethylene under homogeneous conditions in the presence of organoaluminium compounds. The kinetic behaviour of the polymerization reaction was studied. It was observed that the presence of MgCI2 transformed the Ti centre from a dimerization to a polymerization catalyst.

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In this paper, we show that mechanically stretching an immiscible blend made from a nematic side-chain liquid crystalline polymer and a conventional polymer is an efficient way to induce a rapid macroscopic orientation of the mesogenic groups along the stretching direction. The basic condition for this achievement is to perform the mechanical stretching at temperatures between the glass transition temperature and the clearing temperature of the nematic polymer in order to take advantage of the intermolecular co-operativity which is indispensable for a rapid alignment of the nematic domains. The alignment is monitored by determining the orientation of the mesogenic groups using the i.r. dichroism technique. The liquid crystalline polymers investigated are two nematic polyacrylates, and the conventional polymers used are a styrene-butadiene-styrene triblock copolymer, which is a thermoplastic elastomer, and a poly(vinyl chloride).

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The deformational behaviour of linear high density polyethylene (HDPE) in simple shear to large strains and the mechanisms involved in this deformation were investigated. The specimens were sheared at a constant rate at room temperature. The structure and morphology of the samples of HDPE deformed to various permanent shear strains up to 6.3 were studied using wide-angle and small-angle X-ray scattering and transmission electron microscopy. The results show that the simple shear deformation of HDPE is controlled by crystallographic slip mechanisms, mostly the (100)[001 ] chain slip supported by the (100)[010] transverse slip and (010)[-001] chain slip. The crystallographic deformation mechanisms were found to be active in the whole range of the strain history. At strains up to 3.0 the deformation by these mechanisms is supported by shear in the amorphous interlamellar layers (interlamellar sliding) which also alters the orientation of the crystalline phase. This sliding appears to be partially reversible on unloading. At moderate strains chain slip becomes unstable, which causes the localization of deformation within numerous fine shear bands. Further deformation concentrated in bands leads to the destruction of the crystalline lamellae and the transformation of the sample morphology into a microfibrillar one at a shear strain near 4.3. Further deformation, mostly by chain slip, in the crystals arranged after their fragmentation into microfibrils results in a sharp, nearly axial texture with the chain axis c tilted a few degrees away from the direction of shear.

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New soluble aromatic polyimides have been prepared from 4,4'-(hexafluoroisopropylidene)bis(phthalic anhydride) (6FDA) and 4,4'-(alkylenediyldioxy)dianilinesT. heir structures were determined by i.r., *H n.m.r. and 13C n.m.r, spectroscopic measurements, based on model compounds prepared by reacting 6FDA with p-anisidine. These polymers show low glass transition temperatures and good solubility in various solvents, and are stable up to 440°C in a nitrogen atmosphere

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We analyse the conformation of copolyamides with regularly alternating glycine and ~o-amino acid units (nylons 2In). These polymers have a crystalline structure with hydrogen bonds running in three different directions; the standard structure of nylons with parallel sheets of hydrogen-bonded molecules is no longer present. The detailed structure depends on whether n is odd or even, which respectively gives rise to trigonal or hexagonal crystalline structures

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Samples of injection moulded poly(aryl-ether-ether-ketone) (PEEK) resin with molecular weights covering the range, M,= 15000-50000, have been subjected to a variety of thermal treatments, and the resulting material properties measured. It was found that crystallinity could be increased by annealing the mouldings, but also that an effective ceiling value depended on the molecular weight, i.e. the higher the Mw, the lower the maximum crystallinity. Tensile modulus and yield strength of the moulded polymer increased with increasing crystallinity, but the molecular weight had no detectable effect in these cases. In contrast, both crystallinity and molecular weight independently influenced the toughness. Toughness was found to increase with increasing molecular weight, and to decrease with increasing crystallinity. Implications of these effects on the injection moulding of components of PEEK are discussed

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The microvoid formation process that takes place during the plastic deformation of fl-form polypropylene (PP) was investigated at different crystallization and drawing temperatures. It was found that the porosity increased with both a higher crystallization temperature and a lower drawing temperature. This fact could be understood in terms of the stability of the fl crystals of the original film. The more stable /3 crystals that formed at a higher crystallization temperature had a lower molecular chain mobility and thus hindered the bulk contraction of the film, while at the same time the volume contraction caused by either a fl-~ or a/3-smectic transformation inside the film enlarged the microvoids at the end, or between the microfibrils

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Twenty semicrystalline polyimides based on well-known aromatic dianhydrides and aliphatic ct,(o-diamines have been synthesized and characterized. Poly(BTDA-DAB) synthesized in a two-step process from 3,Y,4,4'-benzophenonetetracarboxylic dianhydride (BTDA) and 1,4-diaminobutane (DAB) exhibits a rather exclusive balance between thermal/mechanical properties and processability. In the series of ct, co-diamines and BTDA the glass transition temperature (Tg) increases linearly with the decrease in CH 2 units, while the melting temperature (Tin) shows the well-known odd-even effect. For the as-synthesized poly(BTDADAB) Tg and T,, are 175 and 277°C, respectively. After melt processing a sharp decrease in crystallinity is observed with X-ray and d.s.c., however annealing of injection moulded test bars results in a higher crystallinity. The semicrystalline poly(BTDA-DAB) exhibits interesting mechanical properties, e.g. a G' modulus of 1.7 kN mm- 2 and an Izod impact of 3.4 kJ m- 2.

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