Yu.G. Yanovskii

The viscoelastic properties of linear polymers in the state of flow and the transition to the high elastic state. Review

The results of experimental research on the viscoelastic properties of linear polymers with a narrow MWD, and of mixtures and solutions of these, are discussed and generalized. A rational classification of macromolecular compounds that lays down a clear boundary between oligomers and polymers is proposed. In comparison of polymers of different homologous series, their molecular weights must be standardized with respect to the number of monomer units between points of molecular entanglement, and for this the reference temperature is taken as 100° above the glass temperature. The transition of polymers from the flow state to the high elastic state, brought about by increase in deformation rate (frequency), is studied systematically. The transition of linear high polymers to the high elastic state takes place within a narrow range of critical stresses (in the region of 0·1 → 1·0 × 107 dyne/cm2) and is not dependent on molecular weight, whereas the critical rates of strain (frequencies) are dependent on molecular weight and viscosity, these rates falling very rapidly with increase in these characteristics. Polydispersity affects the properties of polymeric systems to a great extent. As the rate of deformation is increased, components of higher molecular weight pass successively into the high elastic state. This gives rise to nonlinear, especially non-Newtonian, behaviour of systems comprising components with linear characteristics. The durability of raw rubbers in the high elastic state exhibits the same relationships as for vulcanized rubbers. This means that the three dimensional network of uncrosslinked macromolecules, behaves similarly to networks with chemical crosslinkages.

Effect of inorganic salts on reaction rate in high-conversion polymerization of N-trimethylammoniumethyl methacrylate methyl sulphate in aqueous solutions

The effect of simple inorganic electrolytes on the kinetics of radical polymerization of N-trimethylammoniumethyl methacrylate methyl sulphate (TMS), initiated by ammonium persulphate, has been studied in aqueous solutions. The presence of salts practically does not affect the initial rate of polymerization, but in the region of high conversions (> 15%) the polymerization is markedly accelerated in the presence of Na2SO4. The phenomenon has been explained (from viscometric, spectrophotomeric, dilatometric, and rheological measurements) as resulting from structure formation in the system, accompanied by a rise in viscosity, so that the gel-effect sets in at lower conversions and the polymerization rate increases.

Superslow relaxation processes in amorphous linear polymers and their interpretation

Abstract Relaxation processes in the region of the flow state (the terminal zone) in 1,4-polybutadiene with a narrow MWD have been investigated by a dynamic method at low frequencies over a wide temperature range. Superslow relaxation processes observed in experiments are discussed in terms of the theory of viscoelasticity of linear polymers.

The importance and evaluation of temperature transitions of amorphous linear polymers from one physical state into another using modern dynamic methods

Abstract A study was made of results of investigating visco-elastic dynamic characteristics of 1,2-polybutadienes of narrow MWD and different molecular weights obtained under conditions of transition from the fluid to the high-elastic and from the high-elastic to the glassy state for the case of low-amplitude periodic shear deformation in a wide range of frequency and temperature. Limiting possibilities were indicated for using the method of temperature-frequency reduction. Results of dynamic investigations were compared under different conditions of deformation: at constant frequency and variable temperature, at variable frequency and constant temperature and at constant frequency and temperature.

Aspects of the influence of plasticizers of varied nature on the physicomechanical properties and structure of polymethylmethacrylate

Abstract The authors have investigated the effect of various plasticizers on the physicomechanical properties and structure of PMMA by translucent electron microscopy, low amplitude periodic deformation and a phytochromic kinetic label. With increase in the plasticizer content the system was found to be microheterogeneous to the point of release of plasticizer into a separate phase.

Rheological properties of polymers in the fluid state

The possibilities and conditions of correlation are determined for the principal rheological characteristics of single-phase polymer systems measured for one-dimensional shear deformation in steady-state flow regimes, on transition from rest to steady-state flow, and in harmonic vibration regimes. Special significance attaches to the quantitative results of measuring the high-elastic properties of the polymer systems. It is shown that the Lodge theory, describing the flow behavior of high-elastic media, is well-founded in the linear region of deformation, i.e., for the limiting case of shear rates and shear stresses tending to zero, whereas the Mooney-Rivlin-Weissenberg theories are not in accord with the experimental data even in this limiting deformation regime.

Study of poly(organosiloxane) network formation by analysis of viscoelastic characteristics

The process of crosslinked polymer formation was studied for the case of anionic copolymerization of spirocyclosiloxane with α, ω-oligodimethylsiloxane by the methods of small-amplitude periodic deformation, sol-gel analysis and swelling. The effect of initial content of initiator and spirocyclosiloxane on the time dependences of dynamic modulus and gel-fraction was demonstrated. The structural parameters of the networks were determined The mean length of the elastically active chain in the network considerably exceeds the chain length of the initial α, ω-oligodimethylsiloxane. Increased spirocyclosiloxane content affects the viscoelastic characteristics of the network.

Visco-elastic properties of linear polymers and their mixtures with narrow molecular weight distribution☆

A study was made of visco-elastic, dynamic characteristics of mixtures based on 1,4-polybutadienes of narrow molecular weight distribution (MWD) with different molecular weights of the matrix and additive (from 104 to 106) in the range of low concentrations of the high molecular weight component. Concentration dependences were determined for initial viscosity, the initial coefficient of high-elasticity and equilibrium compliance. It was shown that the relative variation of components of the dynamic modulus of the initial matrix increases with an increase in MW of the additive and decreases with an increase in MW of the matrix. It was established that for minimum concentrations of the high molecular weight component in a low molecular weight matrix special features in the behaviour of the latter are determined by properties of the visco-elastic medium. Characteristic values of elastic moduli and the coefficient of high-elasticity of mixtures (i.e. systems of maximum dilution) were calculated, when the medium is not only viscous, but also elastic.

The mechanism of viscoelastic behavior of linear polymers

The motion of a concentrated solution or a melt of polymers is modeled by the movement of an aggregate of independent necklaces with the friction coefficient of a chain-length unit, which increases from the middle of the macromolecule to its ends in accordance with exponential law. The set of relaxation times in the system was found and the dynamic shear modulus was calculated. A comparison with the experimental data shows that this theory gives a satisfactory description of the basic regularities in the viscoelastic behavior of polymers.

Rheological properties of polymethyl mechacrylate blends with elastomers as a function of thermodynamic interaction of the components and the degree of blend dispersion

Abstract The rheological properties of impact resistant compositions obtained by melt mixing are studied, using model polymethyl methacrylate mixtures with various elastomers. The thermodynamic interaction of the polymers was evaluated from the Flory interaction parameter, from the solubility limits of the rubbers in the polymethyl methacrylate, and from the Hildebrand equation. The decrease in effective viscosity of the mixture blends is mainly due to deformation of the low viscosity disperse phase. The high viscosities of the blends containing strongly interacting components is due to the effect of the phase interface.