A new poly(ethylene glycol) derivative, 1-methoxypoly(oxyethylene)benzocyclobutene (1) was prepared from the reaction of 1-benzocyclobutenyl 1-hydroxyethyl ether with mesylate of methoxypoly(oxyethylene) in tetrahydrofuran. The degree of end-group conversion, as determined by NMR, was 100%. The Diels-Alder reactions of 1 with maleic anhydride and N-phenylmaleimide were carried out in refluxing toluene to obtain the corresponding adducts (2 and 3, respectively) in excellent yields. NMR analyses of 2 and 3 indicated complete conversion of 1 to the corresponding products. The reaction of 2 with o-toluidine resulted in complete conversion of the anhydride adduct to the corresponding products. (C) 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1934-1938, 2004.