Atom transfer polymerisation of methyl methacrylate: use of chiral aryl/alkyl pyridylmethanimine ligands; with copper(I) bromide and as structurally characterised chiral copper(I) complexes

Abstract

The use ofchiral catalysts in the living radical polymerisation of methyl methacrylate via atom transfer polymerisation (ATP) has been investigated in an effort to control the stereochemistry of the polymer backbone. Two enantiomerically pure chiral catalysts have been prepared and used in the ATP of methyl methacrylate: the structurally characterised complex, bis[N-(1-phenylethyl)-2-pyridylmethanimine]copper() tetrafluoroborate, [Cu(C₁₄H₁₄N₂)₂ ][BF₄ ], and the reaction product of copper() bromide with N-(1-cyclohexylethyl)-2-pyridylmethanimine, [Cu(C₁₄H₂₀N₂)₂ ][Br]. Both catalysts were found to be suitable for the ATP of methyl methacrylate in conjunction with either ethyl 2-bromo-2-methylpropanoate in xylene at 90 °C or 4-methoxybenzenesulfonyl chloride in diphenyl ether at 90 °C. The system yields polymer of relatively narrow polydispersity; however, the use of these chiral catalysts did not significantly affect the stereochemistry of the polymer backbone. This may be due to the chiral centre being too distant from the propagating site to exert any influence over the monomer addition step, or that the reaction proceeds via a completely free-radical mechanism. This is, however, the first time a discrete, structurally characterised copper complex has been used as an effective ATP catalyst. The bond lengths of the complexed ligand indicate the oxidation state of the copper to be +1 in the complex.