Cationic polymerization of 4-methylene-2-phenyl-2-styryl-1,3-dioxolane (1) was carried out. Monomer 1 was very sensitive to acid, and even the glass surface afforded polymer 2. Acidic glass or silica gel was also a good catalyst for the formation of the high (M(n)) over bar polymer ((M(n)) over bar = 54 000-340 000). The polymerization proceeded through selective cationic double isomerization (ring-opening/allyl isomerization) and gave a 1,7-addition polymer. Polymer 2 can be degraded by water or amine.