Polymerization of methyl acrylate and as comonomer with ethylene using single-site catalysts

Because of the excellent control over polymerizations provided by single-site catalysts (SSCs), numerous research groups are trying to find such catalysts, which would also be efficient for the polymerization of polar monomers. However, many SSCs are deactivated by undergoing reactions with the electronegative atoms in the polar groups. In the present work, we attempted to copolymerize ethylene with methyl acrylate using three SSCs: (1) a bis(imino)pyridyl iron(II) chloride / methylaluminoxane catalyst, (2) a chiral metallocene / tris(pentafluorophenyl) borane catalyst, and (3) an in situ trifluromethyl substituted nickel (II) enolate catalyst. Only the first two catalysts led to polymer formation. The metallocene had relatively low activities and formed polymethyl acrylate. The most efficient catalyst for the synthesis of the copolymers was the ironbased catalyst 1. The ethylene consumption indicates that its activity reaches a maximum after which it steadily declines. By kinetic measurements, 1H and 13C NMR spectroscopy and the measurement of glass and melting temperatures, we could show that copolymers of ethylene and methyl acrylate were not formed. The products formed were blends, of high density polyethylene and methyl acrylate. Homopolymerizations of methyl acrylate using the three catalyst systems were also studied. Again it was found that the catalyst 1 had the highest activities. Atactic polymers were formed. There was a clear dependence of the activity and molecular weight on the Al/Fe-ratio, which indicates that the polymerization mechanism is coordinative and not initiated by radical species