1993 рік

Polypropylene fibres with different crystal modifications were investigated using thermoluminescence (TL). Unirradiated, ultraviolet-irradiated and ~,-ray-irradiated fibre specimens were studied from room temperature to 200°C. It was found that the glow curves obtained for fibres with both monoclinic and pseudohexagonal modifications have a sharp peak at the melting temperature, but the glow intensities for the fibres with the pseudohexagonal modification were much stronger than for the monoclinic ones. The TL glow peak at the melting temperature for the specimens with the pseudohexagonal modification was found to extend to a temperature as low as 100°C, suggesting that the characteristic molecular motion may occur during the transition of the crystal modifications. In addition, a weak TL peak was detected at about 65°C for the 7-ray-irradiated specimens, which corresponds to the temperature at which polypropylene achieves its maximum crystallization rate constant

Детальніше...  

This paper reports the synthesis and polymerization of a new methacrylamide derivative, N-[4-(4-methoxyphenylacetyloxy)phenyl]methacrylamide, which supports functional side groups of potential biomedical interest. Polymers obtained by free radical polymerization in a solution of N,N-dimethylformamide at moderate temperatures were characterized by 1H and aaC n.m.r., being predominantly syndiotactic, with an isotacticity parameter or=0.19, somewhat lower than that of poly(methyl methacrylate) (PMMA, tr = 0.22) or poly[N-(4-methacryloyloxyphenyl)2, -(4-methoxyphenyl)- acetamide][poly(OM), a=0.27]. This behaviour seems to be a consequence of the stiffness of the methacrylamide side groups with respect to the methacrylic ester function of poly(OM) and PMMA

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The use of supercritical fluids as media for several types of polymer modification is demonstrated. Treatment of mixtures of chitosan with glucose or malto-oligosaccharides in supercritical carbon dioxide afforded the corresponding water soluble imine-linked, branched chitosan derivatives with high degrees of conversion. These transformations were substantially more facile and complete than previously reported equivalent reactions in conventional media. Phosphorylations of amylose and poly(vinyl alcohol) were conducted in supercritical carbon dioxide, yielding phosphate ester derivatives with phosphorus contents of 3.70% and 0.88%, respectively. Treatment of poly(vinyl alcohol), starch, maltodextrins, cellulose acetate and paper with mixtures of supercritical carbon dioxide and oxygen (19:1 v/v) led to the corresponding oxidized materials.

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Wide-angle X-ray diffraction studies of pure Nistari silk fibres and also fibres annealed at various temperatures for different periods of time were carried out to evaluate crystal size and lattice distortion parameters, as these determine the properties of silk fibres

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Homogeneous undoped films of poly(1,4-phenylene) (PPP) can be deposited onto a solid cathode by electroreduction of 4,4'-dibromobiphenyl (DBB) activated by an unusual zero-valent nickel complex. The Ni(O)D 2, described as a non-reactive complex against aromatic halide, is obtained by electrochemical reduction of NiClzD and D [-D = 1,2-bis(diphenylphosphinoethane)] equimolar mixture. Electrodeposition was carried out from electroanalytical study of the above complex without and then with DBB.PPP thin layers exhibit an improved electroactivity; indeed, they can either be oxidized or unusually reduced in the presence of lithium salt as supporting electrolyte in acetonitrile

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Charged poly (L-lysine) forms a random coil in water (pH 7) and an a-helix in methanol. Cyanine (NK-2012) dyes combine with these charged poly(L-lysine)s to produce S-chiral and R-chiral dimers in water and methanol, respectively. The dimers on the a-helix show a circular dichroism strength (with a single Davydov splitting) 10 times greater than on the random coil (with several circular dichroism bands). These results indicate that the binding state of NK-2012 dyes is remarkably dependent on the secondary structure of poly(L-lysine) and the a-helix provides a single binding mode for the dyes.

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The nitration of cellulose in technical mixed acids has been studied by X-ray photoelectron spectroscopy and 13 C nuclear magnetic resonance. The study was carried out in order to better our understanding of the nitration mechanism, and of the factors that control the extent of nitration achieved in these mixes. From this work two major conclusions can be drawn: (1) that the nitronium ion, NO~, is the important nitrating species of cellulose; and (2) contrary to previous arguments, fibre crystal structure does play an important role in determining the degree of substitution (DOS) achieved, but not as previously envisaged.

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2,3-Di-(4-fluorophenyl)buta-1,3-diene has been prepared and copolymerized with methyl methacrylate and with styrene (ST) by a radical mechanism. In both cases, cleavage of the residual carbon-carbon double bonds of the diene units in the copolymer with ozone leads to telechelic oligomers with 4-fluorophenyl ketone end groups. 19F n.m.r, spectra of the copolymers and oligomers show that the diene units are incorporated predominantly in 1,4-configurations with little or no 1,2-enchainment. Also, a ST-2-(4-fluorophenyl)buta-l,3-diene copolymer has been prepared and cleaved by ozonolysis to give an oligomer with both 4-fluorophenyl ketone and carboxylic acid end groups. In this system also, the 19F n.m.r, spectra of the copolymer and oligomer show that the diene is incorporated almost exclusively in the 1,4-configuration

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In this work orientation effects in rubber materials have been studied by X-ray scattering measurements. The rubber materials were made by injection moulding and were anisotropic as judged from mechanical and swelling measurements. In X-ray diffractograms it was possible to detect preferred orientation of both rubber molecules and zinc oxide. It may also be concluded that zinc oxide acts as an indicator of macromolecular orientation in an anisotropic rubber material.

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In a previous paper, the usefulness of SEM image analysis for the characterization of the size and shape of Ziegler-type quasi-spherical catalyst particles and polypropylene particles was shown. In the present paper, the method is extended to silica-supported and unsupported catalysts for ethylene polymerization. The shapes of these catalysts are more or less remote from a sphere. It was shown that the selected circularity index allows us to distinguish between spherical, polyhedric and more complex shapes. However, the sampling for SEM examination is more difficult the more remote the particles are from spheres. Moreover, the digitization on 512 x 512 pixels -- necessary for non-spherical particles -- leads to a four-fold increase in computer time. As far as the determination of the 'true' dispersion of a catalyst particle batch is concerned, it is not possible to obtain it from a single sample. One very interesting result is the shape evolution between silica-supported catalysts and the corresponding prepolymers.

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