A tripodal heptadentate Schiff base as an active ligand for atom transfer radical polymerization

Abstract

The use of a tripodal heptadentate Schiff base, tris[N-(2-pyridylmethyl)-2-iminoethyl]amine (Py₃Tren), as an active ligand for atom transfer radical polymerization (ATRP) is reported. The coordination between Py₃Tren and CuBr₂ in solution is investigated by electrospray ionization mass spectrometry, which reveals the generation of a tripod claw-shaped complex by using equimolar quantities of CuBr₂ and Py₃Tren. Electrochemical studies of CuBr₂/Py₃Tren complexes demonstrate more negative redox potentials and higher activities compared with those of bidentate CuBr₂/N-ethyl-2-pyridylmethanimine (PyEthyl) complexes. Subsequently, CuBr/Py₃Tren is employed as a catalyst for the normal ATRP of methyl methacrylate (MMA). Well-defined poly(MMA) with controlled molecular weight and narrow polydispersity could be synthesized with high conversions and fast rates even at ambient temperature (30 °C). Activators regenerated by electron transfer (ARGET) ATRP and supplemental activators and reducing agents (SARA) ATRP of acrylate monomers using Py₃Tren as the ligand are also performed to reduce the amounts of metal catalysts for polymerizations.