Rationally Designed Poly(heptazine imide) for Highly Efficient Photoinduced Reversible Deactivation Radical Polymerization

Polymerization regulated via photocatalysts offers unprecedented spatiotemporal control over reversible deactivation radical polymerization, enabling the preparation of macromolecules with precise molecular weight control and well-defined architectures. Photoinduced electron/energy transfer reversible addition–fragmentation chain transfer (PET-RAFT) polymerization is highly adaptable owing to its wide range of monomer applicability, oxygen tolerance, and mild polymerization conditions. There has been a push to develop innovative photocatalysts with extended light harvesting ability and enhanced photoactivity for the purpose of potential green chemistry. Herein, judiciously designed potassium poly(heptazine imide) (K-PHI) is proposed as a highly effective photocatalyst for oxygen-tolerant PET-RAFT polymerization under visible light. K-PHI is crafted via post-treatment of graphitic carbon nitride (g-C3N4) in molten salts, which facilitates the mass transfer and polymerization of melon-based structure. Such post-treatment substantially boosts the crystallinity of K-PHI and imposes a profound impact on photophysical properties and carrier transport efficiency of K-PHI. As a result, structurally optimized K-PHI enables a 16.6-fold increase in photopolymerization rate compared to traditional g-C3N4 while maintaining excellent control features (i.e., low dispersity, high chain-end fidelity, etc.). Furthermore, universal monomer adaptation, general chain transfer agent, and recycle capability are scrutinized to demonstrate the robustness and versatility of K-PHI in the oxygen-tolerant PET-RAFT polymerization.