AbstractAmphiphilic surface active vinyl monomers (alkyl‐2‐methacryloyloxyethyldimethylammonium bromides) with a long alkyl chain (C8/, C12, C14, C16, and C18) were investigated with respect to their polymerization behavior in the absence of an initiator. These monomers polymerized spontaneously in water, through a free‐radical mechanism, except for the ‘C8monomer’. In the polymerization of the ‘C16monomer’, the polymer yield depended on polymerization temperature, and the intrinsic viscosity of the resulting polymer varied with the initial concentration of the monomer just like in ordinary polymerization. The ‘C18monomer’, having low reactivity, became highly polymerizable upon mixing with a quaternary surfactant (dodecyl‐2‐isobutyryl‐oxyethyldimethylammonium bromide) in a particular mole ratio, owing to a change in the monomer aggregation state. In benzene, all of the quaternary methacrylates polymerized spontaneously, too. It is obvious that formation of monomer aggregates, micelles or reverse micelles is essential for the spontaneous polymerization. The spontaneous polymerization of other quaternary monomers, having a hexadecyl group and a polymerzable acryloyl, acrylamido, or methacrylamido moiety, did also occur, yet with lower rate than in c