Isopropenyl tert-butyl ketone (IPTBK) does not undergo radical homopolymerization under standard conditions. Anionic polymerization is an equilibrium process with a ceiling temperature below 0 °C and is quite sluggish. The low polymerizability of IPTBK in contrast to the high reactivity of typical vinyl ketones can be explained in terms of the high electron density on the 0-carbon resulting from distortion of the usual planar s-cis or s-trans conformation. This monomer is not a fully conjugated system due to the bulky tert-butyl group. The presence of the unconjugative, twisted conformation has been confirmed by 1H and 13C NMR and UV spectroscopies. Nevertheless, high molecular weight polymers have been synthesized by anionic polymerization with n-butyllithium/18-crown-6 in tetrahydrofuran at –78 °C. © 1986, American Chemical Society. All rights reserved.