A.Ya. Malkin

Viscoelastic properties of butadiene-styrene block copolymers

SummaryThe viscous properties of SBS block copolymers (of “Cariflex TR-1102” in this work) have been determined with the rate of shear being varied by 108 times. It has been shown that in the region of low shear rates the polymer behaves as a structured highly concentrated disperse system which exhibits sharply pronounced thixotropy. In the region of high shear rates, the viscous properties of the polybutadiene matrix are of decisive importance. At low values of shear stress the compliance of the SBS block copolymer exceeds that of the polybutadiene matrix almost by a decimal order.At high shear stresses, just as in the case of viscous properties, the elastic behaviour of the SBS block copolymer approaches that of the polybutadiene matrix. Measurements of the dynamic characteristics at frequencies, which vary by a million times, most spectacularly point to the specificity of the viscoelastic properties over a wide temperature range. Under conditions of low temperatures the SBS block copolymer behaves as a rubber, while at temperatures above the glass transition temperature of polystyrene, at low loading intensities (low amplitudes and small deformations) the block copolymer shows low fluidity. This is most clearly seen from the frequency dependence of the loss modulus, especially in comparison with the relation typical of polybutadiene.ZusammenfassungDie viskosen Eigenschaften von SBS-Block-Copolymeren (hier „Cariflex TR-1102“) werden in einem Bereich von acht Zehnerpotenzen der Schergeschwindigkeit untersucht. Es wird gezeigt, daß im Bereich niedriger Schergeschwindigkeiten das Polymer sich wie ein strukturiertes hochkonzentriertes disperses System verhält, das eine ausgeprägte Thixotropie besitzt. Im Bereich hoher Schergeschwindigkeiten sind dagegen die viskosen Eigenschaften der Polybutadien-Matrix von entscheidender Bedeutung. Bei niedrigen Schubspannungswerten übersteigt die Komplianz des SBS-Block-Copolymeren diejenige der Polybutadien-Matrix höchstens um etwa 10%.Bei hohen Schubspannungen nähert sich das elastische Verhalten analog wie bei den viskosen Eigenschaften demjenigen der Polybutadien-Matrix an. Die Messung der dynamischen Charakteristiken über einem Frequenzbereich von sechs Zehnerpotenzen lassen die spezifischen viskoelastischen Eigenschaften in einem weiten Temperaturbereich sehr deutlich erkennen. Bei tiefen Temperaturen verhält sich das Polymer wie ein Gummi, während bei Temperaturen oberhalb der Glasübergangstemperatur des Polystyrols unter geringer Belastung (d.h. kleinen Amplituden bzw. Deformationen) das Polymer eine geringe Fluidität zeigt. Dies erkennt man am deutlichsten an der Frequenzabhängigkeit des Verlustmoduls, insbesondere durch Vergleich mit derjenigen bei Polybutadien.

Experimental estimation of wall slip for filled rubber compounds

The phenomenon of wall slip during flow of rubber compounds through capillaries is investigated for a typical styrene-butadiene elastomer with carbon black. It was found that at low temperature (110°C) the dependencies of slip velocity Vc on shear stress are described by the power law but, additionally, Vc depends on radius of a channel. At high temperatures there is a critical shear stress below which sliding is absent. Sliding appears only at higher shear stresses where, again, Vc depends on shear stress and the radius of a channel.

The nonisothermal anionic polymerization of caprolactam

With the anionic activated polymerization of caprolactam as an example it is shown that the kinetic function f(η) and the kinetic constants of a thermokinetic model may be found by solving an inverse problem, involving the use of experimental data on temperature changes during the nonisothermal bulk polymerization process. The autocatalytic character of the anionic polymerization of caprolactam came to light through use of the inverse method.

Rheological properties of liquid crystalline polymer systems. Review

Abstract The viscous, viscoelastic and highly elastic properties of liquid crystalline solutions and melts of polymers are described. The main feature of the rheological behaviour of these systems is the dependence of the measured characteristics on the orientation of the preparation practically absent for isotropic systems. This leads to sharp change in the rheological properties on passing from the isotropic to the liquid crystalline state. Change in the mechanism of flow of anisotropic solutions and melts of polymers is particularly graphically manifest in presence of a fluidity limit and the existence of the viscosity maximum at a certain concentration and temperature. In addition, unusual effects for isotropic polymer systems observed in the liquid crystalline state are the negative value of the first difference in nornal stresses, the dependence of the rheological properties on the thermal and mechanical prehistory and the absence of a quantitative correlation between the resutls of dynamic and stationary shear experiments.

Role of the functionality of activators during isothermal crystallization accompanying the activated anionic polymerization of ϵ-caprolactam☆

Abstract Analytical dependences of rate constants of crystallization accompanying the polymerization of ϵ-caprolactam on concentration and on the functionality of activators have been derived by means of quantitative analysis of calorimetric data under isothermal conditions.

Method for the complex study of rheological properties of polymer systems

Abstract A description is given of a device used for the complex measurement of visco-elestic properties of polymer systems under conditions of continuous harmonic shear deformation. The fundamental system of the device, technical properties and typical examples of determining rheological characteristics of polymer systems are dealt with.

Fracture of polymers in the visco-fluid state on stretching. Review☆

Abstract The experimental data and existing theoretical notions of the patterns of fracture of polymers in the visco-fluid state on uniaxial stretching in different loading regimes are reviewed. The possible mechanisms of fracture and the quantitative criteria characterizing the conditions of rupture of a jet are discussed.

Effect of plasticization on relaxation properties of polydodecane-amide

Abstract Using polydodecane-amide as a typical crystalline polymer a study was made of the effect of the low molecular weight component on the position and intensity of relaxation transitions and the variation of dynamic mechanical properties of the composition. It was found that with an increase in the concentration of the low molecular weight component, the range of α-relaxation is displaced to reduced temperatures and low-temperature transitions (β and γ) undergo degeneration. The plasticizer introduced into the polymer in the low temperature region produces an increase in the elastic modulus, i.e. a typical ‘antiplasticization’ effect takes place. A study was made of the effect of moisture on relaxation properties of the initial and plasticized polydodecane-amide samples.

Orientational structure formation in lyotropic, liquid crystals of poly-p-benzamide☆

Abstract The relationship between the conditions of deformation and structure- formation in liquid crystals of poly- p -benzamide (PBA) has been investigated. Use of a combination of physicochemical methods has enabled it to be shown that orientation of the macromolecules in flow can be different in different sections of the flow curve. If deformation is brought about by stresses close to the yield point, when flow is stopped after-orientation takes place, ending in formation of domains of regular shape. Structural features of the domains are discussed, bearing in mind their electro magnetic nature.

Rheokinetics of radical polymerization

Abstract Kinetic mechanisms and rheological properties of polymerization systems were examined and concrete mathematical ratios describing the increase in the viscosity of reaction masses during radical polymerization, derived. The conclusions drawn were confirmed by experimental results of radical polymerization of methyl methacrylate and styrene available in the literature.