Novel quinone methide ketals, 8-[1'-cyano-1'-(ethoxycarbonyl)methylene]-1,4-dioxaspiro[4.5]deca-6,9-diene (1 a) and. 8-(1',1'-dicyanomethylene)-1,4-dioxaspiro[4.5]deca-6,9-diene (1b), were synthesized, and their polymerization behavior was investigated. Polymerizations of 1a and 1b initiated with BPO and BF3.Et2O gave corresponding novel ring-opening polymers, but no polymerization with BuLi. Copolymerization of la with St in the presence of AIBN at 60 degreesC gave the monomer reactivity ratios r(1)(1a) = 0.50 +/- 0.1 and r(2)(St) = 0.1 +/- 0.02, and Q and e values of la were 2.46 and +0.93, indicating that la is a highly conjugative, electron-accepting monomer. Homopolymers of la and 1b had better thermal stability than that of 7-cyano-7-(ethoxycarbonyl)-1,4-benzoquinone methide.