Catalyzed chain growth of polyethylene on magnesium for the synthesis of macroalkoxyamines: Application to the production of block copolymers using controlled radical polymerization

A synthetic method for the production of polyethylene (PE) chains carrying alkoxyamine end-group has been proposed first by successfully reacting the well-known 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) and N-(2-methyl-2-propyl)-N(1-diethylphosphono-2,2-dimethylpropyl)-N-oxyl (commonly called SG1) stable radicals with dipolyethylenylmagnesium compounds to give PE-TEMPO and PE-SG1. Since the homolytic cleavage of these two macroalkoxyamines for the production of block copolymers using controlled radical polymerization would require temperatures higher than 160 degrees C, two original new nitroxides (4-[(2,2-dimethyl-4-(N-tert-Butyl-N(1-diethoxyphosphoryl-2,2-dimethylpropyl)aminoxy)-4-n-butoxycarbonyl)butanoyloxyl]- 2,2,6,6-tetramethylpiperidinyl-1-oxy, DD1) and 4-[(2,2-dimethyl-4-(N-tert-Butyl-N-(1-diethoxyphosphoryl-2,2-dimethylpropyl)aminoxy)-4-phenyl) butanoyloxyl]-2,2,6,6-tetramethylpiperidinyl-1-oxy, DD2) containing a TEMPO moiety and incorporating an SG1-based alkoxyamine (cleavage temperature: 60 degrees C) were then synthesized. NMR analyses showed that the resulting PE-DD1 and PE-DD2 were obtained using this functionalization strategy though with low to moderate yields (from 17% to 40%). PE-DD2 (40% functionalization) was used under controlled radical polymerization conditions of n-butyl acrylate. SEC analyses together with H-1 NMR analysis showed that a poly(ethylene-b-n-butyl acrylate) block copolymer was produced and that the polymerization proceeded under control. (c) 2007 Wiley Periodicals, Inc.