Syndiospecific Polymerization of Styrene with Half-Sandwich Titanocene Catalysts. Influence of Ligand Pattern on Polymerization Behavior

Abstract

As modifications of the effective catalyst precursor for syndiospecific styrene polymerization, namely [2-Me-thBenz[e]Ind]TiCl3 (Ic), [2,3-Me2-thBenz[e]Ind]TiCl3 (IIc), [1,2,3-Me3-thBenz[e]Ind]TiCl3 (IIIc), and [2-Me-3-Ph-thBenz[e]Ind]TiCl3 (IVc) have been synthesized to examine the influence of ligand pattern on the catalyst activity and polymer properties. These complexes, activated by methylaluminoxane (MAO), showed high activities compared with previously employed titanocene catalysts. Of all titanocenes examined, [2-Me-3-Ph-thBenz[e]Ind]TiCl3 (IVc)/MAO showed the highest activity and stability at an even fairly low Al/Ti ratio of 1000, revealed the excellent control over the stereoregular insertion of monomer, and exhibited a significant increase of the ratio of the propagation rates to chain transfer termination as evidenced by the kinetic results, thus producing polymers with the highest syndiotacticity and molecular weight. The kinetic investigations, combined with the EPR spectrum and polymerization experiments, showed that the higher activity of tetrahydrobenz[e]indenyl-based systems is due to a great number of active species.

Complex Branched Polyolefin Generated from Quasi-living Polymerization of 4-Methyl-1-pentene Catalyzed by α-Diimine Palladium Catalyst

“…Figure 5 shows 13 C NMR spectra of poly(4MP)s obtained at 0 and 35 8C are very similar, suggesting the presence of similar branch structures in the polymer. The approximate integrals ratio of characteristic peak of 2-methylhexyl at 39.2 ppm to methine resonances of 2-methylalkyl (including i Bu, 2-methylhexyl, and more long 2-methylalkyl) at 25.2 ppm changes from 0.46 at 0 8C to 0.65 at 35 8C according to 13 C NMR spectra, while the total branching number is nearly invariable, indicating much more formation of long 2-methylalkyl. The increasing intensity of the resonances at low field (46-48 ppm) from 0 to 35 8C also supports the presence of more complex long branches.…”

“…The obtained products are viscous oil at a low 4MP concentration ([4MP] < 0.8 M), while the obtained polymers are wax when monomer concentration is 3.2 M. The determinations of GPC show that the obtained poly(4MP)s have high molecular weights (M n > 24 000), indicating that the obtained polymers have unique branches and complex structure, which is obviously different from the isotactic poly(4MP) produced by early transition metal center catalyst. [12,13] 1 H NMR was carried out to study the microstructure of the poly(4MP), and a typical spectrum was shown in Figure 1. Methyl signals are observed in the broad region form 0.75 to 0.90 ppm.…”

“…To have an insight into microstructure of the poly(4MP), further investigations using 13 C NMR spectroscopy were undertaken. 13 C NMR spectra of poly(4MP) produced at 0.8 M is shown in Figure 2, which is much more complicated than the isotactic poly(4MP) catalyzed by Ziegler-Natta or metallocene titanium catalysts.…”

“…13 C NMR spectra of poly(4MP) produced at 0.8 M is shown in Figure 2, which is much more complicated than the isotactic poly(4MP) catalyzed by Ziegler-Natta or metallocene titanium catalysts. [15,16] Two significant differences are the occurrence of more intense methyl signals at around 20 ppm, and the absence of long -(CH 2 ( i Bu)) nruns whose methylene (S aa ) lies at %40 ppm, indicating the presence of the complex branches.…”

Optimization of the Polymerization Parameters for Syndiotactic Polymerization of Styrene Using Supported Catalysts

“…The same result was reported for homogeneous catalysts which were stabilized by the introduction of appropriate ligands. [21] Effect of MAO concentration: The influence of the MAO concentration for the two catalytic systems is presented on Table 6: For a concentration of 0.01 m MAO, the molecular weights are higher for the Ti(OBu) 4 supported catalyst than for the CpTiCl 3 species. This result is also reported in the literature for the homogeneous catalysts.…”