A one-potsynthesis of a hyperbranched polyether using a A2B type monomer under mild conditions is described. The monomer, 5-(bromomethyl)-l, 3-dihydroxy benzene, undergoes self-condensation in the presence of potassium carbonate and 18-crown-6 to give polymers with weight-average molecular weights exceeding 10s. Spectroscopic analysis of the hyperbranched polymers reveals that both O-alkylation and C-alkylation occurs during polymerization. The polymers contain a large numberof phenolic hydroxyl groups located both at chain ends and at monomer units involved in irregular growth. The phenolicgroups of the hyperbranched polyethers can be modified readily and completely by simple acylation, benzylation, or silylation processes. Comparison of the size-exclusionchromatography data with absolute molecular weight measurements by low-angle laser light scattering supports the proposed hyperbranched structure of the polyethers.