ATRP in Water: Kinetic Analysis of Active and Super-Active Catalysts for Enhanced Polymerization Control

Atom transfer radical polymerization (ATRP) in water is characterized by very high catalytic activity, i.e. the rate constant (kact) of the “activation” reaction between Cu(I) complexes and alkyl halides (RX) is very large. To accurately study such fast reactions in water, we developed a collection of electrochemical methods applicable for the determination of a vast range of kact values (>7 orders of magnitude). These included rate constants of extremely fast reactions with kact > 10^7 mol−1 dm3 s−1. We studied three widely used ATRP catalysts ([Cu(I)PMDETA]+, [Cu(I)TPMA]+, and [Cu(I)Me6TREN]+) and an extended series of water-soluble initiators. Accurate results were obtained in the range 1 < kact < 10^8 mol−1 dm3 s−1, allowing to build for the first time precise structure−reactivity correlations for aqueous ATRP, in both pure water and water/monomer mixtures. The results were compared to traditional ATRP systems in organic solvents. The collected data greatly expand the available range of investigated catalyst/initiator systems.