Synthesis and radical polymerization of a vinylcyclopropane bearing a cyclic carbonate moiety, 1-vinyl-5,7-dioxaspiro[2.5]octan-6-one (1), examination of volume change on the polymerization, and thermal analysis of the polymer formed were carried out. 1 was prepared by the reaction of 1,1-bis(hydroxymethyl)-2-vinylcyclopropane with ethyl chloroformate. Radical polymerization of 1 was performed in the presence of an appropriate radical initiator (3 mol % vs 1) at 60-120-degrees-C. Polymers with M(n) = 15500 and 14100 were obtained by the polymerizations in N,N-dimethylformamide (DMF) for 48 h at 60 and 80-degrees-C, respectively. The structure of the polymer was determined to consist of two 1,5-ring-opened units 3 and 3’ and an unknown unit bearing no olefinic moiety. Cross-linked polymers were obtained in the polymerization in bulk and in chlorobenzene at any temperature. Selectivity in the direction of the cleavage of the cyclopropane ring of 1 during the polymerization was well explained by the difference in two-center energies between the two C-C bonds. Volume change during the polymerization of 1 was determined by the density gradient tube method to range from -0.9 to -6.1%, depending on the polymerization conditions. Minimum volume shrinkage was 0.9%, which was attained in the polymerization in DMF at 60-degrees-C where the obtained polymer contained no cross-linked part. The degree of volume shrinkage on the polymerization of 1 increased with increasing polymerization temperature. The glass transition temperature (T(g)) of the polymers was in the range 93-110-degrees-C. Some cross-linked polymers did not show their T(g)s. The 10% weight loss temperature under nitrogen of the polymers was in the range 276-356-degrees-C, and that of the cross-linked polymers was higher than that of the non-cross-linked polymers.