A novel captodatively substituted benzoquinone methide, 7-cyano-7-(phenyl)benzoquinone methide (3), was synthesized successfully as an isolable crystal at room temperature. 3 polymerized spontaneously on dissolving it in highly polar, basic solvents such as DMSO and DMF. The acid-catalyzed 1,6-addition reaction of 3 was investigated. Acid-catalyzed 1,6-addition reactions of 3 with phenol and N,N-dimethylaniline afforded 1:1 adducts. In the reaction with hydrogen chloride, a 1,6-addition adduct was also formed.. Homopolymerizations of 3 and 7,7-di(cyano)benzoquinone methide (la) with radical, anionic, and cationic initiators were investigated. 3 and la are homopolymerizable with an anionic initiator but not with radical and cationic ones. 3 is copolymerizable spontaneously with styrene in an alternating fashion. The copolymer structure of 3 with styrene was determined on the basis of the spectral data of model compounds and the polymerization mechanism was discussed.