1993 рік

The linear poly (2-methoxycyanurate) of bisphenol-F was synthesized by interfacial polycondensation from bisphenol-F and 2-methoxy-4,6-dichloro-s-triazine. The fractions obtained by fractional precipitation were characterized by light scattering, osmometry and viscosity. The short- and long-range interaction parameters were determined in different solvent systems and at four different temperatures. The results were examined in the light of excluded volume theories to determine the conformation of the polymer.

Детальніше...  

Novel cyclotriphosphazene-containing poly(ether imide)s have been developed by nucleophilic displacement of active nitro groups of tris[4-(Y-nitrophthalimido)phenoxy]tris(phenoxy)- cyclotriphosphazene (I) or tris [4- (4'-nitrophthalimido) phenoxy ] tris (phenoxy)cyclotriphosphazene ( 11 ) and a bisnitrophthalimido derivative by the dianion of bisphenol A. The synthesized polymers were characterized by Fourier-transform infra-red and tH, 13 C and 3ap nuclear magnetic resonance spectroscopy, differential scanning calorimetry (d.s.c.) and thermogravimetric analysis (t.g.a.). The d.s.c, of the polymers demonstrated glass transition temperatures in the range of 179-184°C. The thermal stabilities of the polymers were evaluated in nitrogen and in air by dynamic t.g.a. The synthesized polymers were thermally stable. The dynamic t.g.a, showed thermal decomposition starting at 410-415°C and char yield of 59-42% in nitrogen at 800°C and 30-32% in air at 700°C. Gel permeation chromatography showed a weight-average molecular weight of the polymer of 6.5 x 103. The polymer prepared from cyclotriphosphazene monomer I showed thermoplastic melt processing at 250°C to tough film and moulding.

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Our previous polymeric multigrain model (PMGM) for the slurry polymerization of propylene is extended to account for the presence of gas-liquid mass transfer resistance and the gradual build-up of the monomer concentration in the liquid medium in an isothermal, semibatch reactor. Results are obtained for the situation where one starts with a pure n-heptane liquid medium. The Soave-Redlich-Kwong (SRK) equation is used for predicting gas-liquid equilibrium, and appropriate correlations are used to estimate mass transfer coefficients and interfacial areas for both the gas liquid and liquid-solid interfaces. It is found that the initial transient in the monomer concentration leads to important effects on the rate of polymerization, the mean degree of polymerization (DP) and the mean polydispersity index (Q) and one must account for these phenomena. The effects of changing the various parameters are also studied. It is found that products with polydispersities higher than about 2.0 can be formed because of the presence of multiple activity catalyst sites and not because of diffusional limitations, at least for the parameters studied.

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A novel copolyamide-hydrazide having aromatic as well as aliphatic units has been synthesized by low temperature solution polycondensation of oxalylodihydrazide and p-aminobenzohydrazide with terephthaloyl chloride in N,N-dimethylacetamide containing dissolved lithium chloride. Its intrinsic viscosity was 2.06 dl g-1 Differential thermal analysis and thermal gravimetric analysis were carried out and the mechanical properties of the copolymer were investigated

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Poly(dimethylsiloxane-2-ethyl-2-oxazoline) (PDMS-PEOX) diblock copolymers with narrow molecular weight distributions were prepared in two steps. The first involved living anionic ring-opening polymerization of hexamethyltrisiloxane and functional termination to afford monofunctional poly(dimethylsiloxane) oligomers with benzyl chloride endgroups. The second step involved the cationic ring-opening polymerization of 2-ethyl-2-oxazoline initiated by the activated halide on the monofunctional poly(dimethylsiloxane) oligomers. The well defined structure of these copolymers has allowed a fundamental investigation of structure-property relationships, which has included a study of solid, solution, and surface behaviour of these materials.

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The shear creep behaviour of polystyrene PS N 7000 under the influence of physical ageing is thoroughly investigated. The theory of linear viscoelastic behaviour under the influence of ageing at constant temperature is briefly reviewed. Emphasis is given to the evaluation of the time-age shift function from creep experiments as well as to finding a suitable theoretical description of the time-age shift function and the creep behaviour. It has been shown that the multiparameter model based on free volume leads to an excellent description and prediction of the ageing behaviour in shear creep at constant temperature after various preconditioning times and at various ageing temperatures. Taking into account the history of the sample prior to the creep experiment, the creep behaviour under all given conditions is predicted from only one optional equilibrium creep curve.

Детальніше...  

The time development of spinodal decomposition in a blend of tetramethyl bisphenol-A polycarbonate with polystyrene can be followed using permanganic etching and scanning electron microscopy. This method of observation provides a real-space technique for observing the morphology of spinodal decomposition at high resolution

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This paper examines the influence of adding polycarbonate/polystyrene graft copolymers to blends of a chlorinated polycarbonate and polystyrene; the backbone of the graft copolymers is the same chlorinated polycarbonate. The interaction parameter between the polycarbonate and polystyrene is calculated. The copolymer acts as an interfacial agent and its influence on the morphologies, dynamic-mechanical properties and interfacial area of the blends is investigated. Morphologies of both polycarbonate-rich and polystyrene-rich blends were determined; in one case dispersed particles of the minor phase are stabilized by polycarbonate chains with one end attached to the interface, in the other case stabilization is by polystyrene chains with two ends attached to the interface (loops). This system is one in which the component polymers are very immiscible. The results are compared with data determined previously on a system based on the same polycarbonate and poly(methyl methacrylate), which is characterized by very limited miscibility.

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Experiments were conducted to determine the influence on impact strength of small amounts of low molecular weight polybutadiene pools dispersed within the glassy matrix of high impact polystyrene (HIPS)/polystyrene blends or acrylonitrile-butadiene-styrene (ABS)/polystyrene blends. The blends of HiPS and polystyrene or ABS and polystyrene were formulated to obtain materials containing small amounts of composite particles to act as craze initiators. Izod impact tests were conducted on standard single notched samples. The fracture surfaces of the Izod specimens and of double-notched tensile specimens were studied by means of scanning electron microscopy, and the internal morphologies of the blends were examined by transmission electron microscopy. Addition of low molecular weight polybutadiene does not increase the impact strength of the blends because, at the high strain rates of the Izod test, the low molecular weight polybutadiene loses its effectiveness as a local plasticizer of craze fibrils. Tensile tests at various strain rates were conducted in order to estimate the strain rate where the mobility of the low molecular weight polybutadiene cannot keep up with the rate of craze propagation through the polystyrene matrix; this critical strain rate is in the region of 10 2 s-I at 20°C for the particular low molecular weight polybutadiene (3400 g tool- 1, 74% 1,4 microstructure) employed here.

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Molecular orientation parameter values measured by laboratory-based X-ray scattering techniques are reported for liquid crystalline solutions of hydroxypropylcellulose in water subjected to a range of steady shear rates. The global orientation exhibits a marked transition from a low orientation at low shear rates to high values ~0.5 at higher shear rates. This transition occurs at shear rates in the range of 0.3-1 s-1 and correlates quantitatively with similar transitions observed using small-angle light scattering. This behaviour is attributed to an out-of-shearing plane to an in-shearing plane transition which has been predicted theoretically by Larson and Ottinger.

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