Syntheses and radical ring-opening polymerization of 1,1-bis(hydroxymethyl)-2-vinylcyclopropane (1a) and 1,1-bis(methoxymethyl)-2-vinylcyclopropane (1b) were examined. Novel polymers bearing hydroxyl and methyl ether moieties in the side chains as well as olefinic moieties in the main chain were obtained. The main structure of the polymers, obtained by radical polymerization, originated from the cleavage of the cyclopropane ring near the hydroxymethyl or methoxymethyl groups. The difference in the two-center energies and bond orders of the C-C bonds of the cyclopropane ring well explained the selectivity in the direction of the cleavage. The number-average molecular weights ((M) over bar(n)) of poly(1a) and poly(1b) were 94200 and 11200 in the polymerization in bulk at 60 degrees C, respectively. The intermolecular hydrogen bonding of la might increase the radical polymerizability. The oxygen permeability of poly(1a) was 6.19 mL.20 mm.m(-2).day(-1).atm(-1) at 35 degrees C, demonstrating that poly(1a) could be a good oxygen barrier material.