1994 рік

The preparation of a novel family of polyamide network gels is described. In these networks, the segments are stiff and longer than the critical axial ratio for mesomorphic behaviour. The junctions are trifurcated and flexible. The gels were prepared at 10% network concentration. They are intensely birefringent in the relaxed nascent state, unlike fully rigid or flexible network gels. Upon swelling in N,N-dimethylacetamide (DMAc) to equilibrium, the gels lose their birefringence, which is recovered when the equilibrated gels are heated to less than 120°C and then cooled. The birefringence of the present gels is clearly associated with the coexistence in them of both long, stiff mesogenic segments and flexible trifurcated junctions. X-ray diffraction studies reveal the gelled networks to be fully amorphous. Thermal studies by differential scanning calorimetry indicate very strong attractive interactions between the polyamide networks and DMAc solvent, manifested by pronounced solvent retention in the gels at high temperatures and substantial lowering of both freezing and melting points of the DMAc in the gels relative to its transitions in the bulk

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The crystallization behaviour of the poly(ethylene terephthalate-co-l,4-cyclohexylene dimethylene terephthalate) (P(ET/CT)) random copolyesters is studied by d.s.c, analysis. ET units can crystallize with complete rejection of the CT units from the crystals, whereas CT units can co-crystallize with incorporation of ET units to some extent, resulting in a minimum melting temperature at an intermediate composition of about 30--40 mol% CT. A good linear relation is found between the compositions at which the melting point exhibits a minimum experimentally in various random copolyesters and those at which the cohesive energies for two components estimated by group contribution methods are identical.

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Dielectric and viscoelastic relaxation measurements have been performed on poly(2-chloroethyl methacrylate) and poly(3-chloropropyl methacrylate) between -140°C and the glass transition temperatures. The splitting of the dipolar relaxations from those of conductive origin in the dielectric spectra was performed

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The effects of pH, ionic strength and concentration of the phase-transfer catalyst, tetrabutylammonium bromide, on the rate of decomposition of potassium peroxydisulfate under conditions of free-radical phase-transfer-catalysed (PTC) polymerization have been studied. The resulting rates of initiation and polymerization of methyl methacrylate under the same conditions, which reveal the effect of transfer of initiating species into the organic phase, are also presented. Low ionic strength of the aqueous phase and a pH value of 34 are the most favourable conditions to achieve the highest generation rate of free radicals in the organic phase under the conditions of PTC polymerization.

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An electrochemical process for preparing thermoplastic matrix-graphite fibre composites has been developed. Graphite fibre-poly(maleimide-co-styrene) matrix composites were prepared using unsized AS-4 graphite fibre preforms as the working electrode. Copolymers of a wide range of N-substituted maleimides and styrene were formed directly on the surface of the graphite fibres. The rate of electrocopolymerization varied with the electrocopolymerization parameters, such as the comonomer concentration, current density, supporting electrolyte concentration, electropolymerization time, nature of the solvent, solvent/dilute sulfuric acid ratio and the structure of the maleimide. Graphite fibre preforms preimpregnated with the electropolymerized thermoplastic matrices were processed into unidirectional composite laminates. The electrosynthesized thermoplastic matrix composites showed excellent physical and mechanical properties.

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Poly(oxy-l,4-benzenediylcarbonyl) (POB) whiskers from p-acetoxybenzoic acid were prepared in mixtures of liquid paraffin having many branched carbons (LP) and completely linear paraffin (SW). The crystal shapes of the POB whiskers obtained were largely changed by the mixing ratio of LP and SW. When the content of SW in the solvents increased: (i) both the length and the width of the whiskers decreased; (ii) the tip angle of the whiskers increased; and (iii) radial growth of the whiskers increased. The size of the POB whiskers was attributed to both the number and the size of those lamellar crystals with screw dislocations (primary nuclei for whisker growth) which had formed in the early stages of polymerization. In SW, larger numbers of smaller lamellar crystals were formed than in LP, owing to the lower solubility of POB oligomers at 330°C in SW; that is, the higher supersaturated state of the POB oligomers produced a larger number of smaller primary nuclei for whisker growth. Hence, whiskers having smaller lengths and widths were obtained as the content of SW increased. The other characteristic changes in whisker shapes, i.e. tip angles and radial growth, also seemed to be attributable to the degree of supersaturation of the POB oligomers, though further study is required. The thermal properties of the whiskers were evaluated by differential scanning calorimetry and thermogravimetric analysis.

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The mechanical properties of aromatic and heteroatom-containing aliphatic polyacetylenes were examined. Regarding tensile properties, aromatic polyacetylenes [i.e. ring-substituted poly(phenylacetylene)s and poly(diphenylacetylene)s] showed large Young's moduli (500-2000 MPa) and small elongations at break (1-8%), implying that these polymers are hard and brittle. In contrast, Young's moduli of Si- and S-containing aliphatic polyacetylenes were rather small (several hundred megapascal), and their elongations at break were relatively large (several tens per cent); i.e. they are soft and ductile. This tendency was remarkable in the polymers having long n-alkyl chains. According to dynamic viscoelastic measurements, the glass transition temperatures (Tgs) of poly(diphenylacetylene)s were >200°C, whereas those of poly(phenylacetylene)s were 110-200°C, depending on the kinds of substitutents. The Tgs of aliphatic polyacetylenes are 40-160°C, lower than those of aromatic polyacetylenes. The effects of substituents on Tg are discussed in comparison with those of vinyl polymers.

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Poly(styrene-b-2-vinylpyridine) diblock copolymer films with horizontally oriented lamellar microdomains were obtained by the casting method. Poly(2-vinylpyridine) (P2VP) layers were not only quaternized but also crosslinked with 1,4-diiodobutane vapour with the intention of immobilizing the supermolecular structure. Cu 2 ? ions (oxidant) were introduced into P2VP layers by complexation based on the pyridine nitrogen interacting with the metal ions. Electrically conducting films were synthesized with such an oxidizing agent being added to a mixture of pyrrole and water vapour. The element distributions on a vertical section of the composite films were measured by energy dispersive X-ray spectrometry. These films showed conductivities of 10-1 S cm- 1 parallel to the film plane and had high anisotropic conductivity.

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The base-induced polymerization of 1,4-bis(tetrahydrothiopheniomethyl)-2-cyano-5-methoxybenzene dibromide in aqueous acetonitrile yields a soluble polyelectrolyte which may be thermally eliminated to give the electronically 'push-pull' substituted poly(2-cyano-5-methoxy-l,4-phenylene vinylene). Ultraviolet- visible and infra-red spectral studies showed production of the conjugated polymer, with a band gap of ca. 2.6-3.0 eV (410--480 nm) that varied somewhat as a function of elimination conditions. Elemental analysis indicates some retention of tetrahydrothiophenium side groups in the polyelectrolyte polymer, despite the use of a variety of elimination conditions. The retention of side chains in this synthesis is possibly due to a significant degree of irregularity in the positions of the cyano and methoxy substituents in the eliminated polymer, resulting from non-regioselectivity in this polymerization. This reaction demonstrates the potential in the Wessling process for polymerization of p-xylylenes that have electronically very asymmetric ('push-pull') substitution patterns.

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The compatibilization effect of poly(styrene-b-methyl methacrylate) on the immiscible polymer blend of polystyrene and poly(styrene-co-acrylonitrile) was examined by dynamic mechanical spectroscopy. Special regard was taken of additional relaxation processes in the flow region, which were analysed using weighted relaxation-time spectra. Furthermore, an important topic of our research was the characterization of the morphology by energy-specific transmission electron microscopy. By increasing the amount of compatibilizer, the average particle size decreases from large polystyrene domains (R~-0.2 #m) down to micellar dimensions (R = 60 nm). In this way, typical morphological structures in the blends were related with rheological behaviour. With a modified emulsion model from Choi and Schowalter, some correlations between particle size and trends in interfacial tension could be established dependent on compatibilizer concentration. Especially, it was found that the particle size reduction and the reduction of interracial tension occur in different ranges of block-copolymer concentration

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