1992 рік

A new method of evaluation for the meridional amorphous X-ray scattering of nylon-6 fibres is proposed. The facts (1) that the observed (040) profile is broader than those from other (0k0)s and (2) that the value of the crystallite orientation function evaluated from the (040) peak is smaller than those from other (0k0)s are considered to be due to the amorphous scattering overlapping on the crystal (040) diffraction. Under these circumstances, the profile of the meridional amorphous scattering overlapping on the crystal (040) profile was evaluated by a new method. This method is based on the condition that the observed (020), (060), (0140) profiles are hardly affected by the amorphous scattering because such scattering has no structure in the regions of their diffraction angles. The results show that the change of observed (040) profile with extension of fibres is not only due to the increase of crystallite size, as suggested by Kaji (Makromol. Chem. 1974, 175, 311 )i, but also to the concentration of the amorphous scattering caused by orientation.

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Two series of toughened epoxy resin systems, which are models of matrix resins for use in carbon fibre reinforced plastics, were prepared. Evaluations of the cured epoxy resins, measuring fracture toughness, impact properties, tensile properties and dynamic mechanical properties were conducted. The correlations between these properties and the apparent concentration of network chains in the resins, v, were investigated and the fracture surfaces were examined with a scanning electron microscope. The superior toughness of these resin systems was obtained without considerable loss in modulus. Unified maximum peak was observed in the plots of Izod impact strength, where the v value of the cured resins was increased.

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Formation of a complex between a long polymer chain and several spherical particles with surface attractive adsorption layers is studied using scaling arguments. It is shown that if the spatial position of particles is fixed, the polymer chain in the complex becomes highly stretched. In this case the polymer is adsorbed on many particles and adopts an extended conformation; its dimensions substantially exceed those of a free coil. Complex formation (adsorption) is a first order phase transition. By contrast, if adsorption on mobile particles is considered, additional stretching vanishes and the dimensions of the adsorbed polymer chain are of the same order as those of a corresponding free coil. In this case adsorption of polymer macromolecule remains a first order phase transition. However, its features are similar to those of the second order phase transition, because the approach to the critical point of adsorption results in considerable swelling of adsorption layers of particles involved in the complex.

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Blends of poly(ethylene oxide) with various isomers and derivatives of dihydroxybenzene generate rich macroscopic phase behaviour characterized by solid-solid-liquid (eutectic) transformations. These phase transitions, which occur above ambient temperature, are measured directly by d.s.c., and a thermal analysis summary is contained in the temperature-composition projections. The work described here focuses on site-specific interactions at the molecular level that are responsible for this unique phase behaviour. Solid state n.m.r, spectroscopy is useful as a diagnostic probe of strong interactions and crystal structure modifications. The isotropic 13C chemical shift detects phase coexistence at temperatures well below the eutectic and liquidus transitions where the d.s.c, thermograms are featureless. I.r.-detectable hydrogen bonds between the ether oxygen of poly (ethylene oxide) and the hydroxyl protons in either hydroquinone, 2-methylresorcinol or 5-methylresorcinol distort electron density within the n-orbitals of the aromatic ring. Consequently, the aromatic carbon n.m.r, signals of the resorcinol-like small molecules are sensitive to hydrogen bonding and the formation of molecular complexes. Multiple signals are observed for chemically equivalent carbon sites in the small molecules when phase coexistence is favoured. Crystal structure considerations and molecular packing within the unit cell also generate 13C chemical shift multiplicities, illustrated here for undiluted hydroquinone. The correlation between phase behaviour and ~3C n.m.r. diagnostics provides a phenomenological interpretation of the spectroscopic results, particularly for trieutectic blends of poly (ethylene oxide) with 2-methylresorcinol. The combination of n.m.r, and thermal analysis allows high-temperature d.s.c.-measured phase boundaries to be extrapolated to lower temperatures dictated by the n.m.r, experiment

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A correlation between the equation of state and the pressure dependence of the glass transition temperature T, in polymers such as polystyrene (PS) and poly(methyl methacrylate) (PMMA) and the pressure dependence of the melting temperature T m in polymers such as polyethylene (PE), in rare-gas solids such as argon (At) and in hydrogen (H 2) has been examined based on the experimental data by Simha, Zoller and Rehage for polymers and Cheng, Mills and Zha for rare-gas solids and an equation of state derived in a previous work. The volume-pressure relation at constant temperature for solid and liquid states is expressed by : Vx(P o, T)/Vx(P, T) = A:,(P + Px) "x where Vx(Po, T) is the volume at constant pressure P0 and temperature T, V~(P, T) is the volume at P and T, Px is a function of temperature, mx is a constant and the subscript x means a state such as x = 1 for liquid and x = s for solid. It is found that values of Px change discontinuously with increasing temperature in the vicinity of Tg, while rn x changes discontinuously at T m where Px is continuous with respect to temperature. Values of Fro, s defined by Fm.s = 1 - Vs(Pr., O)/Vs(Pm, Tm) for a rare-gas solid such as Ar are calculated based on the experimental data and are around 0.09 for Ar, independent of pressure, where Vs(Pm, Tin) is the volume of solid phase at T m. Values of Fg defined by F s = 1 - V~(P v To)/V(Pg, Tg) at Tg are 0.036-0.055 for PS and 0.018-0.036 for PMMA. A three dimensional P-V-T surface over the temperature region including Tg and T,, is established based on the experimental data.

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Phase behaviour and sol-gel transition of poly(vinyl alcohol) (PVA) aqueous solutions in the presence of borate ions were investigated. PVA molecules are known to form charged complexes with borate ions in aqueous solutions containing borax (Na2B407 . 10H20 ) or a mixture of boric acid and sodium hydroxide. These complexes show the following viscosity and phase behaviour as a function of the concentrations of boric acid, sodium hydroxide, and salt. 1. At a given combination of PVA concentration and ionic strength, the system underwent a clear-opaque-clear transition with increasing boric acid concentration. 2. The intrinsic viscosity [r/] decreased first and then increased with increasing boric acid concentration in alkaline solution. 3. The opaque region grew to some extent with time and/or by adding salt (i.e., NaC1). 4. When the polymer concentration increased, a thermoreversible sol-gel transition took place without phase demixing. The gelation concentration was close to the chain overlap concentration estimated from [~/]. All the above phenomena can be explained by a balance of the excluded volume effect due to intra- and inter-chain crosslinks and electrostatic potentials

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Iron 2-ethylhexoate is a salt of ferric iron and 2-ethylhexanoic acid. It is incorporated into silicone elastomeric formulations to provide high temperature stability by counteracting oxidative embrittlement. Though metallic salts are commonly used, the reaction of the salt with the siloxane is poorly understood. In this paper, the incorporation of iron 2-ethylhexoate as thermal stabilizer in the elastomer is studied with dynamic mechanical spectroscopy, FT-i.r. spectroscopy and 29Si n.m.r. The reaction involves conversion of the ferric salt to ferric silicate, volatilization of small, cyclic siloxanes, and reaction of the salt to hexanoic acid with partial conversion to anhydride.

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Solubility and permeability coefficients for gases in a series of fluorinated and non-fluorinated polyimides were measured to investigate the effects of chemical structure on permeability and permselectivity. Polyimides with higher concentration of fluorine had lower chain packing density and higher permeability. Polyimides with -C(CF3) 2- linkages had higher permeability with relatively higher permselectivity. 2,2-Bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride/2,2-bis (4-aminophenyl) hexafluoropropane (6FDA-BAHF) polyimide with two -C(CF3)2- linkages in the polymer repeat unit displayed excellent performance for CO2/CH4 and O2/N2 separations; its permeabilities for 02 and CO2 were 3.7 and 3.1 times, respectively, larger than those of 6FDA-pp'ODA (4,4'-oxydianiline), a conventional 6FDA-based polyimide, while the permselectivities for O2/N2 and CO2/CH4 were 13% and 22%, respectively, smaller. On the other hand, polyimides having two -C(CF 3)2- linkages together with two ether ones in the repeat unit had lower permeability with a similar level of permselectivity as compared with 6FDA-BAHF polyimide. For H2/CH4 and H2/CO separations, potyimides prepared from 6FDA and meta-oriented non-fluorinated diamines were preferable. These separation properties were discussed in connection with packing density and local segmental mobility.

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The u.v./vis, and i.r. spectra, current-voltage characteristics, carrier trapping levels and carrier mobilities of three poly(substituted phenylacetylene)s, one having an acceptor group o-CF3, one having a donor group o-SiMe3 and one having a 2,6-dimethyl-4-t-butyl group, have been studied. All three polymers show rather low conductivity, with the donor substitution leading to much higher conductivity than the acceptor substitution. Both holes and electrons take part in the severely trap-modulated conduction. In the case of poly(2,6-dimethyl-4-t-butylphenylacetylene) two trap levels with Gaussian distributions of trap energies have been found by isothermal decay current measurement. These trap energies agree closely with the apparent activation energy observed for conduction, consequently the dark conduction has its origin in thermal detrapping. In the case of poly(o-trimethylsilylphenylacetylene) and poly(2,6-dimethyl-4-tbutylphenylacetylene) hole and electron drift mobilities have been determined by the time-of-flight method using Scher-Montroll treatment of data to be 4 x 10-7 and 1.7 x 10-5 cm 2 V-1, respectively, for both carriers. Donor substitution to the phenyl ring of poly(phenylacetylene) significantly enhances the photoconduction of the poly(phenylacetylene).

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This study describes the impact modification of brittle styrene maleic anhydride (SMA) copolymers with primary amine functionalized ethylene propylene (EP) elastomers. Compatibilization of functional EP in SMA is achieved by chemical reaction of complementary functional groups to form a graft in situ. FTi.r. methods and differential solvent extraction techniques demonstrate graft copolymer formation. Morphological studies indicate that the domain size of the dispersed elastomer ranges from 1 to 3/~m. This may represent an optimum for SMA, which fails by crazing. Rheological characteristics of SMA and SMA/EP blends were studied by using both capillary and parallel-plate viscometers. Graft polymer formation does not substantially increase viscosity at high strain rate, but introduces an apparent yield stress at low shear

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