Activator Generated by Electron Transfer for Atom Transfer Radical Polymerization

Abstract

A novel procedure was developed for activation of an oxidatively stable catalyst complex added to an atom transfer radical polymerization (ATRP). Tin(II) 2-ethylhexanoate (Sn(EH)2) was used as a reducing agent of various Cu(II) complexes in ATRP of various monomers initiated by alkyl halides. This approach further improves a simultaneous normal and reverse initiation (SR&NI) by eliminating free radical initiators for the activation of the higher oxidation state catalyst complex. As a result, "activator generated by electron transfer" (AGET) ATRP allows the preparation of pure block copolymers. Several combinations of monomer/catalyst complex precursor were studied, including styrene/CuCl2/dNbpy, octadecyl methacrylate/CuCl2/dNbipy, methyl methacrylate/CuCl2/PMDETA, n-butyl acrylate/CuBr2/PMDETA, and methyl acrylate/CuCl2/Me6TREN. Polymerization proceeded in a controlled way for all systems, producing well-defined polymers with controlled degree of polymerization and narrow molecular weight distribution, demonstrating the robust nature of AGET ATRP. Additionally, Sn(EH)2 was used simultaneously as a reducing agent for ATRP of octadecyl methacrylate and a catalyst for ring-opening polymerization (ROP) of ε-caprolactone, allowing direct synthesis of the corresponding block copolymer.