Minoru Terano

Stopped-Flow Techniques in Ziegler Catalysis

The stopped-flow method, by which a quasi-living polymerization process can be realized within an extremely short period (ca. 0.2 s), has been proven to be one of the most powerful techniques for studies on the nature of the active sites and elucidation of the olefin polymerization mechanism based on the information from the polymers obtained in the initial stage of polymerization. It has been demonstrated that a better and deeper understanding of many controversial problems in Ziegler catalysis has been achieved, such as arguments concerning the non-uniformity of the active sites, the intrinsic kinetic parameters, the effects of catalyst preparation conditions, the role of cocatalysts, hydrogen and electron donor, etc. The successive modifications to the basic stopped-flow system have led to extensive applications in investigating the catalyst pretreatment effects induced by various reagents, as well as developing a series of novel block copolymers.

Polypropylene-block-poly(ethylene-co-propylene) addition to polypropylene/poly(ethylene-co-propylene) blends: morphology and mechanical properties

Abstract The additive effects of a diblock copolymer of polypropylene and ethylene–propylene rubber PP- b -EPR(50–50) on the morphology and mechanical properties of PP/EPR(50/50) blends were investigated. It was found from an electron microscopy study that the block copolymer is compatible with the PP phase but incompatible with the EPR phase. Dynamic mechanical spectra showed that the PP- b -EPR block copolymers are incorporated into the PP phase, and consequently, the EPR portions of the block are trapped into the interlamellae of PP.

Mechanistic implications of the unprecedented transformations of ethene into propene and butene over Phillips CrOx/SiO2 catalyst during induction period

Abstract In this work, an industrial calcined Phillips CrOx/SiO2 catalyst engaged in the induction period through interaction with ethene at ambient conditions was characterized by temperature-programmed desorption (TPD) equipped with a quadrupole mass spectrometer (MS). It was unprecedented to find that the first hydrocarbon species had already been formed and was observed to be propene instead of the expected butene. In fact, butene is the second hydrocarbon species formed after propene during the induction period. This evidence strongly implied that the initiation in terms of Cr–carbon bond formation on the Phillips catalyst occurs through an ethene metathesis mechanism during the induction period. Three most possible routes regarding the ethene metathesis initiation and formation of the first hydrocarbon species propene during the induction period on the Phillips catalyst were proposed.

New aspects of the induction period of ethene polymerization using Phillips CrOx/SiO2 catalyst probed by XPS, TPD and EPMA

Abstract In this work, an industrial Phillips CrO x /SiO 2 catalyst engaged in the induction period through interaction with ethene at room temperature (RT) was studied by the combination of surface analytical methods: X-ray photoelectron spectroscopy (XPS), temperature programmed desorption (TPD) and electron probe microanalysis (EPMA). XPS method disclosed the reduction of surface chromate species (expressed as Cr(VI)O x ,surf ) into surface-stabilized Cr 3+ and Cr 2+ species (expressed as Cr(III)O x ,surf and Cr(II)O x ,surf , respectively) by monomer during the induction period and the simultaneous formation of two kinds of surface carbon species, namely, formaldehyde and unsaturated hydrocarbons. The hydrocarbon species were supposed to be composed of not only coordinated ethene, but also adsorbed longer olefin chains. TPD measurement confirmed the formation of formaldehyde. EPMA characterization revealed that the surface Cr aggregation occurred in a low extent during the induction period resulting in a few Cr islands in sizes of several microns on catalyst surface. It was demonstrated that reduction and alkylation of Cr species as well as initiation of ethene insertion had already occurred even in the induction period. A mechanism concerning the reactions occurred during the induction period on the Phillips catalyst was proposed. The Cr(II)O x ,surf species coordinated with one formaldehyde and one ethene is postulated to be the active sites precursor for the alkylation as well as initiation of the ethene insertion. The coordinatively-adsorbed formaldehyde molecules on the catalyst are supposed to be the very reason for the hindered ethene oligomerization rather than normal polymerization, as well as for the induction of the surface Cr aggregation.

Direct observation of MgCl2‐supported Ziegler catalysts by high resolution transmission electron microscopy

The surface atomic structure of MgCl 2 crystalline particles and MgCl 2 -supported Ziegler catalysts was observed by means of high resolution transmission electron microscopy. Step-terrace surface structures, characteristic of the structure of the MgCl 2 crystal, are found in the observed images of MgCl 2 particles. The observation of the structure of MgCl 2 -suuported Ziegler catalysts shows that the MgCl 2 crystals are severely deformed by the processes of catalyst preparation. Due to the preparation procedure used the structure of the catalyst changes from crystalline to amorphous

XPS study of the interaction of titanium species with internal electron donors on MgCl2-supported Ziegler catalysts

Abstract Two types of MgCl2-supported Ziegler catalysts prepared by a similar procedure with different internal electron donors were analyzed using X-ray photoelectron spectroscopy (XPS) to elucidate the interaction of the titanium species with the internal donors. The XPS measurement was also performed with an internal donor-free supported catalyst and TiCl4·ester complexes. The binding energies the Ti2p3/2 peak in the three supported catalysts were almost the same in spite of the difference in the internal donor. The higher values of the binding energy in the TiCl4·ester complexes, compared with the supported catalysts, indicated that the TiCl4·internal donor complex itself did not exist on the surface of the supported catalysts. The comparison of the binding energies among the supported catalysts after the reaction with triethylaluminium (TEA) showed that the reduction of the titanium species on the supported catalysts proceeded at the same level, regardless of the kind of the internal donor and of the catalyst preparation method. From the results obtained in this study, it was concluded that the internal electron donor existed free from titanium species on the supported catalysts, but the nature of the active sites was affected by the change in the environment through the interaction of the donor with MgCl2.

Double-stimuli-responsive degradation of hydrogels consisting of oligopeptide-terminated poly(ethylene glycol) and dextran with an interpenetrating polymer network.

Biodegradable hydrogels consisting of oligopeptide-terminated poly(ethylene glycol) (PEG) and dextran (Dex) with an interpenetrating polymer network (IPN) structure were prepared as models of novel biomaterials exhibiting a double-stimuli-response function. The IPN-structured hydrogels were synthesized by sequential cross-linking reaction of N-methacryloyl-glycylglycylglycyl-terminated PEG and Dex. In vitro degradation of the IPN-structured hydrogels was examined using papain and dextranase as model enzymes of hydrolyzing oligopeptide and Dex, respectively. Specific degradation in the presence of papain and dextranase was observed in the IPN-structured hydrogel with a particular composition of oligopeptide-PEG and Dex. This same hydrogel was not degraded by one of the two enzymes. The IPN-structured hydrogels were characterized by water content, thermal mechanical analysis, and wide-angle X-ray diffraction, and the results were compared with those of co-cross-linked hydrogels consisting of N-methacryloyl-glycylglycylglycyl-terminated PEG and methacryloyl Dex. The results suggest that the IPN-structured hydrogels contain physical chain entanglements between networks as well as chemical cross-linked networks. It is concluded that the double-stimuli-responsive degradation observed in the IPN-structured hydrogel is achieved by controlling the chain entanglements between the two biodegradable polymers. Such degradation property of the IPN-structured hydrogel can be useful as a fail-safe system for guaranteed drug delivery and/or medical micromachines.

Variation in the Isospecific Active Sites of Internal Donor-Free MgCl2-Supported Ziegler Catalysts: Effect of External Electron Donors

The stopped-flow polymerization of propylene was carried out using an internal donor-free MgCl 2 -supported Ziegler catalyst in the absence or presence of external electron donors. The variation in the isospecific active sites was investigated based on the isotacticity distribution of the poly(propylene) analyzed by the TREF method. Highly isospecific active sites derived from the highest isotactic fraction (elution temperature by TREF: >112 °C) exist in the electron donor-free catalyst system. The addition of external electron donors converted parts of the aspecific into isospecific active sites, but showed no effects on the highests isospecific active sites. The external electron donor sterically affects a coordination vacancy of each aspecific titanium species and, consequently, transfers if into an isospecific active site of high, but not highest isospecificity.

Variation in oxidation state of titanium species on MgCl2-supported Ziegler catalyst and its correlation with kinetic behavior for propylene polymerization

Abstract The variation in the oxidation state of the titanium species after reaction with various alkylaluminiums was investigated by X-ray photoelectron spectroscopy (XPS). The reaction of an MgCl2-supported Ziegler catalyst with alkylaluminium was observed to induce a chemical shift to lower binding energy and a broadening of the full width at half maximum intensity (FWHM), depending upon the kind of alkylaluminium. The polymerization kinetics was examined for slurry and stopped-flow polymerization to estimate the relationship between polymerization stages. The catalyst activation and the decay during the polymerization were found to be related to the variation in the titanium species arising from various alkylaluminium compounds.

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.