Design Principles for Oxygen-Tolerant Surface-Initiated Photoinduced Atom Transfer Radical Polymerization toward Thick Polymer Brushes

Abstract

Polymer brushes are one of the most promising surface modification strategies, owing to their well-defined interfacial architecture. With recent advances in oxygen-tolerant atom transfer radical polymerization (ATRP), visible-light-driven photoATRP with dual photoredox/copper catalysis is particularly versatile. However, translating oxygen-tolerant ATRP from solution-phase polymerization to surface-initiated polymerization is not straightforward because polymer brush growth is governed by both solution-phase kinetics and surface-specific processes. In this study, we report design principles for oxygen-tolerant SI-photoATRP by systematically correlating surface-initiated polymer brush growth with solution-phase polymerization using eosin Y (EY)-mediated dual photoredox/copper catalysis as a model system. The initial concentration of the free initiator was found to be a key factor governing surface growth efficiency. The kinetic analysis performed at representative initiator concentrations further clarified the relationship between the surface-initiated polymer brush growth and solution-phase polymerization. An iterative SI-photoATRP process successfully facilitated the growth of thick polymer brushes with a maximum dry film thickness of 438 nm, without deoxygenation. The interfacial properties in the thick polymer brushes were also tunable according to the molecular design, as demonstrated by contact angle measurements. These findings provide a practical framework for the rational design of polymer interfaces via SI-photoATRP under oxygen-tolerant conditions.