1992 рік

Some aspects of the structural, thermal and mechanical properties of ethylene-vinyl acetate (EVA) blended with biodegradable BIOPOL copolymers have been investigated in this work. X-ray measurements and thermal analysis showed that a homogeneous mixture of the two components was not formed : two crystalline structures, melting regions and glass transitions were found, relating to the BIOPOL and EVA components separately. Phase separation was also investigated by scanning electron microscopy of plasma-etched and biodegraded samples. Dynamic mechanical measurements showed that the EVA component reduced the dynamic modulus over the whole temperature range of measurement. The fracture behaviour was markedly dependent on blend composition. Weight loss measurements of soil-degraded samples indicated that only the BIOPOL component degraded biologically

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Responsive associative terpolymers of acrylamide, 0.5 mol% N-(4-butyl)phenylacrylamide and 5 and 25 mol% of one of the following: sodium acrylate, sodium-2-acrylamido-2-methylpropanesulphonate or sodium-3-acrylamido-3-methylbutanoate were synthesized by a micellar polymerization method. Terpolymer composition was determined by a combination of u.v. spectroscopy and elemental analysis. Solution properties were determined by low shear rheometry as functions of polymer concentration, solution ionic strength, pH and urea concentration. The carboxylate terpolymers exhibited high viscosities in the presence of up to 0.5 M NaCI and 0.17 M CaC12, but lose much of their viscosity at low pH and high urea content. The sulphonate-containing terpolymers are less responsive at low pH and high electrolyte concentration than the carboxylate-containing terpolymers.

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Experimental investigations of light scattering are presented for two ternary systems (two chemically different polymers with a solvent): polystyrene(PS)-poly(methyl methacrylate)(PMMA)-benzene (or toluene) and PS-poly(vinyl acetate )( PVAc )-styrene. These systems show similarities with respect to the incompatibility between the two unlike polymers. Experiments are reported for mixtures with different molecular weights and for concentrations ranging from dilute solution to the onset of phase separation. Thermodynamic analysis is undertaken by evaluating the polymer-polymer interaction parameters. For both systems, the polymer-polymer interaction parameters are constant in dilute solution but increase in the semi-dilute regime. A more complete study is performed on the PS-PMMA-toluene system by analysing the angular distribution of the scattered intensity.

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This paper compares the morphologies observed in two blend systems, namely blends of isotactic and atactic polystyrene, and blends of linear and branched polyethylene. Crystallization of isotactic polystyrene at high temperatures (>~ 200°C) produces immature sheaf-like aggregates of lamellae. Addition of atactic polymer results in modified morphologies that are based upon bundles of lamellae, separated from one another by non-crystalline regions. At high atactic contents sheaf-like objects are no longer observed, crystallization occurring to give structures that are better described as multilayered crystals. At temperatures below ~ 200°C, mature spherulites develop. Addition of atactic polystyrene again results in morphologies in which lamellae are grouped into stacks separated from one another by non-crystalline regions. Again, at high atactic contents a less complex (sheaf-like) overall morphology is observed. In all the above microstructures, lamellae exhibit an inherently hexagonal habit. However, at lower crystallization temperatures observations suggest that lateral lamellar growth may be restricted. Isothermal crystallization of linear polyethylene at temperatures above ~ 125°C results in morphologies in which a complex lamellar hierarchy exists, as a consequence of molecular fractionation during crystallization. Addition of branched polyethylene, which is unable to crystallize at these temperatures, suppresses fractionation such that the resulting morphologies may be described in terms of only one dominant and one subsidiary lamellar population. When viewed along the crystallographic b axis, dominant lamellae appear planar or mildly S-shaped in profile, whilst subsidiary lamellae are planar and inclined at an angle of ~25 ° to the local dominant population. In blends with a high branched content, apparently non-crystalline regions can be seen between individual lamellae. Thus, in polyethylene blends, the non-crystallizing component is located between individual lamellae rather than between bundles of lamellae, as is the case in polystyrene. This difference arises from the parallel growth of dominant and subsidiary lamellae in polystyrene as opposed to the inclined development of subsidiaries with respect to the dominant lamellae in the

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A new route to the functionalization of polysiloxanes is described. Polysiloxanes having pendant silyl ketene acetals are synthesized through hydrosilation of poly(methylhydrosiloxane) with a terminal olefin bearing a silyl ketene acetal. The functionalized polysiloxanes can be reacted with electrophiles such as p-nitrobenzenesulphenyl chloride, affording derivatives having highly polar pendants. These materials have dielectric constants as high as 9 and dissipation factors as low as 0.02-0.06 at 100 kHz at room temperature. The temperature dependencies of the dielectric constants are a function of polar pendant group concentration

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New results from experiments on light scattering from spherulites of polyethylene and isotactic polystyrene have been obtained. It was found that H v scattering can be explained well by the sum of the scattering from a perfect spherulite, i.e. a polycrystalline aggregate with radial symmetry, and that from randomly oriented crystallites. The orientation-correlation function of the randomly oriented crystallites has a form of exp(-r/a), where a is the correlation length, which is about one-sixth of the radius of the spherulite.

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The effect of shear flow on the phase behaviour of partially miscible polymer blends exhibiting a lower critical solution temperature behaviour was investigated. Miscibility was detected, with and without the application of flow, as a change from optical clarity to turbidity using light scattering and as a shift in the glass transition temperature. Light scattering data were collected on a rhea-optical device that was designed to monitor phase changes in polymer blends undergoing shear flow between parallel glass plates in a temperature-controlled environment. Glass transition temperatures of quenched sheared blends were measured using a differential scanning calorimeter. It was found that shear-induced demixing and shear-induced mixing may be observed within the same blend depending on the magnitude of the applied flow. The magnitude of the increase or decrease in the lower critical solution temperature varied with the blend composition and also among the three blends used in this study.

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The possibility of using imidazole as a catalytic component in the direct synthesis of poly(pphenyleneterephthalamide) and poly(p-benzamide) by phosphorylation with triphenylphosphite was investigated. In the presence of imidazole it was possible to perform the whole synthesis in a homogeneous solution, thus avoiding the formation of a precipitate or a swollen gel, as usually described in literature, particularly for poly(p-phenyleneterephthalamide). Higher molecular weights were obtained in our systems, as compared to typical values from the direct synthesis method

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The relation between molecular weights and electrical properties was investigated for electrochemically prepared poly(3-hexylthiophene) (PHT). The PHT films with weight-average molecular weight (Mw) in the range 12 500-58 000 were prepared by controlling the polymerization conditions. For Mw < 25 000, the electrical conductivities (tz) of as-polymerized PHT films increased rapidly from 10 -1 to 101 S cm-1 with increasing Mw. For Mw > 25 000, the increase in a with Mw was minor. The visible absorption maximum (Tr-Tr* absorption band) of the neutral PHT films shifted to the red side as Mw increased. The shift was more prominent in the samples with low Mw ( < 25 000). Wide-angle X-ray analyses of the films showed that the increase in Mw resulted in an increase in regularity of supermolecular structure in the as-polymerized PHT films, which enhanced the development of a ~z-conjugated system in the sample.

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This paper reports investigations into the phase behaviour of six blend systems containing linear with branched polyethylenes. Five systems used linear polyethylenes of differing molecular weight blended with the same branched polyethylene. The sixth system involved a branched polyethylene of lower branch content and shorter branches. The main experimental methods used were differential scanning calorimetry and transmission electron microscopy. Very good agreement was found between results obtained from both experimental methods. The phase diagrams deduced are of the same general form, all but one showing liquid-liquid phase separation in the melt with both upper and lower critical temperatures. This phase separation is most extensive where the molecular weight of the linear polymer is highest. At the other extreme, for a linear component of molecular weight of 2155, no liquid liquid phase separation is observed. Of the two branched polyethylenes, that with the higher branch content is more prone to phase separation. These results lead us to conclude that the phase diagram found previously for a similar blend pair is not unique since the various systems studied here all give similar thermal results, morphologies and phase diagrams

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