1992 рік

It has been shown that the photoconductive characteristics of a dispersion composite of a photoconductive inorganic metal oxide, such as TiO2, with a polymer are significantly enhanced by annealing. For the poly(methyl methacrylate) (PMMA) dispersion composite TiOz-PMMA, the relative sensitivity is 101 ~ l0 2 times higher than that of the unannealed sample. The space-charge limited current is observed in the dark current-voltage characteristics of the annealed TiO2-PMMA. From the light intensity index of the annealed TiO2-PMMA, it is found that the annealed sample has a large sensitizing effect.

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Dynamic mechanical properties of a series of crosslinked polyester resins have been determined by a freely oscillating torsional pendulum in the temperature range - 175 to 270°C. The materials were obtained by adding various amounts of two different flexibilizers, one crosslinkable and the other non-crosslinkable with itself, to a basic polyester resin. The results confirm the indications, derived from previous d.s.c. measurements, that the addition of the crosslinkable flexibilizer gives substantially homogeneous network structures, while the addition of the non-crosslinkable flexibilizer gives heterogeneous polyphasic network structures. It has also been shown that the lowering of the glass transition temperature by the addition of the crosslinkable flexibilizer is attributable partly to a reduction in the degree of crosslinking and partly to the effect of variation in chemical composition.

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The preparation and physical properties of conducting ionomers have been investigated. A two-step process was used to prepare a polyethylene-based film grafted with poly(styrenesulphonic acid). A pre-irradiation technique was applied to carry out the grafting of polystyrene on various polyethylene films. The grafted films were then sulphonated to yield the ionomer. Chemical polymerization of pyrrole into the ionomer was carried out in aqueous solutions and caused a four orders of magnitude increase in the conductivity of the film. Better conductivities were obtained when l,l,2-trichloroethane was used as the chain transfer reagent during grafting of polyethylene with styrene. The conductivity, structure, composition and mechanical properties of the electrically conducting ionomers were evaluated. Films having high conductivities and improved mechanical properties were obtained.

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The molecular orientation in poly(ethylene terephthalate) (PET) drawn by necking was studied before and after crystallization by 2H nuclear magnetic resonance (n.m.r.) and by wide-angle X-ray scattering (WAXS) pole figures. In order to determine separately the orientation of the benzene ring and of the ethylene groups, the n.m.r, investigations were performed on samples in which only the benzene ring was deuterated as well as on samples in which only the ethylene groups were deuterated. By applying different 'waiting times' in the n.m.r, measurements, it was also possible to determine separately the orientation of chains of different mobilities. Thus, more detailed and more complete information on molecular orientation is obtained by n.m.r, than by WAXS. As far as a comparison was possible, agreement between n.m.r, and WAXS was obtained. In addition, the n.m.r, results show that, for example, a parallelization of the planes of the benzene rings occurs not only in the crystals but also in the amorphous regions, and that the ethylene groups are oriented to a smaller degree in the draw direction than the benzene ring parts of the chain

Детальніше...  

Monolayers of poly[N,N'-bis(phenoxyphenyl)pyromellitimide] deposited on highly oriented pyrolytic graphite substrates by the Langmuir-Blodgett technique were successfully observed by scanning tunnelling microscopy.

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The microdomain morphology of block copolymers at the free surfaces of solution-cast films was investigated by means of transmission electron microscopy and ultramicrotomy. The free surfaces of block copolymers consisting of amorphous components obey the thermodynamic requirements, i.e. the constituent block chains with lower critical surface tension always cover the free surface even for block copolymer films in which the component with higher critical surface tension forms the matrix. On the other hand, the free surfaces of block copolymers with crystalline components are governed by the crystallization kinetics, and their morphology depends on the orientation of the crystalline lamellae near or at the free surface. Therefore, the surface composition may vary with the method of preparation, and both amorphous and crystalline components can have a chance to be exposed to the free surface.

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Nuclear magnetic resonance relaxation-time measurements performed on poly (ethylene oxide)-deuteriated poly(methyl methacrylate) blends of low-molecular-weight components were analysed as functions of concentration • and temperature T. A number of results can be derived from the homogeneity properties of the transverse relaxation functions Mx(t, ~, T). The temperature dependence of poly(ethylene oxide) proton relaxation times in the blend is found to obey a Williams-Landel-Ferry equation with a temperature reference T*(~) = Tg((I~) q- 50 K, Tg(~) being the glass transition temperature of the blend. It is shown that the transverse magnetization dynamics is concentration-independent at the reference temperature T*(?). The dependence of transverse relaxation upon temperature and poly(ethylene oxide) molecular weight provides qualitative information about the terminal relaxation spectrum

Детальніше...  

The theoretical surface tensions 7vs of poly (vinylidene fluoride-co-hexafluoro acetone) (hexafluoro acetone content: 6.5, 8.3, 10.4 mol%) were calculated according to Prigogine's corresponding states theory, as has already been extended to surfaces by Patterson and co-workers. The resulting ~,Ts was nearly consistent with the experimental surface tension 7cs evaluated by a log(1 + cos 0) versus log(TL) plot based on the contact angle method.

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The features of the crystallization of syndiotactic polystyrene were investigated by X-ray diffraction, differential thermal analysis, thermogravimetry and density measurements. This polymer exhibits polymorphism: there are principally four distinct crystalline phases. Melt-crystallization yields a planar zigzag form. As-cast samples from solutions with a variety of solvents are molecular compounds with the solvents used, in which the polymer chains assume a twofold helical conformation of type (TTGG)2. On annealing the molecular compounds at moderate temperatures below ~ 130°C, they are transformed in common, by removal of the solvent molecules, to a (TTGG)2 twofold helical form free from solvents. On annealing at higher temperatures, the helical form is transformed to a planar zigzag form, which is distinguished from the melt-crystallized planar zigzag form in terms of the mode of molecular arrangement

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A series of polyether urethane films with varying hard/soft segment ratio were synthesized using toluene-2,4-diisocyanate (TDI) and polypropylene glycol (PPG) in order to evaluate them as biomaterials. In order to obtain medical purity the polymerization reactions were carried out in bulk without using any other ingredients such as solvent, catalyst, u.v. absorber, etc. The effects of chemical composition and the presence of the chain extender on some properties were examined. For the samples with higher TDI to PPG ratio, a decrease in ultimate elongation and an increase in tensile strength were observed. Addition of chain extender caused an increase in both. On the other hand, the ultimate elongation increased and tensile strength decreased with an increase in molecular weight of the PPG used. As the chemical compositions are changed by increasing the polyol content, an increase in oxygen permeability is also observed

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