Hyperbranched polymers with both highly branched structures and numerous vinyl functional groups have been synthesized via reversible activation/deactivation controlled polymerization of multifunctional vinyl monomers. By controlling the competition between propagation and reversible termination using a deactivation enhanced method, the growth rate of polymer chains is decreased and the onset of gelation is prevented until the system has achieved much higher levels of conversion than has previously been reported for nonenhanced systems. Here, we demonstrate this strategy by synthesizing highly branched, irregular dendritic polymers with a multiplicity of reactive functionalities such as vinyl and halogen functional groups, and controlled chain structure via deactivation enhanced atom transfer radical polymerization (ATRP) of a commercially available multifunctional vinyl monomer-divinylbenzene (DVB) and ethylene glycol dimethacrylate (EGDMA).