Open-Air Growth of Polymer Brushes by Surface-Initiated PhotoATRP under Red-Light Irradiation

The translation of polymer brushes into technologically relevant coatings hinges on the development of scalable and robust fabrication strategies that are tolerant of environmental conditions. Surface-initiated photoinduced atom transfer radical polymerization (SI-photoATRP) has emerged as a powerful tool for synthesizing functional brushes with precise control over their architectural parameters. However, traditional SI-photoATRP requires high-energy light and confined setups to mitigate oxygen inhibition within nondeoxygenated mixtures, limiting substrate versatility and process scalability. Herein, we report a red-light-driven SI-photoATRP process enabled by a catalytic system composed of methylene blue (MB⁺) and a Cu-based ATRP catalyst, which achieves efficient polymer brush growth under fully open-air conditions. Systematic variation of reaction parameters─including light intensity, composition of the catalytic system, and solvent─enabled rapid growth of compositionally different brushes with high and tunable thickness. The deep penetration capability of red light was exploited to decorate microporous three-dimensional materials with polymer brushes. Spatially defined brush growth was demonstrated by shifting the wavelength of light irradiation, alternatively stimulating surface-initiated polymerization in the outer volumes of the support or uniformly across the entire microporous material.