Heterogeneous Polymerization Catalysts Research Articles

Homo- and hetero-polymerization of ethylene catalyzed by α-diimine nickel complexes with hydroxyl groups

Heterogeneous olefin polymerization catalysts have received wide interests from academia and industry because their distinct advantages in thermostability, avoidance of reactor fouling and continuous production operations. In this work, hydroxy functional groups are introduced to the α-diimine nickel framework, which can serve as reactive functionality to react with MgCl2/AlRn(OEt)3-n and form ionic anchoring interaction that bind the catalyst strongly to the surface of the supports. These heterogeneous catalysts are highly active in ethylene polymerization to produce polyethylene with higher molecular weight (up to 280.5 × 104 g·mol−1), lower branching density and higher tensile strength (up to 26.7 MPa) than those generated by the homogeneous counterparts. More importantly, the nickel complexes with multiple hydroxy groups lead to high loading capacity on MgCl2/AlRn(OEt)3-n supports, affording polyethylene products with minimum inorganic contamination.

Ethylene polymerization with a crystallographically well-defined metal–organic framework supported catalyst

Crystallographic characterization of a heterogeneous ethylene polymerization catalyst elucidates a chromium–carbon bond after alkyl aluminum activation and provides mechanistic insights.

Ligand Exchange Reaction in [Co4O4]-Cobalt Cubane: A Versatile Strategy Towards the Preparation of Cobalt Cubane-based Functional Small Molecules and Polymeric Materials

Herein, we report the mechanistic and application study of ligand exchange reaction in Co4O4-cobalt cubane, a well-known water oxidation catalyst (WOC). The ligand exchange reaction involves the instantaneous dissociation of attached pyridine ligand and replacement of target ligand in an appropriate solvent. The kinetic and thermodynamic parameters were quantified for the ligand exchange reaction under mild conditions. Activation parameters revealed that the ligand exchange mechanism follows dissociative (D) or interchange-dissociative (Id) pathway in case of Co4O4, as it is evident by the high activation enthalpy (ΔH‡) and the positive activation entropy (ΔS‡) values. The effects of ligand derivatization, reaction temperature and type of the solvent on the exchange kinetics and the product purity were also investigated in detail. Furthermore, our theoretical studies disclosed the most probable ligand exchange pathway in case of Co4O4. Finally, this methodology was successfully applied to the preparation of Co4O4-containning functional poly-4vinylpyridine (P4VP) and cross-linked heterogeneous polymeric catalysts. The present mechanistic study clearly demonstrates that the ligand exchange method is an efficient and versatile method for the preparation of Co4O4-based functional materials.

Synthesis of Nanosheets Containing Uniformly Dispersed PdII Ions at an Aqueous/Aqueous Interface: Development of a Highly Active Nanosheet Catalyst for Mizoroki-Heck Reaction.

A method was developed to synthesize a nanosheet at the interface of an aqueous layer of PdII ions and an aqueous layer of hydrophilic polymer bearing a metal coordination unit (HPMC). The nanosheet was synthesized through generation of an interface by the addition of an aqueous solution of PdII ions with a low specific gravity (1.03 g/cm3) to a dispersed aqueous solution of HPMC with a high specific gravity (1.50 g/cm3), resulting in rapid cross-linking at the interface. An electron probe microanalysis mapping image showed that the PdII ions were uniformly dispersed in the nanosheet. The nanosheet showed a high catalyst activity for the Mizoroki–Heck cross-coupling reaction with a turnover number (TON) and turnover frequency (TOF) greater than 3,333,333 and 138,889 h–1, respectively. These are the greatest TON and TOF values reported for heterogeneous polymeric catalysts for the Mizoroki–Heck reaction.

Tuning the Ti3+ and Al3+ Synergy in an Al2O3/TiClx Catalyst To Modulate the Grade of the Produced Polyethylene

A multitechnique approach (comprising in situ Fourier transform infrared, diffuse reflectance ultraviolet–visible, and advanced electron paramagnetic resonance spectroscopies, coupled with differential scanning calorimetry analysis) was employed to investigate the local structure and the activation of a heterogeneous ethylene polymerization catalyst obtained by grafting TiCl4 onto a transitional alumina. The activation procedure was found to affect the electronic structure and the coordinative environment of the reduced Ti sites, as well as their interaction with the Al3+ sites, measured in terms of spin density transfer from Ti3+ to nearby Al3+ ions. It was found that the extent of interaction between the two metal sites correlates with the microstructures of the obtained polyethylene. Tuning the synergy between the Ti3+ and Al3+ Lewis acid sites is proposed as an efficient way to modulate the polyethylene microstructure, switching from a high-density polyethylene to a highly branched polyethylene.

Metal–Organic Frameworks with Pyridyl-Based Isophthalic Acid and Their Catalytic Applications in Microwave Assisted Peroxidative Oxidation of Alcohols and Henry Reaction

Reactions of 5-{(pyridin-4-ylmethyl)amino} isophthalic acid (H2L1) with copper(II), zinc(II), and cadmium(II) were studied, and the obtained metal–organic frameworks (MOFs) [{Cu(L1)(DMF)}·DMF·H2O]n (1), [Zn(L1)(H2O)]n (2), and [Cd(L1)]n (3) were characterized by elemental analysis, Fourier transform infrared spectroscopy, and X-ray single-crystal diffraction. As shown by X-ray crystallography, novel hybrid organic–inorganic coordination-driven assemblies were obtained which exhibit different two- and three-dimensional (2D and 3D) polymeric architectures. Compounds 1 and 2 have 2D structures, whereas compound 3 features a 3D network type polymer with a dimetallic core acting as a secondary building unit. These frameworks act as heterogeneous polymeric solid catalysts (the most effective one being the copper MOF 1) for solvent-free microwave assisted peroxidative oxidation of primary and secondary alcohols. They also effectively catalyze the nitroaldol (Henry) reaction of different aldehydes with nitroalkan...

Nanoporous lanthanide metal–organic frameworks as efficient heterogeneous catalysts for the Henry reaction

A series of self-assembled lanthanide coordination polymers formulated as [La(L1)2]n·1n(DMF)H·3n(DMF) (1), [Ce(L1)2]n·1n(DMF)H·2n(DMF) (2), [Sm(L1)2]n·1n(HCONH2)H·2n(HCONH2) (3), [La(L2)(HL2)(H2O)(DMF)2]n (4) and [Ce(L2)(HL2)(H2O)(DMF)2]n (5) [H2L1: 2-acetamidoterephthalic acid and H2L2: 2-benzamidoterephthalic acid] has been synthesized from the reactions of H2L1 or H2L2 with different lanthanide salts under hydrothermal conditions and characterized by elemental analysis, IR spectroscopy, X-ray single-crystal diffraction, powder X-ray diffraction, thermogravimetry and photoluminescence spectroscopy. X-ray diffraction analyses reveal that frameworks 1–3 have similar types of three-dimensional structures, composed of L12− ligands and trinuclear lanthanide nodes, in which two crystallographically independent lanthanide atoms are present. Frameworks 4 and 5 are isostructural, featuring a double chain-type one-dimensional coordination polymer which expands to 3D by means of H-bond interactions. These frameworks act as heterogeneous polymeric solid catalysts for the nitroaldol (Henry) reaction of different aldehydes with nitroalkanes, in water, and can be recycled without losing appreciable activity.

The Oxidation of Sulfur-Containing Compounds Using Heterogeneous Catalysts of Transition Metal Oxides Deposited on the Polymeric Matrix

We investigate the activity of heterogeneous catalysts of transition metal oxides deposited on the polymeric matrix in the oxidation of sulfur-containing compounds. It is shown that MnO2-10/CuO-10 has the highest catalytic activity. The physicomechanical properties of polymeric heterogeneous catalysts of transition-metal oxides, including the specific surface area, elongation at break and breaking strength, specific electrical resistance, and volume resistivity were studied by using an Inspekt mini 3 kN universal tensile machine in accordance with TCVN 4509:2006 at a temperature of 20 ± 2°C. Results show that heterogeneous polymeric catalysts were stable␣under severe reaction conditions. Scanning electron microscopy, and energy-dispersive analysis are used to study the surfaces of the catalysts. Microstructural characterization of the catalysts is performed by using x-ray computed tomography. We demonstrate the potential application of polymeric heterogeneous catalysts of transition-metal oxides in industrial wastewater treatment.

New application of cross-linked poly(N-bromoacrylamide) and poly(N-bromosuccinimide) as highly efficient and chemoselective heterogeneous polymeric catalysts for deprotection of 1,3-dithianes and 1,3-dithiolanes under mild conditions

ABSTRACTCross-linked poly(N-bromoacrylamide) (PNBA) and poly(N- bromosuccinimide) as the mild and efficient heterogeneous polymeric catalysts were applied for selective deprotection of 1,3-dithianes and 1,3-dithiolanes to their corresponding carbonyl compounds. They were also effective as a reagent in aqueous media. These methods are very simple and the polymer catalysts could be recycled several times. Deprotection of thioacetal and thioketal without enolizable hydrogens proceeded very well to give only the corresponding aldehyde and ketone in high to excellent yield. Nevertheless, in the case of thioketals carrying enolizable hydrogens, deprotection accompanied with the formation of a minor ring-expanded product is observed. However, using the PNBA/H2O system, ring expansion of these thiolketals with enolizable hydrogen was not detected. These methods provide advantages, such as chemoselectivity, easy preparation, simple work up, excellent yields, and the ability to recycle the catalyst, which makes this method more useful compared to other known methodologies.

Probing the Redox Chemistry of Titanium Silicalite‐1: Formation of Tetrahedral Ti3+ Centers by Reaction with Triethylaluminum

Transition-metal ions with open-shell configurations hold promise in the development of novel coordination chemistry and potentially unprecedented redox catalysis. Framework-substituted Ti(3+) ions with tetrahedral coordination are generated by reductive activation of titanium silicalite-1 with triethylaluminum, an indispensable co-catalyst for heterogeneous Ziegler-Natta polymerization catalysts. Continuous-wave and pulse electron paramagnetic resonance methods are applied to unravel details on the local environment of the reduced transition metal-ions, which are shown to be part of the silica framework by detection of (29)Si hyperfine interactions. The chemical accessibility of the reduced sites is probed using ammonia as probe molecule. Evidence is found for the coordination of a single ammonia molecule. Comparison to similar systems, such as TiAlPO-5, reveals clear differences in the coordination chemistry of the reduced Ti sites in the two solids, which may be understood considering the different electronic properties of the solid frameworks.

Core/Shell and Hollow Ultra High Molecular Weight Polyethylene Nanofibers and Nanoporous Polyethylene Prepared by Mesoscopic Shape Replication Catalysis

Polyvinyl alcohol (PVA) nanofibers, produced by electrospinning, represent attractive high‐surface‐area supports for olefin polymerization catalysts. Tethered with metal alkyls, PVA nanofibers immobilize a great variety of transition metal compounds, thus producing highly active nanofiber‐supported Ziegler‐, metallocene‐, and post‐metallocene catalysts. Whereas most conventional heterogeneous polymerization catalysts form particles, PVA‐nanofiber‐supported catalysts enable polyolefin nanofiber and nanostructure formation by mesoscopic shape replication using electrospun nanofibers as templates. At low ethylene pressure, linear correlation between average PE/PVA core/shell fiber diameter and polymerization time are made. At elevated pressure, this control is lost, accounting for the formation of reactor blends consisting of PE granules and built‐in PE/PVA nanofibers. Whereas conventional catalysts produce micrometer‐sized particles of ultrahigh molecular weight PE (UHMWPE), PVA‐nanofiber supported chromium catalysts afford new families UHMWPE materials. They range from UHMWPE/PVA core/shell nanofibers and nonwovens to hollow UHMWPE fibers and nanoporous UHMWPE, obtained by removing the PVA component.

Development of Olefin Polymerization Catalysts Based on Catalyst Surface Characterization and Computational Simulation of Catalysis

Isotactic polypropylene (PP) is one of the most useful plastics for modern human life. Saving energy and resources is the most important issue of the PP production. Nowadays, PP is mainly produced by gas phase process with sophisticated heterogeneous catalysts in industry. First, the history of development of PP manufacturing process is briefly reviewed and second, development of heterogeneous polymerization catalysts, studies of polymerization mechanism, are described. The importance of characterization of catalysts, especially TEM, SEM, and EDX is impressed. Simulation of polymerization based on an atomistic modeling of active sites is necessary for catalyst development to get rational working hypotheses. Finally, cluster model approach for clarifying roles of doner compounds in MgCl2 supported catalysts is presented.

Solid-State 91Zr NMR Spectroscopy Studies of Zirconocene Olefin Polymerization Catalyst Precursors

(91)Zr (I = 5/2) solid-state NMR (SSNMR) spectra of the zirconocene compounds, Cp(2)ZrCl(2), Cp*(2)ZrCl(2) (1), Cp(2)ZrBr(2) (2), (Me(3)SiC(5)H(4))(2)ZrBr(2) (3), O(Me(2)SiC(5)H(4))(2)ZrBr(2) (4), (1,3-C(5)H(3))(SiMe(2)OSiMe(2))(2)(1,3-C(5)H(3))ZrBr(2) (5), Ind(2)ZrCl(2) (6), Cp(2)ZrMeCl (7), Cp(2)ZrMe(2) (8), and [Cp(2)ZrMe][MeB(C(6)F(5))(3)] (9) have been acquired. Static (91)Zr SSNMR spectra have been acquired for all complexes at magnetic fields of 9.4 and 21.1 T. Cp(2)ZrCl(2) and complexes 1 to 5 possess relatively narrow central transition powder patterns which allows for magic-angle spinning (MAS) (91)Zr solid-state NMR spectra to be acquired at a moderate field strength of 9.4 T. Complexes 6 to 9 possess ultrawideline central transition SSNMR spectra necessitating piece-wise acquisition techniques. From the static and MAS (91)Zr SSNMR spectra, it is possible to measure (91)Zr electric field gradient (EFG) and chemical shift (CS) tensor parameters, as well as the Euler angles which describe their relative orientation. Basis sets and methods for the accurate quantum chemical calculation of (91)Zr EFG and CS tensors have been identified. The origin of the observed EFG and CS tensor parameters are further investigated by visualization of the EFG and CS tensor orientations within the molecular frames. Correlations between the observed and calculated NMR tensor parameters and molecular symmetry and structure are made. All of these observations suggest that (91)Zr SSNMR spectroscopy can be utilized to probe the molecular structure of a variety of homogeneous and heterogeneous olefin polymerization catalysts.

The effect of the compostion of heterogeneous polymerization catalyst on ethylene–1-butene copolymerization

The effect of ethylaluminium dichloride (EADC) in the heterogeneous Ziegler-Natta catalyst on the ethylene–1-butene copolymerization and the molecular structure of the resulting copolymer was investigated. SiO 2-supported TiCl 4 catalysts having different EADC/Ti molar ratio were prepared by changing the amount of EADC in feed during the catalyst preparation. Ti oxidation states of the prepared catalysts were changed with EADC/Ti molar ratio, and it contained the higher fraction of Ti(3+) and Ti(2+) at the higher EADC/Ti molar ratio. The change in EADC/Ti molar ratio of the catalyst was also shown to influence on the copolymerization performance. Xylene-solublility value corresponding to the fraction having low molecular weight with higher 1-butene content, decreased as EADC/Ti molar ratio decreased. The chemical compositional distribution of PE copolymer was shown not to be affected by EADC/Ti molar ratio of the catalyst significantly.

Semibatch Atom Transfer Radical Copolymerization of Styrene and Butyl Acrylate

AbstractSummary: Batch and semibatch butyl acrylate (BA) polymerizations are carried out using a heterogeneous atom transfer radical polymerization (ATRP) catalyst system, with excellent molecular weight (MW) control maintained at temperatures below 80 °C. A kinetic model, using rate coefficients from literature and catalyst solubility data from this study, provides a good representation of the experimental results, after modifying the model to account for the decrease in rate caused by intramolecular chain transfer. It is also demonstrated experimentally that well‐defined random, gradient, and block styrene/BA copolymers can be synthesized by manipulating monomer feed profiles in the ATRP semibatch process.

A Flat Model Approach to Tethered Bis(imino)pyridyl Iron Ethylene Polymerization Catalysts

AbstractA surface science model for a silica supported bis(imino)pyridyl iron complexes is applied to reveal the surface chemistry of these heterogeneous polymerization catalysts. The polymerization activity of these models and the molecular weight distribution of the resulting polymer are comparable to similar catalysts supported on amorphous silica. The catalyst deactivates partially during the first hour of ethylene polymerization. Based on photoelectron spectroscopy (XPS) we attribute this deactivation to iron extrusion by the aluminium alkyl activator.

Catalyst Solubility and Experimental Determination of Equilibrium Constants for Heterogeneous Atom Transfer Radical Polymerization

The solubilities of heterogeneous atom transfer radical polymerization (ATRP) catalysts are determined for the first time and used to calculate previously unquantified ATRP equilibrium constants (KATRP). These new data are essential for understanding, modeling, and designing ATRP processes with low catalyst concentrations. KATRP values for CuIBr/1,1,4,7,10,10-hexamethyltriethylenetetramine (CuIBr/HMTETA) and CuIBr/N,N,N‘,N‘,N‘ ‘-pentamethyldiethylenetriamine (CuIBr/PMDETA) are 8.66 × 10-6 and 1.44 × 10-6, respectively. The limited solubility of the CuIBr/HMTETA catalyst explains why large reductions in metal salt concentration can be made without affecting polymerization rates. Catalyst solubility and polymerization rate increase with ligand concentration. In contrast, increasing the metal salt concentration in excess of the ligand's causes a drop in catalyst solubility. This unexpected observation is attributed to the formation of insoluble catalyst networks (gels). The solubility data point to differences in the ionic character of the catalyst complexes formed. The following solubility trend is observed at ATRP conditions (toluene, 90 °C): CuIBr/PMDETA ≫ CuIIBr2/PMDETA > CuIIBr2/HMTETA > CuIBr/HMTETA.

Surface science of single-site heterogeneous olefin polymerization catalysts

This article reviews the surface science of the heterogeneous olefin polymerization catalysts. The specific focus is on how to prepare and characterize stereochemically specific heterogeneous model catalysts for the Ziegler-Natta polymerization. Under clean, ultra-high vacuum conditions, low-energy electron irradiation during the chemical vapor deposition of model Ziegler-Natta catalysts can be used to create a "single-site" catalyst film with a surface structure that produces only isotactic polypropylene. The polymerization activities of the ultra-high vacuum-prepared model heterogeneous catalysts compare well with those of conventional Ziegler-Natta catalysts. X-ray photoelectron spectroscopic analyses identify the oxidation states of the Ti ions at the active sites. Temperature-programmed desorption distinguishes the binding strength of a probe molecule to the active sites that produce polypropylenes having different tacticities. These findings demonstrate that a surface science approach to the preparation and characterization of model heterogeneous catalysts can improve the catalyst design and provide fundamental understanding of the single-site olefin polymerization process.

Hepta-coordinate halocarbonyl molybdenum(II) and tungsten(II) complexes as heterogeneous polymerization catalysts

[MX 2(CO) 3(DAB)] (M = Mo, W; X = I, Br) ( 5– 8) complexes bearing the 1,4-diazobutadiene (DAB) ligand RN C(Ph) C(Ph) NR [R = (CH 2) 3Si(OEt) 3] were immobilized in MCM-41 mesoporous silica. The tethering, stepwise procedure started with treatment of the MCM-41 mesoporous material with a toluene solution of the 1,4-diazobutadiene ligand, under reflux. The molybdenum and tungsten organometallic cores were subsequently introduced into the ligand-silicas by pore volume impregnation of a solution of the complexes [MX 2(CO) 3(NCMe) 2] (M = Mo, W; X = Br, I). The modified materials were extensively characterized by several techniques, such as FTIR, solid-state MAS and CP MAS NMR ( 13C, 29Si), powder XRD, and nitrogen adsorption–desorption measurements. These new materials (containing 2.6–2.9 wt.% Mo or 0.4–0.6 wt.% W) catalyze the ring-opening metathesis polymerization (ROMP) of norbornene (NBE) and norbornadiene at 328 K, in contrast with the very low activity exhibited by the precursor complexes and with their behavior at lower temperature. Addition of AlCl 3 as a co-catalyst enhanced the catalytic performance of the material MCM-DAB-MoBr 2 ( 12) in the ROMP of NBE.

Main kinetic features of ethylene polymerization reactions with heterogeneous Ziegler–Natta catalysts in the light of a multicenter reaction mechanism

AbstractA previously developed kinetic scheme for ethylene polymerization reactions with heterogeneous Ziegler–Natta catalysts (see Y. V. Kissin, R. I. Mink, & T. E. Nowlin, J Polym Sci Part A: Polym Chem 1999, 37, 4255 and Y. V. Kissin, R. I. Mink, T. E. Nowlin, & A. J. Brandolini, J Polym Sci Part A: Polym Chem 1999, 37, 4273, 4281) states that the catalysts have several types of active centers that have different activities and different stabilities, produce different types of polymer materials, and respond differently to reaction conditions. Each type of center produces a single polymer component (Flory component), a material with a uniform structure (copolymer composition, isotacticity, etc.) and a narrow molecular weight distribution (weight‐average molecular weight/number‐average molecular weight = 2.0). This article examines several previously known features of ethylene polymerization and copolymerization reactions on the basis of this mechanism. The discussed subjects include temperature and cocatalyst effects on the polymerization kinetics and molecular weight distribution of polymers and reaction parameter effects (temperature, ethylene and hydrogen partial pressures, and α‐olefin and cocatalyst concentrations) on the molecular weights of Flory components. The results show that the formulation of the multicenter kinetic scheme and the development of kinetic tools necessary for the application of this scheme significantly expand our understanding of the working of heterogeneous polymerization catalysts and provide additional means for their control. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1681–1695, 2001