MgCl2-supported Catalyst Research Articles

Temperature effect on the kinetic profile of Ziegler–Natta catalyst in propene polymerization

Propene polymerization kinetic profiles with a diether-based Ziegler–Natta MgCl2-supported catalyst were investigated in a stainless-steel batch reactor. The initial 10 min period characterizes various temperature levels with a constant volume of liquid propene. The lowest temperature level corresponds to the usual prepolymerization temperature (10 °C), and the highest level corresponds to the usual main polymerization temperature (70 °C). The effects of the starting temperature levels were evaluated through polymerization kinetic patterns computed namely from the second polymerization period carried out at 70 °C for the next 90 min. Based on the heat transfer data, the kinetic profiles were fitted to suitable semi-empirical equations derived from fundamental kinetic approaches using the first and second orders of the catalyst active sites decay. Both approaches adequately describe the dependence of the initial activities and deceleration constants on the temperature during the initial period.

Mechanistic study on comonomer effect in ethylene/1-hexene copolymerization with TiCl4/MgCl2 model Ziegler-Natta catalysts

Two MgCl2-supported Ziegler-Natta model catalysts were prepared by contacting activated MgCl2 with deficient or excess amount of TiCl4. Ethylene/1-hexene copolymerization with the catalysts was conducted under different 1-hexene feed, and active center concentration of the reaction system was determined by quench-labeling method using thiophene-2-carbonyl chloride as the quencher. The catalytic activity was only moderately enhanced (increment <50%) by adding 1-hexene in ethylene polymerization with the model catalyst (Cat-1) of 0.1 wt% Ti content, and the active center ratio ([C*]/[Ti]) was only slightly increased (from 64 to 72 mol%). The comonomer activation effect in Cat-1 catalyzed copolymerization was mainly attributed to increase of apparent propagation rate constant by the comonomer, which can be explained by reduction of mass transfer barrier in the polymer/catalyst particles because of larger monomer diffusion coefficients in the copolymer phase than in the more crystalline polyethylene phase. In contrast, the activity was nearly tripled by adding 1-hexene when the catalyst of 1.47% Ti content (Cat-2) was used, meanwhile its [C*]/[Ti] was also tripled (from 15 to 49 mol%). The strong comonomer activation effect in Cat-2 catalyzed copolymerization was caused by marked increase of active center concentration. In this case, fragmentation of the polymer/catalyst particles was intensified by adding the comonomer, and more active centers that were originally inaccessible to the cocatalyst and monomer were exposed through the particle fragmentation. According to the results of this work, the comonomer effect in conventional supported Ziegler-Natta catalysts can be explained by the combination of physical factor (increase in diffusion coefficient) and chemical factor (exposure of inaccessible active center precursors through particle fragmentation).

Effects of Various Amounts of New Hepta-Ether as the Internal Donor on the Polymerization of Propylene with and without the External Donor

The new hepta-ether compound as the internal donor was synthesized using the Williamson reaction of dipentaerythritol with sodium hydride as the strong base and iodomethane as the alkyl halide. The hepta-ether compound was characterized by NMR, FTIR, and GC techniques. The MgCl2-supported catalysts incorporated with different amounts of hepta-ether compound as the internal donor and without the internal donor were synthesized and characterized. The propylene polymerization was carried out using these catalysts in the presence of triethylaluminum as a co-catalyst and hydrogen as a chain transfer agent, with and without the external donor. The effect of a new internal donor on propylene polymerization using prepared MgCl2-supported Ziegler-Natta catalysts was investigated.

New penta-ether as the internal donor in the MgCl2-supported Ziegler-Natta catalysts for propylene polymerization

The penta-ether compound was synthesized by the reaction of di(trimethylolpropane) with sodium hydride as the strong base and methyl iodide as the alkyl halide. This compound was characterized by NMR, FTIR, and GC techniques. The MgCl2-supported titanium catalysts were incorporated with varying amounts of penta-ether compound as the internal donor and also the catalysts without the internal donor were synthesized. The synthesized catalysts and the conventional Ziegler- Natta catalyst were characterized. The titanium contents were determined by spectrophotometry, magnesium by complexometric titration and chloride by argentometric titration. The effects of the new internal donor on propylene polymerization with the prepared MgCl2-supported Ziegler-Natta catalysts were investigated and then these results were compared to the results obtained using the conventional diisobutyl phthalate-besed-Ziegler-Natta catalyst. The highest crystallinity degree, melting temperature, and isotacticity of polypropylene were obtained using the catalyst with a penta-ether/Mg molar ratio equal to 0.21.

Preparation of ultra high molecular weight polyethylene with MgCl2/TiCl4 catalyst: Effect of hydrogen and cocatalyst on molecular weight and molecular weight distribution

The ultra high molecular weight polyethylene (UHMWPE) of a special class of HDPE was a linear polyethylene (PE) with a molecular weight numbering in the millions and was also known as high modulus PE or high performance PE. UHMWPE was a unique polymer with outstanding physical and mechanical properties. Most notable were its chemical inertness, lubricity, impact resistance and abrasion resistance. These properties of UHMWPE have been exploited in a wide range of industrial applications, including pickers for textile machinery, lining for coal chutes and dump trucks, runners for bottling production lines, as well as bumpers and siding for ships and harbors. Ethylene polymerization by typical MgCl2-supported Tibased catalysts, and trialkylaluminiums was the most commonly used cocatalyst. On the other hand, H2 is known to be the most efficient industrial regulator of the molecular weight of the olefin polymerization as a chain transfer agent. The use of H2 as a molecular weight regulator was based on the hydrogenolysis of metal to polymer bonds, and the rate of chain transfer to H2 was substantially higher than others. As reported by Hindryckx, the catalyst activity and the molecular weight drastically decreased with the introduction of H2 for ethylene polymerization, while the PDI increased with the increasing H2 pressure. It is well known that molecular weight distribution has a significant effect on the processability and end-use properties of olefin polymers. Therefore, it is necessary to control the molecular weight distribution of polyolefin to produce various grades suitable for the many end-use applications of polyolefin. However, the effects of H2 and cocatalyst on PDI value of UHMWPE have not been reported until now. Therefore, the aim of the present work was to study the effect of H2 feed ratio, H2 feeding time (tH) and cocatalyst on activity, thermal property, molecular weight and molecular weight distribution of UHMWPE produced by using MgCl2-supported Ti catalyst systems. The molecular weight distribution of UHMWPE was analyzed through both GPC and rheometry measurements in this study.

Effect of EtOH/MgCl2 Molar Ratios on the Catalytic Properties of MgCl2-SiO2/TiCl4 Ziegler-Natta Catalyst for Ethylene Polymerization

MgCl2-SiO2/TiCl4 Ziegler-Natta catalysts for ethylene polymerization were prepared by impregnation of MgCl2 on SiO2 in heptane and further treatment with TiCl4. MgCl2·nEtOH adduct solutions were prepared with various EtOH/MgCl2 molar ratios for preparation of the MgCl2-supported and MgCl2-SiO2-supported catalysts in order to investigate the effect on polymerization performance of both catalyst systems. The catalytic activities for ethylene polymerization decreased markedly with increased molar ratios of [EtOH]/[MgCl2] for the MgCl2-supported catalysts, while for the bi-supported catalysts, the activities only decreased slightly. The MgCl2-SiO2-supported catalyst had relatively constant activity, independent of the [EtOH]/[MgCl2] ratio. The lower [EtOH]/[MgCl2] in MgCl2-supported catalyst exhibited better catalytic activity. However, for the MgCl2-SiO2-supported catalyst, MgCl2 can agglomerate on the SiO2 surface at low [EtOH]/[MgCl2] thus not being not suitable for TiCl4 loading. It was found that the optimized [EtOH]/[MgCl2] value for preparation of bi-supported catalysts having high activity and good spherical morphology with little agglomerated MgCl2 was 7. Morphological studies indicated that MgCl2-SiO2-supported catalysts have good morphology with spherical shapes that retain the morphology of SiO2. The BET measurement revealed that pore size is the key parameter dictating polymerization activity. The TGA profiles of the bi-supported catalyst also confirmed that it was more stable than the mono-supported catalyst, especially in the ethanol removal region.

Dependence of comonomer effect and hydrogen effect on internal donor in ethylene/1-hexene copolymerizations with MgCl2-supported catalysts

AbstractEthylene homopolymerization and copolymerizations with 1-hexene by three types of MgCl2-supported catalysts were compared. Cat-1 contains no internal electron donor (ID), Cat-2 contains phthalic anhydride (PA) as ID, and Cat- 3 contains anisole as ID. The influences of two kinds of ID on comonomer effect, the role of hydrogen, polymerization kinetics in ethylene/1-hexene copolymerization were investigated. The addition of ID improves the catalysts activities in ethylene polymerization. In comparison with ethylene homopolymerization, these ethylene/1-hexene copolymerization systems all showed strong comonomer effects. However, internal donor, especially anisole, weakens the extent of comonomer activity enhancement. When the concentration of 1-hexene is 0.6 mol/L, catalysts activities increase remarkably with adding a small amount of hydrogen. But, the addition of ID reduces the sensitivity of catalyst activity to hydrogen. The introduction of anisole increases the homo-polymerization rate rapidly at the initial stage, but makes it decay earlier. In ethylene/1-hexene copolymerization with hydrogen, the addition of phthalic anhydride as ID can stabilize the polymerization rate, but anisole accelerates the decaying trends. The results are discussed based on a kinetic mechanistic model of the ID effect on ethylene copolymerization.

A new strategy to prepare branching polyethylene by using an α-diimine nickel (II) complex covalently supported on MgCl2/AlRn(OEt)3-n

A new strategy was developed to prepare MgCl2-supported nickel-diimine catalysts for ethylene polymerization, in which an amino-functionalized nickel-diimine complex, bis(4-(4-amine-3,5-diisopropylbenzyl)-2,6-diisopropylphenylimino)acenaphtheneNiBr2 (abbreviaed as NiLBr2), was covalently supported on MgCl2/AlRn(OEt)3-n. The most significant feature of the supported catalyst is that it polymerizes ethylene with high activities in the presence of inexpensive general alkylaluminum compounds. According to the results of high temperature GPC, the number-average molecular weights of the polymers ranged from 0.35 × 106 to 1.08 × 106 and the polydispersities ranged from two to three. By modulating the polymerization temperatures, the products of different morphologies were obtained. The resultant PE was confirmed by 13C NMR to contain significant amounts of not only methyl but also ethyl, propyl, butyl, amyl, and long branches (longer than six carbons).

Theoretical investigation of (MgCl2)xpolynuclear species formed during preparation of MgCl2-supported Ziegler–Natta catalysts from solid solvates

A novel approach for the study of the nature of the active species in Ziegler–Natta catalysis is described. This approach is based on the study of reliable structural models for disordered (MgCl2)xpolynuclear species which develop during the preparation of MgCl2-supported catalysts starting from MgCl2–Lewis-base adducts, and the calculation of X-ray diffraction patterns of these models. A method for the calculation of the X-ray powder diffraction patterns of the model structures is devised. This diffraction modelling method may be useful for the correct interpretation of the nature of some diffraction features in the X-ray diffraction patterns recorded during the structural evolution of MgCl2–Lewis-base adducts, which occurs in the preparation of the catalyst systems used for Ziegler–Natta polymerization of olefins.

SUPPORTED ZIEGLER-NATTA CATALYSTS FOR ETHYLENE SLURRY POLYMERIZATION AND CONTROL OF MOLECULAR WEIGHT DISTRIBUTION OF POLYETHYLENE

The effect of chemical composition of highly active supported Ziegler-Natta catalysts with controlled morphology on the MWD of PE has been studied. It was shown the variation of transition metal compound in the MgCl2-supported catalyst affect of MWD of PE produced in broad range: Vanadium-magnesium catalyst (VMC) produce PE with broad and bimodal MWD (Mw/Mn = 14−21). MWD of PE, produced over titanium-magnesium catalyst (TMC) is narrow or medium depending on Ti content in the catalyst (Mw/Mn = 3.1−4.8). The oxidation state of the initial titanium compounds in TMC has only slight effect on MWD of PE produced. Based on MWD data of PE heterogeneity of active centers of TMC and VMC was studied. The results of resolution of experimental GPC curves into Flory components indicated three Flory components are sufficient to describe MWD curve of PE, produced with TMC; six Flory components are required in the case of VMC. In the case of copolymerization of ethylene with 1-hexene over TMC the addition of 1-hexene leads to decrease of MW and to slight effect on Mw/Mn values. On the contrary the strong effect of 1-hexene on MWD of PE produced over VMC was found: the introduction of 1-hexene results in considerable broadening of MWD due to the shifting of the main MWD peak to low MW region. At that comonomer doesn't affect the position of high molecular weight shoulder. The results indicate that some of active centers of VMC producing high MW polymer are not active in the reaction of chain transfer with comonomer.

Synergetic Effect of a Nickel Diimine in Ethylene Polymerization with Immobilized Fe-, Cr-, and Ti-Based Catalysts on MgCl2 Supports

Significant increases in the productivity of iron-, chromium-, and titanium-based MgCl2-supported catalysts for ethylene polymerization have been obtained by incorporation of a limited amount of a nickel diimine catalyst giving branched polyethylene. Formation of the latter during the early stages of polymerization reduces the monomer diffusion limitation inherent in ethylene homopolymerization, thereby increasing the productivity of the main catalyst component. The final products are essentially linear, high-density polyethylenes containing very small amounts of branched polymer. As well being effective for catalysts prepared by coimmobilization of the Ni and Fe, Cr, or Ti component on the MgCl2 support, it is also shown that the productivity of preformed Ziegler−Natta catalysts can be improved significantly by impregnation with the nickel diimine component. In the latter case, more rapid increases in rate throughout the polymerization indicated easier fragmentation of the support in the presence of the ...

Studies on Synthesis of Low Isotactic Polypropylene by Using a Novel MgCl2-supported and Low Ti-loading Catalyst

: A novel, MgCl2-supported catalyst with 0.8 wt.% Ti-loadings is prepared using a new one-pot ball milling method that can control the Ti-loadings expediently. Propylene polymerization and polymerization kinetics with this novel catalyst have been investigated. The effects of Al/Ti ratio, polymerization temperature, and catalyst concentration on catalytic activity, polymerization kinetics, and soluble weight fraction of the resultant polymer in boiling heptane (SWFBH) were studied in detail. The maximum of catalytic activity can be obtained at the Al/Ti molar ratio 40 and the polymerization temperature 40°C. It was found that with the variation of catalyst concentration during polymerization, the SWFBH changed little, but the catalytic activity existed at a maximum. With the decrease of polymerization temperature, the SWFBH increased. It can be concluded that this novel, MgCl2-supported and low Ti-loading catalyst has a high activity (3.5 kg PP/g Ti.h), its soluble weight fraction in boiling heptane can reach 74.3%, and it is suitable to prepare the polypropylene with a high nonstereoregular structure.

Development of Single-Site New Olefin Polymerization Catalyst Systems Using MgCl2-Based Activators: MAO-Free MgCl2-Supported FI Catalyst Systems

Abstract MAO-free new single-site catalyst systems have been developed for olefin polymerization, which are comprised of bis(phenoxy-imine) Ti, Zr, or V complexes (Ti–, Zr–, or V–FI Catalysts) and MgCl2-based compounds. These new catalyst combinations are highly active single-site (Ti–FI Catalysts), exceptionally active (Zr–FI Catalysts), or highly active, thermally robust, single-site (V–FI Catalyst) catalysts for ethylene polymerization. The catalysts can display higher catalytic performance (i.e., catalytic activity, stereoselectivity, thermal stability) than those activated by the well-established MAO activators. In addition, these catalysts are supported, and thus possess a technological advantage vis-à-vis control over polymer morphology, which is essential for commercial application. Therefore, the application of MgCl2-based compounds capable of working both as an activator and a support for non-metallocene complexes provides a conceptually new strategy for the development of high-performance supported single-site catalysts.

Propene/Ethene-[1-13C] Copolymerization as a Tool for Investigating Catalyst Regioselectivity. 2. The MgCl2/TiCl4−AlR3System

The propene/ethene-[1-13C] copolymerization method has been applied to measure precisely the regioselectivity in propene polymerization of the “simple” MgCl2/TiCl4 catalyst (activated with Al(iBu)3), which can be viewed as the ancestor of all present-day MgCl2-supported industrial catalysts containing Lewis bases as selective modifiers. It has been found that the average content of 2,1-regiomistakes in the polypropylene produced is fairly high (ca. 0.7 mol %), althoughnot unexpectedly, due to the multisite catalyst naturethese are distributed rather nonuniformly throughout the polymer. The difficulty in detecting the 2,1-units, despite their relatively high concentration, in the 13C NMR spectra of homopolymer samples at natural 13C abundance has been traced to their occurrence in a variety of stereochemical environments, which leads to splitting and broadening of the corresponding resonances. The fraction of “dormant” polypropylene chains with a 2,1-last-inserted unit was estimated to be in the 20−50% ran...

Advances in propene polymerization using MgCl2-supported catalysts. Fundamental aspects and the role of electron donors

The fundamental factors determining the performance of state-of-the-art MgCl 2 -supported catalysts for polypropylene are becoming increasingly evident. Polymer yield, isotacticity, molecular weight and molecular weight distribution are dependent on the regio- and stereoselectivity of the active species. Chain transfer with hydrogen after the occasional regioirregular (2,1-) insertion has a strong effect on molecular weight and is the main reason for the high hydrogen response shown by high-activity catalysts containing diether donors. Hydrogen response is also dependent on stereoselectivity. The probability of a stereo- or regioirregular insertion can be related to the lability of donor coordination in the vicinity of the active species. Results with different catalyst systems can be interpreted on the basis of a propagation model involving interconverting active species, such that polypropylene produced using MgCl 2 -supported catalysts can be regarded as a stereoblock polymer comprising (highly) isotactic sequences, moderately isotactic (isotactoid) sequences and syndiotactoid sequences. Strongly coordinating donors will give stereoregular polymers in which highly isotactic sequences predominate.

Ziegler–Natta MgCl 2-supported catalysts: relationship between titanium oxidation states distribution and activity in olefin polymerization

The chemical interaction between the procatalyst MgCl 2/TiCl 4/EB (EB=ethylbenzoate) and the cocatalyst triethylaluminium was investigated with the purpose to find a relationship between the degree of titanium reduction and the catalytic activity in ethene and propene polymerizations. This interaction was studied in dependence on Al/Ti molar ratio, activation temperature and aging time by measuring the changes of titanium oxidation states during either aging time and polymerization course. Ti(III) and Ti(II) were determined by two redox titrations, while Ti(IV) was calculated by difference, the total titanium amount being known. It was found that Ti(IV) undergoes reduction to lower oxidation states owing to treatment with AlEt 3 and this process is dependent on activation temperature, aging time and Al/Ti molar ratio. However, in contrast to literature reports, the Ti(IV) reduction appears to be incomplete also by using an excess of cocatalyst AlEt 3 or long aging times. Thus, a catalyst activated for 2 h at 70°C with a molar ratio Al/Ti=200, showed the following distribution: Ti(IV):Ti(III):Ti(II)=9:31:60. The activated catalysts were tested in the ethene and propene polymerizations carried out under the same conditions and the obtained activities were compared with the variation of the titanium oxidation state distribution. Whereas both Ti(III) and Ti(II) species appear to be active in the ethene polymerization, in the case of propene only the species in the higher oxidation states, such as Ti(III) and possibly Ti(IV), are catalitycally active. In particular, the variation of the catalyst activity in the propene polymerization is consistently parallel with the variation of the Ti(III) species. Finally, in order to verify the possible influence of free monomer on the titanium reduction process, the changes in titanium oxidation states during the course of 1-hexene polymerization in heptane solution were measured.

Effects of Internal and External Donors on the Regio- and Stereoselectivity of Active Species in MgCl2-Supported Catalysts for Propene Polymerization

Poly(propylene)s prepared using MgCl2-supported catalysts containing different electron donors have been characterized using temperature rising elution fractionation (TREF), gel permeation chromatography (GPC) and 13C NMR analysis. In addition, the regio- and stereochemical composition of oligomeric fractions present in selected polymers has been determined. The results indicate that catalysts in which the internal donor is a diether have a relatively narrow distribution of active species, for which the effects of regioselectivity on chain transfer with hydrogen are particularly prominent. The regio- and stereoselectivity of active species in catalysts in which the internal donor is diisobutyl phthalate is dependent on the nature of the alkoxysilane external donor used in polymerization. The effects of different alkoxysilanes on polymer tacticity and molecular weight distribution are interpreted in terms of lability of donor coordination in the vicinity of active species, a labile as opposed to a stable donor coordination giving rise to a higher proportion of defect-rich sequences in the polymer chain. Such species will also give relatively low molecular weight as a result of an increased probability of chain transfer with decreasing regio- and stereoselectivity. A broad tacticity and molecular weight distribution in poly(propylene) prepared using monoesters as internal and external donors indicates that these systems may contain not only a significant proportion of labile active species, but also species that do not require the presence of an electron donor in their immediate vicinity for high selectivity.

Highly active MgCl2-supported catalysts containing novel diether donors for propene polymerization

A new generation of MgCl2-supported catalysts for the polymerization of propene without any external donors was prepared. Two diethers, 9,9-bis(methoxymethyl)fluorene (for Cat-A) and 2,2-dipropyl-1,3-dimethoxypropane (for Cat-B) differing in the bulkiness of alkyl substituents in position 2, have been used as internal donors in MgCl2/TiCl4/diether-AlR3 catalysts. The weight-average molecular weights produced with both catalysts were over 3.5×105 at low temperature in slurry polymerization (< 40°C). Cat-A showed higher activity and produced higher isotactic polypropene than Cat-B. The activity of both catalysts proved to be dependent on the temperature.

Development of novel MgCl2 supported catalyst with trivalent titanocene complex of CP2TiCl2AlCl2 for propylene polymerization

Three kinds of MgCl2-supported trivalent titanocene catalyst (Cat. 1: Cp2TiCl2AlCl2/MgCl2, Cat. 2: CpCp*TiCl/MgCl2, Cat. 3: Cp2TiCl/MgCl2) were prepared and tested for propylene polymerization. It was found that Cat. 1, combined with ordinary alkylaluminum as cocatalyst, produced PP containing 31.8 wt % of isotactic PP in fairly good yield. On the other hand, Cats. 2 and 3 hardly showed any activity. The effects of diisopropyldimethoxysilane (DIPDMS) on isospecificity of the Cat. 1 also were investigated. The isotactic index (I.I.) of PP was improved drastically by the addition of DIPDMS as external donor and reached the value as high as 98.4%, even in the absence of any internal donors. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3355–3359, 2000

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.