The Effect of Isoprene Rubber Plasticization on the Tangent of the Angle of Mechanical Losses of Its Vulcanizates at 60 °C. Part 3. Study of the Contributions of Molecular Weight and the Degree of Impact of Rubber Plasticization

Abstract

The third (final) part of the article is devoted to the study of the effect of plasticization of isoprene rubber (SKI-3) on the tangent of the angle of mechanical losses at 60 °C of its vulcanizates (tg60). In this paper, the dependences of the contributions of the molecular weight (MM) (γ^mm) and the degree of impact of plasticization (α) (γ^α) on the tg60 index are studied in detail. It was found that alkyl and allyl macroradicals, appearing during the mechanocreaking process, contribute to the reduction of tg60 due to factor α. The process of oxidative destruction of SKI-3 macromolecules, which leads to the appearance of oxygen-containing macroradicals, on the contrary increases tg60. An undesirable increase in tg60 is especially noticeable at an elevated plasticization temperature due to a sharp increase in γ^mm. Assumptions have been made to explain the different effects of alkyl, allyl and oxygen-containing macroradicals on the value of tg60. The process of recombination of macroradicals of different chemical nature increases tg60 due to an increase in the contributions of γ^mm and γ^α to this indicator. The presence of SKI-3 macromolecules, that have not undergone the plasticization process, has a positive effect on the tg60 index: it decreases markedly with a decrease in MM of SKI-3 macromolecules with an increase in the duration of its plasticization.