Polymer Science U.s.s.r.最新文献

The temperature variation of the absolute heat capacity values of crystalline and amorphous gelatin at various water concentrations was studied by the DSC method in a broad temperature range (from -50 to 130°C). At all concentrations of bound water (5–30%), with amorphous gelatins a heat capacity jump is observed, caused by devitrification (softening). The value of this jump was determined to amount to 0.50±0.05 J/g K. With increasing content of bound water, the glass temperature decreases. The appearance of free water in the system substantially affects the process of devitrification (softening). In contrast to bound water, free water does not act as plasticizer, but on the contrary, it forms a rigid ice matrix which prevents the appearance of a glass transition. It was determined how the glass-transition process is manifested in the course of heating of crystalline gelatins, of various heats of melting. In gelatins with small heats of melting, ≤ J/g, the glass-transition process practically does not differ from the process in amorphous gelatins of the same water content. In gelatins with greater heats of melting (≈ 30 j/g), softening only leads to the appearance of an additional small maximum on the linear heat-capacity-temperature plot, a heat-capacity jump is not observed.

Globular soluble intramolecularly crosslinked polystyrene (PS) was prepared both by reaction of individual PS coils with monochlorodimethylether in the presence of tin chloride, and by reaction of chloromethyl groups in previously chloromethylated coils with the phenyl rings of the same macromolecule. The concentration of the initial polymer solution subjected to intramolecular crosslinking was 0.1–0.5%. By viscometric, electron microscopic and GPC methods it was established that the globules represent individual PS macromolecules strengthened by a large number of intramolecular crosslinks. The globules of intramolecularly crosslinked PS exhibit the same properties as supercrosslinked PS networks: their internal specific surface reaches 800–1000 m²/g and they can swell in methanol. The equivalence of these unusual properties directly proves that they result from the specific features of supercrosslinked structures at molecular level.

The effect of MM on the strain of high density polyethylene (HDPE) in liquid media is studied. It is established that the effectiveness of the action of the liquid media, as evaluated from the value of the decrease in yield point of the polymer, is inversely related to the MM of the HDPE. This effect is determined by the decrease in the liability of the crystalline polymer to undergo crazing in liquid media with increase in MM.

The phase equilibrium of PS gels with a network of different density in cyclohexane in the non-deformed state in conditions of uniaxial stretching and all-sided compression has been studied. The pulsing mechanism of phase separation of the gels was found manifest in the fluctuational character of the rate of their clouding, squeezing out of the solvent and non-monotonic change in their geometric dimensions and also the radii of the light-scattering particles.

The mechanical relaxational properties of cast materials based on the original and glass-filled polyalkanimide are studied. Temperature regions are observed in which the relaxation process parameters are weakly dependent on temperature, and also in which there is an anomalous decrease in the rate of the relaxation process with rise in temperature on approximating to the softening point. The given relaxation changes are compared with the results of analysis by the DSC method, which provides a means of explaining the anomalous course of the relaxations in terms of recrystallization processes. As a result, the optimum reprocessing conditions are found. The stress relaxation curves are approximated with the aid of new relaxation kernels, based on an analysis of the entropy changes during relaxation. Correlations coefficients close to unity are obtained.

A thermomechanical analysis has been made of polyester urethane ureas with non-crystallizable rigid blocks and an amorphous flexible matrix. The glass transition temperature, the devitrification interval and the compression modulus depending on the degree of phase separation are regulated not only by change in the solubility parameter of the rigid block but also by the number and position of the “hinge” groups in it. The behaviour of the polyester urethane urea elastomers at high temperatures is determined by the same factors and also by the polarity of the rigid block reflected in the temperature of the onset of devitrification of the rigid phase and the interval of its devitrification which in the end determines the performance of polyester urethane urea elastomers at high temperatures.