7-Methyl-2-methylene- (1) and 7-methyl-2,3-dimethylene-1,4,6,9-tetraoxaspiro[4.4]nonane (2) were synthesized and characterized by elemental analysis, IR, H-1 NMR and C-13 NMR spectroscopy. Radical polymerization of the spiro orthocarbonates (SOC) 1 and 2 show that they undergo primarily vinyl polymerization with a low degree of ring-opening reaction. Homopolymerization of 2 at 120 degrees C with di-tert-butyl peroxide gives a transparent crosslinked polymer and the polymerization generates a 12,5% shrinkage in volume.