Divinyl monomers consisting of an acryloyl group bearing large a-substituents containing allyl and methallyl groups were synthesized and their cyclopolymerizations were studied. Both monomers were found to be highly homopolymerizable to yield soluble polymers in solution or bulk. The formation of the highly cyclized polymers were confirmed by H-1-NMR spectroscopy, although the size of the cyclic units could not be determined. The intramolecular addition of the acryloyl radical to the allyl or methallyl group is expected to form a six membered ring because of the steric hindrance to the formation of a five-membered ring.