1-Benzocyclobutenyl vinyl ether (1) was easily prepared by the elimination reaction of hydrogen bromide from 1-benzocyclobutenyl 1-bromoethyl ether obtained by 1-bromobenzocyclobutene and ethylene glycol via two steps in a good yield. Cationic polymerizations of 1 was carried out at -78 degrees C for 2 h in toluene in the presence of BF3OEt2 as an initiator to give quantitatively the corresponding polymers (2) as white solids. As a model reaction of the polymer reaction of 2 with dienophiles, the Diels-Alder reactions of 1-methoxybenzocyclobutene with maleic anhydride (MA) in toluene at 100-140 degrees C for 3 h were carried out to obtain the corresponding Diels-Alder adduct quantitatively at 140 degrees C. The polymer reactions of 2 with MA and N-phenylmaleimide (MI) in toluene were carried out to yield the corresponding Diels-Alder adduct polymers in good yields. The degree of introduction of the dienophile could be controlled by temperature, and the unreacted benzocyclobutene moiety could further react with another benzocyclobutene moiety or dienophile. The properties (solubilities, T-g, and temperature of 10% weight loss) of the polymers obtained from the polymer reaction were quite different from those of 2.