Polymerization Of Alpha-olefins Research Articles

Stereospecific Octahedral Group 4 Bis(phenolate) Ether Complexes for Olefin Polymerization

Octahedral group 4 bisphenolate ether complexes, activated by methylaluminoxane, are highly active and stereospecific alpha-olefin polymerization catalysts. X-ray crystallographic analysis reveals the Zr and Hf complexes to be closely isostructural; the bond lengths of the Hf complex are slightly shorter, but the maximum deviation is only 0.062 A. Despite the structural similarity of the Hf and Zr complexes, the Hf complexes generate more highly stereoselective catalysts. In addition to the influence of the transition metal, the structure of the ligand has a large influence on the stereospecificity. Bis-tert-butyl phenyl substituted complexes of Hf and Zr, when activated by MAO at 50-80 degrees C, generate high molecular weight polypropylene (M(n) = 130,000-360,000 g/mol) with isotacticities [mmmm] > 97% and melting points as high as 165 degrees C.

Book Review of Tailor-Made Polymers: Via Immobilization of Alpha-Olefin Polymerization Catalysts

Book Review of Tailor-Made Polymers: Via Immobilization of Alpha-Olefin Polymerization Catalysts

Recent advances in organothorium and organouranium catalysis

In this critical review we summarize the latest results obtained during the last decade concerning the catalytic activities of organoactinide complexes. We begin with a brief summary of the synthesis and characterization of uranium and thorium complexes that later will be used as catalysts for demanding chemical transformations. Hydroamination, hydrosilylation of terminal alkynes, coupling of terminal alkynes with isonitriles, catalytic reduction of azides and hydrazines, ring opening polymerization of cyclic esters and polymerization of alpha-olefins are covered in this review (118 references). The topics covered in this review regarding organoactinide chemistry will be of interest to inorganic, organic and organometallic chemists, material and catalytic scientists due to its unique mode of activation as compared to late transition-metals. In addition, the field of organoactinide complexes in catalysis is steadily growing, because of the complementary reactivity of organoactinides as compared to other early or late transition complexes, in demanding chemical transformations.

Design of organometallic group iv heteroallylic complexes and their catalytic properties for polymerizations and olefin centered transformations

The use of metallocenes in many stoichiometric and catalytic processes has been the impetus for the development of new organometallic complexes, especially those containing early transition metals. The formation of coordinative unsaturated complexes using allylic, benzamidinate and aminopyridine families is presented. The synthesis and structural parameters of the new complexes, their activation and use in the polymerization of alpha-olefins and dienes, in the dehydrogenative coupling of silanes and in the hydroamination reactions comprise the objectives of this review.

Degenerative transfer living Ziegler-Natta polymerization: application to the synthesis of monomodal stereoblock polyolefins of narrow polydispersity and tunable block length.

The neutral dimethyl pentamethylcyclopentadienylzirconium acetamidinate, (eta(5)-C(5)Me(5))ZrMe(2)[N(t-Bu)C(Me)N(Et)], can serve as a highly active initiator for the living Ziegler-Natta polymerization of alpha-olefins to produce polyolefins of narrow polydispersity (D < or = 1.05) when "activated" through mono demethylation by a substoichiometric amount of the borate, [PhNMe(2)H][B(C(6)F(5))(4)]. The mechanism by which this living polymerization proceeds is through a process of degenerative transfer involving rapid and reversible methyl group exchange between cationic (active) zirconium propagating centers and neutral (dormant) methyl, polymeryl zirconium end groups. Facile metal-centered epimerization of the dormant species is responsible for a loss of stereocontrol during propagation that produces iso-rich material in contrast to the pure isotactic polymer microstructure obtained when degenerative transfer is not present. By turning degenerative transfer "on" and "off" between successive monomer polymerizations, a successful strategy for the production of monomodal stereoblock polyolefins of narrow polydispersity and tunable block length has been demonstrated.

Direct observation of the structural isomerization of a cationic group 4 Ziegler-Natta insertion product.

An experimental model that allows for direct observation of a structural isomerization that is relevant to the group 4 metal-mediated Ziegler-Natta polymerization of alpha-olefins is presented. More specifically, several features of this system are consistent with current theories presented for chain epimerization that occurs during propene polymerization.

Homogeneous vanadium-based catalysts for the Ziegler-Natta polymerization of alpha-olefins.

Although their activity is often inferior to that of other systems, the use of vanadium-based catalysts in homogeneous Ziegler-Natta polymerizations allows the preparation of high-molecular-weight polymers with narrow molecular-weight distributions, ethene/alpha-olefin copolymers with high alpha-olefin incorporation, and syndiotactic polypropene. The main reason for the low activity of these catalysts is their deactivation during catalysis by reduction of active vanadium species to low-valent, less active or inactive species. We here present an up-to-date review of this area with particular emphasis on the attempts to improve catalyst performance and stability by the use of additives or ancillary ligands.

Living polymerization and block copolymerization of alpha-olefins by an amine bis(phenolate) titanium catalyst.

An amine bis(phenolate) dibenzyl titanium complex having a methoxy donor on a side arm leads, upon activation with tris(pentafluorophenyl)borane, to unique living properties in alpha-olefin polymerization: exceptionally high molecular weight poly(1-hexene) is obtained in a living fashion at room temperature, living polymerization of 1-hexene is obtained above room temperature, and block copolymerization of 1-hexene and 1-octene at room temperature is described as well.

Homogeneous single-component betaine Ziegler-Natta catalysts derived from (butadiene)zirconocene precursors.

(Butadiene)zirconocene adds B(C(6)F(5))(3) at a terminal diene carbon atom to yield the zirconocene-(mu-hydrocarbyl)-borate betaine Cp(2)Zr[C(4)H(6)-B(C(6)F(5))(3)] (4). The dipolar complex 4 contains a distorted pi-allyl moiety and features an additional stabilizing Zr-F-C(arene) coordination. Under kinetic control, an isomeric betaine system is formed, characterized by an internal Zr(+).CH(2)[B](-) ion-pair interaction, that rearranges to 4 upon heating. A great variety of ansa-metallocene(butadiene) complexes and related systems cleanly form analogous metallocene-(mu-conjugated diene)-borate betaines upon treatment with B(C(6)F(5))(3) and related Lewis acids. Most of these systems represent very active homogeneous single-component Ziegler-Natta catalysts for alpha-olefin polymerization and copolymerization. In addition, these betaine catalysts are ideally suited for carrying out mechanistic studies in active Ziegler-Natta catalyst systems. They allow for an experimental observation of the first alkene insertion step at the active single-component catalyst. This feature has been used for studying the mechanism of transfer of the stereochemical information from the bent metallocene backbone and for an experimental characterization of the energy profile of the alkene addition/alkene insertion reaction sequence in active homogeneous Ziegler-Natta systems. The neutral dipolar single-component catalysts (e.g., 4) produce a polyolefin-modified R'-(CHR-CH(2))-C(4)H(6)-B(C(6)F(5))(3)(-) counterion at the end of the initiation period upon entering into the repetitive active catalytic cycle.

Toward Quantitative Prediction of Stereospecificity of Metallocene-Based Catalysts for alpha-Olefin Polymerization.

Toward Quantitative Prediction of Stereospecificity of Metallocene-Based Catalysts for alpha-Olefin Polymerization.

5625012 Process for reducing polymer build-up in recycle lines and heat exchangers during polymerization of alpha olefins

5625012 Process for reducing polymer build-up in recycle lines and heat exchangers during polymerization of alpha olefins

5604171 Catalytic system which may be used for the polymerization of alpha-olefins and process for this polymerization

5604171 Catalytic system which may be used for the polymerization of alpha-olefins and process for this polymerization

5625013 Preparation of a supported catalyst for the polymerization of alpha-olefins

5625013 Preparation of a supported catalyst for the polymerization of alpha-olefins

5608018 Alpha-Olefin polymerization catalyst system and process for producing alpha-olefin catalyst

5608018 Alpha-Olefin polymerization catalyst system and process for producing alpha-olefin catalyst

5585447 Catalyst for the (co)polymerization of alpha-olefins, a process for its preparation and (co)polymerization process making use thereof: Adisson Emmanuel; Bujadoux Karel; Fontanille Michel; Deffieux Alain Divion, France assigned to ECP-Enichem Polymeres France S A

5585447 Catalyst for the (co)polymerization of alpha-olefins, a process for its preparation and (co)polymerization process making use thereof: Adisson Emmanuel; Bujadoux Karel; Fontanille Michel; Deffieux Alain Divion, France assigned to ECP-Enichem Polymeres France S A

Advances in the catalyses of polymerizations

Abstract Nearly all technical processes for the production of polymers are carried out in the presence of catalysts. In the case of addition polymerization reactions, two mechanisms are possible: Start of the reaction via an initiator (e.g., peroxides) or start via a true catalyst (e.g., Ziegler/ Natta systems). In both areas remarkable progress has been made: Cationic “living” polymerizations of oxacycloalkanes, group transfer polymerization, metal-catalyzed alternating copolymerization of ethylene with carbon monoxide, and metallocene-catalyzed polymerizations of alpha-olefins. The polymerization of alpha-olefins with metallocene catalysts not only leads to the improvement of well-known polymers like polyethylene and polypropylene, but also enables the production of new polymers like syndiotactic polypropylene, syndiotactic polystyrene, and cycloolefin copolymers on an industrial scale.

Rheological properties and lubricity of poly-alpha-olefin oils

Oils were obtained by polymerization of alpha-olefins with a complex aluminum chloride catalyst, followed by neutralization of the polymerized product, distillation, and hydrogenation. Materials were tested to determine the kinematic viscosity at above- and below-freezing temperatures and dynamic viscosity at below-freezing temperatures. Poly-alpha-olefin oils were obtained at different levels of average molecular weight by varying the conditions of polymerization and distillation. The antiwear properties of petroleum, PAOO, and alkylbenzene oils having equal viscosities and an addition of zinc dialkyldithiophosphate were compared. The dialkylbenzene oil had strong associative-solvation properties with respect to the additive.

Ligand field effects on kinetic profiles in ethylene, alpha-olefin copolymerization

One of the more popular fields of study in inorganic chemistry revolves around the examination of the effects of ligand field changes on the reactivity patterns of transition metal ions. By varying the size, number and type of first coordination sphere ligand fields, a variety of reactivities can be induced to occur at the metal center. Employing this approach, a series of novel Ti(IV) complexes having different ligand fields has been synthesized, characterized and employed as Ti sources in high efficiency, high temperature heterogeneous Ziegler style alpha-olefin polymerization catalysts. Dramatic changes in catalyst efficiencies,exotherms and ethylene consumption rates can be induced by altering the ligand field of the Ti center. These effects are discussed in detail.

Amorphous polyolefins: A relationship between molecular structure, submolecular motion, and mechanical behavior

Abstract : The thermomechanical spectra of two series of amorphous polyolefins represented by ((CH2)m-C(CH3)2)n and ((CH2)m-C(CH3)(C2H5))n where m = 1, 2, and 3, are presented from -180C to a point above the glass transition temperature. The polymers were obtained by cationic polymerization of alpha-olefins. The mechanical spectra show a maximum in glass transition temperature and secondary transition temperature for the second member of each series. This maximum is interpreted in terms of a proposed intermolecular interlocking considered to be at a maximum for the second member of the series, and serving to restrict the submolecular motions associated with the transitions. The proposal is discussed in terms of its consequences upon free volume, density, cohesive energy density, and chain flexibility. (Author)

Morphology of Nascent Ziegler-Natta Polymers

In the polymerization of alpha-olefins with heterogeneous Ziegler-Natta catalysts, the polymer is formed directly as long fibrillar units with folder chains. It is proposed that the fibrils are formed by the crystallization of polymer chains growing from the active sites on the catalyst surface, a process which is likened to root growth in whiskers.