Polycarbonate (PC) is one of the most important engineering plastics, which is produced by polycondensation reaction of bisphenol A (bis-A) with phosgene. To achieve a more economical and safe process, a direct one-step synthesis of PC from bis-A and carbon monoxide was developed on the basis of Pd catalyzed oxidative carbonylation. New catalyst systems for the one-step synthesis of diphenyl carbonate (DPC) from carbon monoxide and phenol were investigated in the model reaction to develop efficient catalyst systems. The Pd-Sn complex including [Pd-Pd-Sn] or [Sn-Pd-Pd-Sn] structure with a Mn redox catalyst was found to produce DPC effectively without addition of any ammonium halide. In the presence of an ammonium halide, Pd catalyst systems, such as the Pd dinuclear complex possessing a 2-pyridylphosphine ligand, Pd-diimine complex derived from 2, 6-di-iso-propylaniline with a 1, 2-diketone or 1, 2-dialdehyde, and Pd-bipyridyl complex consisting of a 6, 6′-disubstituted-2, 2′-bipyridyl ligand, promoted the oxidative carbonylation of phenol more effectively. The immobilization of Pd complex catalyst systems was also investigated. These novel Pd complex catalyst systems were applied to the one-step synthesis of PC from bis-A and carbon monoxide. PC with the number- and weight-average molecular weights of 5600 and 12900 respectively, was successfully obtained using Pd-6, 6′-disubstituted-2, 2′-bipyridyl complexes. These molecular weights were much higher than the one-step synthesis of PC by oxidative carbonylation using conventional Pd catalyst systems such as PdBr₂.

View full abstract

Propylene polymerization was carried out with titanium diamide catalysts activated by methylaluminoxane (MAO) and AlR₃/B cornpound under various polymerization conditions. The catalyst system using MAO and Al (ⁱBu) ₃/Ph₃CB (C₆F₅) ₄ as cocatalyst afforded a mixture of isotactic and atactic polypropylenes at high concentration of propylene. The polymerization activity for isotactic polymer increased more than linearly while increasing the concentration of monomer. In order to clarify this phenomena, we carried out the polymerization of propylene in the presence of cyclohexene, which does not polymerize with the title catalyst, but could possibly coordinate to the active sites. Some isotactic polymers were obtained even under low propylene concentration by adding cyclohexene, and the activity increased linearly with an increase of cyclohexene concentration. In addition, it was obvious that the molecular weight of the isotactic polymer significantly increased as a function of polymerization time. Based on this fact, the successive polymerization of propylene and 1-hexene was performed with this catalyst system and gave isotactic poly (propylene-block-1-hexene). These results strongly demonstrated the high potential of titanium diamide catalyst for isospecific living polymerization of propylene.

View full abstract

As a result of “Ligand-Oriented Catalyst Design” research, group 4 transition metal complexes having two phenoxy-imine chelate ligands, named FI Catalysts, were found to exhibit the highest ethylene polymerization activities. The maximum activity reached 6552 kg-PE/mmol-cat·h at 25°C at atmospheric pressure. Selection of the metal and cocatalyst, and/or change in the ligand structure revealed that these complexes produced polyethylenes or poly (ethylene-co-propylene) s having very low (M_v; 0.5× 10³) to exceptionally high (M_v; 5×10⁶) molecular weight values and poly (1-hexene) having unique structure. Furthermore, Titanium FI Catalysts having fluorine-containing substituents in the ligands enabled the living polymerization of ethylene, propylene, and ethylene/propylene above room temperature. Using this technique, a new series of polyolefinic block copolymers were successfully prepared. These facts indicated that FI Catalysts possess very high potential as a new generation of olefin polymerization catalysts.

View full abstract

Stereospecific polymerization of substituted aromatic acetylenes such as p-3-methylbutoxyphenylacetylene (p3MBPA), o-trifluorophenylacetylene (oTFMPA), p-amidophenylacetylene (pAPA), 3-n-octylthienylacetylene (3OTA), and N-n-octyl-3-carbazolylacetylene (NOCzA) was carried out by using the Rh complex, [Rh (norbornadiene) Cl] ₂ to produce the corresponding polymers. These have a cis isomer as the main structure and are obtained in fairly high yields in the presence of ethylalcohol, water, and triethylamine (TEA). The resulting polymers were characterized in detail using ¹H NMR, laser Raman, diffuse reflective UV-Vis, electron spin resonance, and wide angle X-ray diffraction methods. The data showed that the obtained polymers were composed of amorphous and pseudohexagonal structures, i. e., columnar. We found that the absorption maximum of the columnar polymer appeared at somewhat longer wavelength than that of the amorphous polymer. Further, the columnar structure composed of helical main chain can be destroyed by compression under reduced pressure to produce the trans isomer, even though the absorption maximum of the obtained trans isomer is shifted to a lower wavelength region compared to that of the original columnar polymer. Based on these data, we concluded that the color of these polymers can be easily controlled by formation of columnars which are composed of the helical polymer chains.

View full abstract

We explored a high-performance and inexpensive activator (cocatalyst) for metallocene catalyst systems and found that high activity is obtained with the combination of metallocenes and clay minerals. In addition, we found that clay minerals are not simple activators. They have functions to change molecular weight distribution and composition distribution of the polymer produced. Furthermore, they also work as carriers because they are solid. Therefore, a clay mineral-based catalyst is applicable to a slurry, bulk, and gas-phase polymerization process as a“drop-in catalyst”. In this article, we focus our attention on clay minerals in the catalyst system comprised of metallocenes and clay minerals. We will show their basic functions, versatility, chemical modification for the improvement of the properties of polyethylenes, and commercialization for a polypropylene production process.

View full abstract

N-Propargylamides have proven to polymerize in the presence of Rh catalysts to give stereoregular (cis-transoidal) polymers in good yields. Intramolecular hydrogen bonds are constructed between the pendant amide groups, which induces and stabilizes the helical conformation of the main chain. The helical structure is readily deformed into the randomly coiled state, which is promoted by the external stimuli such as heating or adding polar solvents. The transition from the disordered to helical conformations was spectroscopically evidenced to involve negatively large entropy and enthalpy changes.

View full abstract

This article covers recent developments in transition metal-catalyzed living radical polymerization, specifically focusing on the design of the metal complexes. The metal-catalyzed systems, each consisting of an organic halide (initiator) and a metal complex (catalyst), polymerize a wide variety of vinyl monomers to give polymers with controlled molecular weights, their narrow distributions, and well-defined main-chain and/or end-group structures. The polymerization proceeds via radical species generated by the reversible and homolytic activation of terminal dormant carbon-halogen bonds by transition metal complexes. Careful selections of the central metal and the ligands are necessary depending on the types of monomers. In addition to the scope and the design of the metal catalysts, the article also outlines the polymerization mechanism and living radical polymerization in aqueous media.

View full abstract

The polymerization of methyl methacrylate (MMA) with diisocyanate-Cu (acac) ₂ complexes prepared from alicyclic diisocyanates, 2, 5 (2, 6) -bis (isocyanatomethyl) bicyclo [2. 2. 1] heptane (NBDI), 1, 3-bis (isocyanatomethyl) cyclohexane (H₆XDI), and 3-isocyanatomethy1-3, 5, 5trimethylcyclohexylisocyanate (IPDI), and copper acethylacetonate was investigated. When polymerizations catalyzed by diisocyanate-Cu (acac) ₂ complexes were carried out for 24h at 60°C in THF, IPDI-Cu (acac) ₂ complex showed high activity and the narrow molecular distribution (M_w /M_n=1.26), and the number average molecular weight (M_n) of the resulting polymer was 971000. From a kinetic study using the copper complex, the polymerization rate (R_p) can be expressed as R_p=k [MMA] ^2.3 [IPDI-Cu (acac) ₂] ^0.44. The overall activation energy of the polymerization was determined to be 42.5kJ / mol. In the case of IPDI-Cu (acac) ₂ complex, the resulting polymers were somewhat rich in isotactic structure.

View full abstract

A group 4 metallocene complex that serves as olefin polymerization catalyst was tethered on a solid support such as silica gel by covalent bonds. A zirconocene complex that has a vinyl group on its cyclopentadienyl ligand was hydrosilated or hydroborated to introduce a functional anchor for immobilization reactions. The complex with a Si-Cl group was tethered on a silica surface by the reaction with a surface Si-OH group. The zirconocene with a BH group was immobilized on a silica gel modified with chlorodimethylvinylsilane. Ethyl-ene polymerization using the tethered catalysts showed that the hydroboration-method seems more effective than the hydrosilation-method. It exhibited comparable catalytic activity to the corresponding homogeneous catalyst and produced polyethylene of a higher molecular weight.

View full abstract

Heterogeneous Ziegler-Natta catalyst is widely used for the commercial production of the polypropylene. Attempt to understand the Ziegler-Natta catalyst system have continued by means of several experimental or calculation methods from the early stage to today. The nature of the active site or polymerization reaction over Ziegler-Natta catalyst is not yet clear. This is mainly because of the complexity of this catalyst system. Under these circumstances, we studied the Ziegler-Natta catalyst model by molecular dynamics simulation (MD). In this study, we examined the behavior of the polymer chain bonded to titanium species on MgCl₂ surfaces by MD simulation.

View full abstract

The catalyst system comprising a soluble vanadium complex tris (2-methyl-1, 3-butandionato) vanadium (V (mbd) ₃) /diethyl aluminum chloride (Et₂AlCl) can bring about a living polymerization of propylene. Such a catalyst system shows a slow rate of formation of the active sites. We studied the effect of electron donors on the catalyst composition in the hope of increasing the number of active sites. The rate of the formation of the active sites was much accelerated by the addition of an ester or ether. The accelerating effect was found to be dependent on the charge density on the oxygen atom of the respective electron donor as calculated by MOPAC, giving the maximum activation at the charge density -0.34, irrespective of the kind of the donor oxygen. Analyses of the stereoregularity of the resulting polymers showed that the additives did not alter the nature of the active sites, but only increased the number of the active sites.

View full abstract

A series of chromium complexes having Cp-amine type ligands, (R'₂NC₂H₄C₅R₄) CrX₂, were synthesized, whose catalytic behaviors for olefin polymerization were investigated upon activation with modified methylaluminoxane (MMAO). With increasing steric bulkiness of the complex, the catalytic activity increased for ethylene polymerization. These complexes showed high activity for copolymerizations of ethylene with a -olefins as well as for homopolymerizations. A indenyl type complex tended to produce polymers with higher molecular weights. The molybdenum analogues showed relatively high activities for ethylene polymerization among the reported molybdenum complexes, although their activities were much lower than those of the chromium catalysts and Group 4 metallocene catalysts. The corresponding iron complex, [ (Me₂NC₂H₄C₅Me₄) FeCl] ₂, showed no catalytic activity for ethylene polymerization. Catalyses of variously substituted vanadium tris (acetylacetonate) (V (acac) ₃) /MMAO systems were also studied. Introduction of electron-withdrawing groups tended to enhance the catalytic activity, while catalysts having bulky substituents yielded polyethylenes with high molecular weight and narrow molecular weight distribution.

View full abstract

In order to compare with silylene-bridged group 4 metallocenes, C₂ symmetric dimethylgermylene-bridged zirconocene and hafnocene dichlorides were prepared and employed as the catalyst for polymerization of propylene in combination with methylaluminoxane (MAO). Germylene-bridged metallocenes always produced isotactic polypropylene of higher molecular weight than that produced by silylenebridged analogues. The molecular structures of four metallocenes prepared from dimethylsilylene and germylenebis (2, 3, 5-trimethylcyclopentadienyl) were detemined by X-ray diffraction and showed no substantial differences of geometry between silylene- and germylene-bridged ones.

View full abstract

Polymerization of ethylene and propylene was conducted with a Tebbe-type Ti (III) complex [Cp₂Ti (μ-C1) ₂AlXY, (X, Y=Et, Cl) ] combined with methylaluminoxane (MAO) cocatalyst. The polymerization activity increased with decreasing number of the Et-group in the Tebbe-type complex. The activity was improved also by removal of the AlMe₃ from MAO. This indicated that the “mononuclear” alkylaluminum compound [AlR_nX_3-n] decreases the activity. The propylene polymerization caused partial inversion of the sequence (6.5%) of the polypropylene produced.

View full abstract