Olefin Polymerization Catalysis Research Articles

FI Catalysts: Unique Olefin Polymerization Catalysis for Formation of Value-added Olefin-based Materials

This review describes the olefin polymerization behavior of bis(phenoxy-imine) and bis(phenoxy-ketimine) early transition metal complexes (a.k.a. FI catalysts). FI catalysts display unique catalytic properties due to the coordination of a pair of non-symmetric, electron-withdrawing and reactive [O−, N] chelating ligands (FI ligands). Moreover, FI ligand structures can be readily tailored from the electronic and steric point of view. Thus, FI catalysts in combination with appropriate activators are capable of producing a wide variety of unique olefin-based materials (FI polymers). Specific examples of FI polymers include selective vinyl-terminated polyethylenes, ultra-high molecular weight linear polyethylenes, well-defined and controlled multimodal polyethylenes, ethylene/polar monomer copolymers, highly syndiotactic and isotactic polypropylenes with exceptionally high Tms, ethylene- and propylene-based end-functionalized polymers, a wide array of polyolefinic block copolymers from ethylene, propylene and higher α-olefins, and ultra-fine non-coherent polyethylene particles. These FI polymers display new or enhanced material properties, and to this end, several FI polymers are now entering the industrial phase.

Catalyzed chain growth (CCG) on a main group metal: an efficient tool to functionalize polyethylene

The incorporation of functional groups at the end of polyolefin chains offers an opportunity to prepare polyolefin building blocks. The latter can be used to construct polymer architectures based on polyolefins with many desirable properties. For this purpose, the reactivity of the carbon-metal bond formed during a catalytic olefin polymerization process is particularly appealing. The possibility of taking advantage of this reactivity has indeed been enhanced by the discovery of systems in which fast and reversible chain transfer reactions between the active metal center and a main group metal centre are occurring. The recent developments of this catalyzed chain growth (CCG) concept are briefly reviewed. A specific system using a (C5Me5)2NdCl2Li(OEt2)2 complex in conjunction with n-butyloctylmagnesium is then employed to synthesize an array of end functional polyethylene chains. The potential of these building blocks to build up new macromolecular architectures is discussed.

Mechanistic Detail Revealed via Comprehensive Kinetic Modeling of [rac-C2H4(1-indenyl)2ZrMe2]-Catalyzed 1-Hexene Polymerization

Thorough kinetic characterization of single-site olefin polymerization catalysis requires comprehensive, quantitative kinetic modeling of a rich multiresponse data set that includes monomer consumption, molecular weight distributions (MWDs), end group analysis, etc. at various conditions. Herein we report the results obtained via a comprehensive, quantitative kinetic modeling of all chemical species in the batch polymerization of 1-hexene by rac-C(2)H(4)(1-Ind)(2)ZrMe(2) activated with B(C(6)F(5))(3). While extensive studies have been published on this catalyst system, the previously acknowledged kinetic mechanism is unable to predict the MWD. We now show it is possible to predict the entire multiresponse data set (including the MWDs) using a kinetic model featuring a catalytic event that renders 43% of the catalyst inactive for the duration of the polymerization. This finding has significant implications regarding the behavior of the catalyst and the polymer produced and is potentially relevant to other single-site polymerization catalysts, where it would have been undetected as a result of incomplete kinetic modeling. In addition, comprehensive kinetic modeling of multiresponse data yields robust values of rate constants (uncertainties of less than 16% for this catalyst) for future use in developing predictive structure-activity relationships.

High‐Throughput Screening in Olefin‐Polymerization Catalysis: From Serendipitous Discovery Towards Rational Understanding

High-throughput-screening (HTS) tools and methods are used more and more, especially in industry, in the search for new, selective organometallic catalysts. In most cases, the approach is, in essence, empirical, and the strategy is to increase the number of experiments that can be run at a given place in a given time. Highly miniaturized, parallel reaction setups have been implemented for the rapid assessment of whether novel catalysts resulting from the structural amplification of a basic framework are "good" or "bad" with respect to the properties of interest, and, depending on the response, worthy of a subsequent, more-careful evaluation. In this article, we demonstrate that it is possible to utilize these state-of-the-art HTS platforms with a different strategy: the rapid generation of reliable kinetic data for mechanistic studies in view of a thorough understanding and rational catalyst design. Ziegler-Natta-type catalytic olefin polymerization will be used throughout as an example.

Facile Cyclometalation Reactions of Cp–Zirconium Complexes with Weakly Lewis Acidic Pendent Boron Functionalities

Methyl anion abstraction from group 4 metallocene dimethyl complexes by B ACHTUNGTRENNUNG(C6F5)3 or functionally related maingroup element Lewis acids (e.g. MAO) represents the most important activation pathway in homogeneous metallocene Ziegler–Natta olefin polymerization catalysis. It seemed tempting to search for intramolecular versions of this reaction. The simplest approach would be to attach a suitable Lewis acid functionality to the cyclopentadienyl (Cp) ring of a metallocene or related group 4 metal complex system by means of a saturated hydrocarbon tether. We and others have previously shown that such bifunctional systems are readily obtained by hydroboration of alkenyl-functionalized zirconocene dichlorides. The chemistry of related complexes with active s-hydrocarbyl ligands at the group 4 metal center proved to be more challenging. Typical previously reported examples include complexes 1 and 3 (see Scheme 1). The former turned out to be unstable with regard to “self attack” of the strongly electrophilic borane on the adjacent Cp ring. This electrophilic aromatic substitution sequence resulted in the clean formation of the stable zwitterionic product 2 with liberation of benzene. The bifunctional complex 3 was reported to react by a sequence of alkyl abstraction reactions to eventually form 4. These examples all contained the strongly electrophilic B ACHTUNGTRENNUNG(C6F5)2 group. We have now found that even systems featuring the much weaker 9-borabicycloACHTUNGTRENNUNG[3.3.1]nonane (9BBN) electrophile tethered to a Cp ring system show related reactivities. Herein we wish to describe some selected representative examples, mostly from the ZrCp3 series, that show how general such consecutive reactions take place at bifunctional alkyl group 4 metal complexes, even when a weakly Lewis acidic borane functionality is attached to a Cp ring by an oligomethylene tether. [Zr ACHTUNGTRENNUNG(allyl-Cp)ACHTUNGTRENNUNG(CH3)ACHTUNGTRENNUNG(Cp2)] (7) was synthesized along the pathway that we previously developed for the preparation of the parent [Zr ACHTUNGTRENNUNG(CH3)ACHTUNGTRENNUNG(Cp3)] complex. We have shown that it is advantageous to introduce the [Zr]-CH3 functionality at an early stage in the synthesis. Consequently, we treated the starting material [Zr ACHTUNGTRENNUNG(CH3)(Cl) ACHTUNGTRENNUNG(Cp2)] (5) with the K ACHTUNGTRENNUNG(allyl-Cp) reagent 6 (see Scheme 2). Workup of the reaction mixture from toluene eventually gave the functionalized tris(cyclopentadienyl)Zr product 7 in 55% yield. Complex 7 was characterized spectroscopically (H NMR in CD2Cl2: d=0.28/16.3 ( H/C; [Zr]-CH3), 5.64 (s, 10H; Cp), 5.25/5.66 (AA’BB’, 2H each; C5H4), 3.19 (CH2), 5.02/ 5.07 ppm (=CH2) and by X-ray crystal structure analysis (single crystals were obtained from a toluene/heptane mix[a] Dipl.-Chem. M. Emmert, Dr. G. Kehr, Dr. R. Frchlich, Prof. Dr. G. Erker Organisch-Chemisches Institut der Universit t M nster Corrensstr. 40, 48149 M nster (Germany) Fax: (+49)251-83-36503 E-mail : erker@uni-muenster.de [] This author was responsible for X-ray crystal structure analyses. Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.200900981, and contains experimental details and characterization of the compounds 7–18. CCDC721637 (10), -721638 (7), and -721639 (12) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif. Scheme 1.

Development and Application of FI Catalysts for Olefin Polymerization: Unique Catalysis and Distinctive Polymer Formation

Catalysts contribute to the efficient production of chemicals and materials in almost all processes in the chemical industry. The polyolefin industry is one prominent example of the importance of catalysts. The discovery of Ziegler-Natta catalysts in the 1950s resulted in the production of high-density polyethylenes (PEs) and isotactic polypropylenes (iPPs). Since then, further catalyst development has led to the production of a new series of polyolefins, including linear low-density PEs, amorphous ethylene/1-butene copolymers, ethylene/propylene/diene elastomers, and syndiotactic PPs (sPPs). Polyolefins are now the most important and the most produced synthetic polymers. This Account describes a family of next-generation olefin polymerization catalysts (FI catalysts) that are currently being used in the commercial production of value-added olefin-based materials. An FI catalyst is a heteroatom-coordinated early transition metal complex that combines a pair of nonsymmetric phenoxy-imine [O(-), N] chelating ligands with a group 4 transition metal. The catalytically active species derived from FI catalysts is highly electrophilic and can assume up to five isomeric structures based on the coordination of the phenoxy-imine ligand. In addition, the accessibility of the ligands of the FI catalysts and their amenability to modification offers an opportunity for the design of diverse catalytic structures. FI catalysts exhibit many unique chemical characteristics: precise control over chain transfers (including highly controlled living ethylene and propylene polymerizations), extremely high selectivity for ethylene, high functional group tolerance, MAO- and borate-free polymerization catalysis, significant morphology polymer formation, controlled multimodal behavior, high incorporation ability for higher alpha-olefins and norbornene, and highly syndiospecific and isospecific polymerizations of both propylene and styrene. These reactions also occur with very high catalyst efficiency. The reaction products include a wide variety of unique olefin-based materials, many of which were previously unavailable via other means of polymerization. We have produced selective vinyl- and Al-terminated PEs, ultrahigh molecular weight linear PEs, regio- and stereoirregular high molecular weight poly(higher alpha-olefin)s, ethylene- and propylene-based telechelic polymers, a wide array of polyolefinic block copolymers from ethylene, propylene, and higher alpha-olefins, and ultrafine noncoherent PE particles. FI catalysts are important from the organometallic, catalytic, and polymer science points of view, and the chemical industry is now using them for the production of value-added olefin-based materials. We anticipate that future research on FI catalysts will produce additional olefin-based materials with unique architectures and material properties and will offer scientists the chance to further study olefin polymerization catalysis and related reaction mechanisms.

Unusual Reactivity of N,N,N′,N′-Tetramethylethylenediamine-Coordinated Neutral Nickel(II) Polymerization Catalysts

Tmeda-coordinated species [(N,O)NiCH3(tmeda)] (tmeda = N,N,N′,N′-tetramethylethylenediamine), obtained by reaction of [(tmeda)NiMe2] with salicylaldimines, (NO)H, are reactive and versatile intermediates for olefin polymerization catalysis. Solution NMR spectroscopic studies of 1-tmeda (N,O= 2,6-(3,5-(F3C)2C6H3)2C6H3-N═CH-(3,5-I2-2-OC6H2)) revealed two major binding modes of the tmeda ligand, open κ1- and, unexpectedly, chelating κ2-fashion, which interconvert slowly on the NMR chemical shift time scale, and form equilibria with solvent complexes 1-L (L= dmso, methanol). Binding of tmeda is favored by 2−3 orders of magnitude at the temperatures studied (25 to 80 °C) over binding of solvent. Chelating κ2-coordination of tmeda renders the monoanionic bidentate salicylaldiminato ligand κ1-coordinate. Exposure of dmso solutions of 1-tmeda to excess ethylene in an NMR tube at 55 °C resulted in the very minor formation of propylene and an equilibrium mixture of Ni(II)-ethyl complexes 2-dmso and [(κ1-N,O)Ni(αCH...

Chemisorption Pathways and Catalytic Olefin Polymerization Properties of Group 4 Mono- and Binuclear Constrained Geometry Complexes on Highly Acidic Sulfated Alumina

Mono- and binuclear “constrained-geometry catalyst” (CGC) group 4 hydrocarbyls Me2Si(Me5C5)(tBuN)ZrMe2 [CGCZrMe2, 1], 1-Me2Si(3-ethylindenyl)(tBuN)ZrMe2 [EICGCZrMe2; Zr1, 2], (μ-CH2CH2-3,3′){(η5-indenyl)[1-Me2Si-(tBuN)](ZrMe2)}2 [EBICGC(ZrMe2)2, Zr2, 3], and (μ-CH2CH2-3,3′){(η5-indenyl)[1-Me2Si-(tBuN)](TiMe2)}2 [EBICGC(TiMe2)2, Ti2, 4] undergo rapid chemisorption on highly Brønsted acidic sulfated alumina (AlS) surfaces. 13C CPMAS NMR spectroscopy of the chemisorbed 13CαH3-enriched complexes EICGCZr13Me2/AlS (2*/AlS) and EBICGC(Zr13Me2)2/AlS (3*/AlS) reveals that chemisorption involves two processes, M−C σ-bond protonolysis at the strong surface Brønsted acid sites and heterolytic M−C scission with methide transfer to strong surface Lewis acid sites, forming similar “cation-like” electrophilic organo-group 4 complexes such as EICGCM13Me+. Relative rates of ethylene homopolymerization mediated by the catalysts prepared via chemisorption on AlS are 4/AlS > 2/AlS > 3/AlS > 1/AlS, for ethylene polymerization at 75 psi ethylene and 25 °C. Ethylene/1-hexene copolymerizations mediated by the same set of catalysts display relative polymerization rates of 4/AlS > 3/AlS > 2/AlS > 1/AlS, for copolymerizations at 75 psi ethylene, 0.8 M 1-hexene, and 25 °C.

Proximity and Cooperativity Effects in Binuclear d0 Olefin Polymerization Catalysis. Theoretical Analysis of Structure and Reaction Mechanism

This contribution focuses on the distinctive center-to-center cooperative catalytic properties exhibited by bimetallic "constrained geometry catalysts" (CGCs), and analyzes metal-metal proximity effects on ethylene polymerization processes mediated by (mu-CH(2)-3,3'){(eta(5)-indenyl)[1-H(2)Si((t)BuN)](ZrMe(2))}(2) (Zr(2))-derived catalysts using density functional theory. Precatalyst geometries are first discussed, and then ion-pair formation/heterolytic dissociation processes involving the binuclear bis(borane) cocatalyst 1,4-(C(6)F(5))(2)BC(6)F(4)B(C(6)F(5))(2) (BN(2)), are analyzed and compared with those in the parent mononuclear analogue. It is found that, on proceeding from the mononuclear to binuclear catalyst system, ion-pair dissociation energies increase due to the stronger catalyst center-counterdianion interactions. Moreover, in the binuclear case, the interaction energies are markedly sensitive to geometrical matching between the binuclear bis(borane) and the precatalyst Zr-methyl positions. Binuclear catalytic effects between the metal centers are then explored, with the specific contribution from the proximity of the second metal center. Possible agostic interactions of alpha-alkenes pi-coordinated to one Zr center with the second Zr center of the binuclear catalyst are scrutinized for the case of 1-octene. It is argued that these agostic interactions are at least partly responsible for the unusual enchainment properties of the bimetallic catalysts. In particular, the greater polyethylene product branch densities found experimentally for the bimetallic catalysts can be correlated with an intramolecular reinsertion process, assisted by agostic interactions. Moreover, these same agostic interactions involving a chain growing at one metal site with the second metal site of the binuclear catalyst modify the environment to increase propagation/termination rate ratios, in turn favoring increased product molecular weight (M(n)). These effects are observed experimentally at closer Zr...Zr proximities in olefin polymerizations mediated by binuclear CGC catalysts.

フェノキシ配位子を有するヒドロトリス(ピラゾリル)-ボラン配位チタン錯体の合成・同定とオレフィン重合

フェノキシ配位子を有するヒドロトリス(ピラゾリル)-ボラン配位チタン錯体の合成・同定とオレフィン重合

Group 4 Metal Complexes of Fluorous (Di)Alkoxide-(Di)Imino Ligands: Synthesis, Structure, Olefin Polymerization Catalysis, and Decomposition Pathways

The coordination chemistry of fluorous (di)alkoxide-(di)imino ligands onto Ti(IV), Zr(IV), and Hf(IV) centers has been studied. The diimino-diol [(CF3)2C(OH)CH2C(Me)═NCH2−]2 ({ONEtNO}H2) reacts selectively with Ti(OiPr)2Cl2 and Zr(CH2Ph)4 to give the corresponding complexes {ONEtNO}TiCl2 (1) and {ONEtNO}Zr(CH2Ph)2 (2), with concomitant alcohol and alkane elimination, respectively. Reactions of the imino-alcohols (CF3)2C(OH)CH2C(R1)═NR2 ({ONR1,R2}H; R1 = Me, Ph; R2 = Ph, CH2Ph) with Ti(OiPr)4 and M(CH2Ph)4 (M = Zr, Hf) gave the corresponding complexes Ti(OiPr)2{ONR1,R2}2 (3a,b) and M(CH2Ph)2{ONR1,R2}2 (M = Zr, 7a,b,c; M = Hf, 8a,b). Dibenzyl complexes 7 and 8 decompose above −30 °C by abstraction of a hydrogen from the methylene ligand backbone by a benzyl group to give M(CH2Ph){ONR1,R2}{ON−R1,R2} complexes (M = Zr, 9a−c; M = Hf, 10a), in which a ligand unit ({ON−R1,R2}) has been transformed to an α,β-unsaturated amido-alkoxy dianionic moiety. A slightly different process was observed for the pentafluoroph...

Effect of Reaction Conditions and Catalyst Design on the Rheological Properties of Polyolefins Produced in Gas‐Phase Olefin Polymerization Reactors

AbstractA model is developed to predict the viscoelastic behavior of polyolefins produced in catalytic polymerization reactors. The approach is based on the solution of different sub‐models (e.g., a kinetic model, a single particle model, a macroscopic reactor model and a rheological model). From the calculated rheological curve, the polymer melt index is determined. The ability of the proposed model to predict the viscoelastic behavior of linear polymer melts quantitatively is examined for the operation of a catalytic olefin polymerization cascade‐loop reactor process. In addition, the transient rheological properties of polyolefins produced in a Ziegler‐Natta gas‐phase olefin polymerization fluidized‐bed reactor are calculated.magnified image

Synthesis and Structural Analysis of (Cyclopentadienyl)(pyrrolide)titanium(IV) Complexes and Their Use in Catalysis for Olefin Polymerization

Cp*TiCl2(L) [L = C4H4N (1), 2,5-Me2C4H2N (2), 2,4-Me2C4H2N (3), 2,4-Me2-3-EtC4HN (4)], Cp*TiCl(2,4-Me2-3-EtC4HN)2 (5), and Cp*Ti(C4H4N)3 (6) were prepared by treating Cp*TiCl3 with the corresponding lithium salts in toluene or n-hexane. The structures of 3−6 determined by X-ray crystallography indicate that the complexes have a distorted tetrahedral geometry around Ti, and the nitrogen atom binds to Ti in an η1 fashion. The dimethyl analogues Cp*TiMe2(L) [L = C4H4N (7), 2,5-Me2C4H2N (8)] could be prepared by adopting a route that involves in situ generation of Cp*Ti(Cl)Me2, prepared by the reaction of Cp*TiCl3 with 2.0 equiv of MeLi in Et2O, and the subsequent treatment with the corresponding lithium salts. The Cp analogues CpTiCl2(L) [L = C4H4N (9), 2,5-Me2C4H2N (10), 2,4-Me2C4H2N (11), 2,4-Me2-3-EtC4HN (12)] were also prepared by treating CpTiCl3 with the corresponding lithium salts in Et2O or n-hexane. The crystallographic analyses of 9−11 indicate that the dimethylpyrrolide ligand in 10 coordinates to Ti in η5 mode, whereas the nitrogen atom in the pyrrolide ligand (in complexes 9 and 11) binds to Ti in an η1 fashion (σ bonding in addition to π donation). These complexes (1−4, 7−12) exhibited moderate catalytic activities for ethylene polymerization in the presence of methylaluminoxane (MAO), and the activities were highly affected by the substituent on the pyrrolide ligand. In the polymerization using a series of dichloro complexes, the Cp*-pyrrolide analogue 1 exhibited the highest catalytic activity, and an increase in the steric bulk led to the decrease in activity, whereas the activity of the Cp analogues increased upon increasing the steric bulk in the pyrrolide ligand. The dimethyl complexes (7, 8) exhibited notable catalytic activities in the presence of MAO, and the activities increased in the presence of iBu3Al/[Ph3C][B(C6F5)4] cocatalyst in place of MAO. The resultant polymers possessed unimodal molecular weight distributions. These complexes also exhibited moderate catalytic activities for syndiospecific styrene polymerization, and the activities of the Cp* analogues increased at high temperature.

Immobilized organometallic catalysts in the catalytic polymerization of olefins

Studies in the field of supported Ziegler-Natta catalysts employed for the polymerization of olefins that were begun by works performed under the guidance of Prof. Chirkov are reviewed in brief. The development of immobilization procedure for metallocene catalysts including the synthesis of alkylaluminoxanes heterogenized on the support surface via the partial hydrolysis of AlR3 by water contained in the support and subsequent supporting of a metallocene is described. It is revealed how the immobilization of various metallocenes on the solid surface affects the activity of the catalysts and the structure and molecular mass of the polymers. The use of immobilized organometallic catalysts for the polymerization filling of polyolefin matrices aimed at the design of new polymer composites with special characteristics and preparation of polyolefin nanocomposites is considered.

Modification of polyolefins as a modern strategy to designing polyolefin materials with a new complex of properties

Experimental data on multistage catalytic olefin polymerization processes are generalized. Such processes as the sequential homo-and copolymerization of ethylene and α-olefins; the copolymerization of ethylene and a cyclic monomer followed by postpolymerization polymer-analogous transformations via the ozonolysis of side vinylidene bonds; and the preparation of multilayer polyolefin compositions by polymerization filling make it possible to control the composition, molecular mass characteristics, supramolecular structure, and properties of polyolefins. The kinetic features of the sequential polymerization of olefins, namely, the monomer effect and the absence of the influence of the preliminary polymerization stage on the composition and molecular mass characteristics of polymer products isolated at subsequent stages, are examined. The mutual influence of components of multiphase polymer systems on the morphology and mechanical characteristics of final products is established.

Bis(imino)pyridine Iron Alkyls Containing β-Hydrogens: Synthesis, Evaluation of Kinetic Stability, and Decomposition Pathways Involving Chelate Participation

Bis(imino)pyridine iron alkyl complexes bearing beta-hydrogens, ((iPr)PDI)FeR (((iPr)PDI = 2,6-(2,6-(i)Pr2-C6H3N=CMe)2C5H3N; R = Et, (n)Bu, (i)Bu, CH2 (cyclo)C5H 9; 1-R), were synthesized either by direct alkylation of ((iPr)PDI)FeCl (1-Cl) with the appropriate Grignard reagent or more typically by oxidative addition of the appropriate alkyl bromide to the iron bis(dinitrogen) complex, ((iPr)PDI)Fe(N2)2 (1-(N2)2). In the latter method, the formal oxidative addition reaction produced ((iPr)PDI)FeBr (1-Br), along with the desired iron alkyl, 1-R. Elucidation of the electronic structure of 1-Br and related 1-R derivatives by magnetic measurements, structural studies and NMR spectroscopy established high spin ferrous compounds antiferromagnetically coupled to chelate radical anions. Thus, the formal oxidative process is bis(imino)pyridine ligand-based (one electron is formally removed from each chelate, not the iron) during oxidative addition. The kinetic stability of each 1-R compound was assayed in benzene-d6 solution and found to produce a mixture of the corresponding alkane and alkene. The kinetic stability of the iron alkyl complexes was inversely correlated with the number of beta-hydrogens present. For example, the iron ethyl complex, 1-Et, underwent clean loss of ethane over the course of three hours, whereas the corresponding 1-(i)Bu compound had a half-life of over 12 h under identical conditions. The mechanism of the decomposition was studied with a series of deuterium labeling experiments and support a pathway involving initial beta-hydrogen elimination followed by cyclometalation of an isopropyl methyl group, demonstrating an overall transfer hydrogenation pathway. The relevance of such pathways to chain transfer in bis(imino)pyridine iron catalyzed olefin polymerization reactions is also presented.

Axial Donating Ligands: A New Strategy for Late Transition Metal Olefin Polymerization Catalysis

An alpha-diimine ligand (1) containing an axial donating pyridine group is developed for late metal polymerization catalysis. Despite having no substitution on the bottom face of the ligand, the nickel and palladium complexes of 1 are highly active for ethylene polymerization, producing linear high molecular weight polymers. For example, 1-NiBr2 (3) forms PE with a Mn of up to 109 224 g/mol with 1.4 branches/1000 C's. Similarly, 1-PdMeCl (5) forms PE with a Mn of up to 880 379 g/mol with 5.1 branches/1000 C's. In sharp contrast, catalysts containing the control ligand (2) consisting of a noncoordinating phenyl group gave only low molecular weight branched oligomers. It is observed that AlMe2Cl plays a specific role in generating the active species for the pyridine-based complexes. Presumably, the pyridine group may interact with AlMe2Cl to form a bimetallic species which suppresses the beta-hydride elimination process, hence resulting in reduced chain transfer and more linear structure.

Modified mathematical model for gas phase olefin polymerization in fluidized-bed catalytic reactor

Abstract A modified model for the gas phase catalyzed olefin polymerization fluidized-bed reactors (FBR) using Ziegler–Natta catalyst is presented in this study. This mathematical model accounts for mass and heat transfer between the bubbles and the clouds without chemical reaction, between the clouds and the emulsion without chemical reaction, and between emulsion and solid with chemical reaction that occurs at the surface of the catalyst particles. The model accounts for the effect of catalyst particles type and porosity on the rate of reaction. In this work, the concentration and temperature profiles in the bubble, and emulsion phases are calculated and the effect of catalyst solid phase on the system is estimated. The effect of important reactor parameters such as superficial gas velocity, catalyst injection rate, and catalyst particle growth on the dynamic behavior of the FBR is investigated and the behavior of mathematical model is compared with the reported models for the constant bubble size model , well - mixed model and bubble growth model . Moreover, the results of the model are compared with the experimental data in terms of molecular weight distribution and polydispersity of the produced polymer at steady state. A good agreement is observed between our model prediction and the actual plant data.

Catalytic Emulsion Polymerization of Olefins: Ab-Initio Polymerization of a Family of Norbornene-Derived Monomers

The use of late transition metal catalysts for the polymerization of olefins in aqueous media has created new opportunities to produce latex particles based on ethylene and its olefinic derivatives. In this work we report on the production of water-based latices from a variety of monomers based on the strained cyclic olefin, norbornene. These have been carried out as ab-initio batch emulsion polymerizations using allylpalladium catalysts and a lithium borate activator as well as sodium dodecyl sulfate surfactant. We find that the n-alkylnorbornenes can be polymerized in aqueous emulsion and that the mechanisms for latex particle formation are likely the same as that for norbornene monomer alone. The latex particles created are small, averaging about 45 nm in diameter. As in the case of norbornene, large amounts of coagulum can be formed if the catalyst and activator are allowed to reach the emulsified monomer droplets and effect polymerization in that location. As the substituents on the norbornene become larger and nonpolar, it is necessary to consider their effect on the water solubility of the monomers in order to analyze the experimental results in an effective manner. Our studies included butyl- and decylnorbornene, vinyl- and butenylnorbornene, and methanol−norbornene.

Mathematical Model and Advanced Control for Gas-phase Olefin Polymerization in Fluidized-bed Catalytic Reactors

In this study, the developments in modeling gas-phase catalyzed olefin polymerization fluidized-bed reactors (FBR) using Ziegler-Natta catalyst is presented. The modified mathematical model to account for mass and heat transfer between the solid particles and the surrounding gas in the emulsion phase is developed in this work to include site activation reaction. This model developed in the present study is subsequently compared with well-known models, namely, the bubble-growth, well-mixed and die constant bubble size models for porous and non porous catalyst. The results we obtained from the model was very close to the constant bubble size model, well-mixed model and bubble growth model at the beginning of the reaction but its overall behavior changed and is closer to the well-mixed model compared with the bubble growth model and constant bubble size model after half an hour of operation. Neural-network based predictive controller are implemented to control the system and compared with the conventional PID controller, giving acceptable results.