1994 рік

Polymeric pyridinium salts were synthesized and used as photoinitiators for the cationic polymerization of cyclic ethers and vinyl ethers. A possible application of these salts as positive photoresists is also demonstrated

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Cellulose-chitosan blend films with varied mixing ratios (0-100%) were prepared by dissolving the polymers in chloral/dimethylformamide followed by casting onto glass plates. X-ray diffraction patterns of the films showed a gradual transition from partially crystalline cellulose to non-crystalline chitosan with increasing chitosan content. The tensile strength and Young's modulus of the blend films were greater than those calculated by adding the values of the two components according to the blend ratios. Maxima in these properties appeared at chitosan contents of 10-20%. Chitosan in the blend films showed increased resistance to extraction with acetate buffer (pH 4.5). These results suggest the occurrence of specific interactions between cellulose and chitosan molecules, probably based on the structural similarity. Solute permeability in the blend films was greater than that for pure cellulose or chitosan film.

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Cloud-point data to 170°C and 2800 bar (280 MPa) are presented for poly(ethylene-co-(31 mol%) methyl acrylate) at ~ 5 wt % in propane and in hexane and in mixtures of propane plus 5, 10, and 15 wt % hexane, hexene, methanol, ethanol, n-propanol and n-butanol. Hexane and hexene, which densify the propane, have no effect on the pressure-temperature location of the copolymer-propane cloud-point curve; however, the alcohols, which hydrogen bond to the acrylate repeat units, lower the curve by as much as 75°C. The magnitude of the temperature shift of the cloud-point curve decreases with increasing alcohol content as the acrylate units become saturated and the alcohol preferentially self-associates. Methanol is the least effective cosolvent as it self-associates more than the other alcohols at a given temperature

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We report on the synthesis and characterization of a series of semiflexible polyesters containing a non-coplanar biphenylene unit and a flexible alkylene spacer of variable length. The number of methylene groups in the spacer was varied from three to eight. The polyesters were synthesized by interracial polycondensation. The polymer properties were characterized by thermal analysis, optical microscopy and wide-angle X-ray diffraction. Melting transitions and glass transition temperatures show a strong odd-even effect with respect to the number of methylene groups in the flexible spacer. The crystallinity is reduced by the incorporation of the 2,2'-dimethylbiphenylene unit. In the polyesters with an odd number of methylene groups the crystallization is suppressed and indications of a crystalline phase were only observable after extensive annealing.

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A reactive polypropylene (PP) containing oxazoline functional groups was prepared by the melt grafting of 2-iso-propenyl-2-oxazoline onto a PP homopolymer and used to introduce varying amounts of interfacial chemical reaction in PP/acrylonitrile-co-butadiene-co-acrylic acid rubber (NBR) blends. A technique has been successfully developed to control the rubber particle sizes of PP/NBR blends such that various PP/NBR blends with the same rubber particle size can be obtained by using different combinations of processing conditions and the amount of interfacial reaction. It has been found that moderate levels of interfacial chemical bonding are required for a transition from a brittle to ductile failure to be observed in PP/NBR blends. Blends without any interfacial chemical bonding showed no improvement in impact energy whereas up to a 13.5-fold improvement in impact energy (notched Charpy test) was observed for reactive blends above the brittle-tough transitions.

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The compatibility of the poly(ethylene oxide)-atactic poly(methyl methacrylate) (PEO-aPMMA) system has been studied using Patterson's theory of polymer-polymer miscibility. Specific volumes and thermal pressure coefficients for both polymers have been accurately determined; the characteristic parameters V*, T* and P* are obtained from the experimental results. Experimental heat-of-mixing data were used to calculate the interaction energy between the two components. The shape of the curve of )~12/V~ versus temperature indicates that PEO-aPMMA mixtures are miscible in the liquid state over all the composition and temperature range explored.

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Crystals of the dimeric and trimeric cyclic oligocarbonates of bisphenol A have been prepared by recrystallization from benzene, and these have been examined by X-ray diffractometry. The trimeric oligomer crystals have been shown to include solvate molecules of benzene, and were efflorescent, so that special precautions and measuring conditions were required in order to elucidate the crystal structure. The conformations of the cyclic oligocarbonates are strained, and the release of this steric strain on ring opening combined with a favourable entropic conversion are the proposed motivating factors in the polymerization of these precursors to a linear polycarbonate chain structure.

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The variation of degradation, as measured by change in percentage elongation with time, was evaluated at different temperatures for low density polyethylene-starch composite films containing varying amounts of manganese and iron as pro-oxidant. An equation for change of peroxy radicals with time was derived to reflect change of percentage elongation with time. This equation was then used in curve fitting results of percentage elongation of films and estimating oxidative degradation rates in the form of half lives of starch polymer composite films. This adaptation of the model by Guryanova appears to describe remarkably well the variation in elongation of polyethylene film with degradation, and may also be instrumental in linking variation of mechanical properties to chemical kinetics. The model was applied to experimental data and the curve parameters and half-lives derived appeared to vary in an Arrhenius fashion with temperature. The variation of the curve parameters with temperature in conjunction with the model equation describing percentage elongation with time were then used to derive an equation describing degradation with temperature and time for low density and linear low density polyethylene-starch composite films containing metal pro-oxidants.

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Polydiarylsiloxanes and polydialkylsiloxanes, with alkyl groups larger than methyl, have liquid-crystalline states, presumably as the result of a chain-rigidifying effect from steric interactions of the bulky aryl or alkyl groups along the chain. In the first paper of this series, we reported on the thermal behaviour of a number of diarylsiloxane polymers with phenyl and/or p-tolyl substituents, all of which showed liquidcrystalline behaviour at high temperatures. The solution properties of several of the 'mixed' poly(phenyl/ptolyl) siloxane polymers have now been investigated in order to characterize their chain stiffness properties and to relate these to the tendency to form a liquid-crystalline state in bulk. The 'mixed' poly(phenyl/ptolyl) siloxanes were chosen for investigation since they have a major advantage in experimental convenience over the 'unmixed parent' polymers, polydiphenylsiloxane and polydi(p-tolyl)siloxane. The former are soluble at room temperature in common solvents, whereas the latter polymers are only soluble at temperatures above 150°C. The various diarylsiloxane polymers were prepared by anionic polymerization of the cyclic trimers, and the preservation of the triad sequences (absence of 'scrambling') was confirmed by 29Si n.m.r. Values of the Mark-Houwink-Sakurada exponent, a, for three different types of poly(phenyl/ptolyl) siloxanes are essentially equal, at ~0.83. This value of the exponent is below the value expected for a rigid chain (a > 1.0) but is above the maximum value expected for a flexible random-coil polymer in a good solvent (a ~< 0.8). The shear viscosity of solutions of the mixed poly(phenyl/p-tolyl)siloxane polymers increases monotonically with increasing polymer concentration up to 60 wt%, and does not show an abrupt drop in viscosity above a critical concentration, as is often observed with rigid-rod polymers. This observation, together with the value of the Mark-Houwink-Sakurada exponent, a < 1, indicates that these polymers do not behave in solution as rigid-rod polymers, but most likely as worm-like chains with a relatively large persistence length.

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(AB). star copolymers were prepared by crosslinking poly(styrene-b-isoprene) diblock anions with divinylbenzene. The microphase-separated structures of (AB). star copolymers (arm number, n= 16, 16-19wt% polyisoprene blocks) were formed with the dimensions of a unimolecular micelle in strong segregation. We carried out small-angle X-ray scattering measurements for (AB), star copolymers in the form of dry film. These star copolymers formed the superlattice with a face-centred cubic structure in the bulk film.

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