We study an effect of a rate of extension, type and ratio of the polymers mixed and type of a vulcanization system, as well, on the mechanical properties of the thermal-elastoplastics based on polypropylene, ethylene-propylene-diene caoutchouc, and copolymers of ethylene and octene “Engage”. We prove that the limiting strength increases with the increase of the rate of extension, when using the copolymers of octene and ethylene, as well as when applying a sulphuric vulcanization system. We analyze the results obtained within a viscous-elastic approximation. We make an assumption that at the initial stage of deformation of the mixture, polyolefin deforms first, and only then, the interphase layer at the interface of the phases does. The limiting values of strength and elongation were determine mainly by extension of a cross-linked elastomer.