A 100% hyperbranched polymer was successfully prepared by using 2-[4-(4-mereaptobutoxy)phenoxy]-9H-fluoren-9-one as an AB(2) monomer in trifluoroacetic acid. The kinetics of the model reaction between 9-fluorenone and 3-mercaptopropicnic acid was investigated. The reaction obeyed the second-order kinetics, indicating that the first reaction, that is, the formation of the intermediate from 9-fluorenone and 3-mercaptopropionic acid, is considerably slower than the second one, that is, the reaction of the intermediate with 3-mercaptopropionic acid. On the basis of this finding, a new monomer expected to produce a 100% branched hyperbranched polymer, 2-[4-(4-mereaptobutoxy)phenoxy]-9H-fluoren-9-one, was designed and prepared. The obtained polymer was characterized by H-1 and C-13-NMR spectroscopy, which confirmed that the polymer was a 100% branched hyperbranched polymer. (c) 2008 Wiley Periodicals, Inc.