Ethylene polymerization by self-immobilized neutral nickel catalysts bearing allyl groups

[Ni(Ph)(PPh3)(N,O)] complexes containing phenyliminophenolato ligands (N,O) (1: N,O = A; 2: N,O = B; 3: N,O = Q 4: N,O = D; 5: N,O = E) have been synthesized and characterized. The molecular structure of 4 was determined by single-crystal X-ray analysis. Complexes 2-5 bearing allyl groups have been investigated as self-immobilized catalysts for ethylene polymerization without the use of co-catalysts. The high ethylene polymerization activities of ca. 10(5) g.PE mol(-1) Ni.h(-1) and high molecular weight (M-w approximate to 10(5)) of polyethylene could be accomplished by changing the ligand structures and reaction conditions. The self-immobilization of catalysts brings about a dramatic increase in the catalytic activities of ethylene polymerization.

Multiple melting behavior of isotactic polypropylene and poly(propylene-co-ethylene) after stepwise isothermal crystallization

The multiple melting behavior of several commercial resins of isotactic polypropylene (iPP) and random copolymer, poly(propylene-co-ethylene) (PPE), after stepwise isothermal crystallization (SIC) were studied by differential scanning calorimeter and wide-angle X-ray diffraction (WAXD). For iPP samples, three typical melting endotherms appeared after SIC process when heating rate was lower than 10 degreesC/min. The WAXD experiments proved that only alpha-form crystal was formed during SIC process and no transition from alpha1- to alpha2-form occurred during heating process. Heating rate dependence for each endotherm was discussed and it was concluded that there were only,two major crystals with different thermal stability. For the PPE sample, more melting endotherms appeared after stepwise isothermal crystallization. The introduction of ethylene comonomer in isotactic propylene backbone further decreased the regularity of molecular chain, and the short isotactic propylene sequences could crystallize into gamma-form crystal having a low melting temperature whereas the long sequences crystallized into alpha-form crystal having high melting temperature.

Polymer immobilized silane bridged metallocene catalysts for ethylene polymerization

Ansa-zirconocene complex with an allyl substituted silane bridge [(CH2=CHCH2)CH3Si(C5H4)(2)]ZrCl2 (1a) has been synthesized and characterized. The molecular structure of la has been determined by X-ray crystallographic analysis. The polymer immobilized metallocene catalyst 1b is prepared by the co-polymerization of la with styrene in the presence of radical initiator. The result of ethylene polymerization showed that the polymer immobilized metallocene catalyst kept high activity for ethylene polymerization and was a potential supported catalyst for olefin polymerization.

Self-immobilized catalysts for ethylene polymerization: neutral, single-component salicylaldiminato phenyl nickel(II) complexes bearing allyl substituents

A new family of self-immobilized ethylene polymerization catalysts, derived from neutral, single-component salicylaldiminato phenyl nickel complexes, is described.

Toughening PA1010 with a functionalized saturated polyolefin elastomer

Polyamide (PA)1010 is blended with a saturated polyolefin elastomer, ethylene-cu-olefin copolymer (EOCP). To improve the compatibility of PA1010 with EOCP, different grafting rates of EOCP with maleic anhydride (MA) are used. The reaction between PA1010 and EOCP-g-MA during extrusion is verified through an extraction test. Mechanical properties, such as notched Izod impact strength, elongation at break, etc., are examined as a function of grafting rate and weight fraction of elastomer. It was found that in the scale of grafting rate (0.13-0.92 wt %), 0.51 wt % is an extreme point for several mechanical properties. Elastomer domains of PA1010/ EOCP-g-MA blends show a finer and more uniform dispersion in the matrix than that of PA1010/EOCP blends. For the same grafting rate, the average sizes of elastomer particles are almost independent on the contents of elastomer, but for different grafting rates, the particle sizes are decreased with increasing grafting rate. The copolymer formed during extrusion strengthens the interfacial adhesion and acts as an emulsifier to prevent the aggregation of elastomer in the process of blending. (C) 2000 John Wiley & Sons, Inc.

Preparation and application of a novel core-shell-particle-supported zirconocene catalyst

The use of functional groups bearing silica/poly(styrene-co-4-vinylpyridine) core-shell particles as a support for a zirconocene catalyst in ethylene polymerization was studied. Several factors affecting the behavior of the supported catalyst and the properties of the resulting polymer, such as time, temperature, Al/N (molar ratio), and Al/Zr (molar ratio), were examined. The conditions of the supported catalyst preparation were more important than those of the ethylene polymerization. The state of the supported catalyst itself played a decisive role in both the catalytic behavior of the supported catalyst and the properties of polyethylene (PE). IR and X-ray photoelectron spectroscopy were used to follow the formation of the supports. The formation of cationic active species is hypothesized, and the performance of the core-shell-particle-supported zirconocene catalyst is discussed as well. The bulk density of the PE formed was higher than that of the polymer obtained from homogeneous and polymer-supported Cp2ZrCl2/methylaluminoxane catalyst systems. (C) 2001 John Wiley & Sons, Inc.

On morphology and the competition between crystallization and phase separation in polypropylene-polyethylene blends

Blends of polypropylene (PP) and low density polyethylene (LDPE) have been examined for a series of compositions using differential scanning calorimetry and permanganic etching followed by transmission electron microscopy. Thermal analysis of their melting and recrystallization behaviour suggests two possibilities, either that below 15 wt % PP the blends are fully miscible and that PP only crystallizes after LDPE because of compositional changes in the remaining melt, or else that the PP is separated, but in the form of droplets too small to crystallize at normal temperatures. Microscopic examination of the morphology shows that the latter is the case, but that a fraction of the PP is nevertheless dissolved in the LDPE. (C) 1998 Kluwer Academic Publishers.

Synthesis of lanthanide-alkylaluminium bimetallic complexes and studies on their catalytic activities for polymerization of some polar monomers

Three new lanthanide (Ln)-alkylaluminium (Al) bimetallic complexes with the formula [(mu-CF3CO2)(2)Ln(mu-CF3CHO2)AIR(2) . 2THF](2) (Ln = Nd, Y, R=i-C4H9 (i-Bu); Ln=Eu, R=C2H5(Et); THF=tetrahydrofuran) were synthesized by the reaction of Ln(CF,CO,), (Ln=Nd, Y) with HAI (i-Bu)(2) and of Eu(CF3CO2)(3) with AlEt(3), respectively. Their crystal structures were determined by X-ray diffraction at 233 K. [(mu-CF3CO2)(2)Nd (mu-CF3CHO2)Al(i-Bu)(2) . 2THF](2) (Nd-Al) and [(mu-CF3CO2)(2)Y(mu-CF3CHO2)Al(i-Bu)(2) . 2THF](2) (Y-Al) are isomorphous and crystallize in space group with a=12.441(3) Angstrom [12.347(5) Angstrom for Y-Al], b=12.832(3) Angstrom [12.832(4) Angstrom], c=11.334(3) Angstrom [11.292(8) Angstrom], alpha=104.93 (2)degrees [104.45(4)degrees], beta=98.47(2)degrees [98.81(4)degrees], gamma=64.60(2)degrees [64.30(3)degrees], R=0.519 [0.113], R(w)=0.0532 [0.110], Z=1 and [(mu-CF3CO2)(2)Eu(CF3CHO2)AlEt(2) . 2THF](2)(Eu-Al) in space group P2(1)/n with a=11.913(6) Angstrom, b=14.051(9) Angstrom, c=17.920(9) Angstrom, alpha=101.88(11)degrees, beta=gamma=90 degrees, R=0.0509, R(w)=0.0471 and Z=2. The six CF3CO2- (including CF3CHO2-) of each complex, among which pairs are equivalent, coordinated to Ln and Al in three patterns: (A) the two oxygen atoms in one of the three CF3CO2- type coordinated to two different Ln; (B) the two oxygen atoms in the second of CF3CO2- type coordinated to Ln and Al, respectively; (C) one of the two oxygen atoms in the third CF3CO2- type bidentately coordinated to two Ln and another oxygen coordinated to Al and one of the two Ln, respectively. Unlike types A and B, in type C the carboxyl carbon with a hydrogen atom bonded to it was found to appear as an sp(3)-hybridized configuration rather than an sp(2)-one. 1D and 2D NMR results further confirmed the existence of such a disproportionated CF3CHO2- ligand. Methyl methacrylate (MMA) and epichlorohydrin (ECH) could be polymerized by Y-Al or Eu-Al as a single-component catalyst and highly syndiotactic poly(MMA) was obtained. THF could also be polymerized by Y-Al in the presence of a small amount of ECH.

THE GENERAL AN INDEX AND ITS APPLICATION .4. THE APPLICATION OF GENERAL AN INDEX TO HYDROCARBONS

The general a(N) index (GAI) was used to characterize the cis, trans isomers of hydrocarbons. The best one-variable equations were obtained with GAI for several physicochemical properties of seven pairs of olefin cis, trans isomers. The linear correlation coefficients are in the range of 0.975 to 0.997. GAI was also compared with the other five topological indices, Randic connectivity index chi, Wiener number W, Hosoya index Z, the average distance sum connectivity J proposed by Balaban and a(N) index introduced by Yang, in correlating with the octane number (MON) of heptanes and octanes.

SYNTHESIS OF TETRAPHENYLBUTADIENE LANTHANIDE METALLACYCLES

The cyclic derivatives of transition metals have been extensively investigated in recent years since they are believed to serve as key intermediates in various homogeneous catalytic processes of olefine and alkyne metathesis. The synthesis of the title compounds has not been reported before.

Effect of variations in acid properties of HZSM-5 on the coking behavior and reaction stability in butene aromatization

In order to investigate the effect of acid properties on the coke behavior and stability of butene aromatization, we prepared the AHZSM-5 samples with various acid properties by the methods of hydrothernial treatment and K addition. The reaction of butene aromatization was carried out at 350 degrees C and 0.5 MPa in a continuous flow fixed bed. The characterization of the fresh/coked catalysts with NH3-TPD, N-2 adsorption-desorption measurement, and TG techniques has shown that a large amount of acid sites (high acid density) of the AHZMS-5 catalyst can cause a large quantity of coke deposit and serious channel blockage, and so result in a rapid loss of aromatization activity. On the contrary, after a great reduction in strong acid sites of AHZSM-5 catalyst resulting from some K-modification, the presence of only many weak acid sites also could not lessen the formation of coke nor improve the reaction stability of butene aromatization. Interestingly, the simultaneous reduction in the strong and weak acid sites to a desirable level by hydrothermal treating the AHZSM-5 catalyst at a proper temperature can effectively suppress the coke formation and channel blockage, and thus improve its olefin aromatization stability. (c) 2005 Elsevier B.V. All rights reserved.

Heterogeneous enantioselective epoxidation catalyzed by Mn(salen) complexes grafted onto mesoporous materials by phenoxy group

Three chiral Mn(salen) complexes were immobilized into different mesoporous material via phenoxy group by a simplified method and they show high activity and enantioselectivity for asymmetric epoxidation of various substituted unfunctional olefins. The heterogeneous Mn(salen) catalysts show comparable ee values for asymmetric epoxidation of styrene and 6-cyano-2,2-dimethylchromene and much higher ee values for epoxidation of a-methylstyrene (heterogeneous 79.7% ee versus homogeneous 26.4% ee) and cis-beta-methylstyrene (heterogeneous 94.9% ee versus homogeneous 25.3% ee for cis-epoxide) than the homogeneous catalysts. These heterogeneous catalysts also remarkably alter the cis/trans ratio of epoxides for asymmetric epoxidation of cis-beta-methylstyrene (heterogeneous 21 versus homogeneous 0.38). The axial tether group does not make a big effect on ee values and the increase in ee value and change in cis/trans ratio are mainly attributed to the axial immobilization mode and the support effect of heterogeneous catalysts. The catalysts keep constant ee values for the recycle tests of eight times for asymmetric epoxidation of a-methylstyrene. And several possibilities were proposed to elucidate the difference in ee values of heterogeneous catalysts from homogeneous catalysts. (c) 2005 Elsevier B.V. All rights reserved.