Zinc Phthalocyanine Covalent Polymers as Recyclable Catalysts for NIR-Photocontrolled RAFT Polymerization in Water

An excellent catalyst plays key roles and is always pursued by researchers for various controlled polymerizations. In this work, flexible triethylene glycol is used for the first time to bridge zinc phthalocyanine to form zinc phthalocyanine covalent polymers (ZnPc-CPs) as highly efficient heterogeneous photocatalysts for the generation of singlet oxygen (1O2) and thereafter to catalyze an aqueous reversible addition–fragmentation chain transfer polymerization under irradiation with near-infrared (NIR) LED light (λmax = 730 nm) at room temperature. The oxygen content is crucial to the polymerization. Trace oxygen in the polymerization produces an active hydrogen peroxide initiator to accelerate the polymerization, while a large amount of oxygen will terminate the polymerization. Additionally, benefiting from the high penetrating power of NIR light, the polymerization can still proceed in the presence of barriers. More importantly, compared to homogeneous photocatalysts, heterogeneous ZnPc-CPs can be reused by simple post-treatment and recycled without a significant decrease in the catalytic efficiency. The significant advantages, including employing NIR LED light irradiation, water as a solvent, a recyclable heterogeneous photocatalyst, and no need of prior deoxygenation, make this polymerization system not only easy to manipulate but also highly economical and environmentally beneficial.