Comparison of ethylene-propylene copolymers obtained with Ti,V and Zr catalyst systems

Summary Ethylene and propylene were copolymerized in n-heptane in the presence of high activity heterogeneous MgCl₂/TiCl₄ catalyst and homogeneous VOCl₃ and Cp₂ZrCl₂ catalysts to study the effect on the catalyst to the microstructure and molecular weight distribution of the copolymer. The copolymer obtained with the zirconium catalyst was much more random in structure than that obtained with the vanadium and titanium catalysts and the molecular weight distribution was very narrow. Ethylene and propylene were also copolymerized in liquid propylene with MgCl₂/TiCl₄ and VOCl₃ catalyst systems. These copolymers were column fractionated and the fractions were analysed by NMR spectroscopy and DSC. The fractions of the copolymer obtained with the titanium catalyst was found to have broader distribution in composition than the copolymer obtained with the vanadium catalyst. This probably explains the traces of crystallinity in the copolymer prepared with the titanium catalyst. However, no effect was seen on the glass transition temperature.     

With different structure ligands heterogeneous Ziegler-Natta catalysts for the preparation of copolymer of ethylene and 1-octene with high comonomer incorporation

Comparison with the conventional Ziegler-Natta catalyst TiCl₄/MgCl₂ (I), the modified supported Ziegler-Natta catalysts (iso-PentylO)TiCl₃/MgCl₂ (II) and (BzO)TiCl₃/MgCl₂ (III) were prepared as efficient catalysts for copolymerization of ethylene with 1-octene. The complexes (II) and (III) were desirable for the production of random ethylene/1-octene copolymers coupled with higher molecular weight, higher comonomer incorporation within copolymer chain and good yield even at high temperature 80 ^°C and fairly low Al/Ti molar ratio of 100. The effects of catalysts ligands, Al/Ti molar ratio, polymerization temperature, as well as concentration of 1-octene on the catalytic activity, molecular weight and microstructure of the copolymer were investigated in detail. The structure and properties of the copolymers were characterized with ¹³C NMR, GPC, DSC and WAXD. The kinetic results also indicate that these catalysts (II) and (III) show higher catalytic activity and the produced polymers feature higher molecular weight, because of lower ratio of K_trm/K_p and K_tra/K_p, and higher ratio of K_tra/K_trm which indicates that chain transfer to cocatalyst is predominant.     

Solid-State NMR characterization of a superactive supported ziegler–natta catalyst

The formation of CH-type catalysts has been investigated by high-resolution and solid-state NMR. These catalysts are prepared from a soluble MgCl₂ and 2-ethyl-1-hexanol adduct (MgCl₂·3EH) by reaction with phthalic anhydride (PA) to form dioctylphthalate (DOP) and then with TiCl₄ in the presence of di-i-butylphthalate (BP). In the model systems MgCl₂·3EH/PA, MgCl₂/BP, and MgCl₂/TiCl₄/BP, the ester is complexed with MgCl₂ and /or TiCl₄ in two or more states. Only single-ester C?O and OCH₂ resonances are seen in TiCl₄/BP, probably due to exchange of ester coordinations. CH-catalysts prepared by three different procedures exhibit a single mode of bonding for the ester. The chemical shift values are consistent for ester complexed with MgCl₂. The most active and stereoselective catalyst has the most shielded chemical shift values for the C?O and —OCH₂— carbons, shortest T^H₁ and T^H_1p, and longest T_CH relaxation times. These parameters change monotonically with the decrease of activity and stereoselectivity of the catalyst preparation. © 1993 John Wiley & Sons, Inc.     

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.     

Synthesis mechanisms of poly[styrene‐co‐(acrylic acid)]‐supported TiCl4 catalysts modified by magnesium compounds

Soluble poly[styrene‐co‐(acrylic acid)] (PSA) modified by magnesium compounds was used to support TiCl₄. For ethylene polymerization, four catalysts were synthesized, namely PSA/TiCl₄, PSA/MgCl₂/TiCl₄, PSA/(n‐Bu)MgCl/TiCl₄, and PSA/(n‐Bu)₂Mg/TiCl₄. The catalysts were characterized by a set of complementary techniques including X‐ray photoelectron spectroscopy, Fourier‐transform infrared spectroscopy, X‐ray diffraction, thermogravimetric analysis, scanning electron microscopy, and element analysis. Synthesis mechanisms of polymer‐supported TiCl₄ catalysts were proposed according to their chemical environments and physical structures. The binding energy of Ti 2p in PSA/TiCl₄ was extremely low as TiCl₄ attracted excessive electrons from ? COOH groups. Furthermore, the chain structure of PSA was destroyed because of intensive reactions taking place in PSA/TiCl₄. With addition of (n‐Bu)MgCl or (n‐Bu)₂Mg, ? COOH became ? COOMg‐ which then reacted with TiCl₄ in synthesis of PSA/(n‐Bu)MgCl/TiCl₄ and PSA/(n‐Bu)₂Mg/TiCl₄. Although MgCl₂ coordinated with ? COOH first, TiCl₄ would substitute MgCl₂ to coordinate with ? COOH in PSA/MgCl₂/TiCl₄. Due to the different synthesis mechanisms, the four polymer‐supported catalysts correspondingly showed various particle morphologies. Furthermore, the polymer‐supported catalyst activity was enhanced by magnesium compounds in the following order: MgCl₂ > (n‐Bu)MgCl > (n‐Bu)₂Mg > no modifier. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Preparation of soluble TiCl3 catalysts by reduction of TiCl4 with Grignard reagents and their use for copolymerization of ethylene with propylene

Summary Preparations of soluble TiCl₃ catalysts by reduction of TiCl₄ with some types of Grignard reagents were carried out in halogenated hydrocarbon solvents by using appropriate ethers as donor. The soluble TiCl₃·MgX₂·ether complex catalysts and triisobutylaluminum as co-catalyst showed high activities for the copolymerization of ethylene with propylene. It was first found that the soluble TiCl₃·MgX₂·ether complex catalysts enhance the activities for the copolymerizations in the same manner as solid titanium catalysts supported on MgCl₂ which show high activities for homopolymerizations of olefin monomers. The copolymers obtained possessed low crystallinities. Also, the copolymers seem to contain microblock sequences and have outstandingly high tensile strength and elongation at break compared to copolymers by the conventional VOCl₃/Al(Et)_1.5Cl_1.5 catalyst system.     

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     

Hybrid titanium catalyst supported on core‐shell silica/poly(styrene‐co‐acrylic acid) carrier

Hybrid titanium catalysts supported on silica/poly(styrene‐co‐acrylic acid) (SiO₂/PSA) core‐shell carrier were prepared and studied. The resulting catalysts were characterized by Fourier transform infrared (FTIR) spectroscopy, laser scattering particle analyzer and scanning electronic microscope (SEM). The hybrid catalyst (TiCl₃/MgCl₂/THF/SiO₂·TiCl₄/MgCl₂/PSA) showed core‐shell structure and the thickness of the PSA layer in the two different hybrid catalysts was 2.0 μm and 5.0 μm, respectively. The activities of the hybrid catalysts were comparable to the conventional titanium‐based Ziegler‐Natta catalyst (TiCl₃/MgCl₂/THF/SiO₂). The hybrid catalysts showed lower initial polymerization rate and longer polymerization life time compared with TiCl₃/MgCl₂/THF/SiO₂. The activities of the hybrid catalysts were enhanced firstly and then decreased with increasing P/P. Higher molecular weight and broader molecular weight distribution (MWD) of polyethylene produced by the core‐shell hybrid catalysts were obtained. Particularly, the hybrid catalyst with a PSA layer of 5.0 μm obtained the longest polymerization life time with the highest activity (2071 kg PE mol^?1 Ti h^?1) and the resulting polyethylene had the broadest MWD (polydispersity index = 11.5) under our experimental conditions. The morphology of the polyethylene particles produced by the hybrid catalysts was spherical, but with irregular subparticles due to the influence of PSA layer. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

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.     

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).     

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.     

Effects of Ti oxidation state on ethylene, 1-hexene comonomer polymerization by MgCl<Subscript>2</Subscript>-supported Ziegler–Natta catalysts

In this study, the influences of the Ti oxidation state on the catalytic properties of MgCl₂-supported Ziegler–Natta catalysts in ethylene homo- and co-polymerization with 1-hexene were investigated. Three catalysts having different Ti oxidation states were synthesized by milling TiCl₄, TiCl₃, or TiCl₂ together with MgCl₂. With these catalysts having different Ti oxidation states, the polymerization conditions such as the Al concentration, temperature, and 1-hexene concentration were varied to figure out their catalytic abilities in ethylene homo- and co-polymerization. The Ti oxidation state affected the catalyst activity largely, having unique dependences on the polymerization conditions. A higher oxidation state led to a higher activity, slightly larger comonomer incorporation, and lower molecular weight as well as its narrower distribution. However, rough characteristics of copolymers were similar among the different Ti oxidation states.     

The roles of Grignard reagent in the Ziegler–Natta catalyst for propylene polymerization

Grignard reagent PhMgCl was added during the preparation of the catalyst system MgCl₂/di-n-butyl phthalate (DNBP)/TiCl₄—AlEt₃/diphenyl dimethoxyl silane (DPDMS) to improve its performance. It was found that PhMgCl could enhance both the activity of the catalyst and the isotacticity of the products, but decreased the Ti content of the catalysts under the same preparation conditions. The polymerization kinetics showed that PhMgCl accelerates the decay in the same time that it increased the initial and final polymerization rates. By means of UV-vis spectroscopy, electron spin resonance (ESR) spectroscopy, and the Ti content determination of the catalysts, the multiple roles of PhMgCl were disclosed: reduction of Ti⁴⁺ to Ti³⁺, association with MgCl₂ to replace part of TiCl₄ in aspecific active sites, and complexing with the original active sites to form new active sites. © 1997 John Wiley & Sons, Inc. J Appl Polm Sci 65:925–930, 1997     

Molecular weight distribution of polyethylene catalyzed by Ziegler–Natta catalyst supported on MgCl2 doped with AlCl3

Ti‐based Ziegler–Natta catalysts supported on MgCl₂ doped with AlCl₃ were prepared by the reaction of MgCl₂/AlCl₃–ethanol adduct with TiCl₄. No AlCl₃ crystallites were found in the AlCl₃‐doped catalysts by WAXD analysis, suggesting that AlCl₃/MgCl₂ solid solution was formed. The effect of doping on the catalyst performance in ethylene polymerization was investigated. The results showed that the catalysts based on AlCl₃‐doped MgCl₂ support exhibited a slightly higher activity than did the MgCl₂‐supported catalyst and the molecular weight distribution (MWD) of polyethylene (PE) markedly increased (from 10.8 to 47.9) with the increase of AlCl₃ content in catalysts. The changes in catalyst's active center distribution were studied based on nonlinear fitting of the polymer GPC curves by multiple Flory functions. It was found that increase of types of active centers by introducing AlCl₃ into the support should be responsible for the broadening of MWD of PE. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1768–1772, 2006     

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.     

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     

Study of the MgCl2 recrystallization conditions on Ziegler-Natta catalyst properties

Summary Magnesium dichloride supported titanium catalysts were prepared by dissolving anhydrous MgCl₂ in 1-hexanol/isooctane. Then recrystallization took place through different techniques such as evaporation of the solvent, quick cooling, precipitation with silicon tetrachloride and precipitation with titanium tetrachloride. The FT-IR analysis showed that several degrees of dealcoholation took place as a result of the adducts of MgCl₂· XROH. Moreover, it was found that the most active catalysts in the polymerization of ethylene were those obtained recrystallizing MgCl₂ by precipitation with SiCl₄. On the other hand, those directly recrystallized with TiCl₄ were the least reactive and the ones that produced polyethylenes with the highest molecular weights and the lowest degrees of crystallinity. Received: 14 December 1998/Revised version: 17 August 1999/Accepted: 17 August 1999     

Effect of cocatalyst on the chemical composition distribution and microstructure of ethylene-hexene copolymer produced by a metallocene/Ziegler-Natta hybrid catalyst

A silica-magnesium bisupport (SMB) was prepared by a sol-gel method for use as a support for metallocene/Ziegler-Natta hybrid catalyst. The SMB was treated with methylaluminoxane (MAO) prior to the immobilization of TiCl₄ and rac-Et(Ind)₂ZrCl₂. The prepared rac-Et(Ind)₂ZrCl₂/TiCl₄/MAO/SMB catalyst was applied to the ethylenehexene copolymerization with a variation of cocatalyst species (polymerization run 1: triisobutylaluminum (TIBAL) and methylaluminoxane (MAO), polymerization run 2: triethylaluminum (TEA) and methylaluminoxane (MAO)). The effect of cocatalysts on the chemical composition distributions (CCDs) and microstructures of ethylene-hexene copolymers was examined. It was found that the catalytic activity in polymerization run 1 was a little higher than that in polymerization run 2, because of the enhanced catalytic activity at the initial stage in polymerization run 1. The chemical composition distributions (CCDs) in the two copolymers showed six peaks and exhibited a similar trend. However, the lamellas in the ethylene-hexene copolymer produced in polymerization run 1 were distributed over smaller sizes than those in the copolymer produced in polymerization run 2. It was also revealed that the rac-Et(Ind)₂ZrCl₂/TiCl₄/MAO/SMB catalyst preferably produced the ethylene-hexene copolymer with non-blocky sequence when TEA and MAO were used as cocatalysts.     

Copolymerization of propylene with a small amount of ethylene using a MgCl2/TiCl4 and a TiCl3 catalyst system

Summary Copolymerization of propylene with a small amount of ethylene and homopolymerization of propylene were performed using a highly active MgCl₂/TiCl₄-Et₃Al/ethyl benzoate(EB) and a conventional TiCl₃-Et₂AlCl catalyst systems. The obtained polymers were fractionated into n-decane (C₁₀) soluble and insoluble portions. In all homopolymer fractions with the investigated catalyst systems and copolymer fractions with TiCl₃ catalyst system, the inversion of the direction of arrangement of the propylene unit was not observed by ¹³C-NMR analysis. On the other hand, in C₁₀ soluble fractions of copolymer using MgCl₂/TiCl₄ catalyst system, regardless of the presence of EB, a significant amount of the inversion unit was detected.     

Modification of Ziegler-Natta catalysts by cyclopentiadienyl-type ligands: Activation of titanium-based catalysts

Conventional Ziegler-Natta catalysts, based on TiCl₄ supported on MgCl₂, were modified by substituting a part of the chlorides by cyclopentadienyl (and derivatives) ligands. Although these catalysts are very active (activities up to 10⁵ g PE/g catalyst/h) they exhibit a conventional Ziegler-Natta behavior (methylaluminoxane is not necessary, polyethylene produced with a rather broad molar weight distribution, low sensitivity to hydrogen). It was attributed to cluster effects: an increase of the number of conventional TiCl₄ active sites by adding cyclopentadienyl ligands on titanium neighbors. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 2281–2288, 1997