Copolymerization of ethylene/α‐olefins using bis(2‐phenylindenyl)zirconium dichloride metallocene catalyst: structural study of comonomer distribution

Catalysts have a major role in the polymerization of olefins and exert their influence in three ways: (1) polymerization behaviour, including polymerization activity and kinetics; (2) polymer particle morphology, including bulk density, particle size, particle size distribution and particle shape; and (3) polymer microstructure, including molecular weight regulation, chemical composition distribution and short‐ and long‐chain branching. By tailoring the catalyst structure, such as the creation of a bridge or introducing a substituent on the ligand, metallocene catalysts can play a major role in the achievement of desirable properties. Kinetic profiles of the metallocene catalyst used in this study showed decay‐type behaviour for copolymerization of ethylene/α‐olefins. It was observed that increasing the comonomer ratio in the feedstock affected physical properties such as reducing the melting temperature, crystallinity, density and molecular weight of the copolymers. It was also observed that the heterogeneity of the chemical composition distribution and the physical properties were enhanced as the comonomer molecular weight was increased. In particular, 2‐phenyl substitution on the indenyl ring reduced somewhat the melting point of the copolymers. In addition, the copolymer produced using bis(2‐phenylindenyl)zirconium dichloride (bis(2‐PhInd)ZrCl₂) catalyst exhibited a narrower distribution of lamellae (0.3–0.9 nm) than the polymer produced using bisindenylzirconium dichloride catalyst (0.5–3.6 nm). The results obtained indicate that the bis(2‐PhInd)ZrCl₂ catalyst showed a good comonomer incorporation ability. The heterogeneity of the chemical composition distribution and the physical properties were influenced by the type of comonomer and type of substituent in the catalyst. Copyright © 2010 Society of Chemical Industry     

Copolymerization of ethylene/5‐ethylidene‐2‐norbornene with bis (2‐phenylindenyl) zirconium dichloride catalyst: I. Optimization of the operating conditions by response surface methodology

In this study, the copolymerization of ethylene with nonconjugated diene (5‐ethylidene‐2‐norbornene) was carried out with a bis(2‐PhInd) ZrCl₂ metallocene catalyst. Some polymerization factors that were considered affective on the catalyst activity, including comonomer content in the feed, ethylene pressure, and polymerization temperature, were investigated via response surface methodology to determine the optimum polymerization conditions. We found that the comonomer content in the feedstock had no enormous effect on the catalyst activity depression. Also, the polymerization temperature increment through the scrutinized range decreased the copolymerization activity. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Ethylene polymerization with a silica‐supported iron‐based diimine catalyst

A supported iron‐based diimine catalyst (SC) was prepared by immobilization of 2,6‐bis[1‐(2,6‐diisopropylphenylimino)ethyl]pyridine iron chloride (I) on silica and employed in ethylene polymerization. The kinetic behavior of ethylene polymerization with SC was studied. The effects of the Al/Fe molar ratio, reaction temperature, and cocatalyst on the catalytic activity as well as the melting temperature, molecular weight, and morphology of the polymers obtained were also investigated. The results showed that good catalytic activities can be obtained even with a small amount of the cocatalyst methylaluminoxane (MAO) or triethylaluminum (AlEt₃). The polyethylenes obtained with a supported catalyst had higher molecular weight, higher melting temperature, and better morphology than those obtained with a homogeneous catalyst. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 466–469, 2003     

Copolymerization of propylene with p‐allyltoluene using metallocene catalysts

Copolymerization of propylene with p‐allyltoluene (p‐AT) was performed using two metallocene catalysts, rac‐ethylenebis(indenyl)zirconium dichloride and rac‐dimethylsilylenebis[1‐(2‐methyl‐4‐phenylindenyl)]zirconium dichloride. The effects of the polymerization conditions, such as the amount of p‐AT in the feed and polymerization temperature, on the properties of the copolymers and the activity of the catalysts were investigated. With increasing p‐AT feed, the incorporation of p‐AT increased, but the activity of the metallocene catalyst, the melting temperature (T_m) and the number‐average molecular weight of the copolymers decreased. Higher polymerization temperature tended to enhance the activity of the metallocene catalyst and the incorporation of p‐AT. The copolymers produced using the two metallocene catalysts were characterized with ¹H NMR, ¹³C NMR and differential scanning calorimetry; the results showed that the copolymers had a random structure. Copyright © 2006 Society of Chemical Industry Society of Chemical Industry     

Modification of a Ziegler-Natta catalyst with a metallocene catalyst and its olefin polymerization behavior

A Ziegler-Natta catalyst was modified with a metallocene catalyst and its polymerization behavior was examined. In the modification of the TiCl₄ catalyst supported on MgCl₂ (MgCl₂-Ti) with a rac-ethylenebis(indenyl)zirconium dichloride (rac-Et(Ind)₂ZrCl₂, EIZ) catalyst, the obtained catalyst showed relatively low activity but produced high isotactic polypropylene. These results suggest that the EIZ catalyst might block a non-isospecific site and modify a Ti-active site to form highly isospecific sites. To combine two catalysts in olefin polymerization by catalyst transitioning methods, the sequential addition of catalysts and a co-catalyst was tried. It was found that an alkylaluminum like triethylaluminum (TEA) can act as a deactivation agent for a metallocene catalyst. In ethylene polymerization, catalyst transitioning was accomplished with the sequential addition of bis(cyclopentadienyl)zirconium dichloride (Cp₂ZrCl₂)/methylaluminoxane (MAO), TEA, and a titanium tetrachloride/vanadium oxytrichloride (TiCl₄/VOCl₃, Ti-V) catalyst. Using this method, it was possible to control the molecular weight distribution (MWD) of polyethylene in a bimodal pattern. In the presence of hydrogen, polyethylene with a very broad MWD was obtained due to a different hydrogen effect on the Cp₂ZrCl₂ and Ti-V catalyst. The obtained polyethylene with a broader MWD exhibited more apparent shear thinning.     

Kinetics of Photocatalyzed Gas Reactions Using Titanium Dioxide as the Catalyst Part II: Photocatalyzed Total Oxidation of Alkanes with Oxygen

In order to obtain a useful expression for the kinetics of the photocatalyzed total oxidation reaction of alkanes with oxygen and TiO₂ as the catalyst, the dependence of the reaction rate on the concentration of the starting material species, the absorbed irradiation intensity, the wavelength of the light and the temperature was investigated. The experiments were performed in a CSTR system. The rate law found for alkane oxidation differs from that obtained for olefin oxidation due to a different reaction mechanism. While a reversible catalyst deactivation process takes place in the latter case, there is no hint of such a process during alkane oxidation. The kinetic data lead to the conclusion that the formation of an alkane and a hydrogen‐radical at a defect site of the catalyst is the first step in the total oxidation reaction of these species followed by the formation of a stronger adsorbed hydroperoxide species. The subsequent transformation of the hydroperoxide into further oxidized species mediated by the electron‐hole pairs generated by the absorbed light on the semiconductor's surface was recognized to be the rate determining step. The reaction behavior for the investigated alkanes could be modeled using this concept with the exception of methane. Its rate law differs strongly from that found for ethane, propane as well as iso‐butane.     

α‐Bis and α,ω‐tetrakis(4‐dimethylaminophenyl) functionalized polymers by atom transfer radical polymerization using 1,1‐bis[(4‐dimethylamino)phenyl]ethylene as tertiary diamine initiator precursor and functionalizing agent

The quantitative syntheses of α‐bis and α,ω‐tetrakis tertiary diamine functionalized polymers by atom transfer radical polymerization (ATRP) methods are described. A tertiary diamine functionalized 1,1‐diphenylethylene derivative, 1,1‐bis[(4‐dimethylamino)phenyl]ethylene (1), was evaluated as a unimolecular tertiary diamine functionalized initiator precursor as well as a functionalizing agent in ATRP reactions. The ATRP of styrene, initiated by a new tertiary diamine functionalized initiator adduct (2), affords the corresponding α‐bis(4‐dimethylaminophenyl) functionalized polystyrene (3). The tertiary diamine functionalized initiator adduct (2) was prepared in situ by the reaction of (1‐bromoethyl)benzene with 1,1‐bis[(4‐dimethylamino)phenyl]ethylene (1) in the presence of a copper (I) bromide/2,2′‐bipyridyl catalyst system. The ATRP of styrene proceeded via a controlled free radical polymerization process to afford quantitative yields of the corresponding α‐bis(4‐dimethylaminophenyl) functionalized polystyrene derivative (3) with predictable number‐average molecular weight (M_n) and narrow molecular weight distribution (M_w/M_n) in a high initiator efficiency reaction. The polymerization process was monitored by gas chromatography analysis. Quantitative yields of α,ω‐tetrakis(4‐dimethylaminophenyl) functionalized polystyrene (4) were obtained by a new post ATRP chain end modification reaction of α‐bis(4‐dimethylaminophenyl) functionalized polystyrene (3) with excess 1,1‐bis[(4‐dimethylamino)phenyl]ethylene (1). The tertiary diamine functionalized initiator precursor 1,1‐bis[(4‐dimethylamino)phenyl]ethylene (1) and the different tertiary amine functionalized polymers were characterized by chromatography, spectroscopy and non‐aqueous titration measurements. Copyright © 2012 Society of Chemical Industry     

Triazine reaction of cyanate ester resin systems catalyzed by organic tin compound: kinetics and mechanism

The mechanism and kinetics of the thermal cure reaction of two cyanate esters (CEs), 1,1′bis(4‐cyanatophenyl)ethane (AroCy L‐10) and bisphenol A dicyanate ester (BADCy), in the presence of dibutyl tin dilaurate (DBTDL) has been investigated using Fourier‐transform infrared spectroscopy (FTIR) and High‐performance liquid chromatography (HPLC). It was found that the organic tin compound (H₉C₄)₂Sn(NCO—R—OCN)₂, an active catalyst, has high catalytic efficiency in the polymerization of cyanate esters. The consuming rate of cyanate concentration showed a first‐order dependence on both active catalyst and the cyanate ester monomer concentration. The apparent activation energies (E_a) and frequency factors of both AroCy L‐10 and BADCy were calculated. A mechanism of cyclotrimerization was proposed, based on the kinetic data and FTIR spectra, which involves the formation of an active catalyst and the catalysis of the active catalyst. Copyright © 2004 Society of Chemical Industry     

Organic/inorganic support for immobilizing (n‐BuCp)2ZrCl2/TiCl3 hybrid catalyst for use in the preparation of polymer blends

Reactor blends of ultrahigh‐molecular‐weight polyethylene (UHMWPE) and low‐molecular‐weight polyethylene (LMWPE) were synthesized by two‐step polymerization using a hybrid catalyst. To prepare the hybrid catalyst, styrene acrylic copolymer (PSA) was first coated onto SiO₂/MgCl₂‐supported TiCl₃; then, (n‐BuCp)₂ZrCl₂ was immobilized onto the exterior PSA. UHMWPE was produced in the first polymerization stage with the presence of 1‐hexene and modified methylaluminoxane (MMAO), and the LMWPE was prepared with the presence of hydrogen and triethylaluminium in the second polymerization stage. The activity of the hybrid catalyst was considerable (6.5 × 10⁶ g PE (mol Zr)^?1 h^?1), and was maintained for longer than 8 h during the two‐step polymerization. The barrier property of PSA to the co‐catalyst was verified using ethylene polymerization experiments. The appearance of a lag phase in the kinetic curve during the first‐stage polymerization implied that the exterior catalyst ((n‐BuCp)₂ZrCl₂) could be activated prior to the interior catalyst (M‐1). Furthermore, the melting temperature, crystallinity, degree of branching, molecular weight and molecular‐weight distribution of polyethylene obtained at various polymerization times showed that the M‐1 catalyst began to be activated by MMAO after 40 min of the reaction. The activation of M‐1 catalyst led to a decrease in the molecular weight of UHMWPE. Finally, the thermal behaviors of polyethylene blends were investigated using differential scanning calorimetry. Copyright © 2011 Society of Chemical Industry     

Elastomeric properties of ethylene/propylene copolymers prepared by zirconocene/methylaluminoxane catalysts

Ethylene/propylene copolymers (EPM) have been prepared by a liquid propylene suspension process, using homogeneous catalysts based on nonbridged zirconocenes and methylaluminoxane (MAO). When bis(η⁵-cyclopentadienyl)zirconium dichloride (Cp₂ZrCl₂), bis(η⁵-cyclopentadienyl) dimethyl zirconium (Cp₂ZrMe₂) and bis(η⁵-cyclopentadienyl), dibenzyl zirconium (Cp₂ZrBz₂) were used as catalyst components, EPM having low average molecular weight (MW) were in general obtained in low yield. On the contrary, a very large improvement of productivity and MW was observed when bis(η⁵-indenyl)zirconium dichloride (Ind₂ZrCl₂) and bis(η⁵-indenyl) dimethyl zirconium (Ind₂ZrMe₂) as well as bis(η⁵-tetrahydroindenyl)zirconium dichloride [(IndH₄)₂ZrCI₂] were employed in combination with MAO. In particular, this last catalytic system allowed one to obtain EPM with a narrower distribution of MW in addition to the above characteristics. Better performances, in terms of rheological and elastomeric properties, were also found for the crude and vulcanized samples prepared by (IndH₄)₂ZrCl₂/MAO catalyst.     

DSC studies on synthesis of superabsorbent hydrogels

Reaction scheme of acrylic-based superabsorbing polymers was monitored by a differential scanning calorimeter. Differential scanning calorimetry (DSC) was used to study the heat effects during the polymer synthesis in DSC pan as a micro-scale reactor. Two distinct observations, i.e. inhibition period (IP) and onset of gel formation were recorded during polymerization. The effect of reaction temperature and initiator (K₂S₂O₈) concentration was assessed on these general observations. It was found that unrestricted access of the reaction mixture to oxygen and unrestricted loss of water could complicate the polymerization behavior of sodium acrylate in aqueous system. A conceptual kinetic approach was followed to describe the complex process. Finally, DSC observations were compared with their corresponding bench-scale figures.     

Palladium(II) Complexes of C2‐Bridged Chiral Diphosphines: Application to Enantioselective Carbonyl‐Ene Reactions

(11bR,11′bR)‐4,4′‐(1,2‐Phenylene)bis[4,5‐dihydro‐3H‐dinaphtho[2,1‐c:1′,2′‐e]phosphepin] [abbreviated as (R)‐BINAPHANE], (3R,3′R,4S,4′S,11bS,11′bS)‐4,4′‐bis(1,1‐dimethylethyl)‐4,4′,5,5′‐tetrahydro‐3,3′‐bi‐3H‐dinaphtho[2,1‐c:1′,2′‐e]phosphepin [(S)‐BINAPINE], (1S,1′S,2R,2′R)‐1,1′‐bis(1,1‐dimethylethyl)‐2,2′‐biphospholane [(S,S,R,R)‐TANGPHOS] and (2R,2′R,5R,5′R)‐1,1′‐(1,2‐phenylene)bis[2,5‐bis(1‐methylethyl)phospholane] [(R,R)‐i‐Pr‐DUPHOS] are C₂‐bridged chiral diphosphines that form stable complexes with palladium(II) and platinum(II) containing a five‐membered chelate ring. The Pd(II)‐BINAPHANE catalyst displayed good to excellent enantioselectivities with ee values as high as 99.0% albeit in low yields for the carbonyl‐ene reaction between phenylglyoxal and alkenes. Its Pt(II) counterpart afforded improved yields while retaining satisfactory enantioselectivity. For the carbonyl‐ene reaction between ethyl trifluoropyruvate and alkenes, the Pd(II)‐BINAPHANE catalyst afforded both good yields and extremely high enantioselectivities with ees as high as 99.6%. A comparative study on the Pd(II) catalysts of the four C₂‐bridged chiral diphosphines revealed that Pd(II)‐BINAPHANE afforded the best enantioselectivity. The ee values derived from Pd(II)‐BINAPHANE are much higher than those derived from the other three Pd(II) catalysts. A comparison of the catalyst structures shows that the Pd(II)‐BINAPHANE catalyst is the only one that has two bulky (R)‐binaphthyl groups close to the reaction site. Hence it creates a deep chiral space that can efficiently control the reaction behavior in the carbonyl‐ene reactions resulting in excellent enantioselectivity.     

Modeling of the propylene polymerization catalyzed by single‐/multi‐active site catalyst: A Monte Carlo study

In the present study, a model is established to describe the propylene polymerization kinetics catalyzed by the typical catalysts with single‐/multi‐active site type in a liquid phase stirred‐tank reactor using the Monte Carlo simulation method, regardless of the mass and heat diffusion effects within the polymer particles. Many kinetic data, including polypropylene yield, concentration transformation of catalyst active sites, number–average molecular weight, etc., are obtained by the model. The simulated kinetic results are found to be in agreement with the reference ones obtained in a population balance model. Furthermore, the comparisons of the kinetic data between the polymerization catalyzed by the catalyst with single‐active site type (typically silica‐supported metallocene) and the catalyst with multi‐active site type (typically MgCl₂‐supported Ziegler‐Natta catalyst) have been studied using the model. Especially, the effects of hydrogen on the polymerization are studied using the model. The studied results show that the theory of catalyst active site can be used to explain the different propylene polymerization kinetics catalyzed by the typical catalyst with single‐/multi‐active site type. In addition, the role of hydrogen in the propylene polymerization needs to be emphasized. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Monomers for adhesive polymers, 8a crosslinking polymerization of selected N‐substituted bis(acrylamide)s for dental filling materials

The free‐radical polymerization of bis‐(N‐ethylacrylamido)‐ethylenglycol ( I ), N,N′‐dimethyl‐1,6‐bis (acrylamido)‐hexan ( II ), and N,N′‐diethyl‐1,3‐bis(acrylamido)‐propan ( III ) were investigated. The cross‐linking polymerization was followed in bulk by using the ampoules technique and gravimetry. Polymerizations exhibited an abnormal kinetic behavior. For the monomer II , for example, the reaction order to 2,2′‐ azobisisobutyronitril (AIBN) initiator of 1.28, and the polymerization overall activation energy of 151 kJ/mol between 50 and 75°C were determined. The increasing temperature and decreasing initiator concentration resulted in an increase of double bonds consumption in the formed polymer network. At 75°C the residual unsaturation was under 2%, compared with 9.9% at 50°C. The monomer conversion‐time dependences were complemented also with differential scanning calorimetry (DSC) recording the heat released during polymerization. The extension of peak time with decreasing the instant heat flow rate at this point sort the studied bis(acrylamide)s according the reactivity in the following sequence: monomer III > I > II . The polymer samples sol–gel analyses in ethanol allowed the determination of the molecular weight M_c between the network crosslinks. The presence of microgel particles at the very beginning of polymerization and the changes in chain conformation with temperature we consider as the way in which was affected the polymerization kinetics of these monomers. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Polymerization of olefins through heterogeneous catalysis. XVII. Experimental study and model interpretation of some aspects of olefin polymerization over a TiCl4/MgCl2 catalyst

Using a high-activity MgCl₂-supported TiCl₄ catalyst, kinetic studies of ethylene and propylene polymerization are conducted in a semi-batch gas phase stirred-bed reactor system. Based on the experimental observations obtained from this study and others in the literature, simple kinetic mechanisms are proposed to explain the data. This model considers both the site formation from the interaction of catalyst and cocatalyst as well as the participation of monomers during site activation. By using this model together with parameters estimated from various sources, some aspects of kinetic behavior have been successfully predicted. These include the rate enhancement introduced by α-olefins, the effect of the Al/Ti ratio on kinetic features such as catalyst activity and decay rate, as well as the different reaction orders observed for various monomers. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:1037–1052, 1997     

Novel monocyclopentadienyl zirconium and hafnium trialkoxide complexes: Syntheses and catalytic properties for olefin polymerization

Monocyclopentadienyl trialkoxy compounds of zirconium and hafnium [CpZr(OR)₃ and CpHf(OR)₃], which cannot be prepared by earlier methods, are synthesized in situ by reacting bis(cyclopentadienyl) magnesium with zirconium tetraalkoxides [Zr(OR)₄] and with hafnium tetraalkoxides [Hf(OR)₄], respectively. The generation of CpZr(OR)₃ and CpHf(OR)₃ compounds involves a highly effective cyclopentadienyl ligand (Cp) transfer reaction from the Cp ligand of bis(cyclopentadienyl) magnesium to Group 4 metal alkoxides. The utilization of CpZr(OR)₃ and CpHf(OR)₃ compounds as catalyst precursors for mediating α‐olefin polymerizations was carefully investigated. Results show that highly active catalysts can be generated by reacting these mono‐Cp Zr and Hf alkoxides with methylaluminoxane. The resulting active CpZr(OR)₃/MAO and CpHf (OR)₃/MAO catalysts induce ethylene polymerization and ethylene/propylene copolymerization with high activity (e.g., 1820 kg PE/mole of catalyst‐h). © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Ring‐opening copolymerization of epoxycyclohexane and phthalic anhydride catalyzed by the asymmetric Salen‐CrCl complex

A new metallic chromium complex with asymmetric salen ligand and ancillary chloride group (complex 1 ) has been synthesized and applied as co‐catalytic system with bis(triphenylphosphine)iminium chloride (PPNCl) for the polymerization of epoxycyclohexane (CHO) and phthalic anhydride (PA). The catalyst loading, polymerization temperature, reaction time and type of co‐catalyst were varied in order to explore the influences on the catalytic activity of 1 . It was found that 1 exhibited relatively good activity in the catalytic copolymerization of PA and CHO to form the product with more than 90% ester linkage content under mild conditions after the addition of the PPNCl co‐catalyst. This was in sharp contrast to the dinuclear [ONSO]CrCl analogue, where the resulting polymer with more than 97% ether units was achieved under identical conditions. According to the kinetic data, the apparent activation energy of CHO ring‐opening copolymerization was 9.0 kJ mol^?1. A reasonable polymerization mechanism was proposed based on the interaction between the single‐metal two‐component catalyst system and the monomer. © 2020 Society of Chemical Industry     

Kinetics of atom transfer radical polymerization of crosslinkable terpolymer P(MMA‐BA‐HEMA)

A crosslinkable terpolymer P(MMA‐BA‐HEMA) was prepared by atom transfer radical copolymerization of 2‐hydroxyethyl methacrylate, methyl methacrylate and butyl acrylate. The structure of the terpolymer was characterized by ¹H NMR and gel permeation chromatography. The effects on the polymerization of ligand, initiator, solvent, CuCl₂ added in the initial stage and reaction temperature were investigated. The optimal reaction conditions were ethyl 2‐bromopropionate as initiator, CuCl/PMDETA as catalyst, cyclohexanone as solvent, catalyst/ligand = 1:1.5, [M]₀:[I]₀ = 200:1 and temperature 70 °C. The reaction followed first‐order kinetics with respect to monomer concentration, indicating the best control over the polymerization process, a constant concentration of the propagating radical during the polymerization, efficient control over M_n of the polymer and low polydispersity (M_w/M_n < 1.3). © 2013 Society of Chemical Industry     

FI Zr-type catalysts for ethylene polymerization

Two FI-type catalysts of Bis[N-(3,5-dicumylsalicylidene)-naphthylaminato]zirconium(IV) dichloride (catalyst (a)) and Bis[N-(3,5-dicumylsalicylidene)-anthracylaminato]zirconium(IV) dichloride (catalyst (b)) were prepared and used for ethylene polymerization comparatively. Methylaluminoxane (MAO) was used as cocatalyst. Polymerization reactions of ethylene using the prepared catalysts at the different conditions of polymerization were carried out. Plurality of the fused aromatic rings on the N atom of the imine in the catalyst structure affected the polymerization activity and molecular weight of the resulting polymer as well. Productivity of the prepared catalysts increased with the addition of [Al]/[Zr] molar ratio. The highest activity was observed at about 35–40 °C for the catalysts. The catalyst (b) produced higher viscosity average molecular weight (M_v) of the obtained polyethylene, while generally the activity of the catalyst (a) was higher than the catalyst (b). Similar behavior was observed for the polymerization carried out at the monomer pressure of 2 to 6 bars using the catalysts. The higher the pressure the more activity of the catalysts obtained, in the range studied. Crystallinity and melting point of the obtained polymer were between 55–65% and 120–135 °C respectively. Higher pressure increased both the crystallinity and the M_v values of the resulting polymer. The polymerization was carried out using different amounts of hydrogen. Higher amount of hydrogen could increase the activity of the catalysts. A linear dependence between the polymerization time and the molar weight was observed, however the polydispersity was broadened with the time.     

Ethylene polymerization using a novel MgCl2/SiO2‐supported Ziegler–Natta catalyst

A novel MgCl₂/SiO₂‐supported Ziegler–Natta catalyst was prepared using a new one‐pot ball milling method. Using this catalyst, polyethylenes with different molecular weight distributions were synthesized. The effects of the [Si]/[Mg] ratio, polymerization temperature and [Al]/[Ti] ratio on the catalytic activity, the kinetic behaviour and the molecular weight and the polydispersity of the resultant polymer were studied. It was found that the polydispersity index of the polymer could be adjusted over a wide range of 5–30 through regulating the [Si]/[Mg] ratio and polymerization temperature, and especially when the [Si]/[Mg] ratio was 1.70, the polydispersity index could reach over 25. This novel bi‐supported Ziegler–Natta catalyst is thus useful for preparing polyethylene with a required molecular weight distribution using current equipment and technological processes. Copyright © 2005 Society of Chemical Industry