an rim method of thermoplastic resin comprises a process for preparing materials in which one compound is mixed with a material for thermoplastic resin to prepare one mixture , and the other compound is mixed with a material for thermoplastic resin to prepare the other mixture , each of two compounds and being inactive to the material for thermoplastic resin but producing a high - active anionic polymerization catalyst by their reaction , a process for polymerization in which the mixture and the mixture are mixed , injected into a mold , and polymerized by the anionic polymerization catalyst , an ejecting process in which a solidified thermoplastic resin molded body is ejected from the mold . therefore , a polymerization reaction cannot be started before the material for thermoplastic resin is injected into the mold , and it begins soon after the material for thermoplastic resin is injected into the mold .