Tripodal heptadentate amine ligands with different nitrogen substituents for SARA- and photo-ATRP

Abstract

Tripodal heptadentate amine ligands, tris[N-(2-pyridylmethyl)-2-aminoethyl]amine (Py3H3Tren) and tris[N-(2-pyridylmethyl)-N-methyl-2-aminoethyl]amine (Py3Me3Tren), are used as the active ligands for atom transfer radical polymerization (ATRP). Both of them evolve from a Schiff base ligand, tris[N-(2-pyridylmethyl)-2-iminoethyl]amine (Py3Tren), through simple reduction and methylation reactions. Electrospray ionization mass spectrometry is used to investigate the coordination between the ligands and CuBr2 at an equimolar amount in the solution. It reveals that CuBr2/Py3H3Tren and CuBr2/Py3Me3Tren are tripod claw-shaped complexes. Electrochemical studies show that CuBr2/Py3H3Tren has a more negative redox potential and higher reactivity than the other two counterparts. The order of KATRP of CuBr2/ligand is Py3H3Tren > Py3Me3Tren > Py3Tren. Subsequently, CuBr2/Py3H3Tren and CuBr2/Py3Me3Tren are employed as the catalysts for the supplemental activators and reducing agents (SARA) ATRP of methyl acrylate (MA). Well-defined poly(MA) with controlled molecular weight and low Mw/Mn could be synthesized with the almost quantitative monomer conversion at room temperature, and CuBr2/Py3Me3Tren has the fastest reaction rate. Photo-induced atom transfer radical polymerization (Photo-ATRP) of MA using Py3H3Tren and Py3Me3Tren as the ligand are also performed. Photo-ATRP using Py3H3Tren has the fastest reaction rate, while the polymerizations using Py3Me3Tren has shown lower polydispersity.