Photoinduced Electron Transfer-Reversible Addition-Fragmentation Chain Transfer (PET-RAFT) Polymerization

Photoinitiated living radical polymerization has attracted wide attention in recent years, because the polymerizations can be performed at ambient temperature and the light is more convenient and environment friendly. Since MacMillan reported enantioselective intermolecular a-alkylation of aldehydes photoredox catalyzed by Ru(bpy)3Cl2 in 2008, many attempts have been directed toward photoredox catalysis reactions, especially photoredox-catalyzed living radical polymerization. Boyer and coworkers have developed a versatile photoinduced living polymerization named photoinduced electron transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization. This polymerization technique suits for a wide range of monomers and affords polymers with well-defined structures and low polydispersities. The photocatalysts, such as fac-[Ir(ppy)3], Ru(bpy)3Cl2, zinc porphyrins, chlorophyll, eosin Y and fluorescein, are used to initiate RAFT polymerization by electron transfer between the catalyst and the RAFT agent.Titanium dioxide (TiO2) is a kind of semi-conducting metal oxide which is widely used in water treatment, photovoltaics, organic synthesis. TiO2 is cheap, easy to access, nontoxic and easy to remove by filtration. Hynd Remita has developed poly(1,4-diphenylbutadiyne) (PDPB) nanofibers, a kind of conducting polymers which have unique one-dimensional delocalized conjugated structures and excellent electrochemical, electrical and optical properties. Upon excitation by light, they all can generate conduction-band electrons (e-) and valence-band holes (h+). They can perform as excellent photoredox catalysts.Photoinduced electron transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerizations using TiO2 or nanoPDPB as photoredox catalysts were successfully carried out. They offer good control over molecular weights and polydispersities (PDI).