Polymerization of propylene by highly active catalysts synthesized with Mg(OEt)2/benzoyl chloride/TiCl4

Summary Active centers have been studied in the polymerization of propylene using highly active Mg(OEt)₂/Benzoyl chloride/TiCl₄ catalysts activated with AlEt₃. The method for the measurement of active centers is based on the inhibiting effect of CO on polymerization. The activity of the present catalysts, which is higher than that of TiCl₃ or MgCl₂-supported catalyst, is mainly due to the higher concentration of active centers by one order of magnitude. In order to investigate the stability of active centers during polymerization the number of active centers are compared at various polymerization times.     

Ethylene and propylene polymerization catalyzed by a model Ziegler-Natta catalyst prepared by gas phase deposition of magnesium chloride and titanium chloride thin films

Model Ziegler-Natta catalysts are prepared by gas phase deposition of ultra-thin TiCl₄/ MgCl₂ films in UHV conditions. A monolayer of TiCl₄ chemisorbed on a solid solution of titanium and magnesium chloride is formed in this way. The reduction and alkylation of TiCl₄ by its reaction with a liquid layer of AlEt₃ condensed on the halide film is monitored by XPS. Most of the TiCl₄ is reduced by AlEt₃ and is incorporated in the mixed titanium /magnesium chloride. The model catalyst is active in the polymerization of ethylene and propylene at 300 K, both in the absence and in the presence of AlEt₃ in the reaction cell. The polymers that form over the catalyst film have been characterized by Raman spectroscopy. The weak signals from methyl end groups and unsaturations suggest high molecular weight for both polymers. The polypropylene film has a high degree of isotacticity even without the use of any electron donor. For the propylene polymerization reaction the overall turnover frequency is in the range between 0.1 and 1 molecule/(site s).     

Surface science studies of Ziegler-Natta olefin polymerization system: Correlations between polymerization kinetics, polymer structures, and active site structures on model catalysts

The surface composition and structure of model Ziegler-Natta catalysts, polymerizing α-olefins to produce polyolefins, have been studied using modern surface science techniques and compared with their polymerization behaviors. Two types of thin films — TiCl_x/MgCl₂ and TiCl_y/Au — were fabricated on an inert gold substrate, using chemical vapor deposition methods, to model the high-yield catalysts of MgCl₂-supported TiCl₄ and TiCl₃-based catalysts, respectively. The model catalysts could be activated by exposure to triethylaluminum (AlFt₃) vapor. Once activated, both catalysts were active for polymerization of ethylene and propylene in the absence of excess AlEt₃ during polymerization. The model catalysts had polymerization activities comparable to the high-surface-area industrial catalysts. Though both catalysts were terminated with chlorine at the surface, each catalyst assumed different surface structures. The TiCl_x/MgCl₂ film surface was composed of two structures: the (001) basal plane of these halide crystallites and a non-basal plane structure. The TiCl_y/Au film surface assumed only the non-basal plane structure. These structural differences resulted in different tacticity of the polypropylene produced with these catalysts. The TiCl_x/MgCl₂ catalyst produced both atactic and isotactic polypropylene, while the TiCl_y/Au catalyst without the MgCl₂ support produced exclusively isotactic polypropylene. The titanium oxidation state distribution did not have a critical role in determining the tacticity of the polypropylene.     

Highly active MgO-supported TiCl4 catalyst for the ethylene polymerization

Summary The MgO-supported TiCl₄ catalysts prepared by heating MgO with TiCl₄ showed a high activity for the ethylene polymerization in combination with Et₃Al or i-Bu₃Al. In these highly active catalysts, it has been shown that MgCl₂ is formed in the MgO-TiCl₄ reaction and is considered to contribute to the enhancement of the activity of the catalysts.     

Microstructure of isotactic polypropylene obtained using Ziegler–Natta catalyst at high polymerization temperature

The microstructure of the isotactic polypropylene obtained with various MgCl₂‐supported catalyst systems at high polymerization temperature of 70–100°C is investigated by discussing the intrinsic relation between the different types of active centers and the polymerization temperatures via gel permeation chromatography, temperature rising elution fractionation, and ¹³C NMR. For the MgCl₂/TiCl₄/di‐n‐butyl phathalate‐AlEt₃/external donor and MgCl₂/TiCl₄/2,2‐diisobutyl‐1,3‐dimethoxypropane‐AlEt₃ catalyst systems, the differences in the isotactic productivity of polymers obtained at different polymerization temperatures mainly result from the variation of both the activity of the different isospecific active centers and the stability constants of the complex of catalyst/donor. The reaction rate of high isotactic active centers reaches maximum at 85–90°C, and this effect contributes to both the highest isotacticity and the narrowest molecular weight distribution. For the MgCl₂/TiCl₄/phthalate ester‐AlEt₃ catalyst system, the isotacticity of polypropylene remains approximately constant in the temperature range of experiments, which could be ascribed to elution of phthalate ester after the activation. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42487.     

Copolymerization of propylene with 1‐octene catalyzed by MgCl2/TiCl4/diether catalyst

MgCl₂/TiCl₄/diether is a fifth‐generation Ziegler–Natta catalyst for the commercial polymerization of propylene. The outstanding features of this catalyst are the high activity and high isotacticity for propylene polymerization without using an external electron donor. In this study, we explored the copolymerization of propylene and 1‐octene with MgCl₂/TiCl₄/diether catalyst. It was found that MgCl₂/TiCl₄/diether catalyst showed higher polymerization activity and led to greater 1‐octene content incorporation, compared with a fourth‐generation Ziegler–Natta catalyst (MgCl₂/TiCl₄/diester). With an increase in 1‐octene incorporation in polypropylene chains, the melting temperature, glass transition temperature and crystallinity of the copolymers decreased distinctly. The microstructures of the copolymers were characterized using ¹³C NMR spectroscopy, and the copolymer compositions and number‐average sequence lengths were calculated from the dyad concentration and distribution. This result is very important for the in‐reactor polyolefin alloying process, especially for the case of a single catalyst and two‐step (or two‐reactor) process. Copyright © 2011 Society of Chemical Industry     

Plausible guard effect on the active sites of heterogeneous Ziegler–Natta catalyst by coordinating monomers and growing polymer chains in the initial stage of propene polymerization

Investigation of propene polymerization by a modified stopped‐flow technique using TiCl₄/ethylbenzoate(EB)/MgCl₂ Ziegler–Natta catalyst with or without pretreating the catalyst with triethylaluminium (TEA) within an ultra‐short period (ca 1 s) was conducted to gain new understanding of the nature of active sites related to TEA in the early stage of polymerization. When the catalyst was pretreated by a cocatalyst, deactivation behaviour was clearly observed, even within an extremely short pretreatment period. In contrast, without pretreatment, the deactivation of active sites can be neglected within the polymerization period indicating that the activated Ti species might be protected from deactivation by TEA when monomer is present in the system. A plausible guard effect on the active sites by coordinating monomer and growing polymer chains in the initial stage of polymerization is proposed to account for this phenomenon. Copyright © 2004 Society of Chemical Industry     

Studies on highly active coordination catalysts for polymerization of α-olefins: 3. Polymerization of propylene with MgCl2/TiCl4/AlEt3 or MgCl2/PhCOOC2H5/TiCl4/AlEt3 systems

Activity and stereospecificity of the $\text{MgCl}{}_2\text{TiCl}{}_4$ catalyst in the polymerization of propylene follow curves showing maxima with grinding time of the MgCl₂ support. Using MgCl₂/PhCOOC₂H₅/TiCl₄ catalysts, no decrease in activity and stereospecificity was observed presumably because of complex formation between MgCl₂ support and ethyl benzoate.     

Studies on the polymerization of propylene using high activity ziegler-natta catalysts. 1: Kinetic models for rate decay in ziegler-natta polymerization

Kinetic models for describing the time dependence of the polymerization rate and active centre concentration for high activity Ziegler-Natta catalyst systems are discussed. It is demonstrated that the decay in the rate of polymerization and in the concentration of active centres with time for the polymerization of propylene with the heterogeneous catalyst system MgCl₂/EB/TiCl₄? Al(i-Bu)₃/EB can be represented better by a modified multi-centre first order decay model than by the other models which are considered.     

Surface science approach to the preparation and characterization of model Ziegler–Natta heterogeneous polymerization catalysts

Ziegler–Natta heterogeneous catalytic systems are extensively used to polymerize ethylene and propylene. Some industrial catalysts consist of TiCl₄ chemisorbed on activated MgCl₂ and subsequently reduced and alkylated by reaction with an aluminum alkyl (generally AlEt₃). Lewis bases are added to the catalytic systems to control the enantio-selectivity for the production of isotactic polypropylene. Our aim is to clarify the chemical composition of the active centers by modern surface science methods. Model catalysts are prepared in the form of ultra-thin films by gas-phase deposition on a gold foil in ultrahigh vacuum. Under these conditions, MgCl₂ films grow to controlled thickness via a layer-by-layer mechanism, as revealed by AES and XPS. TiCl₄ can be deposited on these films near room temperature by both electron irradiation-induced and metallic magnesium-induced chemical vapor deposition. Angle-resolved XPS studies indicate that these films consist of a few layers of TiCl₂ with one monolayer of TiCl₄ chemisorbed on its surface. The exposure of these titanium chloride films to the co-catalyst AlEt₃ produces an active model Ziegler–Natta catalyst. XPS analysis reveals the presence of TiCl₂Et on the catalyst surface: this is believed to be the active site. Prolonged reaction with the co-catalyst reduces the titanium sites to TiClEt_n (n = 1 and/or 2). High molecular weight polyethylene and polypropylene are synthesized on these catalysts, as shown by Raman spectroscopy. Highly isotactic polypropylene is produced without need for stereo-regulating Lewis bases. This revised version was published online in June 2006 with corrections to the Cover Date.     

Ethylene polymerization with heterogeneous Ziegler-Natta catalysts

Summary TiCl₄/SiO₂, Ti(OC₄H₉)₄/SiO₂, MgCl₂/TiCl₄/SiO₂ and MgCl₂/Ti(OC₄H₉)₄/SiO₂ catalysts were prepared by treating silica gel with TiCl₄, Ti(OC₄H₉)₄, MgCl₂/TiCl₄ or MgCl₂/Ti(OC₄H₉)₄ in tetrahydrofuran (THF) solution. Ethylene polymerization was performed with these catalysts activated by common alkylaluminum compounds. The influence of magnesium dichloride on catalyst performance was investigated. MgCl₂ has enhanced the catalyst activity for both titanium compounds. In addition, all catalyst systems were only active when they were washed with AlCl(C₂H₅)₂ (DEAC).     

The influence of cocatalysts on 1-hexene polymerization with various supported magnesium – titanium catalysts

Summary The influence of various cocatalysts on the activity and stereospecificity of a supported magnesium–titanium catalyst, generated by in situ reduction of titanium (IV) chloride using a Grignard reagent (MgCl₂/TiCl₃) or prepared by the recrystallization method (MgCl₂/2M2P/ED/TiCl₄, 2M2P= 2-methyl-2-pentanol, ED= dibutyl phthalate or ethyl benzoate), in the 1-hexene polymerization was investigated. The MgCl₂/TiCl₃ catalyst showed the highest activity but the lowest stereospecificity in the 1-hexene polymerization with all investigated cocatalysts. The MgCl₂/2M2P/ED/TiCl₄ catalyst with dibutyl phthalate as an internal electron donor was characterized by the highest stereospecificity and led to the polymers with high molecular weight. All catalysts showed the highest activity and stereospecificity when triisobutylaluminium was used as a cocatalyst. The addition of a small amount of ethyl benzoate as an external electron donor ([Al]/[ED] 10:1) led to considerable improvement of the stereospecificity of the MgCl₂/TiCl₃ catalyst in comparison with the catalysts prepared by the recrystallization method.     

Effect of 1-allyl-3,4-dimethoxybenzene on the copolymerization of propene and small amount of ethylene with the TiCl4/dibutylphthalate (DBP)/MgCl2 catalyst activated by Al(i-C4H9)3

Summary Copolymerization of propene and small amount of ethylene was conducted with the TiCl₄/DBP/MgCl₂-Al(i-C₄H₉)₃ catalyst in the presence and absence of 1-allyl-3,4-dimethoxybenzene(ADMB). Addition of ADMB caused a decrease in the ethylene content in copolymer with an increase in the activity. From a detailed analysis of the copolymers fractionated with boiling diethylether, it was found that the ADMB-containing system gives ether-soluble polymers with higher molecular weight and narrower molecular weight distribution as well as less content of regioirregular sequences of propene. The microstructures of the ether-soluble parts suggested that ADMB might accelerate the propene polymerization at the aspecific sites formed. Received: 24 June 1998/Revised version: 28 September 1998/Accepted: 26 October 1998     

Preparation of exfoliated isotactic polypropylene/alkyl-triphenylphosphonium-modified montmorillonite nanocomposites via in situ intercalative polymerization

Alkyltriphenylphosphonium-modified montmorillonite(PMMT) was used to prepare TiCl₄/MgCl₂/PMMT compound catalyst and exfoliated i-PP/PMMT nanocomposites were prepared by in situ intercalative polymerization of propylene with TiCl₄/MgCl₂/PMMT catalyst. The catalytic efficiency of the above catalyst under optimum polymerization condition could reach as high as 1300 kg/(molTi h) and the combining of PMMT with Z-N catalyst do not change the stereo-regulation catalytic properties of the Z-N catalyst. The synthesized PP possessed high isotacticity, melting point and molecular weight. Wide angle X-ray diffraction (XRD) and transmission electron microscopy (TEM) examinations evidenced the nanocomposites obtained were exfoliated ones.     

Preparation of porous spherical MgCl2/SiO2 complex support as precursor for catalytic propylene polymerization

The MgCl₂/SiO₂ complex support was prepared by spray drying using alcoholic suspension, which contained MgCl₂ and SiO₂. The complex support reacted with TiCl₄ and di‐n‐butyl phthalate, giving a catalyst for propylene polymerization. The catalyst was spherical and porous with high specific surface area. TEA was used as a cocatalyst, and four kinds of alkoxysilane were used as external donors. The bulk polymerization of propylene was studied with the catalyst system. The effect of the reaction conditions and external donor on the polymerization were investigated. The results showed that the catalyst had high activity, high stereospecificity, and sensitive hydrogen responsibility. Polypropylene has good grain morphology because of duplicating the morphology of the catalyst. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1296–1299, 2005     

Preparation of highly active supported catalysts for producing polypropylene with less content of chloride

Summary Highly active supported catalysts for propylene polymerization have been prepared by treating the complexes of TiCl₃· 3C₅H₅N and MgCl₂·(THF) with AlEt₂Cl in the presence of MgO, Mg(OH) ₂ ^x or SiO₂. Polypropylene with less content or chloride was produced over these catalysts combined with AlEt₃.     

Kinetics of ethylene polymerization at high temperature with Ziegler–Natta catalysts

A kinetic technique is developed for the study of ethylene polymerization reaction at high temperature with Ziegler–Natta catalysts. The technique is based on the calculation of polymerization rate parameters from the data on ethylene consumption vs. time. It takes into account increase of reaction temperature at the beginning of the reaction. Kinetic data in coordinates “polymerization rate–time” are presented for several pseudohomogeneous catalysts (TiCl₄? AlEt₂Cl, Ti(OiC₃H₇)₄? AlEt₂Cl), heterogeneous catalysts (δ-TiCl₃? AlEt₃, δ-TiCl₃? AlEt₂Cl, TiCl₄/MgCl₂? AlEt₃, TiCl₄/MgCl₂? AlEt₂Cl) and solubilized catalysts (δ-TiCl₃? poly-1-hexene? AlEt₂Cl) at 180°C and reaction pressure 14.6 atm for first 10 min of the reaction. These data are useful for the selection of Ziegler–Natta catalysts for testing in ethylene polymerization reaction in continuous high pressure reactors at short residence times.     

High activity mixed metal alkyl cocatalysts for α-olefin polymerization

High activity α-olefin polymerization catalysts are generally obtained by mixing MgCl₂-supported TiCl₄ (MgCl₂/TiCl₄) with an aluminum trialkyl cocatalyst. Surprisingly, AlEt₂Cl, which is the preferred cocatalyst in polymerizations employing nonsupported Ti compounds, is a poor cocatalyst when used with MgCl₂/TiCl₄. It was found that in propylene and 1-butene polymerizations, using different MgCl₂/TiCl₄ catalysts, the cocatalyst activity of AlEt₂Cl can be greatly improved by the addition of a magnesium or lithium alkyl. The mixed metal alkyl obtained from AlEt₂Cl and MgBu₂ is a particularly effective cocatalyst always yielding more polymer, of about the same stereospecificity, than the conventional aluminum trialkyls. The exact nature of the mixed metal alkyl cocatalysts is not known, but the available evidence argues against in situ aluminum trialkyl formation resulting from the alkylation of AlEt₂Cl by the second metal alkyl.     

Active centers of TiCl3 catalysts for propene polymerization

Summary Publications reporting numbers of active centers in TiCl₃ propylene polymerization catalysts are very contradictory. Experimental data from the beginning of the sixties are reevaluated by the author. It is concluded that TiCl₃-catalysts from the Hoechst type (and probably from the Stauffer AA-type) have, after an initial period of polymerization, numbers of active centers in the range of percentage of total TiCl₃. This value increases with temperature. By cooling during polymerization some metal polymer bonds, probably active centers, disappear.Conversion versus time and molecular weight versus conversion for propene polymerization     

A highly non-stereospecific catalyst for propene polymerization

Summary The MgCl₂-supported TiCl₃ catalyst containing a small amount of Ti(about 0.1 wt.%) was prepared by treating the mixture of MgCl₂ and TiCl₃ 3py with an excess amount of AlEt₂Cl. Propene polymerization was conducted at 40°C by using AlEt₃ as cocatalyst. The catalyst system was found to be highly active, which gave atactic polypropylene