The acoustic properties of polymers with an asymmetric potential barrier at liquid-helium temperatures

The pulse-phase compensation method has been used to measure the propagation velocities of longitudinal and shear waves in polyvinyl chloride, polyvinyl fluoride, and polystyrene at frequencies of 1 and 5 MHz on the temperature interval 2.1–240°K. It has been established that as the temperature falls to 2.1°K the speed of ultrasound in these polymers monotonically increases, the dispersion (frequency dependence) of the speed of sound being preserved over the entire temperature interval. Two possible causes of the viscoelastic relaxation observed in the investigated polymers in the region of helium temperatures are considered.Scientific-Research Institute of Plastics, Moscow. Translated from Mekhanika Polimerov, No. 4, pp. 749–751, July–August, 1973.     

Study of mechanical relaxation processes in ladder organosilicon polymers

Dynamic viscoelastic properties of ladder polyorganosiloxanes have been studied by the method of induced resonance oscillations in the temperature range from –150 to 300°C and in the frequency range from 8 to 300 Hz. Two broad maxima of mechanical losses were observed for all the polymers studied independently of their chemical structure, a low-temperature maximum in the –150 to 0°C region and a high-temperature maximum in the 0 to 250°C region. It was found that the introduction of alkyl groups into polyphenylsilsesquioxanes does not noticeably affect the position and nature of the low-temperature relaxation peaks but in certain cases leads to an increase in the dynamic modulus in polyphenylalkylsilsesquioxanes, compared with the modulus of polyphenylsilsesquioxane in the same temperature region. In the high-temperature region, a distinct dependence is observed of the relaxation peak on the length and the content of alkyl groups in the polymer. It has been found that increase in the length and the content of alkyl groups is accompanied by a shift in the peak in the direction of low temperatures and a decrease in the value of the modulus. Hypotheses have been suggested on the nature of the shifts which lead to the relaxation peaks observed in the ladder polyorganosiloxanes.Institute of Heteroorganic Compounds, Academy of Sciences of the USSR, Moscow. Translated from Mekhanika Polimerov, No. 5, pp. 804–809, September–October, 1973.     

A study of the physicomechanical properties of carbon fibers at high temperatures

Conclusions 1. Carbon fibers, similar to graphite materials, are heat-resistant and do not Iose their short-term tensile strength in the temperature range studied — 20 to 2000°C.2. Young's modulus of carbon fibers hardly changes in the temperature range 20 to 1200°C, but a significant decrease is observed upon a further increase in temperature.Translated from Mekhanika Polimerov, No. 4, pp. 626–630, July–August, 1977.     

Effect of temperature on the nature of the tear surface of styrene polymers

The tear surfaces of polystyrene and SKS-85 butadiene-styrene copolymer (85% styrene) have been investigated at temperatures from –45 to +100°C and from –60 to +40°C, respectively. The fracture surface of these polymers changes not only on transition from the glassy to the high-elastic state, but also within the glassy state itself, changes being observed both in the relative extent of the individual zones contributing to the fracture surface and in the nature of those zones. Changes in the nature of the fracture surface associated with a slowing of the fracture process occur at 0 and 40°C in the case of polystyrene and at –10°C in the case of copolymer SKS-85 and are attributable to secondary transitions in the polymers.Moscow Technological Institute of the Meat and Dairy Industry. State Institute of Polymer Adhesives, Kirovakan. Translated from Mekhanika Polimerov, Vol. 5, No. 2, pp. 257–264, March–April, 1969.     

Uniaxial extension of polystyrene with a constant true stress

A apparatus designed for the extension (stretching) of yielding polymers at a constant true stress is described. The changes taking place in the general, rubber-elastic, and irreversible deformations aredetermined, together with the corresponding rates of deformation, as well as the viscosity and relaxation characteristics, during the extension (tensile strain) of block polystyrene at various constant true stresses and a temperatore of 130°C.All-Union Scientific-Research Institute of Synthetic Fiber, Kalinin. Translated from Mekhanika Polimerov, No. 6, pp. 1104–1109, November–December, 1972.     

On the number of relaxation regions in polyformaldehyde

The mechanical relaxation of a polyformaldehyde homopolymer free from surface grease and the additives normally used as stabilizers has been studied at a frequency of 10^–2 Hz in the temperature region 77–413°K. Six relaxation regions are observed on the curve of tangent of angle of mechanical losses as a function of temperature.T. G. Shevchenko Kiev State University. Translated from Mekhanika Polimerov, No. 5, pp. 925–927, September–October, 1973.     

Temperature dependence of the mechanical properties of polymers of different chemical structure in the temperature range from 4.2 to 300°K

Conclusions 1. The temperature dependences obtained for the ultimate alongation, tensile strength, and elastic modulus of various polymers showed that the relationship between the mechanical properties and chemical structure of macromolecules found in our earlier work at 4.2°K is retained at 78°K and, possibly, up to 90°K.2. It was shown that the passage of the tensile strength through a maximum upon warming from 4.2°K results from a corresponding increase in deformability, which is accompanied by a decrease in the elastic modulus and deviation of the polymer bodies from Hooke's law progressively with increasing temperature.3. It was shown that the amorphization of crystallizing polymers, for example, by quenching, gives a marked change in the deformability, tensile strength, and elasticity of the polymer body over the entire range from 300 down to 4.2°K.4. Study of the mechanical properties of polymers at 78°K in a helium medium and liquid nitrogen showed a marked effect of contact of the polymer with liquid nitrogen on these properties. This effect is different for polymers of varying chemical structure as well as for the same polymer in different physical states.Report presented at the Third All-Union Conference on Polymer Mechanics, Riga, November 10–12, 1976.L. Ya. Karpov Scientific-Research Institute of Physical Chemistry, Moscow. Translated from Mekhanika Polimerov, No. 3, pp. 387–391, May–June, 1977.     

Effect of temperature on the chemical relaxation process in rubbers

The effect of temperature on the chemical relaxation of rubbers has been investigated. With reference to nine industrial rubbers it has been shown that during storage in the stressed state (at =const) chemical relaxation is chiefly determined by two processes proceeding at different rates. Furthermore, the chemical relaxation of rubbers is determined not only by the rate constants of these two processes but also by the pre-exponential constants C_0i, the relationship between which varies with increase in temperature. It is possible to extrapolate the rate constants (k_i) and pre-exponential constants (C_0i) from elevated temperatures (110–50° C) to temperatures in the range 20–25° C. An equation is proposed that makes it possible to calculate the change in the elastic properties of rubbers in the stressed state at storage temperatures (20–25° C) by means of results obtained at elevated temperatures.Mekhanika Polimerov, Vol. 3, No. 3, pp. 448–454, 1967     

Behavior of filled polyphenylquinoxalines during friction

Conclusion 1. It has been established that, as the chain of polyphenylquinoxalines becomes more rigid by addition of aromatic nuclei of the naphthylimide group to the macromolecule part, the wear resistance of graphite-filled polymer systems increases.2. It has been demonstrated that during friction with filled polyphenylquinoxalines in the polymer binder there occur complex destructive-structurizing processes whose penetration depth is determined by the chemical constitution of the selected polymers.3. It has been established that in the rigid-chain polyphenylquinoxaline during friction at high temperatures, just below the glass-transition point but within the range of faster relaxation processes, the destructive-structurizing processes abate and then at temperatures above 250°C active gelling occurs.Institute of Heteroorganic Compounds, Academy of Sciences of the USSR, Moscow. Translated from Mekhanika Polimerov, No. 6, pp. 1049–1054, November–December, 1978.     

Relaxation phenomena in rubber-like polymers with small deformation above the glass transition temperature

In the temperature region in which rubber-like polymers have a high elasticity, a high-temperature subregion has been observed which is characterized by the presence on the extension curve of a critical strain at a small deformation (1–2%). The rigidity of the polymer below and above the critical value is different. The relaxation character of this phenomenon is considered.V. I. Lenin Moscow State Pedagogical Institute. Laboratory of Polymer Physics Problems. Translated from Mekhanika Polimerov, No. 3, pp. 544–546, May–June, 1970.     

Viscoelastic parameters of certain polymers in the temperature interval 4.2–240°K

The principal elastic constants of Nylon 6, Nylon 7, Nylon 6.10, Nylon 11, Nylon 12, PVC, PMMA, polystyrene, and polyvinylfluoride have been calculated from data on the velocity of ultrasonic longitudinal and shear waves measured at a frequency of 5 MHz on the temperature interval 4.2–240°K. It is shown that at cryogenic temperatures the dynamic moduli of elasticity are, to a considerable extent, determined by the characteristics of the chemical structure of the polymers. It is suggested that the Poisson's ratios of the polymers depend on their free volume.Scientific-Research Institute of Plastics, Moscow. Translated from Mekhanika Polimerov, No. 4, pp. 604–609, July–August, 1973.     

Automated thermomechanograph for investigating polymer microsamples

An instrument has been developed for recording the thermomechanical curves of microsamples of polymers (30 mg) by the penetration method in the continuous heating regime. The thermomechanical curves are recorded by a PDS-021 two-coordinate recorder; the effective temperature range is 20–400°C.Institute of High-Molecular Compounds, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, Vol. 4, No. 4, pp. 746–749, July–August, 1968.     

Stress relaxation in glassy polymers

Stress relaxation in amorphous linear polymers has been investigated below the glass transition point at various strain rates, temperatures, and strains. A model of a nonlinear viscoelastic body is proposed as a means of describing the effect. It is shown that stress relaxation is well described by the model considered and is correlated with the deformation characteristics of the polymers.A. F. Ioffe Physico-Technical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 6, pp. 987–994, November–December, 1971.     

Polymer fractography and fracture kinetics

The fractographic method makes it possible to determine the test temperature and time at which anomalies appear in the temperature-time dependence of the strength of polymethyl methacrylate and polycaprolactam by finding the conditions of disappearance of specular zones from the fracture surfaces of these polymers. For PMMA these values are –40°C and 10^–2 sec, for PCL –120°C and 10^–7 sec, respectively.For communication 1 see [2].Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 2, pp. 232–237, March–April, 1971.     

Propagation of sound in oriented polymers

The propagation of sound in oriented polymers is considered. Starting from an assumption concerning the superposition of relaxation processes in polymers, expressions are obtained for the speed and absorption of sound as functions of the relaxation spectrum, molecular orientation, and crystallinity. It is shown that the orientation dependence of the acoustic properties is more distinctly expressed in the region of the glassy state.Scientific-Research Institute of Plastics, Moscow. Translated from Mekhanika Polimerov, No. 3, pp. 437–441, May–June, 1969.     

Intermolecular interactions in fiber-forming linear polymers and certain of their mechanical properties

Values of the specific volumetric intermolecular interaction energies of a series of linear polymers have been calculated on the basis of data on the interatomic and intermolecular interactions of the functional groups in the polymer molecules. It is shown that the specific volumetric intermolecular interaction energy is closely correlated with the elastic and relaxation properties of the polymers, which makes it possible to predict a series of mechanical properties of chemical fibers.Leningrad Branch, All-Union Scientific-Research Institute of Synthetic Fibers. Translated from Mekhanika Polimerov, No. 5, pp. 790–795, September–October, 1971.     

Mechanical relaxation processes in polymers

The various kinetic processes are classified and the place of relaxation effects among them is established. The theoretical basis of mechanical relaxation phenomena in polymers is outlined. The characteristics of relaxation processes associated with molecular mobility are examined with reference to various classes of polymers, in particular, amorphous and crystalline polymers, copolymers, and mechanical mixtures. The characteristics of relaxation processes associated with rearrangement of the supermolecular structures in amorphous and crystalline polymers are considered.This article is a review of mechanical relaxation effects in polymers with particular attention to research conducted in the Problem Laboratory of Polymer Physics of the Moscow Lenin State Pedagogical Institute.Problem Laboratory of Polymer Physics, Lenin Moscow State Pedagogical Institute. Translated from Mekhanika Polimerov, Vol. 5, No. 1, pp. 30–53, January–February, 1969.     

Estimation of the molecular characteristics of polymers by the SPRT method and study of their influence on the properties of compositions

Pressure relaxation was examined in the cylinder of an MPT Monsanto processability tester after stopping the piston. The experimental function of the pressure drop F(t) was smoothed over and approximated by cubic splines. The spectra of pressure relaxation times (SPRT) were obtained according to the method of Schwarzl-Staverman. The SPRT method served well for estimating the spectra of the molecular-mass distribution (MMD) of polymers close in their physical sense to the SPRT. The correlation of the characteristic relaxation times and average molecular mass of ethylene-propylene rubbers and polyethylenes obtained by gel permeation chromatography was approximated by optimum models used for calculating the the molecular mass of rubbers according to the measurement results of the relaxation pressure of melts. The SPRT and characteristic relaxation times were used to analyze the significant technical properties of compositions based on polyethylene and rubber. The SPRT method was used to examine the failure of the cure network of butyl rubber and the dependence of the mechanical properties of thermoplastic elastomers on the molecular features of the decomposite.Presented at the 10th International Conference on the Mechanics of Composite Materials (Riga, April 20–23, 1998).Kazan State Technological University, Tatarstan, Russia. Translated from Mekhanika Kompozitnykh Materialov, Vol. 34, No. 5, pp. 691–698, September–October, 1998.     

Spectra of pressure relaxation times of polymer and copolymer melts and their practical use

The possibility of using pressure relaxation of melted polymers for the investigation of the structure of three types of polymers and their compositions and the analysis of the change of their molecular characteristics during aging is shown.Kazan State Technological University, Tatarstan, Russia. Translated from Mekhanika Kompozitnykh Materialov, Vol. 34, No. 4, pp. 531–538, July–August, 1998.     

Dielectric investigation of the molecular mobility of silicone ladder polymers

Dielectric spectroscopy has been used to study the molecular mobility in polyphenylsilsesquioxane, polyphenylisobutylsilsesquioxane with a 1:1 ratio of phenyl to isobutyl groups, and poly-m-chlorophenylsilsequioxane on the temperature interval from –196 to 300°C at frequencies from 10² to 10⁶ Hz. The investigation was carried out in air and in a nitrogen atmosphere. The flexibility mechanism of silicone ladder polymers is considered and the development of molecular mobility is shown to be discrete.Institute of Heteroorganic Compounds, Academy of Sciences of the USSR, Moscow. Translated from Mekhanika Polimerov, No. 1, pp. 3–7, January–February, 1976.