1993 рік

Suspension polymerization of N-vinylcarbazole in toluene/water solvent induced by FeCI 3 in varying mole ratios with the monomer, yields a polymer with appreciably higher specific conductivity (~ 1 x 10-4S cm -1) than that of a conventionally prepared poly(N-vinylcarbazole) (PNVC). Thermal stability, morphology and dielectric characteristics of suspension-polymerized PNVC have also been studied

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Sorption of binary solvents water/dioxane and water/n-propanol in glassy poly(2-hydroxyethyl methacrylate) matrices and concomitant release of theophylline was investigated. The observed sorption profiles of the penetrant as well as the release profiles of theophylline have been explained on the basis of the effect of penetrant concentration on the diffusivity of the penetrant and of theophylline. The model parameters estimated from the release profiles agree well with the values for which an initial burst followed by release at constant rate is predicted.

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The drawing conditions were studied for a polyblend fibre of polypropylene (PP) and a thermotropic liquid crystal polymer (LCP). It was found that, in one-stage drawing, the LCP fibrils were split into short fragments with aspect ratios of around 10. Although fibre properties were improved with the increase in drawing temperature, the best properties of the polyblend fibre from one-stage drawing were poorer than those of the pure polypropylene fibre. A two-stage drawing process was studied in terms of the ratios and temperatures of the first- and second-stage drawings. It was found that the fibre properties were strongly affected by these parameters. At best, the fibre tenacity and initial modulus in the two-stage drawing were 14% and 39% higher than the highest values from the one-stage drawing. The LCP fibrils were found to split to a much lower extent in the two-stage drawing. The optimum drawing procedure was applied to a series ofpolyblend fibres extruded under various extrusion rates and with a number of draw-down ratios

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Polyaniline(s) based on conductive epoxy and poly(urethane-acrylate) systems have been formulated and characterized. The anomalous behaviour of polyaniline(s) in comparison to carbon- or metal-filled systems is attributed to 'molecular level dispersion'.

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The concentration dependence of the glass transition temperature Tg of binary polymeric systems, for the Couchman entropic and enthalpic treatments, has been described by taking into account the temperature dependence of the specific-heat increments Acp(T) and the presence of a characteristic temperature To. It is shown that at To the analytical equations undergo a sudden change. Comparison of the equations obtained with a set of experimental data on the poly(vinyl chloride)~libutyl phthalate system appears to be satisfactory. The treatment allows one to characterize a binary system with suitable thermodynamic parameters.

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The influence of copolymer composition and crystallization temperature on the kinetics of crystallization and the morphology of poly(ethylene oxide)/poly(ethylenel_y-co-vinyl acetatey) 80/20 wt/wt blends was analysed. It was found that the morphology and the crystallization rate are strongly dependent on the copolymer composition, y (mole fraction). In particular, for blends containing the copolymer with low content of vinyl acetate (VAc) (y ~< 0.43), the non-crystallizable material segregates into spherical domains in intraspherulitic regions. The spherulite growth rate G is slightly depressed and the overall crystallization rate is independent of the copolymer composition in the blends. For blends with high VAc content (y/> 0.56), there is no evidence that the copolymer forms segregated domains. For these blends, G and the overall crystallization rate are markedly depressed with respect to that of the pure poly(ethylene oxide) (PEO). The results obtained were accounted for by assuming that the copolymers with y i> 0.56 were miscible with the PEO, whereas those with y~<0.43 formed a two-phase separated system with the PEO.

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Real time X-ray diffraction patterns were recorded as a function of heating and cooling cycles using a synchrotron radiation source for copolyesters of 4-hydroxybenzoic acid (HBA) and 2-hydroxy-6-naphthoic acid (HNA) with monomer ratios 75/25, 58/42 and 30/70. The angular positions of the two main interchain X-ray diffraction reflections 1 1 0 and 2 0 0 were obtained at temperatures below the melting point with a powder diffractometer, and the unit cell dimensions of the copolymers were measured. For the 30/70 and 58/42 compositions the cell dimensions vary linearly and reversibly with temperature. For the 75/25 copolymer the cell dimensions show a clear bend with temperature, which can be associated with a transformation from an orthorhombic to a quasi-hexagonal phase. It is further shown that at higher temperature the dimensions of the D11 o and D2oo coherently diffracting domains increase while the scattering intensity of the diffraction peaks decreases with temperature. These changes are reversible with temperature. Results are discussed in terms of partial melting of smaller crystallites contributing in a reversible manner to the occurrence of a mobile high temperature quasi-hexagonal phase.

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Poly(styrene-co-allyl alcohol) (SAA) with hydroxyl contents of 4.5 and 6.5 wt% can form intermolecular complexes with poly(N-methyl-N-vinylacetamide)( PMVAc) depending on the nature of the solvent(s) and the feed compositions that are used. When methyl ethyl ketone was used as the solvent, complexation between SAA and PMVAc occurred at all feed compositions, but when tetrahydrofuran was used as the solvent, complexation occurred only when the feed was rich in SAA. However, only miscible blends were formed from N,N-dimethylformamide, a strong hydrogen bond breaking solvent. The compositions of the complexes are in the range of 50-70mo1% and 55-74mo1% of PMVAc for the SAA(4.5)/PMVAc and SAA(6.5)/PMVAc systems, respectively. Fourier transform infra-red spectroscopic studies showed the existence of hydrogen bonding interactions in the blends.

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Stress-relaxation occurs in precracked polystyrene specimens accompanied by discontinuous crack growth under fixed displacement conditions. Crack growth is associated with a localized zone of dense crazes. The elliptically shaped craze zone increases in length as well as width with time. A model based on the double layer potential method of elastostatics is proposed to account for the drop in stress due to interactive crack-craze growth. This model successfully explains the observed non-linear stress-relaxation behaviour in terms of crack growth and crazing density.

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The electrocopolymerization of glycidyl methacrylate and methyl methacrylate is described. The compositions of the monomer-electrolyte solution and the parameters of the polymerization coating process that provide formation of thin, even coatings on carbon fibres were determined. The mole fraction of glycidyl methacrylate in the synthesized copolymers was calculated from glass transition temperature, Fourier-transform infra-red and nuclear magnetic resonance determinations. The mechanism of the electrochemical reaction, which leads to grafting of the copolymer onto the carbon fibre surface, is discussed. Composites from carbon fibres coated with the mentioned copolymers showed improved fracture energy during delamination (60-100%) and improved interlaminar shear strength (~ 20%) in comparison with specimens from uncoated fibres.

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