1999 рік

Toughened blends of poly(butylene terephthalate) (PBT) with appropriate ABS materials can be prepared without a compatibilizer within limited melt processing situations. As illustrated by transmission electron microscopy, coarsening of uncompatibilized blends occurs under certain molding conditions resulting in a deleterious effect on blend properties. Methyl methacrylate, glycidyl methacrylate (GMA), ethyl acrylate (MGE) terpolymers were shown to be effective reactive compatibilizers for PBT/ABS blends that broaden the processing window and provide improved low temperature impact properties, ABS dispersion, and morphological stability. A twin screw extruder is more effective than the single screw extruder used here for processing these reactive blends. Several ABS types with different rubber contents were examined; generally, materials with very high rubber contents were found to be more beneficial for toughening PBT. Among these high rubber content materials, the ABS material having the lowest melt viscosity was found to be superior for optimizing morphology and impact properties. At leat 30% of this material, containing a minimum of 36% rubber, is required for producing toughened blends. Moderate amounts of GMA functionality in the compatibilizer (>5%) and small amounts of compatibilizer in the blend (<5%) significantly improve low temperature impact properties and ABS dispersion. Higher amounts of GMA in the blend increase the room temperature impact strength with little effect on the ductile–brittle transition temperature and increase blend viscosity.

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Experiments have been performed to clarify the polymerisation mechanism of chloromethyl-4-(n-butylsulfinyl)methylbenzene 1a and 4chloromethyl-4 0 -(n-butylsulfinyl)methylbiphenyl 1b in NMP. Addition of TEMPO and water to the polymerisation mixture led to the conclusion that radical as well as anionic mechanisms occur which lead to the formation of a high and a low molecular weight polymer fraction, respectively.

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The spin-probed copolymers of styrene and acrylonitrile differing in monomer content and chain structure were examined by the electron spin resonance (e.s.r.) methods in a wide temperature range. The measurements of spin–lattice relaxation time, TDM 1 , in slow motional region by the double modulation e.s.r. technique reveal two distinct relaxation regions in copolymers and pure polyacrylonitrile matrices. At very low temperatures (region I) a very distinct difference between TDM 1 values of pure polyacrylonitrile, alternating and statistical copolymers and polystyrene-rich copolymer is ascribed to the effect of packing density of polymer chains. The density modulates the electron spin–lattice relaxation rates and other vibrational modes contributing to the total relaxation rate. At higher temperatures (region II), where the skeleton of a spin probe begins to move, alternating and statistical copolymers of a similar composition show different relaxation rate. The data are reconciled on the basis of the sequence structure of copolymer chains. The difference in glass transition temperature between alternating and statistical copolymers as determined by the e.s.r. measurements reflects local motional heterogeneity as a consequence of chain microstructure. The presence of local motional heterogeneity of a probe near and above the glass transition results from the styrene-rich sequences contributing to the structural heterogeneity in statistical copolymer.

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Dilute solution properties of four different polyphosphazenes containing 2,2 0 -dioxybiphenyl groups have been studied by size exclusion chromatography, using simultaneously multiangle light scattering and differential refractive index detectors. The polymers present broad molecular weight distributions and the dependence of the dimensions, i.e. radius of gyration, of the polymers on the molecular weight is discussed. Moreover, scaling laws and unperturbed dimensions have been calculated for the fractions with high molecular weight. The polymers behave as random coil chains, the characteristic ratios are in the range 12–17 in good accord with the results reported for other polyphosphazenes.

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Amorphous poly(ethylene terephthalate) (PET) films with different thermal histories were annealed at 308C in a desiccator, in a humid atmosphere and in liquid water respectively, for investigation of enthalpy relaxation by differential scanning calorimetry (DSC). For the quenched sample annealed in a humid atmosphere, the evolution of the endothermic peak near the glass transition temperature (Tg) with annealing time is remarkable. For the aged samples further annealed in the humid atmosphere and water, the shape of the endothermic peak changed from a single peak into broad double peaks with annealing time. However no such change of the endothermic peak can be observed for both the quenched and the aged samples further annealed in the desiccator. The experimental results showed that the change of the DSC curve was reversible, involved only with the physical process. The results may indicate that some ordered structure formed during the physical ageing process.

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A successful micronization of water-insoluble poly(ε-caprolactone) (PCL) into narrowly distributed nanoparticles stable in water has not only enabled us to study the enzymatic biodegradation of PCL in water at 25°C by a combination of static and dynamic laser light scattering (LLS), but also to shorten the biodegradation time by a factor of more than 10 3 compared with using a thin PCL film, i.e. a 1 week conventional experiment becomes a 4 min one. The time-average scattering intensity decreased linearly. It was interesting to find that the decrease of the scattering intensity was not accompanied by a decrease of the average size of the PCL nanoparticles, indicating that the enzyme, Lipase Pseudomonas (PS), ''eats’’ the PCL nanoparticles one-by-one, so that the biodegradation rate is determined mainly by the enzyme concentration. Moreover, we found that using anionic sodium lauryl sulphate instead of cationic hexadecyltrimethylammonium bromide as surfactant in the micronization can prevent the biodegradation, suggesting that the biodegradation involves two essential steps: the adsorption of slightly negatively charged Lipase PS onto the PCL nanoparticles and the interaction between Lipase PS and PCL.

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The isothermal crystallization behaviour has been investigated for several compositions of blends between nylon 6 (N6) and the liquid crystal copolyester Vectra using calorimetric and X-ray diffraction techniques. Differences in the crystallization rates have been related to the structural properties of these systems by means of WAXS and SAXS real time experiments using synchrotron radiation. Other kinetic parameters such as the Avrami exponents, the equilibrium melting temperatures, and the interfacial free energies have been determined from the calorimetric data.

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Immiscible blends of isotactic polypropylene (PP) with a miscible amorphous phase containing varying concentrations of polystyrene (PS) and poly (2,6-dimethyl-1,4-phenylene ether) (PPE) were prepared in the melt, to study the influence of the blend composition and the melt– viscosity ratio, p, on the phase morphology. This model blend system offers the unique opportunity to vary the composition of the miscible amorphous PS/PPE phase, without affecting the global interfacial tension, a crucial parameter with respect to phase morphology development. All immiscible PP/(PS/PPE) blends were prepared in a co-rotating twin-screw mini-extruder under constant processing conditions. The location of the phase inversion region was strongly related to the viscosity ratio. A composite-like morphology was observed in this region. To be able to separate the effects of droplet break-up and coalescence with respect to particle size, blends containing only 1 wt.% dispersed phase were investigated over a viscosity ratio range from 0.05 to 20. The results showed a clear dependence of the blend phase morphology on the viscosity ratio; highly viscous matrices (p p 1) enhance droplet break-up due to their efficient shear stress transfer towards the dispersed phase and the higher dispersive forces acting on it; low viscous matrices (p > 1) often act as a lubricant for the dispersed phase reducing droplet break-up. The influence of the viscosity ratio on droplet break-up is reflected in the particle diameter in blends with a concentration of the dispersed phase up to 20 wt.%. In the latter case, blends with a low viscosity ratio (p < 1) offer the best approach towards a fine and stable phase morphology, unlike suggestions in the literature. Blends containing higher concentrations of the minor phase (>20 wt.%) exhibit strong coalescence during melt-mixing; the influence of the viscosity ratio on the final blend phase morphology becomes less obvious, and the finest dispersion was observed at p ˆ 1. Only blends of a lower viscous matrix in which a highly viscous phase has to be dispersed, do not follow the previous tendency as a result of the strong impact of a changing overall melt-viscosity. A quiescent thermal treatment of the blends showed that the concentration of the dispersed phase is the most important factor determining phase coarsening in blends having nearly equal melt-viscosities. Blending a highly viscous component with a low viscous component seems to counteract quiescent phase coarsening.

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Blend films of polycaprolactone (PCL) and polyvinylalcohol (PVAl) have been obtained by evaporation of a solution of both components in hexafluoroisopropanol. The miscibility of the polymers in the amorphous part of the blend has been studied by conventional methods (optical microscopy, DSC and FTIR) and by solid state NMR. Phase separation is observed in the melt. The absence of any lowering of Tm and the presence of one low temperature Tg near that of pure PCL support the hypothesis of phase separation in the amorphous part of the blend. However, various experimental data suggest the presence of some type of physical interactions between components. These data are: the important decrease of PCL crystallinity in the blend, the morphology of PCL spherulites after crystallization at 45°C and the absence upon annealing the blend at 50°C, of any rearrangement of PCL crystallites into spherulites as observed in pure PCL. The measurement of proton spin-lattice relaxation time T 1 by solid state NMR using cross polarization has shown that the components are compatible at the scale of 60–90 nm and are thus very finely dispersed into each other.

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Some solution properties of polyacetals containing poly perfluoro (oxymethylene-ran-oxyethylene) macromers (PFPE acetals) were investigated. Of the eight fractions selected dynamic light scattering in 1,1,2 trichlorotrifluoroethane and intrinsic viscosity measurements in four solvents of different thermodynamic quality and polarity, including a theta solvent, were performed. Previous results on chain flexibility of the new polymers could be reanalyzed taking into account non-negligible solvent effects. The characteristic ratio of the new PFPE-acetals was confirmed to be slightly higher than that of the corresponding fully fluorinated polyethers.

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