MgCl2-supported Ziegler-Natta Catalysts Research Articles

Novel MgCl 2-supported catalyst containing diol dibenzoate donor for propylene polymerization

A novel MgCl 2-supported Ziegler–Natta catalyst containing 2-isoamyl-2-isopropyl-1,3-propandiol dibenzoate donor for propylene polymerization was studied, and compared with catalysts with different internal donors, such as benzoate, phthalate and diether, in polymerization dynamic behavior, activity, hydrogen response and stereospecificity. It was found that there are two highly isospecific active sites in the catalyst with dibenzoate internal donor system and the effections of temperature are different on the performances of the two highly isospecific sites.

Factors influencing chain transfer with monomer and with hydrogen in propene polymerization using MgCl2-supported Ziegler-Natta catalysts

13C and 1H NMR analysis of polypropylene prepared using various MgCl2-supported catalysts at different polymerization temperatures at different hydrogen concentrations has revealed that chain transfer with monomer, yielding vinylidene-terminated chains, is essentially unaffected by hydrogen but is dependent on catalyst selectivity. Chain transfer with hydrogen and with monomer are therefore processes which operate independently of each other, but in both cases, the incidence of chain transfer increases with decreasing catalyst (site) selectivity. Chain transfer with monomer takes place after primary insertion, while chain transfer with hydrogen takes place after either primary or secondary insertion. Chain initiation via a secondary insertion into a Ti-H species leads either to a 2,3-dimethylbutyl terminal unit, as has recently been observed in metallocene-catalyzed polymerizations, or to a further transfer reaction with hydrogen, generating traces of propane.

In Situ and Ex Situ Microscopic Study of Propylene Polymerization With Heterogeneous Mgcl2-Supported Ziegler-Natta Catalysts

Abstract The large-scale commercial production of polyolefins by catalytic Ziegler-Natta polymerization have stimulated the development of the third, fourth and fifth generation heterogeneous catalysts comprising high surface area defective MgCl2 with TiCl4, electron donors, and AlR3-co-catalysts. In spite of intensive research over the years, the present level of understanding of the catalysts is still incomplete because of their complex composition leading to a multitude of local active site environments. The aim of this work is to provide a new insight into the process via in situ video microscopy of gas phase propylene polymerization over MgCl2-supported Ziegler-Natta catalysts combined with ex situ characterization by light and electron microscopy techniques (SEM, TEM, HRTEM, STEM, PEELS and windowless EDX). Procedures for catalyst synthesis are described elsewhere. The catalysts were stored in a dry box under a He atmosphere (<lppm H2O/O2). Samples were transferred to specimen holders in the dry box and then transferred into the microscopes under high purge N2 conditions to prevent poisoning of the catalysts by air and moisture.

The particle as microreactor: catalytic propylene polymerizations with supported metallocenes and Ziegler–Natta catalysts

This paper deals with some current problems of single-particle modelling of fastly growing porous polypropylene particles. Precise kinetic measurements, investigations in monomer absorption, and microscopic morphology studies have been performed to prove the model assumptions usually made by several investigators. Both liquid pool and gas-phase polymerization have been carried out in stirred batch reactors and rates have been measured by calorimetric and mass flow measurements. Silica-supported single-site metallocenes and MgCl 2-supported Ziegler–Natta catalysts have been studied for comparison. Kinetics, absorption measurements and SEM photographs of ‘normal’ and microtomed catalysts, pre-polymers and polymer particles emphasize the need to develop more realistic single-particle models that respect the real powder morphology. Polymeric flow models, core-shell models and multi-grain models as currently used are not adequate.

Kinetic studies of the injection of comonomers during polymerization of ethene and propene with MgCl2‐supported Ziegler‐Natta catalysts

AbstractThe effects of injecting ethene, propene, 1‐hexene, 2‐methylpropene, 3,3‐dimethyl‐1‐butene, cis‐2‐butene, trans‐2‐butene, 2,3‐dimethyl‐2‐butene, cyclopentene, styrene, 1,3‐butadiene and 1,4‐pentadiene during polymerizations of ethene and propene have been investigated. Catalysts used were a supported MgCl2/EB/TiCl4 ballmilled catalyst and precipitated MgCl2/2‐EH/TiCl4/DIBP catalysts activated with triethylaluminium in presence of EB. (EB = ethyl benzoate, 2‐EH = 2‐ethylhexanol, DIBP = diisobutyl phthalate). The polymerizations were performed at 50°C, in a heptane slurry at 1 atm (1.00 · 105 Pa) total pressure.The instantaneous polymerization rate was observed by continuous monitoring of the monomer consumption, the time resolution of the measurements being less than one second. Two different kinetic effects can be observed after injection of the comonomer. First there is an immediate rate change, usually a rate reduction. Then a secondary effect may follow, which is a slow, and sometimes significant and persistent, activation. The two effects obviously have different causes, and for none of these we found single causes that can explain all the observations. The strongest immediate effect was observed after addition of dienes and indicates a direct association of the comonomer to the active center. A marked nonlinearity in the response may hint to inhomogeneity in the structural environment of the active centers. Addition of α‐olefins during ethene polymerization gave the strongest secondary effect. In general the immediate effects were stronger during propene polymerization than during the polymerization of ethene. A significant difference in the effects of cis‐2‐butene and trans‐2‐butene in the polymerization of propene indicates that steric effects may be important.

External Silane Donors in Ziegler–Natta Catalysis. A Three-Site Model Analysis of Effects on Catalyst Active Sites

A three-site model of the active sites in a MgCl2-supported Ziegler–Natta catalyst was used to simulate the effects of various external alkoxysilane donors on the catalyst active sites. The simulations correlated well with the experimental data, and it is evident that the polypropylene produced by this catalyst system originates mainly from three types of active sites. One site is a highly isospecific enantiomorphic site producing boiling heptane insoluble polymer. Two sites are responsible for the major part of the polymers of the heptane soluble firaction: a moderately isospecific enantiomorphic site (the fluctuating site) and a symmetric Bernoullian syndiospecific site. All the alkoxysilanes tested, including monoalkoxysilanes, exhibited a stabilizing role, making fluctuating sites more isospecific. In addition, the silanes having more than one alkoxy group were capable of deactivating active Ti-sites, and the selectivity of deactivation depends mainly on the size of the hydrocarbon part.

Study of hydrogen effect in propylene polymerization on (with) the MgCl 2-supported ziegler-natta catalyst—part 2. Effect of CS 2 on polymerization centres

The effect of CS 2 on the catalytic system TiCl 4/MgCl 2/DBPH-AlEt 3/TEPS in propylene polymerization in the presence and absence of hydrogen was studied. It was shown that CS 2 poisons active centres in both cases by a similar way. The yield of polypropylene decreases with the CS 2 effect, but the isotactic centres poison to the greatest degree. Results obtained by the study of polymerization kinetics, fractional comosition and molecular mass distribution of polymers permit a conclusion that there is not any differentiation between initial and “hydrogen” centres, i.e. these centres have the same nature. An observed hydrogen activation effect is explained by the revival of “dormant” centres, resulting from 2-1 propylene insertion in the polymer chain in the chain transfer reaction with H 2. Seemingly the competition between the polymerization rate retarding by irregular monomer insertion and the activation by hydrogen takes place. It leads to non-stationary kinetics of propylene polymerization in the presence of hydrogen.

Study of the effect of hydrogen in propylene polymerization with the MgCl 2-supported ziegler-natta catalyst—part 1. Kinetics of polymerization

Propylene polymerization was investigated with the TiCl 4/MgCl 4 supported catalyst with the stereoregulating donor pair dibutylphtalate (DBPH)/triethoxyphenylsilane (TEPS) in heptane with AlEt 3 as cocatalyst in the presence of hydrogen. It was shown that there is an activation effect by the influence of hydrogen. The removal of hydrogen from the polymerization medium results in an immediate disappearance of activation. However, the deactivation of the system is reversible, and it is possible to repeat the activation effect by hydrogen more than once. It was found that the value of the activation energy is the same in the presence of hydrogen and without it and is equal to 11 kcal/mol. From the experimental results it is concluded that the maximum number of active centres is realized in the catalytic system in the presence of hydrogen, but a value of the propagation rate constant is not changed. It was also found that in the presence of hydrogen the system's decay follows the bimolecular law of active centres deactivation.

特集 オレフィン類の配位重合の新展開 ＭｇＣｌ２担持型Ｚｉｅｇｌｅｒ‐Ｎａｔｔａ触媒上のアルコキシシラン化合物のＮＭＲによる解析

特集 オレフィン類の配位重合の新展開 ＭｇＣｌ２担持型Ｚｉｅｇｌｅｒ‐Ｎａｔｔａ触媒上のアルコキシシラン化合物のＮＭＲによる解析

Crystallinity and thermal properties of ethylene-1-decene copolymers

Three copolymers of ethylene and 1-decene, covering a wide range of compositions, have been synthesized with a MgCl2-supported Ziegler-Natta catalyst. The analysis by DSC and X-ray shows a great degree of heterogeneity in these copolymers and appreciable levels of crystallinity, corresponding to the orthorhombic lattice of polyethylene, are present even for very high 1-decene contents.

MgCI2-Supported Ziegler-Natta Catalysts for Olefin Polymerization: Basic Structure, Mechanism, and Kinetic Behavior

Abstract The large-scale production of polyolefins has been enhanced by the development of very high activity MgCl2-supported Ziegler-Natta catalysts. Higher activities mean lower production costs or, as in the cases of the UNIPOL or SHERIPOL gas-phase processes, new production technologies. However, despite their abundant use by industry and an intensive research effort by academic and industrical laboratories, a complete understanding of the catalyst's behavior is lacking. Not only is the catalyst a complex mixture of components (such as highly reactive aluminum alkyls) possessing multiple site types, but physicochemical phenomena such as mass transfer limitations across the gas/liquid interface in slurry reactors [58], catalyst fragmentation behavior at the start of polymerization [155], monomer transport to the active sites and heat transport away [61–63], and possible monomer sorption equilibria in the amorphous polymer regions [74] can further complicate the observed kinetics. The objective of this paper is to review the recent advances in the field in terms of its structure, mechanism, and kinetics of the catalyst based on the accumulation of results from many laboratories. The first part of the review will examine the make-up of a supported catalyst by breaking it down and analyzing its components. From this a discussion of the active site structure and mechanism will evolve. Finally, the polymerization rate kinetics will be reviewed. There is a vast amount of literature for propylene polymerizations and a dearth of publications about these catalysts with respect to their ethylene polymerization kinetics, so much of the discussion will be in reference to propylene polymerization.

Modification of olefin polymerization catalysts. III. A 13C CP-MAS NMR study of adsorption of silyl ethers on MgCl 2-supported Ziegler-Natta catalysts

A 13C CP-MAS NMR and elemental analysis study of adsorption and interaction of silyl ethers, RSi(OMe) 3 (R = Et, Ph, OMe), as internal and external electron donors with MgCl 2-supported Ziegler-Natta catalyst has been carried out. A chemical activation of anhydrous MgCl 2 with EtOH and AlEt 2 3 produces a high-surface-area support stabilized by an organoaluminium compound, AlEt 2(OEt). In a treatment of the aluminium-modified MgCl 2 support with silyl ether, the aluminium surface complex is retained and silyl ether is almost totally incorporated into the support. 13C CP-MAS NMR data of the methoxy region indicate that a mobile liquid-like silyl ether species dominates, except in the case of Si(OMe) 4, where a more strongly bound species is also present on the support. TiCl 4 treatment removes the weakly adsorbed silyl ether species, leaving a species which is attributed to an aluminium-bound silyl ether surface complex. No evidence of titanium-bound silyl ether species was found in the solid state or in solution where TiCl 4 undergoes with silyl ethers an exchange reaction forming a yellow solid identified as [TiCl 2(OMe) 2] x . Activation of the catalyst with AlEt 3 at a high Al: Ti ratio produces a material with a low silyl ether coverage showing a weak methoxy signal in 13C CP-MAS. The linewidths of the observed signals in 13C CP-MAS NMR are in the range 5–10 ppm at every stage of preparation of the catalyst, indicating heterogeneity of the coordination sites on the surface of chemically activated MgCl 2.

Stereochemical investigation of the initiation step in MgCl2-supported Ziegler-Natta catalysts: the Lewis base activation effect

The 13 C NMR analysis of the initiation step is applied to the study of the isotactic propene polymerization. Catalytic systems containing internal bases in the absence and in the presence of external bases are studied. The fact that the increase of isotactic productivity here observed, due to the presence of either internal or the external base, is accompanied by a change of the first step stereoregulatory gives evidence of the direct participation of the Lewis base on the formation of the isospecific centers

Mechanistic aspects in propene polymerization using mgcl 2-supported ziegler-natta catalysts: behaviour of silane as an external lewis base

Silane compounds such as phenyltriethoxysilane (PTES) in the presence of triethylaluminium (TEA) generate a 1:1 complex which is stable under the concentration conditions (mmol 1 −1) and temperature (70°C) used in propene polymerization, when improved MgCl 2-supported Ziegler-Natta catalysts are employed. As demonstrated by 13C and 1 NMR studies, the complexation equilibrium is displaced fully towards the formation of the complex. Under these circumstances, the amount of free external Lewis base (ELB) is much less than in other systems, with the result that ELB is better able to promote the activation of isotactic specific sites on the solid catalyst. Once active sites have been formed via interaction of free or complexed alkylaluminium with titanium, further addition of silane, up to a 1:1 ratio with Al, does not lead to poisoning of the sites. A very stable ternary complex is formed between the titanium site and the silane-complexed alkylaluminium. This complex is strongly attached to the catalyst and the exchange equilibrium between the adsorbed ELB-TEA complex and the external solution, which is quite fast when aromatic esters are used as an ELB, is very slow in this case so that high dilution of the solution or addition of further TEA has no effect on the behaviour of the catalyst. Finally, it has been shown that PTES works exclusively through its complex with TEA.

The role of ‘internal’ and ‘external’ Lewis bases in controlling the stereochemistry of highly active Ziegler–Natta catalysts

Chiral discrimination of the enantiomers of racemic α-alkenes in polymerization with highly active MgCl2-supported Ziegler-Natta catalysts is observed when (–)-menthyl benzoate is used as internal Lewis base; using (–)-menthyl benzoate as an external Lewis base leads to opposite but lower stereoelectivity.

The activation of MgCl 2-supported ziegler-natta catalysts—II : Correlation between activity and structural disorder

The properties have been examined for Ziegler-Natta catalysts comprising TiCl 4 (Ti contents 2.0, 3.4 and 4.2%) supported on MgCl 2 activated by dry ball-milling up to 250 hr. The samples have been investigated by measurements of catalytic activity in polymerization, of surface area and of some structural parameters related to the crystal disorder introduced by ball-milling. It is shown that the TiCl 4 content affects the activation; a relationship has been found between the crystal disorder of the MgCl 2 support and the catalytic activity.

The activation of MgCl 2-supported ziegler-natta catalysts: A structural investigation

A mathematical procedure for the investigation of the lattice disorder by stacking faults in polycrystalline solids has been used in studying samples of MgCl 2 activated by ball milling for various times in the presence of TiCl 4. These samples have been investigated by X-ray diffraction and by measurements of surface area, crystallite dimensions, Ti content after washing and catalytic activity in the polymerization of ethylene. A good relationship has been confirmed between activation time and activity; furthermore, the structural variations introduced by ball milling are mainly associated with rotational disorder of the Cl-Mg-Cl triple layers. Nevertheless, the analysis by X-ray diffraction is not unequivocal about the relationships between structure and activity: other significant parameters, such as the surface area and the porosity, are probably very important.