The anionic ring-opening polymerization of oxetanes containing hydroxyl groups was carried out with potassium tert-butoxide as an initiator in the presence of 18-crown-6-ether in N-methylpyrrolidinone at 180 degreesC; it yielded corresponding multifunctional hyperbranched polymers: poly(3-ethyl-3-hydroxymethyloxetane)s, with number-average molecular weights of 2200-4100 in 83-95% yields, and poly(3-methyl-3-hydroxymethyloxetane)s, with number-average molecular weights of 4600-5200 in 70-95% yields. The synthesized poly(3-ethyl-3-hydroxymethyloxetane)s and poly(3-methyl-3-hydroxymethyloxetane)s were hyperbranched polyethers containing an oxetane moiety and many hydroxy groups at the ends. The postpolymerization of poly(3-ethyl-3-hydroxymethyloxetane)s was performed in the presence of potassium tert-butoxide and 18-crown-6-ether in N-methylpyrrolidinone at 180 degreesC; it yielded corresponding polymers with higher molecular weights in good yields. The cationic polymerization of poly(3-ethyl-3-hydroxymethyloxetane) derivatives was carried out with boron trifluoride etherate as an initiator and was followed by alkaline hydrolysis; this yielded a new branched polymer, a poly(hyperbranched polyether), with many pendant hydroxy groups. (C) 2004 Wiley Periodicals, Inc.