Copolymerization of Ethylene and Polar Vinyl Monomers by Rare-earth Metal Catalysts

The copolymerization of ethylene and 5-hexen-1-ol (M2) masked by 1.1 equivalents of AliBu3 is carried out by four rare-earth metal catalysts bearing different steric hindrances: (Flu-CH2-Ph)Sc(CH2- SiMe3)2(THF) (1), (Flu-CH2-C5H4N)Sc(CH2SiMe3)2 (2), (Flu-CH2CH2-NHC-C6H2Me3-2, 4,6)Sc(CH2SiMe3)2 (3), (Flu-CH2CH2-NHC- C6H4Me)Sc(CH2SiMe3)2 (4). Among them, complex 1 shows the highest catalytic activity (1.32x106 g<middle dot>molSc-1<middle dot>h-1) but gives pure polyethylene without detectable M2 unit, and, in contrast, complex 2 is nearly inert. Under same conditions, the bulkier complex 3 shows moderate activity (0.38x106 g<middle dot>molSc-1<middle dot>h-1) and low comonomer incorporation (0.7 mol%). On switching to the bulkiest complex 4 , the copolymerization process is obviously promoted with a catalytic activity of 1.24x106 g<middle dot>molSc-1<middle dot>h-1 and generates a copolymer with 1.8 mol% M2 . For the polar vinyl monomers having different CH2 spacers between polar and vinyl groups, complex 4 exhibits the best catalytic performance for the copolymerization of ethylene with 10-undecene-1-ol with the highest catalytic activity (1.19x 107g<middle dot>molSc-1<middle dot>h-1) and the strongest incorporation ability (4.9 mol%). The influence of reaction conditions such as comonomer concentration, polymerization temperature and ethylene pressures on the catalytic performance of complex 4 are screened. The microstructures and thermal properties of the resultant copolymers are well-characterized by nuclear magnetic resonance (NMR), gel permeation chromatography (GPC) and differential scanning calorimeter (DSC).