Atom transfer radical polymerization (ATRP) is among the most powerful and robust controlled radical polymerization techniques that facilitates macromolecular engineering by synthesis of polymers with precise molecular weights, low dispersities, and well-controlled architectures. Good control over polymer structures via ATRP is largely attributed to the fast activation/deactivation equilibrium that can be governed by transition metal catalysts (particularly with copper catalysts) or photoredox catalysts. However, the detailed mechanism of ATRP has not been studied thoroughly at the atomic level, which hinders the rational design of better ATRP catalysts. In this study, we employ density functional theory (DFT) and Marcus Theory calculations to investigate both outer-sphere single electron transfer (OSET) and inner-sphere single electron transfer (ISET) pathways for photoinduced ATRP systems with phenothiazine derivatives as photoredox catalyst. In photoinduced ATRP, the activation phase occurs via a dissociative electron-transfer pathway, while an associative electron transfer involving a termolecular encounter is favored in the deactivation process. The computed activation barriers agree well with experimental kinetic data. On the other hand, ISET pathway is favored in the copper-catalyzed ATRP. The ISET halogen transfer transition states are investigated using DFT calculations for the first time. Calculations provided good agreement with experimental activation rate constants. The computational studies revealed important insights into the electronic and steric effects of ligands on the activity of Cu-ATRP catalysts.

Computational studies of copper-catalyzed and photoinduced metal-free atom transfer radical polymerization

254th National Meeting (2017)

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