Schiff bases of types 1, 2, and 3, easily prepared by the condensation of primary amines
with pyridine-2-carboxaldehyde, glyoxal, or 2-acetylpyridine, respectively, are described as ligands for a
copper(I) catalyst in the atom transfer polymerization of a range of methacrylates in toluene and xylene
solution. Increasing the length of the alkyl group on ligands of type 1 increases the solubility of the
catalyst in nonpolar solvents. The rate of polymerization increases on going from R = ethyl to propyl;
however, on increasing the length of R further, we see no effect on the rate. The molecular weight
distribution is narrow for all ligands where R = n-alkyl, and the number-average molecular weight (M
n)
increases linearly with conversion. A decrease in rate and a loss of control are observed when branching
is introduced in the α-position of the side chain. The polymerization is approximately first order in initiator,
0.90 ± 0.22, CuBr, 0.90 ± 0.13, and methyl methacrylate, 0.93 ± 0.01. Polymerization with CuBr in
conjunction with diazabutadiene ligands does not proceed very effectively, due to the high stability of
the copper(I) complexes with regard to oxidation. The mechanism of the reaction is complex and may
differ on subtle changes in ligand, metal, solvent, etc. The ligand systems presented in this paper offer
a wide range of versatility when choosing the most effective system for a particular application. The
Schiff base ligands, when used as described, provide an excellent method for achieving the controlled
polymerization of a wide range of methacrylates at relatively mild temperatures in hydrocarbon,
noncoordinating, solvents.
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