Cationic palladium(II)–acetylacetonate complexes bearing α-diimine ligands as catalysts in norbornene polymerization

A variety of palladium(II)–acetylacetonate complexes bearing α-diimine ligands were synthesized by the reaction of [Pd(acac)(MeCN)₂]BF₄ with N⁀N ligands. When activated with BF₃·OEt₂, these complexes provide access to a new class of alkylating agent free Pd–diimine catalyst systems. Catalyst screening for the vinyl addition polymerization of norbornene showed their high activities of 10²–10⁴ kg_pol mol_cat^− 1 h^− 1.     

Influence of type and positioning of N-aryl substituents on vinyl polymerization of norbornene by Ni(II) α-diimine complexes

Effects of structural variations of the diimine ligand on catalyst activities for vinyl polymerization of norbornene (NB) have been investigated by a series of Ni(II) α-diimine catalysts of the general formula: [{ArN=C(Ac)-C(Ac)=NAr}]NiBr₂ (Ac=acenaphthyl) (Cat(H), Ar=C₆H₅; Cat(2,6-Me), Ar=2,6-C₆H₃Me₂; Cat(2,6-Et), Ar=2,6-C₆H₃Et₂; Cat(2,6- i Pr), Ar=2,6-C₆H₃ i-Pr₂; Cat(2,3-Me), Ar=2,3-C₆H₃Me₂; Cat(2,4-Me), Ar=2,4-C₆H₃Me₂; Cat(2,5-Me), Ar=2,5-C₆H₃Me₂; Cat(3,5-Me), Ar=3,5-C₆H₃Me₂; Cat(2,4,6-Me), Ar=2,4,6-C₆H₂Me₃). In situ reactions with methylaluminoxane generated the active catalysts, and they showed good activity towards NB polymerizations. As indicated by relatively higher activities of Cat(H) and Cat(3,5-Me), it can be generalized that catalysts having 2,6-substituents are less active due to steric interaction between monomer and substituents. In addition, electron donating methyl groups at 2-, 4-or 6-position on the N-aryl have a con effect and that at 3,5-position has a pro effect. This paper was presented at the 11th Korea-Japan Symposium on Catatysis held at Seoul, Korea, May 21–24, 2007.     

Synthesis and characterization of ethylene-propylene copolymer and polyethylene using α-diimine nickel catalysts

The dilute solution properties of polymeric quaternary ammonium betaines derived from poly(N-vinylimidazole) PNVI and containing either a methylene (B1), ethylene (B2), or propylene (B3) betaine group, respectively, were analyzed. A PNVI blank was also tested. The weight-average molecular weight $ {{\overline{M}}_{\text{w}}} $ , second virial coefficient A ₂, radius of gyration R _g, and hydrodynamic radius R _h of unfractionated probes were determined by MALLS (multiangle laser light scattering) and WALLS (wide-angle laser light scattering) measurements. All of these parameters varied with the type of solvent: pure water, an aqueous solution of 0.5?M NaCl, or an alcohol. These solution properties were useful for predicting the interactions of the polycarboxybetaines (acting as antimicrobial agents) with the components of the bacterial cell wall. Some of the polycarboxybetaines exhibited antimicrobial activities, as shown by the Kirby?CBauer diffusion method. A concentration of about 20?mg?mL^?1 for B1 or B3 in an aqueous solution of 0.5?M NaCl is sufficient to inhibit the growth of Escherichia coli.     

Synthesis,structure and norbornene polymerization activity of a bulky β-diketiminato palladium(II) complex

A new bulky β-diketiminato palladium(II) complex was synthesized by direct reaction of (ⁱPr₂Ph)₂nacnacH ((ⁱPr₂Ph)₂nacnac = CH{C(Me)N(C₆H₃-2,6-ⁱPr₂)}₂) with Pd(OAc)₂ which yielded [(ⁱPr₂Ph)₂nacnac]Pd(OAc) as a mononuclear species with chelating nacnac and acetato ligands. Preliminary investigations into the polymerization of norbornene in the presence of BF₃OEt₂ were performed.     

Influence of powder mixing processes on phase composition,microstructure, and mechanical properties of α/β-SiAlON ceramic tool materials

α/β-SiAlON composite ceramics using powders mixed through different processes were prepared via spark plasma sintering. Effects of different powder mixing methods (ball-milling and ultrasonic vibration with mechanical stirring), ball-milling media (Al₂O₃ and Si₃N₄ balls), and mixing times (12 and 24 h) on the components and morphology of mixed powders, phase composition, microstructure, and mechanical properties of α/β-SiAlON ceramics were studied. Results indicate that additional oxides are mixed to powders when ball-milled with Al₂O₃ balls, leading to an increase in the amount of amorphous glass and a decline in α/β ratio and mechanical properties. These effects were reduced when powders were ball-milled with Si₃N₄ balls, and α-SiAlON content and fracture toughness increased significantly. Moreover, α/β-SiAlON ceramics that underwent ultrasonic vibration with mechanical stirring exhibited the highest hardness and oxidation resistance at high temperature, and their α/β ratio was close to expected value.     

Ignition temperature of coal. 1. Influence of the coal’s composition,structure, and properties

The reactions of coal with the materials used in determining the ignition temperature of unoxidized coal according to Ukrainian State Standard DSTU 7611:2014 are analyzed. First, the ignition temperature of various types of coal from Ukraine, Russia, Canada, Australia, the Czech Republic, Poland, and Indonesia is determined. The influence of the composition, structure, and properties of the coal on its ignition temperature is assessed. The ignition temperature of the unoxidized coal is found to be closely related to the content of organic carbon C^daf and aromatic carbon C_ar, the structural parameter δ characterizing the degree of saturation of the coal’s organic mass, and also the vitrinite reflection coefficient R_o and the yield of volatiles V^daf.     

Effect of composition on sinter-crystallization and properties of low temperature co-fired α-cordierite glass–ceramics

This article investigates effect of composition, including SiO₂ and impurity defined to contain K₂O, Na₂O, Fe₂O₃, etc., from K-feldspar, on sinter-crystallization and properties of the low temperature co-fired α-cordierite glass–ceramics. Increasing impurity content from 5.72 wt% to 9.16 wt% leads to enhanced crystallinity, formation of leucite and more pores but the crystallinity and porosity decreased with a further increase to 10.8 wt%. The main impurity K₂O is critical for formation of α-cordierite and leucite. Only α-cordierite was precipitated from the glasses with different SiO₂ contents but an increase of SiO₂ content slightly improves their densification. The impurity and SiO₂ contents greatly affect the properties of glass–ceramics. Notably, some glass–ceramics from K-feldspar show high densification at low temperature, low dielectric constant (6–8), low loss (about 0.005), appropriate linear CTEs (4.32–5.87 × 10⁻⁶ K⁻¹) and flexural strength (above 100 MPa), all of which meet the requirements of LTCC substrates.     

Influence of hafnium oxide on the structure and properties of powders and ceramics of the YSZ–HfO2 composition

Using the X-ray diffraction, internal friction, 4-point bending, and electron microscopy methods we have studied the structural compatibility and influence of Y₂O₃ and HfO₂ dopants addition on the structure and phase composition of ZrO₂ powders and ceramics based on them. The mechanical properties of ZrO₂–Y₂O₃-HfO₂ (YSZ) system have been investigated.It was determined that the similarity of the structure and properties of yttrium and hafnium oxides is not complete. The individual structural features of ZrO₂, Y₂O₃, and HfO₂ oxides reviled themselves during the formation of ternary systems of the YSZ-Hf type. Studies of the nY₂O₃–ZrO₂ - mHf₂O₃ system in the range of hafnium amount from 1 to 15 wt% and yttrium oxide concentration from 0 to 12 mol% showed the possibility of increase in the values of physical and mechanical properties of common two-component zirconium ceramics by the forming ternary systems of the YSZ-Hf type.     

Study of triisobutylaluminum as cocatalyst and processing parameters on ethylene polymerization performance of α-diimine nickel(II) complex by response surface method

In this research work, 1,4-bis(2,6-diisopropylphenyl)-acenaphthenediimine-diboromonickel(II) (1) complex was synthesized and its ethylene polymerization in the presence of triisobutylaluminum (TIBA) as activator was studied. The effects of three critical factors [polymerization temperature (T), cocatalyst to catalyst ratio (CC) and pressure (P)] on the average molecular weight and crystallinity of the final polymers and also reaction yields as the response variables were evaluated with the help of empirical statistical models and visualized with the response surface method. The results show that activity of 1 as well as M _w and crystallinity of the resulting polymers are influenced strongly by the polymerization factors. The activity of TIBA-activated catalyst 1 reaches a maximum at 10 °C after raising pressure and CC to 7 bar and 3,000, respectively. This activity is much higher than previously reported activity for this catalyst. Furthermore, a polymerization condition for reaching desirable responses is predicted and experimentally verified.     

Living and block polymerization of α-olefins using a Ni(II)-α-diimine catalyst containing OSiPh2Bu groups

A new siloxy-substituted α-diimine compound and its corresponding Ni(II) complex, {bis[N,N′-(4-tert-butyl-diphenylsiloxy-2,6-dimethylphenyl)imino]acenaphthene}dibromonickel (6), were successfully synthesized and the molecular structure of 6 characterized by X-ray crystallography. The precatalyst 6 activated by methylaluminoxane (MAO) or diethylaluminum chloride (DEAC) was tested in the polymerization of ethylene, showed to be highly active (e.g. 2.2×10⁷ and 1.8×10⁷ g polymer (mol Ni.h.bar)⁻¹, respectively) and led to a branched polyethylene (ca. 35-55 branches/1000 C). The catalyst system 6/methylaluminoxane (MAO) catalyzes, at −11 °C, living polymerization of propylene, to a polypropylene showing a syndiotactic-rich microstructure (P_r=0.74). 1-Hexene was also successfully polymerized via a living process, both at −11 and +16 °C. The ¹³C NMR spectra of the poly(1-hexene)s obtained at room temperature show a microstructure almost exclusively composed by n-butyl and methyl branches, the latter being present in a much higher number. Diblock polypropylene-block-poly(1-hexene) and triblock poly(1-hexene)-block-poly(propylene-ran-1-hexene)-block-poly(1-hexene) copolymers have also been synthesized and characterized by GPC/SEC, DSC and NMR.     

Effect of acid treatment on the composition and structure of a natural aluminosilicate and on its catalytic properties in α-pinene isomerization

The article deals with the effect of the conditions of modification of a natural aluminosilicate catalyst with a 10% HCl solution on the chemical and phase compositions, porous and crystal structures, and acidity of the material and on its catalytic properties in α-pinene isomerization. Treatment of the aluminosilicate with 10% HCl (25–250 mL per gram of solid) causes cation exchange, increases the concentration of protonic sites on the aluminosilicate surface, and removes impurity calcite and dolomite. The specific surface area of the aluminosilicate increases from 52 to 68–82 m²/g. Treatment of the aluminosilicate with 175.0 or 250.0 mL/g of HCl removes a considerable amount framework Al³⁺, Fe^2+/3+, and Mg²⁺ cations, leading to a partial disruption of its structure and to a decrease in its acidity, specific surface area, and, as a consequence, catalytic activity relative to the same parameters of the samples treated with 50 or 100 mL/g of HCl. The highest catalytic activity is displayed by the aluminosilicate treated with 50 mL/g of HCl. The camphene and dipentene selectivity of the reaction (at 85% α-pinene conversion) with the original catalyst is 55 and 30%, respectively; modifying the aluminosilicate with HCl raises the camphene selectivity and reduces the dipentene selectivity by 5–6%. The catalyst considered here is more active than the commercial titanium catalyst.     

Influence of α-Si3N4 coarse powder on densification,microstructure, mechanical properties,and thermal behavior of silicon nitride ceramics

Silicon nitride (Si₃N₄) ceramics, with different ratios of fine and coarse α-Si₃N₄ powders, were prepared by spark plasma sintering (SPS) and heat treatment. Further, the influence of coarse α-Si₃N₄ powder on densification, microstructure, mechanical properties, and thermal behavior of Si₃N₄ ceramics was systematically investigated. Compared with fine particles, coarse particles exhibit a slower phase transition rate and remain intact until the end of SPS. The remaining large-sized grains of coarse α-Si₃N₄ induce extensive growth of neighboring β-Si₃N₄ grains and promote the development of large elongated grains. Noteworthy, an appropriate number of large elongated grains distributed among fine-grained matrix forms bimodal microstructural distribution, which is conducive to superior flexural strength. Herein, Si₃N₄ ceramics with flexural strength of 861.34 MPa and thermal conductivity of 65.76 W m⁻¹ K⁻¹ were obtained after the addition of 40 wt% coarse α-Si₃N₄ powder.     

Unique microstructure analysis of ethylene-propylene copolymer synthesized using catalytic system based on α-diimine nickel complexes: a comparative study by 13C NMR technique

The microstructure of rubber-like ethylene-propylene copolymer (MN4) produced by a mixed nickel-based system (MN) containing catalysts of dibromo[N,N′-bis(2,6-diisopropylphenyl)-2,3-butanediimine]nickel(II) n1 and dibromo[N,N′-(phenanthrene-9,10-diylidene)bis(2,6-diisopropylaniline)]nickel(II) n2 was determined by ¹³C NMR technique. Sequences distribution of ethylene (E), propylene (P), EP, inverted propylene and uninterrupted methylene and also methylene number-average sequence lengths for the copolymer (MN4) were estimated. The results obtained from the MN4 EP copolymer were compared with reported copolymers which had been synthesized using constrained geometry catalyst (CGC) and vanadium-based Ziegler-Natta catalyst. The results demonstrated that the MN4 EP copolymer had fewer alternating comonomer sequences than ethylene-propylene elastomers obtained by CGC and vanadium-based (V) catalysts. A large number of the inversion structures (66 %) and high mole percent of sequences containing a long branch (3.2 mol%) were also observed in unique microstructure of the copolymer (MN4).     

Double-layer structure,sorption and magnetism properties of metal–organic frameworks with trigonal planar ligand

A new double-layer metal–organic framework [Co₃(tcpt)₂(H₂O)₂] (1) has been synthesized using trigonal planar ligand 2,4,6-tris(4-carboxyphenoxy)-1,3,5-triazine (H₃tcpt) as a bridging ligand and characterized by single-crystal X-ray diffraction, elemental analyses, IR, PXRD and TGA. Structure analysis reveals that compound 1 has a double-layer structure. Gas sorption measurements indicate that compound 1 exhibits selective adsorption capabilities for CO₂ over CH₄ and N₂. Furthermore, the magnetic studies of compound 1 show antiferromagnetic interactions between Co(II) ions.     

Polymerization of 4-methyl-1-pentene catalyzed by α-diimine nickel catalysts: Living/controlled behavior, branch structure, and mechanism

Branched α-olefin, 4-methyl-1-pentene (4 MP), was polymerized with classical α-diimine nickel complexes in the presence of MAO. Influences of structure of α-diimine nickel catalysts and polymerization parameters including temperature and [Al]/[Ni] mole ratio were evaluated. At 0 °C, 4-methyl-1-pentene can be polymerized in a living/controlled manner. The obtained poly(4-methyl-1-pentene)s are amorphous elastomers with low glass transition temperature (T_g). Nuclear magnetic resonance (NMR) and distortionless enhancement by polarization transfer (DEPT) analyses show that various types of branches and microstructural units are present in the polymers. On the basis of assignment of microstructures, mechanistic models that involves the 1,2- and 2,1-insertion, and chain walking were constructed. The influences of temperature and [Al]/[Ni] mole ratio on branching degree, branch type, and insertion pathways were also discussed in detail.     

The effect of processing conditions,amount of additives and composition on the microstructures and mechanical properties of α-SiAlON ceramics

A series of samples with yttrium α-SiAlON compositions and different amounts of additive has been fabricated from α-Si₃N₄, AlN, Al₂O₃ and Y₂O₃ starting powders, using gas pressure sintering and three different sintering procedures. One series of samples was heated up to 1825°C and then held for 3 h, another group of samples was held at a lower temperature (1500 or 1600°C) for 1 h and then heated up to 1825°C and held for 3 h. The results of investigations using scanning electron microscopy showed the effect of composition and sintering procedure on the morphology of α-SiAlON grains. It was found that the amount of elongated grains increased with increasing amount of liquid phase. The mechanical tests showed that all of the samples exhibited HV10 values in the range of 1800–1976 kg/mm and K_IC values in the range of 3.9–6.3 MPam^1/2.     

Effect of pressure and temperature on densification,microstructure and mechanical properties of spark plasma sintered silicon carbide processed with β-silicon carbide nanopowder and sintering additives

The effects of applied pressure and temperature during spark plasma sintering (SPS) of additive-containing nanocrystalline silicon carbide on its densification, microstructure, and mechanical properties have been investigated. Both relative density and grain size are found to increase with temperature. Furthermore, with increase in pressure at constant temperature, the relative density improves significantly, whereas the grain size decreases. Reasonably high relative density (~96%) is achieved on carrying out SPS at 1300 °C under applied pressure of 75 MPa for 5 min, with a maximum of ~97.7% at 1500 °C under 50 MPa for 5 min. TEM studies have shown the presence of an amorphous phase at grain boundaries and triple points, which confirms the formation of liquid phase during sintering and its significant contribution to densification of SiC at relatively lower temperatures (≤1400 °C). The relative density decreases on raising the SPS temperature beyond 1500 °C, probably due to pores caused by vaporization of the liquid phase. Whereas β-SiC is observed in the microstructures for SPS carried out at temperatures ≤1500 °C, α-SiC evolves and its volume fraction increases with further increase in SPS temperatures. Both hardness and Young׳s modulus increase with increase in relative density, whereas indentation fracture toughness appears to be higher in case of two-phase microstructure containing α and β-SiC.