A new synthesis of hyperbranched polymers through proton transfer polymerization of thiol and epoxide groups is presented. For this, an AB(2) monomer bearing two epoxides and a thiol groups is synthesized. Base-catalyzed proton transfer polymerization of this monomer led to the formation of a polythioether-based hyperbranched polymer with a 65-69% degree of branching and carrying about 2% of disulfide-based structural defects. This polymer contained two reactive sites, a hydroxyl group and an epoxide unit, distributed throughout the branched scaffold. The epoxide groups could be employed in anchoring an alkyl, aryl, or ethylene oxide chain through a thiol-epoxy reaction, while the hydroxyl groups produced during the polymerization and the first functionalization reactions could be engaged in attaching positively charged primary ammonium groups to the branched backbone. These sequential postpolymerization modifications transformed the general dual-reactive scaffold into dual-functionalized hyperbranched materials with potential utility in the arena of gene delivery applications.