Spontaneous copolymerization of methoxyallene (1) with N-phenylmaleimide (2) was carried out. In the absence of a solvent, the copolymerization proceeded via a diradical intermediate to afford the corresponding alternating copolymer, along with an adduct of 1 with 2. The polymerization in aprotic solvents such as DMSO yielded a polymer larger than that from the bulk polymerization, The copolymer obtained in the solution polymerization contained a homopolymer of 2. When benzyl alcohol was added to the polymerization mixture of 1 and 2 in DMSO, an adduct of all three compounds was isolated from the mixture, suggesting the formation of a zwitterion of 1 and 2.