Toshiaki Taniike

Surface-Mediated Visible-Light Photo-oxidation on Pure TiO2(001)

We used STM to observe visible light photo-oxidation reactions of formic acid on the ordered lattice-work structure of a TiO(2)(001) surface for the first time. The nanostructured surface makes the band gap significantly smaller than 3.0 eV only at the surface layer, and the surface state of the crystal enables a visible light response.

Propylene Polymerization Performance of Isolated and Aggregated Ti Species Studied Using a Well-Designed TiCl3/MgCl2 Ziegler-Natta Model Catalyst

In propylene polymerization with MgCl(2) -supported Ziegler-Natta catalysts, it is known that the reduction of TiCl(4) with alkylaluminum generates Ti(3+) active species, and at the same time, leads to the growth of TiCl(x) aggregates. In this study, the aggregation states of the Ti species were controlled by altering the Ti content in a TiCl(3) /MgCl(2) model catalyst prepared from a TiCl(3)  · 3C(5) H(5) N complex. It is discovered that all the Ti species become isolated mononuclear with a highly aspecific feature below 0.1 wt.-% of the Ti content, and that the isolated aspecific Ti species are more efficiently converted into highly isospecific ones by the addition of donors than active sites in aggregated Ti species.

Chiral self-dimerization of vanadium complexes on a SiO2 surface: the first heterogeneous catalyst for asymmetric 2-naphthol coupling

The self-dimerized chiral assembly of vanadium-Schiff-base complexes was found to occur on a SiO2 surface and to be the first heterogeneous catalyst for the asymmetric oxidative coupling of 2-naphthol with 100% selectivity and 90% enantioselectivity.

MgO/MgCl2/TiCl4 Core–Shell Catalyst for Establishing Structure–Performance Relationship in Ziegler–Natta Olefin Polymerization

AbstractRecently we successfully established the first structure–performance relationships between the catalyst surface area and propylene polymerization activity using novel MgO/MgCl2/TiCl4 core–shell catalysts with non-porous and non-fragmentable features. In the present paper, we have addressed the physical and chemical natures of these novel model catalysts in comparison with typical Ziegler–Natta catalysts, by means of comprehensive characterization and analyses. It was clarified that the MgO/MgCl2/TiCl4 core–shell catalysts offer an ideal and powerful tool to address relationships between the support architectures and polymerization performance, which had been long un-clarified. Graphical AbstractUnique structure of MgO/MgCl2/TiCl4 core–shell catalysts but yet identical surface chemistry with typical Ziegler–Natta catalyst offers an ideal and powerful tool to address relationships between the support architectures and polymerization performance.

Enhancement in Mechanical and Electrical Properties of Polypropylene Using Graphene Oxide Grafted with End-Functionalized Polypropylene

Terminally hydroxylated polypropylene (PP) synthesized by a chain transfer method was grafted to graphene oxide (GO) at the chain end. Thus obtained PP-modified GO (PP-GO) was melt mixed with PP without the use of a compatibilizer to prepare PP/GO nanocomposites. Mechanical and electrical properties of the resultant nanocomposites and reference samples that contained graphite nanoplatelets, partially reduced GO, or fully reduced GO were examined. The best improvement in the tensile strength was obtained using PP-GO at 1.0 wt %. The inclusion of PP-GO also led to the highest electrical conductivity, in spite of the incomplete reduction. These observations pointed out that terminally hydroxylated PP covalently grafted to GO prevented GO layers from re-stacking and agglomeration during melt mixing, affording improved dispersion as well as stronger interfacial bonding between the matrix and GO.

Degradation behavior of polymer blend of isotactic polypropylenes with and without unsaturated chain end group

Abstract In this work, the relationship between the unsaturated chain end group content and the thermal oxidative degradation rate was systematically studied with binary polymer blends of isotactic polypropylene (iPP) with and without the unsaturated chain end group. The iPPs with and without the unsaturated chain end group were synthesized by a metallocene catalyst in the absence of hydrogen and by a Ziegler catalyst in the presence of one, respectively. The thermal oxidative degradation rate of the binary iPP blends was estimated from the molecular weight and the apparent activation energy (ΔE), which were obtained through size exclusion chromatography (SEC) and thermogravimetric analysis (TGA) measurements, respectively. These values exhibited a negative correlation against the mole content of the unsaturated chain end group. The thermal oxidative degradation rate apparently depends on the content of the unsaturated chain end group. This tendency suggests that the unsaturated chain end acts as a radical initiator of the iPP degradation reaction.

Well-Defined Polypropylene/Polypropylene-Grafted Silica Nanocomposites: Roles of Number and Molecular Weight of Grafted Chains on Mechanistic Reinforcement

Grafting terminally functionalized polypropylene (PP) to nanofillers provides well-defined PP-based nanocomposites plausibly featured with a physical cross-linkage structure. In this paper, a series of PP-grafted silica nanoparticles (PP-g-SiO2) were synthesized by varying the number of grafted chains per silica particle, and influences of the number and the molecular weight of grafted chains were studied on physical properties of PP/PP-g-SiO2 nanocomposites. We found that only 20–30 chain/particle was sufficient to exploit benefits of the PP grafting for the nanoparticle dispersion, the nucleation, and the Young’s modulus. Meanwhile, the yield strength was sensitive to both of the number and the molecular weight of grafted PP: Grafting longer chains at a higher density led to greater reinforcement.

The Use of Donors to Increase the Isotacticity of Polypropylene

Since the discovery of electron donors for MgCl2-supported Ziegler–Natta catalysts, donors have become key components for improving the stereospecificity and activity of these catalysts. Starting from benzoate for third-generation catalysts, the discovery of new donor structures has always updated the performance of Ziegler–Natta catalysts. Numerous efforts have been devoted since the early 1970s, in both industry and academy, not only for discovering new donors but also for understanding their roles in Zielger–Natta olefin polymerization. This chapter reviews the history of these efforts, especially after the twenty-first century. The first half of the chapter describes the history of catalyst developments, with special focus on industrialized donors, and then introduces recent trends in the development of new donors. The second half reviews historical progress in the mechanistic understanding of how donors improve the performance of Ziegler–Natta catalysts.

Ethylene Polymerization by 2-Methyl-8-(benzimidazol)quinolyliron(II) Pre-Catalyst: a DFT Understanding its Chain Propagation and Transfer

The ethylene polymerization mechanism of the 2-methyl-8-(benzimidazol) quinolyliron(II) pre-catalyst is investigated by the DFT calculations, illustrating the possible intermediates with their geometrical and spin configurations. Regarding either methyl or ethyl group bonding on iron cores, the energy barriers for ethylene insertion have been extensively calculated. Within the iron‑methyl species, both resting state and transition state favor the configurations at high-spin state (quintet); whilst the iron-ethyl species prefer the low-spin state. According to the energy barriers, the chain propagation is more favorable than chain transfer for the bidentate iron pre-catalyst, which is well consistent with the experimental observation.

Effects of various poisoning compounds on the activity and stereospecificity of heterogeneous Ziegler?Natta catalyst

Abstract A TiCl4/ethylbenzoate/MgCl2 Ziegler–Natta catalyst was pretreated with chemically different poisoning compounds to investigate their effects on the catalyst activity and stereospecificity for propylene polymerization. The poisoning power on the activity was in the order of methanol > acetone > ethyl acetate. A kinetic analysis using the stopped-flow method revealed that addition of the poisoning materials decreased the activity through the reduction of the number of active sites, whereas the catalyst isospecificity was hardly affected by these materials.