The Experts below are selected from a list of 474 Experts worldwide ranked by ideXlab platform
Philip Mountford - One of the best experts on this subject based on the ideXlab platform.
-
ansa-Linked titanium macrocycle–imido complexes
New Journal of Chemistry, 2020Co-Authors: Nigel A. H. Male, Philip Mountford, Michael E. G. Skinner, Paul Wilson, Martin SchröderAbstract:The first ansa-linked macrocycle–imido complexes are described; they are isolobal analogues of ansa-linked Group 4 bis(cyclopentadienyl) complexes and relatives of constrained geometry cyclopentadienyl–amido Olefin Polymerisation catalysts.
-
Group 4 metal complexes for homogeneous Olefin Polymerisation: a short tutorial review
Applied Petrochemical Research, 2015Co-Authors: Richard A. Collins, Adam F. Russell, Philip MountfordAbstract:The discovery of transition metal-catalysed Polymerisation of Olefins in the 1950s by Ziegler and Natta was of huge importance. Over the last 30 years, the interest in homogenous Polymerisation has not only grown but has changed focus from primarily studying the metallocene complexes of Group 4 to widespread exploration of post-metallocene systems. This is a consequence of extensive patenting of the metallocene catalyst systems, as well as for general interest in the improvement of polyOlefin catalysis. The plastics industry produces more than 10^7 tonnes of polyethylene, polypropylene and polystyrene each year worldwide, and the study of well-defined homogenous catalysts is invaluable in uncovering the mechanism of Polymerisation and the fundamental properties of the active species. This short Tutorial Review gives an overview of homogenous transition metal Ziegler–Natta catalysis in general as well as an overview of a selection of Group 4 post-metallocene catalysts. An overview of the synthesis and reactions of alkyl cations relevant to Olefin Polymerisation is also given. Finally, this review summarises recent advances in bimetallic catalysts for Olefin Polymerisation.
-
the first rare earth organometallic complex of 1 4 7 trithiacyclononane a precursor to unique cationic ethylene and α Olefin Polymerisation catalysts supported by an all sulfur donor ligand
Chemical Communications, 2005Co-Authors: Cara S Tredget, Fanny Bonnet, Andrew R Cowley, Philip MountfordAbstract:[Sc([9]aneS3)(CH2SiMe3)3], the first rare earth organometallic complex of 1,4,7-trithiacyclonane, is a precursor to ethylene and α-Olefin Polymerisation catalysts upon activation with BArF3 or [CPh3][BArF4] (ArF = C6F5); these are the first cationic rare earth organometallic catalysts supported by an all-sulfur donor ligand.
-
transition metal imido compounds as ziegler natta Olefin Polymerisation catalysts
Advanced Synthesis & Catalysis, 2005Co-Authors: Paul D Bolton, Philip MountfordAbstract:Transition metal imido compounds having the general formula [(L)nM(NR)] [where (L)n is a supporting ligand or ligand set, and R typically is alkyl or aryl] have been known for nearly 50 years, and during the last two decades have been the focus of considerable attention. Relatively recently their potential application in the Ziegler–Natta Polymerisation of Olefins has been realised. In this contribution we review the Ziegler–Natta Polymerisation of Olefins by transition metal imido compounds. A general introduction to homogeneous Ziegler–Natta Olefin Polymerisation and key aspects of transition metal imido chemistry is given, followed by a short description of a related imido-based Polymerisation process, namely ring-opening Olefin metathesis Polymerisation catalysed by imido-supported molybdenum and tungsten alkylidenes. A summary of the “design principles” that have been employed in the development of certain imido-based Ziegler–Natta catalysts is presented, followed by a comprehensive survey of the literature in the title area.
-
Transition Metal Imido Compounds as Ziegler–Natta Olefin Polymerisation Catalysts
Advanced Synthesis & Catalysis, 2005Co-Authors: Paul D Bolton, Philip MountfordAbstract:Transition metal imido compounds having the general formula [(L)nM(NR)] [where (L)n is a supporting ligand or ligand set, and R typically is alkyl or aryl] have been known for nearly 50 years, and during the last two decades have been the focus of considerable attention. Relatively recently their potential application in the Ziegler–Natta Polymerisation of Olefins has been realised. In this contribution we review the Ziegler–Natta Polymerisation of Olefins by transition metal imido compounds. A general introduction to homogeneous Ziegler–Natta Olefin Polymerisation and key aspects of transition metal imido chemistry is given, followed by a short description of a related imido-based Polymerisation process, namely ring-opening Olefin metathesis Polymerisation catalysed by imido-supported molybdenum and tungsten alkylidenes. A summary of the “design principles” that have been employed in the development of certain imido-based Ziegler–Natta catalysts is presented, followed by a comprehensive survey of the literature in the title area.
Timothy F L Mckenna - One of the best experts on this subject based on the ideXlab platform.
-
Fragmentation, Particle Growth and Single Particle Modelling
Multimodal Polymers with Supported Catalysts, 2019Co-Authors: Timothy F L Mckenna, Muhammad Ahsan BashirAbstract:In processes that rely on the use of heterogeneous catalysis as the major means of production, it should be quite obvious that understanding how the catalyst particles evolve will play an important role in many aspects related to quality and reactor performance. At the risk of oversimplifying things, the principal roles of the heterogeneous catalyst particles used in Olefin Polymerisation can be seen as being (1) to carry the active sites upon which the polymer is formed; and (2) to provide a structure for creating “solid” particles that can be easily transported, recovered and processed. It is therefore important for us to understand how the process used to make the polymer impacts the particle and the active sites (and vice versa!). From the schema in Fig. 3.1, where these concepts are applied to a heterogeneously catalysed Olefin Polymerisation process, it can be seen that one needs to consider many different length scales, from the reactor which has volumes on the order of several tens of cubic metres, to the catalyst and polymer particles with characteristic diameters on the order of 10−6 to 10−3 m, and finally the active sites with characteristic sizes on the order of Angstroms. The figure also suggests that in many ways one can consider the catalyst and polymer particles as being at the heart of a Polymerisation process. This is of course not to over-simplify the technological challenges of correctly operating the reactors, nor to assume that we have totally mastered the behaviour of the active sites either. However, as we shall see below, the very fact that we are using heterogeneous catalysts implies that mass transfer limitations can eventually limit the concentrations of active species at the active sites, or that the quality of the polymer (sticky/hard, brittle/flexible) can have a major impact on reactor behaviour. For these, and many other related reasons it is therefore of importance to understand what happens to the particles injected into the reactor during the Polymerisation.
-
specialised tools for a better comprehension of Olefin Polymerisation reactors
Macromolecular Symposia, 2013Co-Authors: Timothy F L Mckenna, Christophe Boisson, Vincent Monteil, Elena Ranieri, Estevan TioniAbstract:Summary 2 laboratory-scale reactor systems suitable for gas phase, and for solution or slurry Polymerisations are discussed. The underlying concept behind the design and use of these reactors is that they can be used to understand the impact of conditions specific to different time scales and/or length scales inherent to large reactors that are difficult to recreate at the laboratory scale. For instance the fixed bed gas phase reactor is used to study the influence of different relative gas/solid velocities on the evolution of the molecular weight distribution of the nascent polymer. It is shown that in certain conditions, changing the heat transfer characteristics does not change the observed yield, but will impact the polymer properties. In the case of the solution reactor, the concept is to design and use a reactor to study the activation of unsupported metallocenes. Here it is shown that different metallocenes have very different activation profiles to a point where a stopped flow reactor might not be the ideal tool for their study.
-
catalytic Olefin Polymerisation at short times studies using specially adapted reactors
Canadian Journal of Chemical Engineering, 2013Co-Authors: Timothy F L Mckenna, Estevan Tioni, Maria Maddalena Ranieri, Arash Alizadeh, Christophe Boisson, Vincent MonteilAbstract:Despite the fact that the very early stages (several tens of seconds) of catalysed Olefin Polymerisation processes appear negligibly short with respect to the residence time of most industrial reactors, they are critical in terms of catalyst activation, obtaining good particle morphology, and avoiding irreparable problems caused by particle overheating. The different types of reactors that have been used over the course of the past few years are discussed in this feature article. It is shown that despite the difficulties encountered in finding the perfect experimental tool for this purpose, different configurations of stopped flow reactors can be used successfully to explore different aspects of what happens to the catalyst (supported and molecular) during these critical moments of Polymerisation. © 2012 Canadian Society for Chemical Engineering
-
dynamic modelling of a stopped flow fixed bed reactor for gas phase Olefin Polymerisation
Chemical Engineering Journal, 2012Co-Authors: Barbara Browning, Estevan Tioni, Vincent Monteil, Isabelle Pitault, Nida Sheibatothman, Timothy F L MckennaAbstract:Abstract A heterogeneous 2D dynamic model of a stopped flow fixed bed reactor for gas phase ethylene Polymerisation has been constructed and validated. The reactor contains two solid phases with accumulation of mass within the reactor bed and the experiments modelled are of very short duration (0.1–75 s). There is a good fit between measured data and calculated values, and the model results allow us to interpret the experimentally observed temperature rises. Higher than expected catalyst temperatures are found towards the reactor centre and exit which are due to the initial intensity of the Polymerisation reaction.
-
heat transfer in gas phase Olefin Polymerisation a study of particle surface interactions
Macromolecular Reaction Engineering, 2010Co-Authors: Erik Eriksson, Timothy F L Mckenna, Gunter WeickertAbstract:This work focuses on the heat exchange between a polymer particle and the reactor wall for low gas velocities. The role of different wall materials (or heat transfer conditions) is investigated with an eye to understanding how this influences the likelihood of build up of wall sheeting via melting of particles. The temperature profiles inside growing polymer particles in the vicinity of the reactor wall when it is clean (steel) or covered with a layer of non-reactive polymer are simulated. As a comparison, we have also simulated glass reactor walls to represent bench-scale Polymerisation equipment. The results can help to understand how how we can compare results from bench-scale experiments to industrial scale units.
Silvano Bresadola - One of the best experts on this subject based on the ideXlab platform.
-
mgcl2 ticl4 alet3 catalytic system for Olefin Polymerisation a xps study
Journal of Molecular Catalysis A-chemical, 2002Co-Authors: Daniele Fregonese, Antonella Glisenti, Stefano Mortara, Gian Andrea Rizzi, Eugenio Tondello, Silvano BresadolaAbstract:Abstract A variety of techniques have been applied for 40 years in order to characterise Ziegler–Natta catalysts, however, few studies report the use of surface science technologies in an effort to understand surface structure, composition and chemical bonding in MgCl2 supported catalytic system. In this paper, the synthesis and the characterisation of the MgCl2/TiCl4/AlEt3 catalyst in controlled conditions is reported. Our aim is to understand (1) the activation process of the magnesium chloride support; (2) the interaction between the magnesium chloride support and TiCl4; (3) the chemical structure of the titanium active centres formed by treatment of the procatalyst, MgCl2/TiCl4, with the co-catalyst, TEA (triethylaluminium ); (4) which Tin+ species is active in ethene and propene Polymerisations. These experiments were performed in conditions as similar, as possible, to the ones used for laboratory synthesis and Polymerisation. The experiment consists of different steps: (1) preparation of δ-MgCl2 under strictly inert atmosphere as previously reported [1] ; (2) activation of δ-MgCl2 in a UHV chamber by means of argon ion sputtering; (3) exposure to TiCl4 vapours; (4) exposure to TEA. The surface composition was checked during the experimental steps by means of XPS technique.
-
MgCl2/TiCl4/AlEt3 catalytic system for Olefin Polymerisation: a XPS study
Journal of Molecular Catalysis A-chemical, 2002Co-Authors: Daniele Fregonese, Antonella Glisenti, Stefano Mortara, Gian Andrea Rizzi, Eugenio Tondello, Silvano BresadolaAbstract:Abstract A variety of techniques have been applied for 40 years in order to characterise Ziegler–Natta catalysts, however, few studies report the use of surface science technologies in an effort to understand surface structure, composition and chemical bonding in MgCl2 supported catalytic system. In this paper, the synthesis and the characterisation of the MgCl2/TiCl4/AlEt3 catalyst in controlled conditions is reported. Our aim is to understand (1) the activation process of the magnesium chloride support; (2) the interaction between the magnesium chloride support and TiCl4; (3) the chemical structure of the titanium active centres formed by treatment of the procatalyst, MgCl2/TiCl4, with the co-catalyst, TEA (triethylaluminium ); (4) which Tin+ species is active in ethene and propene Polymerisations. These experiments were performed in conditions as similar, as possible, to the ones used for laboratory synthesis and Polymerisation. The experiment consists of different steps: (1) preparation of δ-MgCl2 under strictly inert atmosphere as previously reported [1] ; (2) activation of δ-MgCl2 in a UHV chamber by means of argon ion sputtering; (3) exposure to TiCl4 vapours; (4) exposure to TEA. The surface composition was checked during the experimental steps by means of XPS technique.
Carl Redshaw - One of the best experts on this subject based on the ideXlab platform.
-
vanadium procatalysts bearing chelating aryloxides structure activity trends in ethylene Polymerisation
Dalton Transactions, 2010Co-Authors: Carl RedshawAbstract:High-valent vanadium complexes bearing a variety of chelating aryloxides including di- and linear tri-phenolates, C/N-capped tripods, phenoxyimines and calixarenes type ligands, when used in combination with dialkylaluminium halides as co-catalyst and a reactivator, are found to act as highly active catalytic systems for α-Olefin Polymerisation. Pro-catalyst structure–catalytic activity trends can be identified for the various ligand families employed.
-
Vanadium procatalysts bearing chelating aryloxides: structure–activity trends in ethylene Polymerisation
Dalton Transactions, 2010Co-Authors: Carl RedshawAbstract:High-valent vanadium complexes bearing a variety of chelating aryloxides including di- and linear tri-phenolates, C/N-capped tripods, phenoxyimines and calixarenes type ligands, when used in combination with dialkylaluminium halides as co-catalyst and a reactivator, are found to act as highly active catalytic systems for α-Olefin Polymerisation. Pro-catalyst structure–catalytic activity trends can be identified for the various ligand families employed.
Vernon C Gibson - One of the best experts on this subject based on the ideXlab platform.
-
iron based and cobalt based Olefin Polymerisation catalysts
Scopus, 2008Co-Authors: Vernon C Gibson, Gregory A SolanAbstract:This chapter describes the brief history of iron or cobalt catalysts for Olefin Polymerisation and oligomerisation. Since the discovery in 1998 that 2,6-bis(imino)pyridine iron and cobalt halides, on activation with MAO, can convert ethylene to highly linear polyethylene, numerous reports have been concerned with ligand modification, mechanisms for precatalyst activation, identifying the active species and understanding the mode of propagation/chain transfer. In addition, heterogenisation of this class of catalysts, their incorporation into macrocycles/ polymers and their use in reactor blending/tandem catalysis has seen some important developments; alternative ligand architectures that can support active iron and cobalt catalysts are also discussed as are different types of Olefinic monomer.
-
bis benzimidazole amine vanadium catalysts for Olefin Polymerisation and co Polymerisation thermally robust single site catalysts activated by simple alkylaluminium reagents
Chemical Communications, 2004Co-Authors: Atanas K Tomov, Vernon C Gibson, Damien Zaher, Mark R J Elsegood, Sophie H DaleAbstract:Vanadium complexes containing bis(benzimidazole)amine ligands, upon activation by simple alkylaluminium reagents, give unusually robust, single-site, catalysts for Olefin Polymerisation/co-Polymerisation.
-
The nature of the active site in bis(imino)pyridine iron ethylene Polymerisation catalysts
Catalysis Communications, 2002Co-Authors: George J. P. Britovsek, Vernon C Gibson, Guy K. B. Clentsmith, David M. L. Goodgame, Stuart J. Mctavish, Quentin A. PankhurstAbstract:Mossbauer and electron paramagnetic resonance (EPR) spectroscopic studies reveal that the iron centres in bis(imino)pyridine iron(II) Olefin Polymerisation pre-catalysts of the type LFeCl2 are oxidised upon treatment with methylaluminoxane (MAO) to give an active species that contains iron solely in the +3 oxidation state. (C) 2002 Published by Elsevier Science B.V.
-
Functionalised polyOlefin synthesis using [P,O]Ni catalysts
Chemical Communications, 2001Co-Authors: Vernon C Gibson, Atanas K TomovAbstract:Nickel Olefin Polymerisation catalysts containing bulky phosphino-enolate ligands are shown to give methyl methacrylate end-functionalised polyOlefins.
-
the effect of bulky substituents on the Olefin Polymerisation behaviour of nickel catalysts bearing p o chelate ligands
Chemical Communications, 2001Co-Authors: Vernon C Gibson, Atanas K Tomov, Andrew J P White, David J WilliamsAbstract:Incorporation of bulky substituents adjacent to the oxygen donor site of [P,O]Ni catalysts affords dramatic increases in Olefin Polymerisation activities
