The dynamic shear modulus and the flow rate through capillaries under constant pressure and under constant velocity of the piston, have been measured for polybutadienes and polyisoprenes of narrow molecular weight distribution with molecular weights ranging, respectively, from 3.8 × 104 to 5.8 × 105 and from 1.06 × 105 to 6.02 × 105. The phenomena of the discontinuous increase of volume flow rate and self‐oscillatory flow regime at critical rates of deformation have been considered in detail. It is proposed that these phenomena are due to the induced transition of the polymer from the fluid to the high‐elastic state at higher deformation rates. As a result, an inference has been made that polybutadienes and polyisoprenes with a narrow molecular weight distribution in the high‐elastic state, behave in certain respects as crosslinked polymers incapable of displaying fluidity. The quantitative relationships among the viscoelastic characteristics measured under dynamic regimes, the parameters determining the critical flow regimes, and the molecular weights of polybutadienes and polyisoprenes have been worked out.

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Translated by P. CurtisThe main feature of the effect of nanomaterials in composites is the considerable increase in the area of contact of the polymer/elastomer matrix with their surface, on account of which the maximum strengthening effect is achieved [1,2]. The effect of nanoparticles based on carbon, silicon, and metal oxides in composites is fairly well known [1,2]. As a rule, nanoparticles possess a high external specific surface (30-300 m 2 /g) and are introduced into the composite in concentrations of the order of 30 wt%. However, as regards the introduction of nanotubes and nanofibres into polymer and elastomer composites, there is no common opinion [3-5], especially taking into account the diversity of the structure and composition of the polymers and the methods of production, the structure, and the composition of the nanotubes. Here, carbon nanotubes are promising materials making it possible to create materials with fundamentally new properties [2]. Nanotubes on average possess a greater specific surface than nanoparticles (350-500 m 2 /g) and, because of their relatively high cost, are still, as a rule, regarded as additives introduced into composites in quantities of the order of 0.01-10 wt% [2].

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