Structural Engineering of Graphitic Carbon Nitrides for Enhanced Metal-Free PET-RAFT Polymerizations in Heterogeneous and Homogeneous Systems.

Developing visible-light-regulated controlled/living radical polymerization techniques for the synthesis of polymers with a predictable molecular weight, spatial and temporal control, and well-defined end-group functionality is being pursued by the macromolecular community worldwide. In this study, a new metal-free photoinduced electron transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization system was developed for controlled macromolecular synthesis in both heterogeneous and homogeneous systems by structural engineering of graphitic carbon nitrides (g-CN) to improve the textural, optical, and electronic properties. A heteroatom-mediated synthesis enabled the preparation of g-CN with improved structural properties and increased absorption in the visible light region. Enhanced PET-RAFT polymerization of vinyl monomers with low dispersity ( < 1.2), temporal control, and high chain-end fidelity was achieved under mild blue light irradiation (λ = 465 nm, 3 mW/cm). Moreover, we demonstrate, for the first time, that the g-CN-catalyzed RAFT polymerization could be realized in a homogeneous system after structural evolution of bulk g-CN into soluble nanosheets with enhanced photocatalytic efficiency up to high monomer conversion. This study provides new insights into the structure-performance relationship of g-CN for photoregulated PET-RAFT polymerization under visible light. Moreover, the development of a homogeneous g-CN-catalyzed photosynthesis system should broaden the application scope of these fascinating photocatalysts while benefiting synthetic upscaling by continuous flow and/or microfluidic reactors.