High-elastic State Research Articles

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.

Flow and rubber elasticity of polymeric systems

Abstract

Nature and mechanism of friction of rubberlike polymers in different physical states

We have investigated the frictional properties of crosslinked butadiene-nitrile and butadiene-styrene copolymers and natural rubber in friction against polished steel under vacuum conditions in the temperature interval from −200 to +150° C, which embraces the glassy and high-elastic states, as well as the transition region between them. The temperature dependence of polymer friction is characterized by two maxima, a principal and a low-temperature maximum. The principal maximum, observed in the glass transition region, is not associated with the mechanical loss maximum observed in the polymers themselves. The temperature dependence of the force of friction is composed of three parts. In the high-elastic region there is an increase in the force of friction with fall in temperature, in accordance with the molecular-kinetic theory of friction of rubberlike polymers. In this region the nature of friction is associated with mechanical losses in the surface layer of polymer. The mechanical losses inside the polymer itself are unimportant. The deviation from the theoretical curve and the fall in the force of friction below a certain temperature in the transition region are chiefly associated with a decrease in the actual area of contact as the polymer passes into the glassy state. In the glassy region the friction is significantly determined by the mechanical losses in the polymer itself associated with the repeated elastic and forced-elastic deformation of the asperities in the layer of polymer in contact with the rigid surface. Therefore the low-temperature maximum is closely related to the mechanical loss maximum observed in the same temperature region in dynamic tests. Apart from this, the friction maximum is also associated with the increase in the forces of adhesion and the reduction of the actual area of contact at temperatures at which a forced-elastic mechanism of compression of the polymer asperities is not realized.

Effect of the physical state on tearing of amorphous polymers

The temperature dependence of the basic tear characteristics of deformation and failure of SKS-85 copolymer in the range from T Tf is examined. It is established that the total work done in tearing the polymer in the brittle state is determined by the work of deformation up to separation of the specimen into two parts. In contrast to this, the total work done in tearing the polymer in the high-elastic state is determined mainly by the work of formation of the tear surface.

Effect of physicalstate on tearing of filled systems based on linear amorphous polymers

A study has been made of the temperature dependence of the service behavior, deformation, and tear rate of filled systems based on SKS-85. It is established that the introduction of fillers which enhance the strength of systems in the high-elastic state effect a loss of strength in the vitreous state. The observed reversal of the strengthening effect from positive to negative is explained by weakening of the adhesive strength of the bond between polymer and filler particles caused by the increase and concentration of shrinkage stresses during cooling of the specimens. This effect is called temperature inversion of the reinforcing action of fillers.

The nature of friction of polymers in high elastic and glasslike states

AbstractThe temperature dependence of the friction of polymers against hard surface is characterized by two maxima: main and low temperatures. The main maximum observed in the glass transition range, contrary to the widespread opinion, is not associated with the maximum of the mechanical losses observed in polymers. The temperature dependence of the friction force consists of three ranges. In the high elasticity range, with decreasing temperature, the friction force is observed to increase according to the molecular kinetic theory of the friction of rubberlike polymers. The nature of the friction for all polymers in this range is associated with the mechanical losses in the surface monomolecular layer of the polymer. The bulk‐mechanical losses in the polymer are not essential. The deviation from the theoretical dependence and the decrease of the friction force below a certain temperature in the transition range are associated mainly with the decrease in the actual contact area of suriaces of the friction pair at the glass transition of the polymer. In the glasslike state, for polymers the friction is essentially dependent on the bulk‐mechanical losses in the polymer at elastic and forced elasticity strain of the roughnesses in the polymer layer being in contact with a solid. Therefore, the low temperature maximum is associated with the maximum of the mechanical losses observed in the same range of temperature at dynamic tests. For polymers with no maximum of the mechanical losses at low temperatures, the maximum of the friction can be attributed to the increase in the adhesion forces and the drop in the actual contact area at temperatures at which the forced elasticity mechanism of compression of the polymer roughnesses is not realized.

Mechanism of large deformations of crystalline polypropylene over a wide temperature range

SINCE the earliest investigations into the nature of the high-elasticity of rubber, s tudy of the mechanism of large deformations of polymers has been based on ideas related to the flexibility of macromolecules and on the resultant transitions in the configurations. Moreover it was thought that large deformations could develop either in the region of the high-elastic state of polymers, or in the region of the glass-like state under the action of large mechanical forces (forced elasticity). In the latter case also, the development of large deformations was again determined by the flexibility of the macromolecules. The object of this paper is to describe several new experimental factors arising from study of large deformations of crystalline polymers, in this case using polypropylene, over a wide raiige of temperatures. As will be demonstrated below, the development of large deformations can occur also under conditions where the flexibility of the macromoleeules is completely suppressed and the deformation process takes place at a supermoleeular level.

The swelling of filled styrene-divinylbenzene copolymers

IT IS now known that the addition of fillers to polymers, especially rubbers, results in additional network formation. In our earlier studies [1-3] we examined the effect of a filler on structure formation in thermoplastic polymers. Study of the special features of structure formation in the case where formation of the polymer takes place simultaneously with formation of the final material is of great interest. Investigation of the conditions of formation of a crosslinked polymer in the presence of a filler would be of great value, particularly to the production of reinforced plastics. We have previously shown that the structure of a linear polymer formed in the presence of a glass surface differs from the structure of the polymer produced in the absence of a filler [4, 5]. The aim of the present work was to discover some of the specific features of formation of a crosslinked polymer in the presence of glass powder of small particle size. A number of papers has been concerned with the s tudy of polymer networks formed in the presence of a filler [6-11]. The materials studied in these papers were exclusively vulcanizates of natural and synthetic rubbers--butadienestyrene, polyurethane etc. In these studies the kinetic theory of elasticity and the F lory-Rehner theory of swelling [12] formed the basis for investigation of the behaviour of the networks in the presence of a filler. By making use of the well known equation of the latter theory, and making a number of assumptions, it is possible to arrive at an estimate of the number of crosslink points in the network of the filled vulcanizate, and thus to estimate the number of additional points of crosslinking due to polymer-filler interaction. I t seemed of interest to apply the theory of the swelling of filled vulcanizates to the swelling of filled, erosslinked polymers that are not in the high-elastic state under the experimental conditions.

A comparison of the elastomeric properties of inorganic glasses and high polymers

The high-elastic properties and structural-mechanical characteristics of inorganic glasses and high-polymer materials are compared. Points of similarity and also differences in the mechanical behavior of organic and inorganic polymers in the high-elastic state are noted. Comparative estimates of the molecular weights of the chains in organic and inorganic polymer networks are given.

Friction properties of high elastic materials

The authors investigate the friction properties of crosslinked butadiene-acrylonitrile, butadiene-styrene copolymers and natural rubber on polished steel in vacuum over a temperature range −100° to + 100°C, which takes in the glassy and high-elastic states of rubbery polymers, and also the transition range between these states. A sharp difference is observed between the friction properties of these polymers below 0°C, investigated in vacuum and under atmospheric conditions. Above the glass-transition temperature, i.e. in the range of high elasticity and in the transition range, the mechanical losses in friction play an insignificant part, and therefore they cannot be used to explain the maximum on the curves of the dependence of the friction force on temperature or on the logarithm of the rate of slip. The alteration in the friction properties on the transition from high to low temperatures and from low to high rates of slip is explained by the alteration in the elastic properties in the rubbery polymers in the glass-transition region, and also by the transition from the molecular-kinetic mechanism of friction to the mechanism of friction characteristic of rigid polymers (below the glass-transition temperature the coefficient of friction is practically independent of the rate of slip and the normal load). In the range of high elasticity the friction properties of polymers are explained by the adhesion molecular-kinetic theory, proposed in 1954 by one of the present authors. Working from this theory the authors introduce the critical rate of slip v k and characteristic temperatures T k and T o , and an explanation is given for their physical meaning. An assessment is made of the influence, the type of polymer and of the normal load on the friction properties of vulcanised rubber. It is shown that the friction force alters in an analogous fashion on reduction in the temperature and raising of the logarithm of the rate of slip, which indicates the applicability of the principle of temperature-time equivalence to the friction properties of polymers.

The Mechanism of the carburization of fused iron catalysts for synthesis from CO and H 2: A. Ya. Rozovskii, M. M. Biryukovich, A. A. Ivanov, L. G. Liberov, V. K. Butyugin, Yu. B. Kagan, Yu. B. Kryukov and A. N. Bashkirov, Neftekhimiya 3, No. 1, 97–103, 1963

In an isothermal calorimeter with a static bomb, the energy of combustion Δcu∘ of hemiisotactic and stereoblock polypropylenes in a high-elasticity state was measured at T = 298.15 K. From these experimental results and those published by us earlier, the standard molar enthalpy of combustion ΔcHm∘, the standard molar enthalpy ΔfHm∘, entropy ΔfSm∘ and Gibbs function ΔfGm∘ of formation of the above polypropylenes were calculated. Dependences of the thermochemical characteristics on the macrotacticity of the polymers under study were revealed and are discussed.

The synthesis and properties of isotactic-atactic polystyrene graft copolymers

RECENT studies of the properties of graft copolymers has enabled certain general characteristics of this class of polymers to be explained.We have shown previously [1-5] on the example of graft eopolymers of the amphipathic type that their structural and thermomechanical properties are a distinctive combination of the properties of the two components. At the same time the solubility of these eopolymers is considerably reduced and this is explained by the mutual screening effect of the components [3, 6]. In our work in this field the graft eopolymers studied were obtained from components differing widely both in chemical nature and physical properties (for example polystyrene-polyacrylic acid and polystyrenepolyvinylalcohol grafts, etc. [1-6] and moreover in these systems one of the polymeric components was a polymer with a rigid chain and a glass temperature (Tg) above its decomposition temperature. Furthermore both homopolymers were non-crystalline systems of irregular structure [3-6]. I t was of interest to s tudy the properties of a graft copolymer consisting of chains of the same chemical nature but possessing different structures. Copolymers of crystalline, isotactie (main chain) and amorphous, atactic (side chains) polystyrene were chosen for the present work. I t is known that in ordinary, atactic polystyrene the high-elastic state is covered by a temperature interval of 50 ° (Tg90°; T m 140°). For crystallized, isotactic polystyrene, with the same chemical structure but a different spatial arrangement of the asymmetric carbon atoms in the backbone (dd or ll) the total absence of the high-elastic state is characteristic, but on the other hand the melting point (230 ° ) is high. On conversion to the amorphous state, when heated above its T~ (90°), this polymer again acquires the properties of a rigid plastic [7]. On grafting on to crystalline, isotactic polystyrene ataetic polystyrene chains, with their characteristic random sequence of asymmetric carbon atoms, the production of a graft copolymer with a well defined high-elastic region while maintaining a high melting point would be expected [5]. Such a graft copolymer would also provide a suitable model for the s tudy of the structural properties

Synthesis of cis and trans polymers of dienes on oxide catalysts and investigation of their structure and properties

AbstractCrystalline 1,4‐trans polymers of butadiene and isoprene of regular structure are formed in polymerization of dienes in a chromia catalyst (chromium oxide on aluminum silicate). 1,4‐trans‐Polybutadiene with a specific gravity of 1.015 has crystalline modifications melting at 75 and 135°C. The 1,4‐trans‐polyisoprene resembles natural gutta‐percha. When α‐butylene undergoes polymerization on the same catalyst, a crystalline polymer is formed of specific weight 0,96 and melting point ca. 140°C. Any disturbance of the 1,4‐trans‐structure by copolymerization of butadiene or isoprene with other compounds leads to a loss of capacity for crystallization and to transition to the high elastic state. The butadiene‐isoprene copolymer contains about 55% butadiene links while preserving the 1,4‐trans structure of the chain and has a glass temperature of ca. −90°C., coinciding with the value calculated on the basis of a linear relation between the copolymer composition and the glass temperature. By copolymerization ethylene units could be incorporated in the trans‐polyisoprene chain to the extent of ca. 40 mole‐%. The polymer formed has a glass temperature of −76°C., as compared with −71°C., for 1,4‐polyisoprene. Polymerization of butadiene induced by the cobalt oxide‐diethyl‐aluminum halides proceeds at a high rate, even at 0°C. The polybutadiene formed contains predominantly links cis‐1,4 (about 85%) and only a small quantity (5–8%) of 1,2 links. Owing to the high content of 1,4 links the polymer has a glass temperature as low as −115°C. Unlike organometallic‐titanium tetrachloride systems, interaction between cobalt oxides and organoaluminum compounds in the temperature range 0–80°C. is not accompanied by formation of gaseous hydrocarbon products.