Titanium precatalysts bearing N-substituted β-amino alcohols for 1-hexene polymerization: The effect of steric crowding

A series of titanium-based non-metallocene precatalysts [2-(2,6-dialkylphenylamino)-1-phenylethoxy TiCl2 were prepared by reacting lithium salts of the corresponding amino alcohols with TiCl4(THF)2. Upon activation with methylaluminoxane (MAO), these precatalysts polymerized 1-hexene in isotactic manner. The catalyst activity and polymer properties depended on the steric features in the ortho positions of the aniline moiety of the ligands. As the bulkiness of the alkyl group in ortho positions of the aniline moiety increased, the catalyst showed better activity with high molecular weight and greater tacticity control. For 1-hexene polymerization, precatalyst 1ATiCl2 showed activity of 3.05 kg of PH/mol-Ti.h at room temperature and the resulting polyhexene had molecular weight of 403,600 (Mw/Mn=1.40) with 80% isotacticity (mmmm). The dibenzylic titanium complexes 1ATi(CH2Ph)2 and 3ATi(CH2Ph)2, upon activation with MAO or Ph3CB(C6F5)4, showed relatively lower activities towards 1-hexene polymerization, yielding polymers of lower molecular weights but with narrow molecular weight distribution.