Highly Active Copper-Based Catalyst for Atom Transfer Radical Polymerization

Atom transfer radical polymerization (ATRP) generally requires a catalyst/initiator molar ratio of
0.1 to 1 and catalyst/monomer molar ratio of 0.001 to 0.01 (i.e., catalyst concentration:  1000−10 000 ppm
versus monomer). Herein, we report a new copper-based complex CuBr/N,N,N‘,N‘-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN) as a versatile and highly active catalyst for acrylic, methacrylic, and styrenic
monomers. The catalyst mediated ATRP at a catalyst/initiator molar ratio of 0.005 and produced polymers
with well-controlled molecular weights and low polydispersities. ATRP occurred even at a catalyst/initiator
molar ratio as low as 0.001 with copper concentration in the produced polymers as low as 6−8 ppm (catalyst/monomer molar ratio = 10-5). The catalyst structures were studied by X-ray diffraction and NMR
spectroscopy. The activator CuIBr/TPEN existed in solution as binuclear and mononuclear complexes in
equilibrium but as a binuclear complex in its single crystals. The deactivator CuIIBr2/TPEN complex was
mononuclear. High stability and appropriate KATRP (ATRP equilibrium constant) were found crucial for the
catalyst working under high dilution or in coordinating solvents/monomers. This provides guidance for further
design of highly active ATRP catalysts.