Synergistic control of particle size and channel ordering in spherical COFs toward efficient photoinduced RAFT polymerization

Photocatalytic PET-RAFT polymerization has emerged as a powerful strategy for controlled radical polymerization, where the efficiency and precision of the reaction critically depend on the properties of the photocatalyst. However, the impact of particle size on covalent organic frameworks (COFs) catalysis and its mechanism in PET-RAFT systems remains largely unexplored. Herein, we report the synthesis of a series of spherical COFs (PCOFs) with highly ordered channels and tunable particle sizes under mild conditions. Comprehensive characterization using UV–Vis diffuse reflectance spectroscopy, photoluminescence, transient fluorescence lifetime, and electrochemical measurements revealed that particle size strongly influences the optical absorption and charge-carrier separation efficiency of PCOFs. PET-RAFT polymerization studies demonstrated that larger PCOF particles exhibit significantly enhanced catalytic activity, primarily due to improved visible-light utilization, stronger electron transfer capability, and more efficient photoinduced electron transfer to the RAFT agent, accelerating polymerization rates while maintaining precise control over number average molecular weight and molecular weight dispersity. On-off light experiments confirmed good temporal control, and chain-extension and monomer-variation experiments highlighted the versatility of PCOF-100 in mediating PET-RAFT polymerization. Recyclability tests further demonstrated the structural stability and reusability of the catalyst. This work identifies the intrinsic role of COF particle size in dictating photocatalytic performance, offering a rational design principle for designing efficient catalysts for photocatalytic PET-RAFT polymerization.