In this communication, surface-initiated photoinduced electron transfer-reversible addition–fragmentation chain transfer polymerization (SI-PET-RAFT) is introduced. SI-PET-RAFT affords functionalization of surfaces with spatiotemporal control and provides oxygen tolerance under ambient conditions. All hallmarks of controlled radical polymerization (CRP) are met, affording well-defined polymerization kinetics, and chain end retention to allow subsequent extension of active chain ends to form block copolymers. The modularity and versatility of SI-PET-RAFT is highlighted through significant flexibility with respect to the choice of monomer, light source and wavelength, and photoredox catalyst. The ability to obtain complex patterns in the presence of air is a significant contribution to help pave the way for CRP-based surface functionalization into commercial application.

The reproducibility of polymer brush synthesis via surface‐initiated controlled radical polymerization is interrogated. Experiments compare the stability of initiating monolayers for surface‐initiated (SI) reversible addition‐fragmentation chain transfer polymerization (SI‐RAFT) and SI atom transfer radical polymerization (SI‐ATRP). Initiator‐functionalized substrates are stored under various conditions and grafting densities of the resulting polymer brush films are determined via in situ ellipsometry. Decomposition of one of the examined SI‐RAFT initiators results in limited reproducibility for polymer brush surface modification. In contrast, initiators for SI‐ATRP show excellent stability and reproducibility. While both techniques bring inherent benefits and limitations, the described findings will help scientists choose the most efficient technique for their goals in chemical and topographical surface modification.