Polymerization of 1-hexene catalyzed by Cp*TiMe3-B(C6F5)3; a mechanistic and structural study

Abstract

Solutions of the Ziegler–Natta system Cp*TiMe3 – B(C6F5)3 in toluene catalyze the polymerization of 1-hexene to mixtures of atactic poly-1-hexenes and complex oligomeric materials, which were characterized by 1H and 13C{1H} NMR spectroscopy and gel permeation chromatography (GPC). The polymer molecular weights and the relative proportions of polymers and oligomers vary with temperature, monomer:catalyst ratios, and degree of dilution and may generally be rationalized in terms of a conventional Ziegler–Natta mechanism. The 13C{1H} NMR spectra of the polymers exhibit resonances suggesting significant degrees of 2,1-insertions during propagation, while experiments utilizing Cp*Ti(13CH3)3 verify that initiation in toluene involves predominantly via 1,2-insertion of the first monomer unit but that 2,1-insertions occur up to 15–20% of the time in CH2Cl2. NMR experiments involving Cp*Ti(13CH3)3 demonstrate that both methyl groups in the presumed active species Cp*TiMe+2 are incorporated into polymerKey words: titanium, polymers, polymerization, Ziegler–Natta