Abstract: The results of a systematic method of toughening, plastic material and thermosetting resin, which included adding inorganic filler, rubber elastomer, plastic material and thermotropic liquid crystal, forming half interpenetrating networks with plastic resin, changing chemical structure of network and controlling the molecular anisotropism of network, and their mechanism were presented. In this paper, the thermodynamic and kinetic data on phase splitting in a system of thermosetting resin modified with rubber elastmer were determined and discussed as well.