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 (<i>k</i><sub>act</sub>) of the “activation” reaction between Cu<sup>I</sup> 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 <i>k</i><sub>act</sub> values (>7 orders of magnitude). These included rate constants of extremely fast reactions with <i>k</i><sub>act</sub> > 10<sup>7</sup> mol<sup>–1</sup> dm<sup>3</sup> s<sup>–1</sup>. We studied three widely used ATRP catalysts ([Cu<sup>I</sup>PMDETA]<sup>+</sup>, [Cu<sup>I</sup>TPMA]<sup>+</sup>, and [Cu<sup>I</sup>Me<sub>6</sub>TREN]<sup>+</sup>) and an extended series of water-soluble initiators. Accurate results were obtained in the range 1 < <i>k</i><sub>act</sub> < 10<sup>8</sup> mol<sup>–1</sup> dm<sup>3</sup> s<sup>–1</sup>, 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.