Mixtures of 5-membered and 6-membered 2-vinyl (2-propenyl or 2-isopropyl)-4-hydroxymethylene or 5-hydroxy-substituted cyclic acetals were synthesized by the reaction of aldehydes with glycerol. Reesterification of the hydroxyl group in position 4 or 5 was achieved using methyl methacrylate. The compounds were subjected to radical copolymerization using different initiating systems. Both radical copolymerization and ring cleavage were observed to be dependent on the reaction conditions. The ring cleavage was confirmed on model compounds of 2-substituted 5-membered and 6-membered cyclic acetals without ally polymerizable substituent. The rate of the ring opening was measured and compared to the rate of copolymerization.