As stable quinonoid compounds of the benzofuran and the naphthalene, 4,7-bis[cyano(ethylthio)methylene]- and 4,7-bis[cyano(phenylthio)methylene]-4,7- (1a and 1b) and 11,12-bis(ethylthio)- and 11,12-bis(phenylthio)-11,12-dicyano-1,4-naphthoquinodimethanes (2a and 2b) were successfully prepared. When 1a, 1b, 2a, and 2b were dissolved in aprotic polar solvents such as acetonitrile, acetone, tetrahydrofuran, N,N-dimethylformamide, and dimethyl sulfoxide, no spontaneous homopolymerizations occurred. An anionic initiator butyllithium induced the homopolymerizations of 1a and 1b at 0 degrees C, and of 2a and 2b at -78 degrees C to give respective oligomers. A radical initiator 2,2’-azobis(isobutyronitrile) (AIBN) induced the homopolymerizations of 1a and 1b at 60 degrees C, but did not of 2a and 2b. Compounds 1a and 1b were copolymerizable with styrene in the presence of AIBN in a nearly alternating fashion to give the monomer reactivity ratios r(1)(1a) = 0.70 +/- 0.40 and r(2)(styrene) = 0.02 +/- 0.04 at 50 degrees C for the la-styrene system and r(1)(1b) = 0.80 +/- 0.30 and r(2)(styrene) = 0.01 +/- 0.03 at 50 degrees C for the 1b-styrene system and the and and e values were and = 9.7 and e = +1.27 for 1a and and = 17.4 and e = +1.40 for 1b. However, when their copolymerizations were carried out at monomer concentrations where 1a and 1b are not homopolymerizable, no copolymerizations took place. The copolymerizations of 2a and 2b with styrene in the presence of AIBN at 50 degrees C did not occur.