The synthesis of difunctional seven-membered cyclic ketenacetals was investigated and the new monomers were characterized by IR-, NMR-spectroscopy, and elemental analysis. It was shown that the bifunctional ketenacetal 5 undergoes a radical homopolymerization forming crosslinked polymers with a high degree of ring-opened units. The copolymerization of the difunctional ketenacetal 5 with the monofunctional ketenacetal 1 leads only to low molecular polymers.