Takefumi Yano

Polymerization of olefins with titanium and zirconium complexes containing hydrotris(pyrazolyl)borate or hydrotris(3,5-dimethylpyrazolyl)borate

Abstract Zirconium and titanium complexes containing hydrotris(pyrazolyl)borate (Tp) or hydrotris(3,5-dimethylpyrazolyl)borate (Tp*) as a ligand have been examined as polymerization precatalysts for ethylene, propylene and styrene. Activation of the group 4 transition-metal complexes by methylaluminoxane exhibits a greater catalytic activity in ethylene polymerization for TpMCl3 (M=Zr, Ti) than for the corresponding mono-cyclopentadienyl analogue, CpMCl3. Dimethyl substitution on the pyrazolyl groups enhances the activity for the Zr complex (Tp*ZrCl3), but not for the Ti complex (Tp*TiCl3). Complete substitution of OtBu or OPh groups for Cl ligands in Tp*ZrCl3 greatly decreases the activity. Mono substitution of an OPh group for one Cl ligand in Tp*TiCl3 does not affect the activity. The addition of propylene comonomer reduces the catalytic activity of Zr complexes containing Tp or Tp* to a considerable degree. The Tp and Tp* complexes of Zr and Ti produce atactic polymers from styrene.

Study on aminosilane compounds as external electron donors in isospecific propylene polymerization

Abstract Propylene polymerization has been studied with a use of MgCl2 supported titanium solid catalyst in combination with triethylaluminium (TEA) and a monoamino- or diamino-dimethoxysilane as an external electron donor. The aminosilanes having a bulkier amino group, or two amino groups show a tendency to give lower isotacticity and broader molecular weight distribution of polymers obtained. Specifically the aminosilanes with piperidinyl group(s) were found to be highly isospecific external donors. 13 C and 1 H NMR studies on the mixtures of TEA and di(piperidinyl)dimethoxysilane (DPIP) indicate that TEA forms a Lewis acid/base adduct through the interaction of aluminum and oxygen atom of methoxy group in the silane as have been reported in the case of TEA and di(hydrocarbyl)dimethoxysilanes.

Butadiene polymerization with various half-titanocenes

Abstract The polymerizations of butadiene were performed with various half-titanocenes in combination with either modified methylalumoxane (MMAO) or (C6H5)3CB(C6F5)4/trialkylaluminum and the latter activator showed higher catalyst activities. The substitution of an alkyloxy group for a Cl atom in CpTiCl3 decreased activity and did not change the microstructure of polymers. CpTiBr3 and half-titanocenes with substituents on a Cp ring exhibited lower activities, but the microstructure of higher vinyl unit contents. The results of activity suggest cationic active species of Ti(+4).

Supported catalyst for olefin polymerization. The role of the third component

Abstract Polymerization of propylene was carried out using a magnesium supported titanium catalyst in combination with triethylaluminium(TEA) and a p-substituted benzoate or a phenylcarbinol as the third component in n-heptane under atmospheric pressure. p-Substituted benzoates produced excellent improvement in isotacticity (95–98%) and there was a linear relationship between isotacticity and Hammetts σ value for the p-substituents. On the other hand, phenylcarbinols (which react with TEA to form hemialkoxides) also increased isotacticity. It is considered that the complexes of TEA with the benzoates are the components which give very high isotacticity ( ≧ 95% ) rather than the reduction products of the benzoates with TEA and that the dissociation of the hemialkoxides is essential for isotacticity, as observed in the case of the phenylcarbinols.

Effects of hydrogen on the polymerization of propylene with a magnesium chloride supported Ziegler-Natta catalyst

Abstract The addition of hydrogen produced no change in the number of active sites and the propagation rate constant in a polymerization system approximating actual conditions in which propylene was polymerized with a magnesium chloride-supported catalyst. A plausible explanation for reversible hydrogen activation is that, on addition of hydrogen to the polymerization system, a rapid ligand exchange occurs favorably between propylene and a terminal unsaturated bond of the polymer, formed by a β-hydrogen elimination from a titanium—polymer bond. On the basis of analyses of FD-MS and 1H-NMR spectra of low molecular weight polymers, it is considered that the β-hydrogen elimination is suppressed to some extent in the presence of hydrogen.

Copolymerization of ethylene with α-olefins at high temperature and characterization of copolymers

Abstract Ethylene copolymerizations were performed with butene-1,4-methylpentene-1 (4MP1), hexene-1, and octene-1 at a high temperature. Comonomer incorporation is markedly poor for 4MP1, but there are negligible differences among the other comonomers. The densities of copolymers having the same comonomer mole content increase with a decrease of molecular weight of the comonomers, whereas the melt temperature of the copolymers decrease except for 4MP1 which has the highest melt temperatures. From an analysis of the copolymers by TREF combined with GPC and 13C-NMR, it is assumed that the copolymers from heavier comonomers comprise heptane-soluble amorphous copolymers and ethylene-rich semicrystalline ones which lead to lower densities and higher melt temperatures, respectively. Therefore, it can be said that heavier comonomers (4MP1 in particular) tend to be incorporated more heterogeneously, resulting in a wider distribution of comonomer composition.