Catalysed chain growth of polyethylene on magnesium for the synthesis of macroalkoxyamines: Application to the production of block copolymers using controlled radical polymerization
Résumé
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 °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 °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 1H NMR analysis showed that a poly(ethylene-b-n-butyl acrylate) block copolymer was produced and that the polymerization proceeded under control.