The process of making a catalyst for the polymerization of 2-pyrrolidone by contacting an alkali metal pyrrolidonate, a quaternary ammonium halide and carbon dioxide in a mol ratio of about 1:0.1-2:0.1-0.5. The alkali metal pyrrolidonate may be prepared by reacting an alkali metal hydroxide with 2-pyrrolidone. The polymerization of 2-pyrrolidone in the presence of this catalyst system produces poly-2-pyrrolidone of high molecular weight.