Metal-free photoinduced electron transfer-atom transfer radical polymerization (PET-ATRP) via a visible light organic photocatalyst

The development of an atom transfer radical polymerization (ATRP) system without any transition metal catalyst for electronic and biomedical applications was considered to be in pressing need. Fluorescein (FL) was used as the organic photocatalyst for the polymerization of methyl methacrylate (MMA) via the proposed photoinduced electron transfer-atom transfer radical polymerization (PET-ATRP) mechanism. In the presence of electron donors provided by triethylamine (TEA), fluorescein can activate alkyl bromide and control radical polymerizations by a reductive quenching pathway. The polymerizations could be controlled by an efficient activation and deactivation equilibrium while maintaining the attractive features of "living" radical polymerization. The number-average molecular weight M-n,M-GPC increased with monomer conversion, and the controllability of molecular weight distributions for the obtained PMMA could be achieved in the polymerization processes. MALDI-TOF MS, H-1 NMR spectroscopy and chain extension polymerizations show reserved chain-end functionality in the synthesized polymers and further confirm the "living" feature of the metal-free ATRP methodology. All these research results support the feasibility of the visible light mediated metal-free PET-ATRP platform for the synthesis of elegant macromolecular structures.