Abstract: Novel copolymers are prepared in the novel process comprising copolymerizing an N-substituted aziridine with a vicinal epoxide or episulfide. Compounds having at least one active hydrogen, such as water or an alcohol, may be advantageously included as coreactants in the process. The structure of the copolymers, exclusive of any chain-extending or terminal groups, is defined by alternating ring-opened units of the N-substituted aziridine monomer and the epoxide or episulfide monomer. The copolymers are useful as stabilizers for chlorinated solvents, rubber cure accelerators, antioxidants, surfactants, lubricants, acid scavengers, dye-retention aids, retention aids for starch, and as flocculants.