Hyperbranched poly(ether sulfone)s were prepared by the self-polycondensation of the novel AB2 monomer, 4-(3,5-hydroxyphenoxy)-4'-fluorodiphenylsulfone. The high-molecular-weight polymers were isolated in good yields. The degree of branching (DB) of the resulting polymers was investigated by the preparation of dendritic and linear model compounds. The DB determined by gated decoupling 13C NMR measurements was in the range 0.170.41 and was dependent on the base used for the self-polycondensation. It was found that cesium fluoride was an effective base to form the polymer having the DB of 0.41. The resulting hyperbranched poly(ether sulfone)s showed good solubility in organic solvents. The solubility and the glass transition temperature of the polymers were influenced by the terminal functional groups. The unique thermal crosslinking phenomenon was observed during the DSC measurements of the hydroxyl-terminated hyperbranched poly(ether sulfone) under air condition. (c) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012