1999 рік

Global conformations of chiral polyisocyanates were discussed in terms of light scattering and viscosity data collected for stereospecifically deuterated poly(hexyl isocyanate)s, poly((R)-2,6-dimethylheptyl isocyanate) (PNIC), and copolymers of hexyl isocyanate (HIC) with (R)-2,6-dimethylheptyl isocyanate (NIC). The light scattering data and viscosity data obtained were analyzed consistently in the framework of the worm-like chain model. The persistence length q was the same for PHIC and deuterated PHIC, but increased with the mole fraction of NIC in the HIC–NIC copolymers, e.g. from 41 to 56 nm in hexane at 25°C. The results were not detailed enough to substantiate the broken worm model in line with the helix reversal model of Lifson et al. Gel permeation chromatographic behavior of the polyisocyanates was also examined, so that it could be used for the determination of the molecular weight distribution of a sample with a very minute amount (at most 1 mg or less).

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Free-radical copolymerizations of vinylbenzyl-terminated polystyrene (PS–VM; M1) and maleate-terminated poly(ethylene glycol methyl ether) PEG–MM; M2) were carried out in benzene. Mixtures of the PEG–MM and PS–VM showed phase separation during copolymerization. The copolymerization reactivity was estimated from the distribution functions by gel permeation chromatography of the comb-shaped copolymers produced. The reactivity ratios (r1 ˆ 0.765 and r2 ˆ 0.064) obtained for the binary macromonomer system were different from corresponding model systems of styrene and maleic acid ethyl ester (r1 ˆ 0.13 and r2 ˆ 0.035) due to phase separation.

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Fluorine-19 NMR analyses allowed to obtain kinetic data about bicyclo[2.2.2]oct-7-ene dianhydrides thermal imidization. It was evidenced that the high reactivity of such a substrate is owing to the combined effects of bifunctionality and ethenylene bridge. This latter effect is inhibited by the presence of an electron-withdrawing group on the double bond. A basic solvent (NMP) does favor the amic acid intermediate formation; an acidic solvent (m-cresol) does accelerate the amic acid cyclization to imide.

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Structure–property relationships in a number of different aromatic high-modulus fibres have been examined in detail. Fibres studied include Kevlar, Twaron, Technora and PBO and it has been shown using Raman spectroscopy that these fibres exhibit similar molecular deformation processes. The stress-induced shift of the 1610 cm -¹ Raman band, assigned to a stretching mode of the p-phenylene ring, is found to be approximately ¹ 4.0 cm -¹/GPa for all of the fibres, independent of their chemical structures and morphologies. A similar rate of shift is found for the same band in poly(ethylene terephthalate) fibres. This implies that the molecular deformation processes in these different fibres are similar even though the fibres have different chemical structures and morphologies, and have been processed differently. It is shown that the mechanical behaviour of the fibres is consistent with deformation following a uniform stress series aggregate model.

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The structure and morphology of lamellar crystals of a sequential copolymer of poly(pirrolidinone) with poly(1 -caprolactam) (nylon 4/6 copolymer) has been studied by transmission electron microscopy, electron diffraction and X-ray diffraction. The results obtained indicate that at room temperature single crystals of this copolymer have an a -form structure which is also the most stable one for both related homopolymers. The crystallographic unit cell is monoclinic with a ˆ 9.60 Å, b (chain axis) ˆ 14.80 Å, c ˆ 8.06 Å and b ˆ 67°. The effects of temperature on the lattice spacings show that the characteristic 200 and 002 equatorial spacings converge with increasing temperature but do not meet prior to the melting temperature. In conclusion, the copolymer and the related homopolymers behave similarly with respect to their room temperature most stable crystal structure and behavior on heating. The second characteristic crystalline phase (g -form) reported for even nylons could only be obtained by treating the polymer sample with iodine–potassium iodide solutions.

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A polyacrylonitrile (PAN) fibre, Dralon T (DT), and a copolymer manufactured as a carbon fibre precursor, Special Acrylic Fibre (SAF), were studied as received and after heat-treatment in air at various temperatures up to 3008C. Wide angle X-ray scattering (WAXS) was undertaken on single fibres, fibre bundles and films, utilizing both conventional and synchrotron sources. With a conventional source, the normal WAXS pattern was observed for both polymers, i.e. two main equatorial reflections, a diffuse equatorial reflection and a diffuse offequatorial reflection. With a synchrotron source, seven equatorial WAXS reflections could be detected in DT. Also, a sharp, meridional reflection was observed in SAF as received and in DT after stretching at 1008C. Unpolarized and polarized infra-red spectra were obtained from single fibres and films by FTIR microscopy. A measure of the extent of reaction (EOR) following heat-treatment was derived from the intensity of the nitrile absorption and the intensity of absorption at 1600 cm 21: EOR ˆ [I1600/(ICN 1 I1600)]. Two complementary measures of orientation were used to follow changes on heat-treatment: the peak width at half-height of an azimuthal plot of the most intense WAXS reflection and the nitrile dichroic ratio from FTIR microscopy. For fibres held under tension during heat-treatment, the degree of orientation by either measure did not decrease until the EOR exceeded 0.5. Solid-state 13C NMR, together with IR results, indicated that at least three chemical processes occurred on heat-treatment: nitrile reaction, conjugated C ˆ C formation and oxidation.

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A systematic modelling analysis for polyaddition of poly(butylene glycol adipate) [PBA] to isophorone diisocyanate (IPDI), xylene diisocyanate (XDI) and hydrogenated xylene diisocyanate (H 6XDI) ternary diisocyanate-based waterborne polyurethane (WPU) synthesized by a modified acetone process was performed. Using a mixture of experimental designs, empirical models are fitted and plotted as contour diagrams, which facilitate revealing the synergistic/antagonistic effects between the mixed diisocyanates. The results indicate that each component demonstrates different performances in either binary (IPDI–XDI, XDI–H 6XDI and IPDI–H 6XDI) or ternary (IPDI–XDI– H 6XDI) systems with the IPDI-based WPU, which possesses the highest tensile strength. The largest ultimate elongation occurs at 1 1 1 3IPDI/ 3H 6XDI/ 3 XDI ternary diisocyanate-mixed WPU. Particle size analysis shows that the larger particles are obtained in the dispersion of IPDI–XDI binary WPU. Differential scanning calorimetry (DSC) results show that PBA polyol and its converted WPU show doublet melting behaviour. A plot of 1/TLm (lower melting temperature) against ¹ lnX IPDI (mole fraction of IPDI in mixed diisocyanates) is approximately linear, indicating that the hard segments are randomly distributed along the molecular chain. Wide angle X-ray diffraction (XRD) and polarized microscopy (POM) on these WPU films were also examined.

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The polymerization of maleic anhydride was investigated under constant current electrolysis in a simple H-type divided cell with 1,4dimethylpyridiniumiodide as supporting electrolyte. The polymer formation depends on polymerization time, current intensity and on the nature of the supporting electrolyte. The polarographic measurements showed that the reduction potential of the supporting electrolyte is less than that of the monomer or the solvent. The product of the electrolysis arising from the supporting electrolyte initiates the polymerization. The mechanism of polymerization is assumed to be an anionic one.

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We report on thermal properties and the phase behaviour of polymer blends comprising poly(e -caprolactone) (PCL) and poly(vinyl methyl ether) (PVME). The blends were subjected to different thermal histories. In all cases, the fraction of PCL, that crystallizes in the blends, increases slightly up to 30% content of PVME. Crystallization rates of PCL are found markedly reduced in blends as compared to neat PCL. Ring-banded spherulites develop during isothermal crystallization. Radial growth rates of spherulites decrease exponentially with increasing PVME content up to approximately 40% of PVME. At higher PVME contents non-exponential decrease was observed. Melting points of PCL in blends were determined applying a step-wise annealing procedure. The glass transition temperatures of the blends reveal formation of PVME-rich phases even after rapid quenching of the homogeneous melt owing to crystallization of PCL. Lower critical solution temperature behaviour of the melts could be determined tentatively by optical inspection. The homogeneous melt phase-separates above approximately 190°C.

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The use of electroactive polymer–SiO 2 nanocomposites for the uptake of gold and palladium from AuCl 3 and PdCl 2 in acid solutions respectively was investigated. The electroactive polymers used were polyaniline (PAN) and polypyrrole (PPY). The change in the physicochemical properties of the nanocomposites with metal uptake were of particular interest. In the case of gold uptake, the reaction rate increases with temperature from 0 to 60°C. The accumulation of elemental gold on the nanocomposites increases the diameter and decreases the surface area. The surface Au/N ratio as determined using X-ray photoelectron spectroscopy (XPS) is highly dependent on the rate of reactions even for the same amount of gold uptake. The uptake of palladium from PdCl 2 is much more difficult to accomplish. High rates of uptake can only be achieved with the electroactive polymers reduced to their lowest oxidation state and unlike the case of gold uptake, the palladium on the microparticles does not exist in the elemental form but as a Pd(II) compound.

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