Spontaneous copolymerizations of 1,1,2,2-tetracyano-3-ethoxycyclobutane (1), which is a cyclobutane adduct of the zwitterionic tetramethylene generated from tetracyanoethylene (TCNE) and ethyl vinyl ether (VE), with oxiranes are described. The cyclobutane adduct 1 reacted with a variety of oxiranes spontaneously at ambient temperature in CH3CN to yield copolymers. Of the oxiranes, cyclohexene oxide (3) resulted in a high molecular weight alternating copolymer of 1 and 3. In the alternating copolymerization, the polymer yields and molecular weights increased with reaction time, whereas the composition of the copolymers remained constant at 1:1 irrespective of time. Furthermore, the polymer yields and molecular weights became maximum at a feed ratio of 1:1. The reaction of 1 with 3 was quenched with acetic acid in the initial stage to yield the acetic acid adduct (4) of the zwitterion generated from 1 and 3. On the basis of the polymerization behavior and the isolation of 4, the proposed mechanism of the copolymerization involves the stepwise reaction of the zwitterion generated from 1 and 3.