Copolymerization of carbon dioxide and propylene oxide with Ln(CCl3COO)(3)-based catalyst: The role of rare-earth compound in the catalytic system

A highly alternative copolymer of carbon dioxide and propylene oxide was obtained using a lanthanide trichloroacetates-based ternary catalyst. The rare-earth compound in the ternary catalyst was critical to dramatically raise the yield and molecular weight of the copolymer in addition to maintaining a high alternating ratio of the copolymer. (C) 2001 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.

A new type of polymer-supported metallocene catalyst for ethylene polymerization

A new polymer-supported metallocene catalyst has been prepared, The polymer-supported metallocene displayed considerably high activity in ethylene polymerization, the highest being 3.62x10(7) gPE/molZr.h, the molecular weight of the polyethylene produced was Mn = 1.29x10(5). about 3-4 times those of corresponding homogeneous zirconocenes. The polymer-supported metallocene keeps the characteristics of homogeneous metallocene catalysts, and offers some features, such as adaptable to gas phase and slurry processes: easy to prepare in low cost: relatively high activity and lower MAO/Zr ratio; lower inorganic residues in the polyolefins as compared to cases of SiO2, Al2O3 or MgCl2; unitary active structure, no complex surface as with SiO2; good control of morphology of the resulting polymer.

Preparation of poly(4-vinylpyridine)/silica hybrids supported cyclopentadienyltitanium trichloride (CpTiCl3) catalyst and styrene polymerization

Poly(4 - vinylpyridine)/silica( PVP/SiO2) organic - inorganic nanoscale hybrid was prepared using sol - gel method, in which PVP was used as an organic component and TEOS as a SiO2 precusor, This hybrid was used as CpTiCl3 support. The XPS and IR measurements showed that two kinds of catalytic active site were formed through analyzing the interaction mode between support and CpTiCl3. The results of styrene polymerization showed that syndiotactic was the highest at 50 degreesC. The catalytic activity was 1.09 x 10(6) g PS/ (mol Ti . h) at 70 degreesC when n(Al)/n(Ti) = 1500. GPC results showed a bimodal molecular weight distribution.

Controlled synthesis of L-lactide-b-epsilon-caprolactone block copolymers using a rare earth complex as catalyst

Well-defined block copolymers of L-lactide-b-epsilon-caprolactone were synthesized by sequential polymerization using a rare earth complex, Y(CF3COO)(3)/Al(iso-Bu)(3), as catalyst system. The compositions of the block copolymers could be adjusted by manipulating the feeding ratio of comonomers. The characterizations by GPC, H-1 NMR, C-13 NMR, and DSC displayed that the block copolymer, poly(epsilon-caprolactone-b-L-lactide) [P(CL-b-LLA)], had a narrow molecular weight distribution and well-controlled sequences without random placement.

The effect of preparation conditions on the catalyst Nd(P-507)(3)/H2O/Al(i-Bu)(3) for the polymerization of styrene

The catalyst system neodymium phosphonate Nd(P-507)(3)/H2O/Al(i-Bu)(3) for the polymerization of styrene was examined. Effects of the addition order of the catalyst components, catalyst aging time and aging temperature on the catalyst activity and the polymer characteristics were investigated. The catalyst activity for isospecific polymerization of styrene increases with aging time and reaches the maximum with a catalyst aged for 45 min at 70 degrees C. The aging time that the catalyst needs to reach the highest activity for isospecific polymerization decreases with increasing aging temperature. The preformed catalyst and the in situ catalyst were compared with respect to the kinetic behavior of the styrene polymerization and the polymer characteristics.

Polymer-supported zirconocene catalyst for ethylene polymerization

The use of crosslinked poly(styrene-co-4-vinylpyridine) having functional groups as the support for zirconocene catalysts in ethylene polymerization was studied. Several factors affecting the activity of the catalysts were examined. Conditions like time, temperature, Al/N (molar ratio), Al/Zr (molar ratio), and the mode of feeding were found having no significant influence on the activity of the catalysts, while the state of the supports had a great effect on the catalytic behavior. The activity of the catalysts sharply increased with either the degree of crosslinking or the content of 4-vinylpyridine in the support. Via aluminum compounds, AlR3 or methylaluminoxane (MAO), zirconocene was attached on the surface of the support. IR spectra showed an intensified and shifted absorption bands of C-N in the pyridine ring, and a new absorption band appeared at about 730 cm(-1) indicating a stable bond Al-N formed in the polymer-supported catalysts. The formation of cationic active centers was hypothesized and the performance of the polymer-supported zirconocene was discussed as well. (C) 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 37-46, 1999.

Partial oxidation of methane to syngas over Pt-Ni/Al2O3 Catalyst

The catalytic partial oxidation of methane to syngas over Ni/Al2O3, Pt/Al2O3 and a series of Pt - Ni/Al2O3 catalysts was investigated. It was found that Pt - Ni/Al2O3 catalysts exhibit higher activity and stability than Ni/Al2O3 and Pt/Al2O3. TPR and TPD methods were used to characterize Pt - Ni bimetallic interactions in the catalysts. A series of Pt - Ni/Al2O3 catalysts and unsupported Pt - Ni samples were studied by XRD and XPS. It was found the formation of Pt - Ni alloy in the Pt - Ni/Al2O3 catalysts and the enrichment of platinum on the surface of the catalysts. It is concluded that the higher activity and stability of Pt - Ni/Al2O3 catalysts were caused by Pt - Ni bimetallic interactions.

Synthesis of isotactic polystyrene with a rare-earth catalyst

Polymerization of styrene with the neodymium phosphonate Nd(P-507)/H2O/Al(i-Bu)(3) catalytic system has been examined. The polymer obtained was separated into a soluble and an insoluble fraction by 2-butanone extraction. C-13-NMR spectra indicate that the insoluble fraction is isotactic polystyrene and the soluble one is syndiotactic-rich atactic polystyrene. The polymerization features are described and discussed. The optimum conditions for the polymerization are as follows: [Nd] = (3.5-5.0) x 10(-2) mol/L; [styrene] = 5 mol/L; [Al]/[Nd] = 6-8 mol/mol; [H2O]/[Al] = 0.05-0.08 mol/mol; polymerization temperature around 70 degrees C. The percent yield of isotactic polystyrene (TY) is markedly affected by catalyst aging temperature. With increase of the aging temperature from 40 to 70 degrees C, TY increases from 9% to 48%. Using AlEt3 and Al(i-Bu)(2)H instead of Al(i-Bu)(3) decreases the yield of isotactic polystyrene. Different neodymium compounds give the following activity order: Nd(P-507)(3) > Nd(P-204)(3) > Nd(OPri)(3) > NdCl3 + C2HF5OH > Nd(naph)(3). With Nd(naph)(3) as catalyst, only atactic polystyrene is obtained. (C) 1998 John Wiley & Sons, Inc.

Layered La-Ba-Cu mixed oxides with perovskite structure as catalyst for NO reduction by CO

The mixed oxides, including LaBa2Cu3O7, LaBaCu2O5, La4BaCu5O12 with perovskite structure, were prepared. The catalysts were characterized by means of chemical analysis, XRD, H-2-TPR. It was found that their structures were layered ABO(3) perovskite structure and they were the active catalysts for the NO reduction by CO. The existence of Cu3+ is an important factor to give the catalysts a high activity for the NO reduction by CO.

Partial oxidation of methane to synthesize gas over Ni/alpha-Al2O3 catalyst promoted by noble metals

The production of synthesis gas by partial oxidation bf methane in oxygen has been examined over Ni/alpha-Al2O3 catalyst promoted by noble metals(Rh, Ru, Pt and Pd), especially with Pt. The reactivity is considered in conjunction with the result of H-2-TPR, CO-TPD, SEM and XRD. It is found that small amount of Pt results in a great improvement of activity for the Ni/alpha-Al2O3 catalyst. The activity order is : Rh-Ni>Pt-Ni approximate to Ru-Ni>Pd-Ni, meantime the Pt improves the stability of Ni/alpha-Al2O3 catalyst except for Pd which is easy to he deactivated by carbon deposition. The results of TPD, SEM and XRD indicate that there is an interaction between Ni and Pt metals in the catalyst. The interaction increases the dispersions of Pt and Nit the presence of Pt suppresses the growth and the migration of Ni grains over the surface of the catalyst.

A novel rare earth coordination catalyst for polymerization of biodegradable aliphatic lactones and lactides

A novel rare earth coordination system composed of lanthanide trifluoroacetates Ln(CF3COO)(3) (Ln = Y, Yb, Nd, Tm, Ho, La, Pr) and triisobutylaluminium Al(i-Bu)(3) was used as catalyst for the polymerization of epsilon-caprolactone (CL), D,L-lactide (DLLA) and their copolymerization. The influence of temperature, time and catalyst concentration on polymerization yields and molecular weights of the polyesters have been studied. It was shown that the ring-opening polymerization of cyclic esters catalysed by Ln(CF3COO)(3)/Al(i-Bu)(3) has some living character and the molecular weight of the polyester could be controlled by adjusting the molar ratio of monomer to catalyst. The DLLA/CL copolymer was synthesized by sequential addition of monomers and the structure of the copolyester was characterized by GPC, NMR and DSC. (C) 1998 SCI.

A novel catalyst for clean production of diphenols - Ferric trisacetylacetonate MCM-41

Ferric trisacetylacetonate has been deposited within the zeolite MCM-41 and the product characterized by XRD and IR. In water at pH 7 it catalyzes the oxidation of phenol by H2O2, giving 58% conversion in 1 h at 50 degrees C: products are catechol (66%), hydroquinone (27%) and benzoquinone (7%). Other oxidants and solvents are much less effective. UV-VIS spectra suggest a radical substitution mechanism, and a pollution-free process for phenol hydroxylation is now possible.

The polymerization of methyl methacrylate with a new Nd(O-i-Pr)(3)-Al(i-Bu)(3) catalyst system

Methyl methacrylate (MMA) was polymerized with the rare earth coordination catalyst-system of Nd(O - i-Pr)(3) in toluene. The influences of various ligands in neodymium complexes, molar ratio of Al/Nd, catalyst concentration, catalyst aging time, solvents, the third component CCl4, temperature and time on the polymerization of MMA were studied. The results showed that the polymerization conversion reached more than 80% at a catalyst concentration of 9.2 x 10(-3) mol/L. The appropriate molar ratio of CCl4/Nd was 4. Hydrocarbon was preferred for the polymerzation to obtain a high conversion and a high <(M)over bar w> of PMMA. The H-1 NMR spectra of PMMA indicated that the lower the temperature, the higher the syndiotactic content of PMMA was obtained.

Stereospecific polymerization of styrene using a homogeneous lanthanide catalyst

Stereospecific polymerization of styrene was catalyzed by homogeneous neodymium phosphonate [Nd(P-507)(3)]-H2O-Al(i-Bu)(3) catalytic system. The polymer was separated into isotactic polystyrene and atactic polystyrene by extracting the latter with boiling 2-butanone. The conversion of styrene and the yield of isotactic polystyrene (IY) were influenced by the [H2O]/[Al(i-Bu)(3)] mole ratio and the solvent polarity. The reaction is first order with respect to monomer at 70 degrees C.