Novel living/controlled radical polymerizations utilizing organomercurials and organocobaloximes as reversible chain terminators
Controlled free radical polymerization is an area of opportunity because it allows for the polymerization, under mild conditions, of a wide range of monomers. The polymers thus produced are well defined and controlled by the stoichiometry of the reaction. These polymers can be re-initiated to form block copolymers and star polymers. There are three requirements for controlled radical polymerization: Fast initiation, a low concentration of radicals in the active state, and rapid exchange between dormant and active species. Controlled free radicals can be divided into three systems: System I is based on reversible termination of growing polymer molecules with stable free radicals; System II is based on atom transfer radical polymerization (ATRP); System III is based on reversible addition-fragmentation chain transfer process (RAFT). Diphenyl mercury controlled radical polymerization of methyl methacrylate. The diphenyl mercury presumably formed a radical adduct with the growing polymer chain. The equilibrium between the radical adduct and the active polymer radical is shifted almost entirely towards the radical adduct side at room temperature. This type of equilibrium reduced the amount of chain transfers and chain terminations during the polymerization. The diphenyl mercury polymerizations of methyl methacrylate have a favorable equilibrium at room temperature as evidenced by laser initiated polymerizations. The polymer free radicals lived for three days without constant initiation.