PE/clay nanocomposites produced via in situ polymerization by highly active clay-supported Ziegler–Natta catalyst

The synthesis of polyethylene/clay (PE/clay) nanocomposites by means of in situ polymerization was achieved using the clay/BOM/chloroform/EtOH/TiCl₄/TEA catalyst system where butyl octyl magnesium (BOM) and triethyl aluminum (TEA) were a modifier for the clay and cocatalyst, respectively. It was found that the catalyst had high activity in ethylene polymerization. The microstructure of the resulting PE/clay nanocomposites was characterized by X-ray diffraction, transmission electron microscopy, and scanning electron microscopy. The examinations evidenced the nanocomposite formation with exfoliated clay in the PE matrix. The thermal properties of the produced nanocomposites were studied by differential scanning calorimetry, oxidation induction time, and thermal gravimetric analysis. Furthermore, the mechanical properties of the nanocomposites were evaluated by the impact and tensile tests. The examinations indicated the improved thermal stability and mechanical properties. Meanwhile, a wide range of molecular weights were produced in the presence of hydrogen.     

Preparation and characterization of polyethylene (PE)/clay nanocomposites by <Emphasis Type="Italic">in situ</Emphasis> polymerization with vanadium-based intercalation catalyst

Summary  Complete exfoliation of clay during vanadium-based Zigler-Natta polymerization of ethylene has been successfully carried out by using clay and MgCl₂ hybrid supports. MgCl₂ offers catalyst loading sites, and the vanadium catalyst is avoided directly anchoring in the surface of the clay, so intercalation catalyst clay/MgCl₂/VOCl₃displays high activity for ethylene polymerization. Exfoliated PE/clay nanocomposites are confirmed by X-ray diffraction (XRD), and transmission electron microscopy (TEM). Strong interaction between the dispersed clay particles and the polymer matrices provides good thermal and mechanical properties. Compared with pure PE, all these nanocomposites show enhancement of the melting temperature (T_m) and the thermal decomposition temperatures. Additionally, the incorporation of clay into the PE matrix significantly improves the mechanical properties of these nanocomposites. The increased tensile strength has been observed in the range of 3.4 to 7.9 MPa. The tensile moduli of the PE/clay nanocomposite are 23.4%-45.3% higher than that of the pure PE.     

Preparation and characterization of Polyethylene/Clay/Silver nanocomposites using functionalized polyethylenes as an adhesion promoter

The performance of Polyethylene (PE)/Clay/Silver nanocomposites is dependent to a great extent on the properties of filler–matrix interface. To improve the interfacial properties in PE/Clay/Silver composites, different types of compatibilizers or adhesion promoters were introduced. The compatibilization provided by maleic anhydride (MA), itaconic acid (IA) and 2-[2-(dimethylamine)-ethoxy] ethanol (DMAE) functionalized PEs for forming PE-based nanocomposites was studied and compared. IA was grafted into PE by melt mixing to obtain PEgIA (compatibilizer 1), thereafter, PEgIA and PEgMA (compatibilizer 2) were reacted with DMAE also by melt mixing to obtain PEgI-DMAE (compatibilizer 3) and PEgM-DMAE (compatibilizer 4). These compatibilizers were reacted using ultrasound with a solution of AgNO₃ 0.04 M and ethylene glycol. Ammonium hydroxide was added in a ratio of 2:1 M with respect to silver nitrate. These silver coated compatibilizers were mixed with PE and with a quaternary ammonium modified montmorillonite clay (Nanomer I28E), thus forming the different hybrid PE/Clay/Silver nanocomposites. FTIR confirmed the formation of these compatibilizers. All the DMAE compatibilized nanocomposites had better filler (clay and silver) dispersion and exfoliation. XRD, oxygen and water transmission rate as well as antimicrobial properties attained showed that the PEgI-DMAE produced the better dispersed PE, clay and silver nanocomposites. The obtained nanocomposites showed enhanced barrier properties and outstanding antimicrobial properties against bacteria, E. coli. PEgI-DMAE offers an outstanding capability for preparing nanocomposites with highly exfoliated and dispersed filler into the PE matrix that offers a new option for obtaining hybrid nanocomposites with enhanced properties to be used in packaging applications.     

Preparation and characterization of polyethylene–clay nanocomposites by using chlorosilane‐modified clay

Clay was modified by trimethylchlorosilane; after modification, hydroxyl groups at the edge of layers were reacted and CEC value was drastically decreased. Polyethylene–clay composites were prepared by melt compounding. Wide angle X‐ray diffraction (WAXD) and transmission electron microscopy (TEM) showed that intercalated nanocomposites were formed using organoclay ion‐exchanged from chlorosilane‐modified clay, but conventional composites formed using organoclay directly ion‐exchanged from crude clay. Dynamic mechanical analysis (DMA) of PE and PE–clay composites was conducted; the results demonstrated that nanocomposites were more effective than conventional composites in reinforcement and addition of organoclay resulted in the increase of glass transition temperature (T_g), but crude clay had no effect on T_g of PE–clay composites. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 676–680, 2004     

Butyl chloride as promoter in ethylene polymerization by magnesium ethoxide‐supported catalyst

The effects of butyl chloride as a promoter in the ethylene polymerization were studied using a Mg(OEt)₂/TiCl₄/triethyl aluminum (TEA) Ziegler–Natta catalyst system, where Mg(OEt)₂, TiCl₄, TEA were used as support, catalyst, and activator, respectively. The influence of BC on the catalyst performance, polymerization rate, and polymer properties were investigated. This study strongly indicates that BC could act as a promoter with high performance in the ethylene polymerization. There was a remarkable increase in the catalyst yield and polymerization rate, in particularly, in the presence of hydrogen which was used for controlling the molecular weight. A reduction in the polymer molecular weight was observed in the presence of BC and hydrogen. The morphology of the polymers was evaluated through scanning electron microscopy and particle size distribution. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40189.     

In‐situ synthesis of poly(ethylene terephthalate)/clay nanocomposites using TiO2/SiO2 sol‐intercalated montmorillonite as polycondensation catalyst

A novel organic montmorillonite, which could act as both polycondensation catalyst of poly(ethylene terephthalate) (PET) and filler of PET/clay nanocomposites, was prepared. Original montmorillonite was first treated with different amounts of poly(vinylpyrrolidone) (PVP), and then intercalated by TiO₂/SiO₂ sol to gain polycondensation catalytic activity. The acquired clay possessed excellent thermal stability and would not degrade during the polycondensation step. PET/clay nanocomposites were prepared via in‐situ polymerization using the organo‐clay as polycondensation catalysts. The morphologies of the nanocomposites were characterized by X‐ray diffraction and transmission electron microscope. The results indicated that the amount of PVP and TiO₂/SiO₂ sol strongly affected the dispersion state of the clay, and finally, partially exfoliated PET/clay nanocomposites were obtained. The nanocomposites had better properties than pure PET due to the incorporation of the delaminated clay layers. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Catalytic activity during the preparation of PE/clay nanocomposites by in situ polymerization with metallocene catalysts

Catalytic activity during the formation of polyethylene (PE)/clay nanocomposites by in situ polymerization with metallocenes was studied. Ethylene polymerization was carried out with the homogeneous metallocene in the presence of the clay particles and using the clay‐supported metallocene catalyst. It was found that the catalytic activity of the homogeneous metallocene does not decrease in the presence of the clay particles and only a slight decrease of activity occurs using the clay‐supported catalyst. The modification of the clay with MAO cocatalyst as well as its intercalation with ODA surfactant were found to play an important role during the in situ formation of the PE/clay nanocomposite. ODA‐intercalated clay apparently facilitates the activation and monomer insertion processes on zirconocene centers located in internal sites of the clay structure. Although metallocene supported on MAO‐treated clay exhibited somewhat lower catalytic activity than that supported directly on the ODA‐intercalated clay, both systems favored the production of PE nanocomposites containing highly exfoliated clay particles. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

In situ polymerization of polyethylene/clay nanocomposites using a novel clay‐supported Ziegler‐Natta catalyst

Polyethylene/clay nanocomposites (PECNC) were synthesized via in situ Ziegler‐Natta catalyst polymerization. Activated catalyst for polymerization of ethylene monomer has been prepared at first by supporting of the cocatalyst on the montmorillonite (MMT) smectite type clay and then active complex for polymerization formed by reaction of TiCl₄ and aluminum oxide compound on the clay. Acid wash treatment has been used for increasing hydroxyl group and porosity of the clay and subsequently activity of the catalyst. The nanostructure of composites was investigated by X‐ray diffraction (XRD) and transmission electron microscopy (TEM). Obtained results show that silica layers of the mineral clay in these polyethylene/nanocomposites were exfoliated, intercalated, and uniformly dispersed in the polyethylene matrix even at very high concentration of the clay. Thermogravimetric analysis (TGA) shows good thermal stability of the PECNCs. Differential scanning calorimeter (DSC) results reveal considerable decrease in the crystalline phase of the PECNC samples. Results of permeability analysis show an increase in barrier properties of PECNC films. POLYM. COMPOS., 2009. © 2009 Society of Plastics Engineers     

Nonisothermal crystallization behavior of melt‐intercalated polyethylene‐clay nanocomposites

The influence of nanoclay particles on the nonisothermal crystallization behavior of intercalated polyethylene (PE) prepared by melt‐compounding was investigated. It is observed that the crystallization peak temperature (T_p) of PE/clay nanocomposites is slightly but consistently higher than the neat PE at various cooling rates. The half‐time (t_0.5) for crystallization decreased with increase in clay content, implying the nucleating role of nanoclay particles. The nonisothermal crystallization data are analyzed using the approach of Avrami (Polymer 1971, 12, 150), Ozawa (Polym Eng Sci 1997, 37, 443), and Mo and coworkers (J Res Natl Bur Stand 1956, 57, 217), and the validity of the different kinetic models to the nonisothermal crystallization process of PE/clay nanocomposites is discussed. The approach developed by Mo and coworkers successfully explains the nonisothermal crystallization behavior of PE and PE/clay nanocomposites. The activation energy for nonisothermal crystallization of neat PE and PE/clay nanocomposites is determined using the Kissinger (J Res Natl Bur Stand 1956, 57, 217) method. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3809–3818, 2006     

Preparation of multifunctional supported metallocene catalyst using organic multifunctional modifier for synthesizing polyethylene/clay nanocomposites via in situ intercalative polymerization

A new type of multifunctional ammonium modifier with carbonyl group and vinyl group was synthesized to prepare multifunctional montmorillonites (F-MMTs), which were used as multifunctional catalyst supports for in situ ethylene polymerization. High loading of metallocene catalyst in the galleries of F-MMT had been achieved due to the presence of carbonyl group in the multifunctional modifier. XRD profiles and TEM images showed that polyethylene/montmorillonite (PE/F-MMT) nanocomposites with exfoliated structure could be synthesized using the intercalated catalyst described above, even when the content of MMT was very high (more than 15.1 wt%). The as-produced PE/F-MMTs nanocomposites were composed of flower-like particles with a diameter of about 5 μm. A thermal stable monoclinic phase was observed in PE/F-MMT nanocomposites. Comparatively, the resultant PE/F-MMT nanocomposites showed low gas permeability. Interfacial interaction between PE matrix and F-MMT was enhanced due to the chemical linking between the two components via copolymerization of ethylene with vinyl group of F-MMT. Thus the resultant PE/F-MMT nanocomposites showed good structural stability.     

Highly exfoliated PE/Na+MMT nanocomposite produced via in situ polymerization by a catalyst supported on a novel modified Na+MMT

A suitable Ziegler–Natta catalyst was prepared by supporting TiCl₄ on sodium montmorillonite (Na⁺MMT) modified by butyl octyl magnesium (BOM). This catalyst was applied for the polymerization of ethylene toward a polyethylene (PE)/Na⁺MMT nanocomposite. Catalyst behavior and nanocomposite properties were studied. It was found that catalyst activity was acceptably high. In addition, it had a smooth rate during ethylene polymerization. Transmission electron microscopy image and X-ray diffraction pattern evidenced an excellent exfoliation of the Na⁺MMT layers in the polymer matrix.     

Copolymerization of ethylene–propylene using high‐activity bi‐supported Ziegler–Natta TiCl4 catalyst

Heterogeneous Ziegler–Natta TiCl₄ catalyst using MgCl₂ and SiO₂ as supports was prepared under controlled conditions. Mg(OEt)₂ was used as a starting material and was expected to convert to active MgCl₂ during catalyst preparation. Due to the high surface area and good morphological control, SiO₂ was chosen as well. Slurry copolymerization of ethylene and propylene (EPM) was carried out in dry n‐heptane by using the catalyst system SiO₂/MgCl₂/TiCl₄/EB/TiBA or TEA/MPT/H₂ at temperatures of 40–70°C, different molar ratios of alkyl aluminum : MPT : Ti, hydrogen concentrations, and relative and total monomers pressure. Titanium content of the catalyst was 2.96% and surface area of the catalyst was 78 m²/g. Triisobutyl aluminum (TiBA) and triethyl aluminum (TEA) were used as cocatalysts, while ethyl benzoate (EB) and methyl p‐toluate (MPT) were used as internal and external donors, respectively. H₂ was used as a chain‐transfer agent. Good‐quality ethylene propylene rubber (EPR) of rubber was obtained at the ratio of [TiBA] : [MPT] : [Ti] = 320 : 16 : 1 and polymerization temperature was 60°C. When TiBA was used as a cocatalyst, a higher and more rubberlike copolymer was obtained. For both of the cocatalysts, an optimum ratio of Al/Ti was obtained relative to the catalyst productivity. Ethylene content of the copolymer obtained increased with increasing TiBA concentration, while inverse results were obtained by using TEA. Addition of H₂ increased the reactivity of the catalyst. The highest product was obtained when 150 mL H₂/L solvent was used. Increasing temperature from 40 to 70°C decreased the productivity of the catalyst, while irregular behavior was observed on ethylene content. Relative pressure of P_P/P_E = 1.4 : 1 and total pressure of 1 atm was the best condition for the copolymerization. Polymers with ethylene contents of 25–84% were obtained. Increasing ethylene content of EPR decreased T_g of the polymer obtained to a limiting value. Viscosity‐average molecular weight (M_v) decreased with increasing temperature and TiBA and H₂ concentration. However, increasing the polymerization time increased the M_v. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2597–2605, 2004     

Preparation of poly(lactic acid)/poly(ethylene glycol)/organoclay nanocomposites by melt compounding

Poly(lactic acid) (PLA)/organoclay nanocomposites were prepared by melt compounding in a co‐rotating twin screw extruder. Two types of commercialized organoclay (dimethyl benzyl stearyl ammonium ion and dimethyl distearyl ammonium ion intercalated between clay platelets named as Clay A and Clay B, respectively) and two grades of poly(ethylene glycol) (PEG) with different molecular weight (M_w = 2,000 and 300,000–500,000 named as PEG2k and PEG500k, respectively) were used in this study. The Young's modulus improved by the addition of organoclay to PLA matrix. The Young's modulus decreased with the addition of PEG to PLA/organoclay nanocomposites. The tensile strength and elongation of PLA/Clay B nanocomposites increased with the addition of PEG2k. The effect of the addition of PEG on d‐spacing of PLA/organoclay nanocomposites is dependent upon the kind of organoclay. The sizes of clay agglomerations in PLA/PEG/organoclay nanocomposites are larger than those of PLA/organoclay ones in the same organoclay. Addition of PEG to PLA/organoclay nanocomposites during melt compounding will not be useful for the preparation of PLA/organoclay having fully exfoliated clay platelets. The shear thinning properties of the nanocomposites are independent of the addition of PEG. On the whole, PEG2k is good plasticizer for PLA/organoclay nanocomposites. POLYM. COMPOS. 27:256–263, 2006. © 2006 Society of Plastics Engineers     

Alkoxysilane modification of a Ti‐based catalyst system for ethylene dimerization: A step forward in enhancing productivity and selectivity

Alkoxysilanes were used as novel enhancing agents in the Ti‐based catalyst for the highly selective ethylene dimerization to butene‐1. The dimerization of ethylene was carried out using the homogeneous Ti(OBu)₄/THF/TEA/alkoxysilane catalyst system, where Ti(OBu)₄, THF (tetrahydrofuran), TEA (triethylaluminum), and alkoxysilane were used as catalyst, additive, activator, and modifier, respectively. The nature and concentration of alkoxysilanes on the dimerization rate, catalyst yield, by‐products production, and selectivity to butene‐1 were investigated in detail. It was found that the performance of alkoxysilanes assisted with the class of the Ti‐based catalyst system, developed in this work, has been furthered by high productivity and selectivity with respect to the bare catalyst system. It proved that alkoxysilanes could play an excellent improving role in the selective ethylene dimerization process. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44615.     

PE/OMMT nanocomposites catalyzed by the OMMT‐intercalated Et[Ind]2ZrCl2 in slurry polymerization: Effects of organic solvent on ethylene polymerization behaviors and the nanocomposite structures

In situ intercalative polymerization for ethylene monomers was carried out to produce PE‐based hybrids through a slurry polymerization method. In this approach, organic solvent for olefin polymerization was found to be one of the most significant factors for the dispersion of the OMMT‐intercalated Et[Ind]₂ZrCl₂ catalysts, which determines that whether olefin monomers polymerize is in a well‐defined confinement environment or not. Understanding the olefin polymerization occurring in between the nanoscale silicate layers of OMMT as well as the corresponding structure of OMMT in an organic polymerization solvent is a critical step toward tailoring and characterizing nanocomposites formed by OMMT in a polyolefin matrix. As we know, the Et[Ind]₂ZrCl₂ catalyst and MAO are both better dissolved in toluene than that in hexane because of the larger polarity of toluene. Thus, in hexane the active sites of the OMMT/Et[Ind]₂ZrCl₂ catalyst exist in the silicate layers of OMMT and the PE chains grow in the middle of them, while in toluene the active specimens are exposed in the gel formed by the OMMT‐intercalated catalyst with MAO, which cause that the PE chains propagated in the mixture liquids. Consequently, when hexane is selected as the polymerization solvent, the formed PE‐based nanocomposites have a good dispersion of OMMT and the nanofiller content (TGA measurement residue at 600°C) is thus higher (>7.0 wt %). However, in toluene, most of the silicate layers of OMMT are agglomerated in the PE matrix. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Novel magnetic polyethylene nanocomposites produced by supported nanometre magnetic Ziegler–Natta catalyst

This paper describes the preparation of novel magnetic polyethylene nanocomposites using a nanometre magnetic Ziegler–Natta catalyst. It was found that novel magnetic polyethylene nanocomposites can be obtained according to the following four steps: (1) preparation of nanometre magnetic particles; (2) reaction between AlR₃ and hydroxyls on the surface of nanometre magnetic particles to form anchor points  AlR₂; (3) addition of TiCl₄, Ti being coordinated to anchor points on the surface of nanometre magnetic particles to form polymerization active centres; (4) ethylene polymerization being carried out in situ on the surface of the nanometre magnetic particles to produce novel magnetic polyethylene nanocomposites. It is found that the activity of ethylene polymerization is essentially unaffected by polymerization temperature and polymerization time. © 2000 Society of Chemical Industry     

Polyethylene‐b‐poly(ethylene glycol) diblock copolymers: New synthetic strategy and application

Polyethylene‐b‐poly (ethylene glycol) (PE‐b‐PEG) was successfully synthesized by a coupling reaction of hydroxyl‐terminated polyethylene (PE‐OH) and isocyanate‐terminated poly (ethylene glycol) (PEG‐NCO). PE‐OH was prepared by coordination chain transfer polymerization (CCTP) using 2,6‐bis[1‐(2,6‐diisopropylphenyl)imino ethyl] pyridine iron (II) dichloride /dry ethylaluminoxane (DEAO) /diethyl zinc (ZnEt₂) as catalyst and subsequent in situ oxidation with oxygen. The active centers of this catalyst system were counted, indicating that the active centers were more stable using DEAO as cocatalyst than using dry methylaluminoxane (DMAO) as cocatalyst. PEG‐NCO was synthesized through the condensation reaction of monomethylpoly(ethylene glycol) (PEG) with isophoronediisocyanate (IPDI). Subsequently, the thermal characterization, morphological characterization and the application of these diblock copolymers was investigated. The results indicated that the diblock copolymers were effective compatilizers for polyethylene/poly(ethylene glycol) blends. Meanwhile, they were excellent surface modification agents for polyethylene membrane and glass sheet, it can efficiently turn a hydrophobic surface into a hydrophilic surface, or vice versa. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42236.     

An in situ matrix functionalization approach to structure stability enhancement in polyethylene/montmorillonite nanocomposites prepared by intercalative polymerization

This paper discusses a strategy of enhancing the structure stability of polyethylene/montmorillonite (PE/MMT) nanocomposites prepared by intercalative polymerization technique. The chemistry centers on an in situ, controlled PE matrix functionalization that is made possible by engaging a reactive comonomer in the intercalative polymerization process to intentionally anchor in the formed PE matrix ready-to-functionalize reactive groups. Thus, ethylene polymerization was conducted in the presence of p-methylstyrene (p-MS) using an OMMT (organically modified MMT)-intercalated metallocene catalyst (Et[Ind]₂ZrCl₂ in combination with MAO), resulting in p-MS-containing PE/OMMT nanocomposites. Subsequent functionalization of the PE matrix then facilely and selectively occurred on the benzyl group in the p-MS unit, including a free radical maleation reaction and a butyllithium-initiated metallation reaction which was followed by an anionic graft-from polymerization of methyl methacrylate (MMA), under very mild reaction conditions. The in situ-incorporated functional groups, including the pendant maleic anhydride groups and the polar poly(methyl methacrylate) (PMMA) side chains, significantly improved miscibility between the PE matrix and laminated silicate layers of MMT, leading to effective stabilization of the nanocomposite structure against processing.     

PE/OMMT nanocomposites prepared by in situ polymerization approach: Effects of OMMT‐intercalated catalysts and silicate modifications

In this article, the surfactants, (2‐hydroxylethyl) octadecyl dimethylammonium nitrate (OH‐C18), hexadecyltrimethylammonium bromide(C16), and mixture of trimethylchlorosilane (TM) and OH‐C18 were ion‐exchanged with cations in the montmorillonite (MMT) to generate three organic MMTs (named as OH‐C18‐MMT, C16‐MMT, and MMMT), leading to different environments of catalyst species in MMT interlayer gallery. Et[Ind]₂ZrCl₂ (abbreviated as EI) was supported on the above three types of OMMTs to prepare the PE/OMMT nanocomposites via in situ polymerization. By contrast, EI/MMMT showed higher activity than EI/OH‐C18‐MMT and EI/C16‐MMT under the same polymerization conditions. The other two types of catalysts, such as [(tert‐Bu)NSi(Me₂)C₅Me₄]TiCl₂ (CGCT) and Bis[N‐(3‐tert‐butylsalicylidene)anilinato] titanium (IV) dichloride (FI) were also supported on the OH‐C18‐MMT for in situ ethylene polymerization. It was found that the activity of FI/OH‐C18‐MMT for ethylene polymerization was much lower than the other two corresponding catalysts under the similar reaction conditions. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Polymerization of propylene using the high‐activity Ziegler–Natta catalyst system SiO2/MgCl2 (ethoxide type)/TiCl4/Di‐n‐butyl phthalate/triethylaluminum/dimethoxy methyl cyclohexyl silane

The bisupported Ziegler–Natta catalyst system SiO₂/MgCl₂ (ethoxide type)/TiCl₄/di‐n‐butyl phthalate/triethylaluminum (TEA)/dimethoxy methyl cyclohexyl silane (DMMCHS) was prepared. TEA and di‐n‐butyl phthalate were used as a cocatalyst and an internal donor, respectively. DMMCHS was used as an external donor. The slurry polymerization of propylene was studied with the catalyst system in n‐heptane from 45 to 70°C. The effects of the TEA and H₂ concentrations, temperature, and monomer pressure on the polymerization were investigated. The optimum productivity was obtained at [Al]/[DMMCHS]/[Ti] = 61.7:6.2:1 (mol/mol/mol). The highest activity of the catalyst was obtained at 60°C. Increasing the H₂ concentration to 100 mL/L increased the productivity of the catalyst, but a further increase in H₂ reduced the activity of the catalyst. Increasing the propylene pressure from 1 to 7 bar significantly increased the polymer yield. The isotacticity index (II) decreased with increasing TEA, but the H₂ concentration, temperature, and monomer pressure did not have a significant effect on the II value. The viscosity‐average molecular weight decreased with increasing temperature and with the addition of H₂. Three catalysts with different Mg/Si molar ratios were studied under the optimum conditions. The catalyst with a Mg/Si molar ratio of approximately 0.93 showed the highest activity. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1177–1181, 2003