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 (k_act) 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 k_act values (>7 orders of magnitude). These included rate constants of extremely fast reactions with k_act > 10⁷ mol^–1 dm³ s^–1. We studied three widely used ATRP catalysts ([Cu^IPMDETA]⁺, [Cu^ITPMA]⁺, and [Cu^IMe₆TREN]⁺) and an extended series of water-soluble initiators. Accurate results were obtained in the range 1 < k_act < 10⁸ 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.