Polymers having hemiacetal ester moieties in the side chain were synthesized and their thermal dissociation was examined. 1-Alkoxyethyl methacrylates (1) were synthesized from methacrylic acid with alkyl vinyl ethers and their radical copolymerizations with butyl methacrylate were carried out at 80 degrees C for 6.5 h using AIBN as an initiator to afford the corresponding copolymers having the hemiacetal ester moieties in the side chain. The hemiacetal ester moieties in the copolymers thermally converted to carboxyl groups with elimination of the corresponding vinyl ethers. The thermal dissociation of the hemiacetal ester moieties in the side chain obeyed first-order kinetics at 140 degrees C, and their reactivities were in the following order: 1-(tert-butoxy)ethyl > 1-isopropoxyethyl > 1-ethoxyethyl > 1-butoxyethyl ester.