Transfer Catalyst Research Articles

Synthesis of Chain End Functional Isotactic Polypropylene by the Combination of Metallocene/MAO Catalyst and Organoborane Chain Transfer Agent

This paper discusses a simple and effective route to prepare chain end functionalized PP and PP diblock copolymers, with high molecular weight and high purity. The reaction scheme involves a versatile “intermediate” of borane-terminated isotactic polypropylene (PP-t-B), which was prepared under a specific reaction condition, involving an iso-specific metallocene catalyst, purified MAO activator (without TMA), 9-borabicyclononane (9-BBN) dimmer chain transfer agent, and ambient reaction temperature. During the propylene polymerization mediated by the rac-Me2Si[2-Me-4-Ph(Ind)]2ZrCl2/MAO catalyst system, the PP propagating chain end (C−Zr active site) engages in a selective ligand exchange reaction with a B−H group in the 9-BBN dimmer. Evidently, the side reaction between the 9-BBN dimmer and the purified MAO is very slow at <35 °C, so that the normal polymerization-chain transfer reaction mechanism can effectively take place to form the PP-t-B polymer. The polymer molecular weight is inversely proportional ...

Dibromotrithiocarbonate Iniferter for Concurrent ATRP and RAFT Polymerization. Effect of Monomer, Catalyst, and Chain Transfer Agent Structure on the Polymerization Mechanism

An iniferter comprising a trithiocarbonate (TTC) moiety and two bromine chain ends was prepared and used to successfully conduct, independently or concurrently, atom transfer radical polymerization...

Experimental Characterisation of Heat Transfer in Exhaust Pipe Sections

This paper describes the characterization of heat transfer in a series of 11 test sections designed to represent a range of configurations seen in production exhaust systems, which is part of a larger activity aimed at the accurate modelling of heat transfer and subsequent catalyst light-off in production exhaust systems comprised of similar geometries. These sections include variations in wall thickness, diameter, bend angle and radius. For each section a range of transient and steady state tests were performed on a dynamic test cell using a port-injected gasoline engine. In each case a correlation between observed Reynolds number (Re) and Nusselt number (Nu) was developed. A model of the system was implemented in Matlab/Simulink in which each pipe element was split into 25 sub-elements by dividing the pipe into five both axially and radially. The modelling approach was validated using the experimental data. The steady state relationship between Re and Nu allow heat transfer in the test section to be predicted with acceptable accuracy over transient test cycles and demonstrates good agreement with relationships in the literature. The model accuracy was enhanced by developing empirical models of heat transfer during the warm-up stage of the transient test.

Modified Decal Method and Its Related Study of Microporous Layer in PEM Fuel Cells

A modified version of the conventional decal transfer method for the fabrication of electrodes for polymer electrolyte membrane fuel cells is introduced. This modified method makes use of a carbon breaking layer to ensure a high catalyst transfer ratio during the process. In order to optimize this method, the effect of the thickness of the microporous layer was also studied using a thin-film/flooded agglomerate model. The structural features of the electrodes made by the modified decal method were investigated by field-emission scanning electron microscopy, electrochemical impedance spectroscopy, mercury intrusion porosimetry, and current-voltage polarization measurements. The results indicate that the modified decal method has the potential to be a reliable and facile method of fabricating electrodes with high performance.

Role of Iron-Based Catalyst and Hydrogen Transfer in Direct Coal Liquefaction

The aim of this research is to understand the major function of iron-based catalysts on direct coal liquefaction (DCL). Pyrolysis and direct liquefaction of Shenhua bituminous coal were carried out to investigate the effect of three solvents (wash-oil from coal-tar, cycle-oil from coal liquefaction, and tetralin) in a N2 or a H2 atmosphere and with or without catalyst. The hydrogen content in the solvent and liquid product and the H2 consumption for every run were calculated to understand the hydrogen transfer approach in DCL. The results showed that the iron-based catalyst promotes the coal pyrolysis, and the dominating function of the catalyst in DCL is to promote the formation of activated hydrogen and to accelerate the secondary distribution of H in the reaction system including the gas, liquid, and solid phases. The major transfer approach of the activated hydrogen is from molecular hydrogen to solvent and then from solvent to coal, and the solvent takes on the role of a “bridge” in the hydrogen tran...

π共役系高分子アーキテクチャー

π-Conjugated polymers are an attractive class of materials due to their potential applications in electronic devices, but the molecular weight and polymer end groups have not been preciously controlled because most of the polymers have been synthesized by typical step-growth condensation polymerization. However, living polymerization process in the synthesis of π-conjugated polymers has been recently attained by catalyst transfer condensation polymerization, in which the metal catalyst is transferred intramoleculary to the polymer end group of the elongated molecule. This highlight review provides the discovery and development of this polymerization method and its application to the synthesis of π-conjugated polymer architectures such as polymer brush and block copolymers.

The Alkaline Solution to the Emergence of Life: Energy, Entropy and Early Evolution

The Earth agglomerates and heats. Convection cells within the planetary interior expedite the cooling process. Volcanoes evolve steam, carbon dioxide, sulfur dioxide and pyrophosphate. An acidulous Hadean ocean condenses from the carbon dioxide atmosphere. Dusts and stratospheric sulfurous smogs absorb a proportion of the Sun's rays. The cooled ocean leaks into the stressed crust and also convects. High temperature acid springs, coupled to magmatic plumes and spreading centers, emit iron, manganese, zinc, cobalt and nickel ions to the ocean. Away from the spreading centers cooler alkaline spring waters emanate from the ocean floor. These bear hydrogen, formate, ammonia, hydrosulfide and minor methane thiol. The thermal potential begins to be dissipated but the chemical potential is dammed. The exhaling alkaline solutions are frustrated in their further attempt to mix thoroughly with their oceanic source by the spontaneous precipitation of biomorphic barriers of colloidal iron compounds and other minerals. It is here we surmise that organic molecules are synthesized, filtered, concentrated and adsorbed, while acetate and methane--separate products of the precursor to the reductive acetyl-coenzyme-A pathway-are exhaled as waste. Reactions in mineral compartments produce acetate, amino acids, and the components of nucleosides. Short peptides, condensed from the simple amino acids, sequester 'ready-made' iron sulfide clusters to form protoferredoxins, and also bind phosphates. Nucleotides are assembled from amino acids, simple phosphates carbon dioxide and ribose phosphate upon nanocrystalline mineral surfaces. The side chains of particular amino acids register to fitting nucleotide triplet clefts. Keyed in, the amino acids are polymerized, through acid-base catalysis, to alpha chains. Peptides, the tenuous outer-most filaments of the nanocrysts, continually peel away from bound RNA. The polymers are concentrated at cooler regions of the mineral compartments through thermophoresis. RNA is reproduced through a convective polymerase chain reaction operating between 40 and 100 degrees C. The coded peptides produce true ferredoxins, the ubiquitous proteins with the longest evolutionary pedigree. They take over the role of catalyst and electron transfer agent from the iron sulfides. Other iron-nickel sulfide clusters, sequestered now by cysteine residues as CO-dehydrogenase and acetyl-coenzyme-A synthase, promote further chemosynthesis and support the hatchery--the electrochemical reactor--from which they sprang. Reactions and interactions fall into step as further pathways are negotiated. This hydrothermal circuitry offers a continuous supply of material and chemical energy, as well as electricity and proticity at a potential appropriate for the onset of life in the dark, a rapidly emerging kinetic structure born to persist, evolve and generate entropy while the sun shines.

Carbenes in Synthesis and Homogeneous Catalysis

N-heterocyclic carbenes are excellent supporting ligands for Rh and Ir complexes that can act as catalysts for hydrogen transfer and Heck reactions. Recent developments on synthesis of ligands and complexes and on catalytic applications from our group are reviewed. Design of imidazolium salts to facilitate chelation is discussed as well as abnormal binding of NHCs.

Converting Step-Growth to Chain-Growth Condensation Polymerization

The development and applications of chain-growth condensation polymerization are reviewed. Well-defined aromatic polyamides, polyesters, and polyethers have been synthesized via substituent effect-assisted chain-growth condensation polymerization, in which the polymer propagating ends are more reactive than the monomers due to resonance or inductive effects between the functional groups of the terminal monomer units. Chain-growth condensation polymerization for the synthesis of aromatic polyamides has been applied to the construction of well-defined block copolymers and star-shaped polymers. Nickel-catalyzed condensation polymerization of 5-metalated 2-halothiophene has been found to proceed in a chain-growth polymerization manner. Detailed investigations revealed that this polymerization is a catalyst-transfer condensation polymerization, in which the chain-growth nature is attributable to intramolecular catalyst transfer. Phase-transfer polymerization in a solid−solution biphasic system, in which the mo...

From Polyoxometalates to Polyoxoperoxometalates and Back Again; Potential Applications

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Model-free kinetics analysis of ZSM-5 catalyzed pyrolysis of waste LDPE

Both thermal and catalytic decomposition of waste LDPE sample is studied to understand the effect of catalyst (ZSM-5) on the decomposition behaviour. The nonlinear Vyazovkin model-free technique is applied to evaluate the quantitative information on variation of E α with α for waste LDPE sample under both catalytic and noncatalytic nonisothermal conditions. The literature reported data on such variation under noncatalytic condition and effects of different catalysts on the LDPE sample are compared with the results of the present study. Results show that the optimum catalyst composition is around 20 wt.%, where the reduction in maximum decomposition temperature is around 70 °C. Presence of ZSM-5 shows similar reduction in maximum decomposition temperature as reported for Al-MCM-41 and MCM-41. Similar trend to literature reported data is observed for variation of E α with α for LDPE under nonisothermal noncatalytic condition. ZSM-5 catalyzed decomposition of the LDPE sample in the present study indicates that E α is strong and increasing function of α and consists of four steps. Cracking of large polymer fragments on the external surface of the catalyst, oligomerization, cyclization, and hydrogen transfer reactions inside the catalyst pores might be the possible reaction mechanisms involved during catalytic decomposition.

Chiral Rhodium(I) and Iridium(I) Amino−Olefin Complexes: pKa, N−H Bond Dissociation Energy, and Catalytic Transfer Hydrogenation

The chiral tetrachelating amino−olefins (R,R)-N,N‘-bis(5H-dibenzo[a,d]cyclohepten-5-yl)-1,2-diaminocyclohexane ((R,R)-trop2dach) and (S,S)-N,N‘-bis(5H-dibenzo[a,d]cyclohepten-5-yl)-1,2-diphenyl-1,2-ethylenediamine ((S,S)-trop2dpen) were prepared and used as ligands in the complexes (R,R)-[Rh(trop2dach)]OTf and (S,S)-[Rh(trop2dpen)]OTf (OTf- = CF3SO3-). Quasi-reversible reductions, d8-[RhI(trop2diamine)]+ + e- → d9-[Rh0(trop2diamine)] and d9-[Rh0(trop2diamine)] + e- → d10-[Rh-I(trop2diamine)]-, at rather negative potentials (trop2diamine = trop2dach, E1/21 = −1.83 V, E1/22 = −2.27 V; trop2diamine = trop2dpen, E1/21 = −1.78 V, E1/22 = −2.24 V; vs Fc+/Fc) indicate the donor capacity of the amine functions. One NH group in (R,R)-[Rh(trop2dach)]OTf (pKa = 15.7(2), NH bond dissociation energy (BDE) 317(2) kJ mol-1) is easily deprotonated to give the neutral amide (R,R)-[Rh(trop2dach-H)], which is quasi-reversibly oxidized at E° = −0.34 V (vs Fc/Fc+) to the radical cation (R,R)-[Rh(trop2dach-H)]•+. The pKa and BDE values of the NH group in these 16-electron complexes are lower than in related pentacoordinated 18-electron complexes. X-ray diffraction analyses show that the rhodium complexes have distorted-square-planar structures. The Rh−N bond shortens by about 7% upon deprotonation. The rhodium complexes are inactive as catalysts for transfer and direct hydrogenation of ketones. However, the distorted-trigonal-bipyramidal iridium complex (S,S)-[IrCl(CO)(trop2dpen)], where the amino−olefin ligand serves as a tridentate ligand, serves as a chiral precursor to an active phosphane-free catalyst in the transfer hydrogenation of acetophenone with 2-propanol, and the R isomer of 1-phenylethanol was obtained in 82% ee (>98% conversion when acetophenone:KOtBu:cat = 1:0.1:0.01, T = 80 °C, reaction time 1 h).

Selective carbon nanotube growth on silicon tips with the soft electrostatic force bondingand catalyst transfer concepts

To integrate a single carbon nanotube (CNT) onto a silicon tip, the area of depositedcatalyst on the apex of the silicon tip, that influences the quantity of grown CNTs, iscritical. Therefore, a method of selective CNT growth with soft electrostatic force bondingand catalyst transfer concepts has been proposed in this paper. In this work, silicon tipswere fabricated by bulk micromachining. The tiny catalyst dot on the tip apex wastransferred from a nickel-deposited sodium-ion-rich glass wafer by wafer bonding. Finally,CNTs were synthesized on the tip apexes by methane thermal chemical vapourdeposition. From the experimental results, the oriented CNTs were observed on roughly10% of the silicon tips. The yield could be further increased by optimizing thesilicon tip structure, contact pressure of soft bonding, and catalyst deposition.

The Oxidation of 3‐Aryl‐1‐propenes by Oxidative System of RuCl3—NaIO4‐Phase Transfer Catalyst.

Abstract Methyleugenol 1a was oxidized to give 3,4-dimethoxyphenylacet-aldehyde by the oxidative system containing the RuCl3-NaIO4-phase transfer catalyst. The yield and spectroscopic properties were obtained from the stable acetaldoxim 3a. Furthermore, this oxidation system could be applied to other arylpropenes, thus, safrole, 4-methoxyallylbenzene, allylbenzene, and the corresponding arylacetaldehyde formed.

The Oxidation of 3-Aryl-1-propenes by Oxidative System of RuCl3-NaIO4-Phase Transfer Catalyst

Methyleugenol 1a was oxidized to give 3,4-dimethoxyphenylacet-aldehyde by the oxidative system containing the RuCl3-NaIO4-phase transfer catalyst. The yield and spectroscopic properties were obtained from the stable acetaldoxim 3a. Furthermore, this oxidation system could be applied to other arylpropenes, thus, safrole, 4-methoxyallylbenzene, allylbenzene, and the corresponding arylacetaldehyde formed.

Process Analysis for the Production of Diacetone Alcohol via Catalytic Distillation

A three-phase nonequilibrium model developed recently in our laboratory was used to provide the optimal design and operating conditions of a catalytic distillation (CD) column for the aldol condensation of acetone. The influence of reflux flow rate, reflux ratio, reaction temperature, feed location, catalyst packing height, packed height of the nonreactive zones, reaction zone location, amount of catalyst, feed rate, and mass transfer on the conversion and product selectivity was investigated. The analysis and graphical representations were used to provide the optimal design and operating conditions of the CD column. Results obtained from our pilot CD column for the production of diacetone alcohol using Amberlite IRA-900 as a catalyst are in excellent agreement with the model predictions. This illustrates that this three-phase nonequilibrium model is effective for design, and this systematic modeling methodology can be used to provide the optimal design and operation parameters of a CD process.

Interfacial Mechanism and Kinetics of Phase-Transfer Catalysis#

As the chemical reactants reside in immiscible phases, phase transfer (PT) catalysts have the ability to carry one of the reactants as a highly active species for penetrating the interface, into the other phase where the reaction takes place, and to give a high conversion and selectivity for the desired product under mild reaction conditions. This type of reaction was termed ‘‘phase-transfer catalysis’’ (PTC) by Starks in 1971 [1]. Since then, numerous efforts have been devoted to the investigation of the applications, reaction mechanisms, and kinetics of PTC. Nowadays, PTC becomes an important choice in organic synthesis and is widely applied in the manufacturing processes of specialty chemicals, such as pharmaceuticals, dyes, perfumes, additives for lubricants, pesticides, and monomers for polymer synthesis. The global usage of PT catalysts was estimated at over one million pounds in 1996, and PTC in industrial utilization is continuously growing at an annual rate of 10–20% [2]. PTC is a very effective tool in many types of reactions, e.g., alkylation, oxidation, reduction, addition, hydrolysis, etherification, esterification, carbene, and chiral reactions [2,3].

Modeling of particle growth and morphology in the gas phase polymerization of butadiene. II. Simulation and discussion

AbstractThe improved multigrain model was used to simulate the gas phase polymerization of butadiene catalyzed by low‐, medium‐, and high‐activity catalysts, respectively. For the low‐activity catalyst, the mass and heat transfer resistances in the particle were negligible. The morphology of the polymeric particles was uniform. For the medium‐activity catalyst, the overall mass transfer effectiveness was &gt; 90%, the maximal temperature rise was 8K, and the heat transfer resistance in the particle was negligible. Mass transfer resistance does not affect the morphology of product particle significantly. For the high‐activity catalyst, the overall mass transfer effectiveness was within the range of 70–96%, the morphology of the product particle was affected by the mass transfer resistance to some extent. The maximal temperature rise was 21K; the heat transfer resistance in the particle was negligible as well. However, there was some severe mass transfer resistance in the particle, and the maximal temperature rise was ≤ 30K for the large catalyst particle with the same activity. Thus, the polymeric particle morphology was comparatively poor, with the occurrence of particle softening and sticking. © 2001 John Wiley &amp; Sons, Inc. J Appl Polym Sci 81: 730–741, 2001

Dynamic modeling and simulation of a fluidized catalytic cracking process. Part I: Process modeling

The purpose of this study is to develop a detailed dynamic model of a typical FCC unit that consists of the reactor, regenerator, and catalyst transfer lines. A distributed parameter model is presented for the reactor riser to predict the distributions of the catalyst and gas-phase velocities, the molar concentrations of 4-lump species, and the temperatures. The regenerator is also modeled in such detail that the two-regime, two-phase behavior of typical fluidized beds can be accounted for. An efficient model solver was constructed on the basis of a modular approach in which the model equations are grouped into 12 modules each corresponding to a specific part of the unit and type of equations. The dynamic model is implemented in Part II of this paper for extensive simulation study on FCC processes.

ChemInform Abstract: Synthesis of Diaryloxymethanes Using Poly(ethylene glycol) as a Phase‐ Transfer Catalyst.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.