Controlled radical initiators, reaction mixtures containing the controlled radical initiators and various ethylenically unsaturated monomers, and polymeric materials formed from the reaction mixtures are provided. The controlled radical initiators are bis-dithiocarbamate or bis-dithiocarbonate compounds with a single carbon atom between the two dithiocarbamate or dithiocarbonate groups. Polymeric materials such as homopolymers, random copolymers, and block copolymers can be prepared using the controlled radical initiators.