A copolymer of acrylonitrile and vinyl acetate was prepared via the room temperature-initiated, self-heating polymerization of a concentrated emulsion. A mixture of the monomers containing an oxidant was first dispersed in an aqueous solution of surfactants to generate a concentrated emulsion with a volume fraction of 0.8 of the dispersed phase. An aqueous solution of reductants was subsequently introduced into the concentrated emulsion to initiate polymerization together with the oxidant. Since the container was properly insulated, the system self-heated because of the energy released from polymerization, and achieved a high conversion in 30 min. The molecular weight distribution was determined using the gel permeation chromatography (GPC), and the composition of the product was determined via elemental analysis. The GPC traces indicated that the molecular weight was a function of time. The longer the polymerization time, the greater the molecular weight. During polymerization, the composition remained almost unchanged. These two results differ from those of the traditional radical polymerization.