Structural Engineering of Graphitic Carbon Nitridesfor Enhanced Metal-Free PET-RAFT Polymerizations in Heterogeneousand Homogeneous Systems

摘要

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-C3N4) to improve the textural, optical, and electronic properties. A heteroatom-mediated synthesis enabled the preparation of g-C3N4 with improved structural properties and increased absorption in the visible light region. Enhanced PET-RAFT polymerization of vinyl monomers with low dispersity (Đ < 1.2), temporal control, and high chain-end fidelity was achieved under mild blue light irradiation (λmax = 465 nm, 3 mW/cm²). Moreover, we demonstrate, for the first time, that the g-C3N4-catalyzed RAFT polymerization could be realized in a homogeneous system afterstructural evolution of bulk g-C3N4 into solublenanosheets with enhanced photocatalytic efficiency up to high monomerconversion. This study provides new insights into the structure–performancerelationship of g-C3N4 for photoregulated PET-RAFTpolymerization under visible light. Moreover, the development of ahomogeneous g-C3N4-catalyzed photosynthesissystem should broaden the application scope of these fascinating photocatalystswhile benefiting synthetic upscaling by continuous flow and/or microfluidicreactors.