A new class of a hyperbranched polymer with 100% degree of branching has been successfully prepared by using 1-(3-phenoxypropyl)piperidine-4-one as an AB, monomer in the presence of methanesulfonic acid. This hyperbranched polymer is based upon a piperidine-4-one ring and is designed to react with aromatic nucleophiles to give an irreversibly formed diarylated compound. The electrophilicity of piperidine-4-one is enhanced by through-space electrostatic repulsion and an inductive effect. The kinetics of the model reaction between 1-ethylpiperidine-4-one and anisole was examined. The reaction followed second-order kinetics, indicating that the first reaction, that is, the formation of the intermediate from the reaction between 1-ethylpiperidine-4-one and anisole, is considerably slower than the second one, that is, the reaction of the generated intermediate with anisole. On the basis of this observation, a new monomer, which was expected to produce a 100% branched hyperbranched polymer, was designed and synthesized. The obtained polymer was characterized by H-1 and C-13 NMR spectroscopy, which affirmed the 100% degree of branching of the hyperbranched polymer.