The Combination of Cis-1,4-Polyisoprene with Ethylene-Propylene-Diene Rubbers and the Properties of Their Covulcanisates

Abstract

In previous studies [1][2][3][4][5][6], investigations have been made of features of the structure formation of green and crosslinked blends of cis-1,4-polyisoprene (PI) of grade SKI-3 with ethylene-propylene-diene elastomers (SKEPT) of grades Keltan (DSM, Germany) and Royalen (Uniroyal, USA) and the properties of their covulcanisates. The SKEPT elastomers of the indicated companies differ in comonomer composition, in degree of isotacticity of the propylene units α [5,6], and in chain microstructure (Tables 1 and 2). The difference in phase structure, in morphology of the green mixes, in physicomechanical properties [1][2][3][4], and in ozone resistance of the covulcanisates [5,6] as a function of the comonomer composition of the SKEPT was established.Earlier, in investigations of the ozone-protective action of SKEPT in covulcanisates with butadiene-acrylonitrile rubbers (BNK) of different polarity [7-9], the structural mechanism of retardation of the ozone degradation of the diene elastomer was established. The dependence of the degradation rate on the phase structure of the blend, the intensity of interphase interaction, the number of crosslinks between the components [8,9], and the degree of crosslinking of the ozone-resistant phase [8] was shown. The influence on the formation of the interphase layer of the content of polar units of the BNK, the comonomer composition of the SKEPT, the diene content, the stereoregularity of the propylene sequences, and the isomerism of the butadiene units was established [7][8][9][10][11].With a low degree of isotacticity of the propylene microblocks a with SKEPT, only the butadiene units of the BNK combine. At high a, the volume of the interphase layer (the depth of interpenetration of sections of the component chains) increases. This is due to the high activation energy of the conformational transitions in isotactic sections of the chains [12], on account of which regions of the BNK that contain, it seems, single acrylonitrile units become accessible to them.Comparison of the results of Livanova et al. [5,6] indicates that the rate of ozone degradation of covulcanisates of cis-1,4-polyisoprene with SKEPT also depends on the stereoregularity of the propylene microblocks.In this work an investigation was also made of the influence on the combination of components, on interphase interaction, and on the ozone resistance of the covulcanisates of the chain microstructure of the SKEPT.The investigation was conducted on covulcanisates of cis-1,4-polyisoprene (PI) of grade SKI-3 with SKEPT of grades Keltan (DSM, Germany) and Royalen (Uniroyal, USA) [5,6]. The content of ethylene and propylene units, the content of the diene comonomer ethylidenenorbornene (ENB), the degree of isotacticity of the propylene units a, the molecular weight characteristics, and the Mooney viscosity are given in Table 1. The chain microstructure, including the content of inverse additions (n = 2), alternating units (n = 3), ethylene microblocks of more than 5 units length (n ≥ 5), and isotactic propylene mic...