Molecular mechanism of orientation in polymers

On the basis of calculations in which the behavior of the chain under load is investigated, it is suggested that, apart from the rotational isomerism mechanism, at low temperatures and high stresses the instability of the folded configuration may play an important part in polymer orientation. A distinctive feature of the proposed mechanism is the high rate of orientation, which for an isolated chain is of the order of the speed of sound.T. G. Shevchenko Kiev State University. Translated from Mekhanika Polimerov, No. 3, pp. 525–528, May–June, 1976.     

Biaxial orientation of amorphous linear polymers

The mechanical properties of biaxially oriented polymethyl methacrylate, obtained on a broad range of stretch ratios and under a variety of orientation conditions, have been investigated. There is a fundamental difference between the variation of the forced elastic limit with increase in stretch ratio, which is monotone increasing, and the variation of such properties as the brittle strength, brittle temperature, true strength and elongation at break, which have an optimum at a certain stretch ratio. It is shown that the presence of an optimum is associated with the transformation of the supermolecular structures in the process of biaxial high-elastic deformation. A relation is established between the mechanical properties of biaxially oriented polymethyl methacrylate (orientation hardening) and the density of the molecular network.For communication 1 see [3].Moscow. Translated from Mekhanika Polimerov, No. 4, pp. 586–593, July–August, 1971.     

Biaxial orientation of amorphous linear polymers

The dependence of the birefringence and orientation stress on the biaxial stretch ratio and orientation conditions has been experimentally investigated. The temperature dependence of these characteristics is explained in terms of the network structure of amorphous polymers. It is shown that the transformations of the supermolecular structures in the process of biaxial orientation depend on the orientation temperature — at higher temperatures better organized structures are formed. There is a formal relationship between the effect of orientation temperature on supermolecular structure formation and on the relaxation process responsible for the formation of a more thermally stable molecular network.Moscow. Translated from Mekhanika Polimerov, No. 5, pp. 17–23, January–February, 1971.     

Reversibility of the orientation effect in linear polymers

It is established that the orientation effect in polymethylmethacrylate, assessed from the alteration in its properties, does not completely vanish after stabilization of the volume of the polymer during heating. A comparative evaluation of the physicomechanical properties in the unoriented, oriented, and oriented-and-restored states of the polymer indicates that some traces of orientation are retained.Lenin Kom somol Riga Institute of Civil-Aviation Engineers. Translated from Mekhanika Polimerov, No. 5, pp. 830–834, September–October, 1973.     

Acoustic measurements in rubberlike polymers during compressive deformation

Problems associated with the method of measurement of acoustical properties of viscoelastic materials and the influence of various external factors (temperature, pressure) on these materials have been examined. The results of measurements of propagation speeds and damping coefficients of waves of the sonic and ultrasonic regions in resins are given for discrete excitation frequencies and during simultaneous static action on the specimen. It is shown that uniaxial compression of the resin results in the appearance of dispersion of the dynamic elastic modulus. A possible explanation of this phenomenon is suggested.Dnepropetrovsk Civil Engineering Institute. Translated from Mekhanika Polimerov, No. 1, pp. 149–156, January–February, 1974.     

On the theory of orientation of linear amorphous polymers

The previously derived orientation equations are solved for uniaxial extension at constant true stress, unloading, stress relaxation, and biaxial orientation at constant strain rate. The dependence of the birefringence of biaxially oriented PMMA on the magnitude and conditions of preliminary orientation has been experimentally investigated. There is good qualitative agreement between the theoretical and experimental results.For communication 1 see [1].Lenin Moscow State Pedagogic Institute. Translated from Mekhanika Polimerov, No. 1, pp. 14–21, January–February, 1973.     

On the theory of biaxial orientation of amorphous polymers

The macromolecule orientation distribution function for biaxial orientation is calculated on the basis of a network model of a linear amorphous polymer. The dependence of the distribution function on the biaxial stretch ratio, orientation temperature, and certain other factors is investigated. A relation is established between the distribution function and the experimentally observed birefringence. The birefringence of biaxially oriented polymethyl methacrylate is measured in relation to the degree of deformation. The experimental data are compared with theory.Moscow Lenin State Pedagogical Institute, Problem Laboratory of Polymer Physics. Translated from Mekhanika Polimerov, No. 5, pp. 771–779, September–October, 1970.     

Acoustic-optical criteria of analysis of orientation ordering in some fiber forming polymers

Conclusions A correlation was established between the scalar field describing the ordering of the structure and the tensor field characterizing the elastic constants of a material. It was proved that it is possible to use the acoustic and optical criteria for the analysis of the structure of some oriented fiber forming polymers. It was shown that the correlation between the suggested acoustic criteria can be used for optimizing the process of orienting drawing.Translated from Mekhanika Kompozitnykh Materialov, No. 5, pp. 771–775, September–October, 1986.     

Effect of molecular mobility,state of stress,orientation, and plasticization on the temperature dependence of the mechanical properties of linear polymers

The temperature dependence of the breaking stress and ultimate creep strain has been investigated in relation to preorientation, plasticization, and state of stress for polymethyl methacrylate, high-pressure polyethylene, polystyrene, and polyvinyl alcohol. The results of the mechanical tests are compared with the NMR data on the molecular mobility. The causes of the observed effects are discussed.Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 1, pp. 30–35, January–February, 1971.     

Experimental determination of the limiting birefringence of oriented polymers

Experimental data on the birefringence and molecular orientation factorf, determined from the IR absorption spectra in polarized light, are compared for polystyrene, polyvinyl alcohol, and polyethylene. Limiting values of the birefringence corresponding to maximum orientation (f=1) for these polymers are found to be equal to 0.16, 0.063, and 0.065, respectively.Mekhanika Polimerov, Vol. 3, No. 6, pp. 1105–1109, 1967     

A molecular model of creep and stress relaxation in crystalline polymers

A possible model of defect formation in a polymer crystal lattice is considered. The results of an investigation of creep and stress relaxation in crystalline polymers are interpreted on the basis of the model proposed.T. G. Shevchenko Kiev State University. Translated from Mekhanika Polimerov, No. 6, pp. 969–975, November–December, 1971.     

Relation of the reinforcing action of fillers with molecular motion in polymers

In the case of filled systems based on butadiene-styrene copolymers, it has been shown that the attainment of mobility of kinetic segments in definite temperature regions leads in amorphous polymers to an increase in their strength and reinforcement effect, and also to a change in the morphology of the breakdown surface in these temperature regions. The established regularity has been examined from the point of view of the adhesion theory of reinforcement.Moscow Institute of Meat and Milk Industry. Central Scientific-Research Laboratory of Chemical Packaging Materials, Moscow. Translated from Mekhanika Polimerov, No. 5, pp. 909–911, September–October, 1972.     

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.     

Limiting stretch ratios of polymers. Role of molecular mobility

Orientation stretching stops before the polymer chains reach full orientation. The reason for the cessation of stretching in linear polymers is considered to be the decreased kinetic flexibility of the macromolecules. With Kapron as an example, it has been demonstrated, using NMR, that on attainment of the limiting stretch ratio under the action of the stretching (orienting) forces, segmental motion in the amorphous regions is almost completely stopped: the amorphous regions are glassy at any orientation temperature, even those close to the melting point of the crystals. The orientation process stops because the polymer under load behaves like a rigid body devoid of rubber-like elasticity.A. F. Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, Vol. 9, No. 3, pp. 387–391, 1973.     

Thermomechanical method for determining the molecular weights of amorphous linear polymers

A thermomechanical investigation of polyisobutylene specimens under various time and stress conditions enabled us to extend the applicability of this method of determining the molecular weight of an undissolved polymer. The previously proposed mechanical model of a polymer, which is the basis of the relationship between the molecular weight of the polymer and the difference between the yield and glass-transition temperatures, must be refined to make allowance for the supramolecular structure.Mekhanika Polimerov, Vol. 3, No. 4, pp. 586–590, 1967     

Relationship between the molecular structure and certain mechanical properties of oriented polymers

The correlations between the molecular structure and intermolecular energy and the fatigue and elastic properties of fibers are considered. It is shown that the maximum of these properties corresponds to an optimal value of the intermolecular energy.Leningrad Branch of the All-Union Scientific-Research Institute of Synthetic Fibers. Translated from Mekhanika Polimerov, No. 4, pp. 734–735, July–August, 1969.     

Relation between molecular orientation characteristics determined from birefringence and acoustic data and the effect of orientation on the strength of polycaprolactam fibers

The mean molecular orientation calculated from birefringence and acoustic data has been investigated in relation to the degree of stretching for polycaprolactam fiber. A correlation has been found between the characteristics calculated by these two independent methods. It is shown that the molecular orientation factor calculated from the speed of sound does not depend on crystallinity if the measurements are made below the glass transition temperature. It is confirmed that the strength of the fiber depends importantly on the degree of orientation of the molecular segments in the amorphous zones.Mekhanika Polimerov, Vol. 3, No. 1, pp. 3–7, 1967