Conventional Ziegler-Natta Catalysts Research Articles

Effects of Polymerization Medium on Nascent UHMWPE Properties and Sintered Material Performance

High-performance and easy-processing UHMWPE products with less entanglement and small particle size are difficult to synthesize efficiently in the polymerization process. In this study, a mixture of heptane and light paraffin is proposed as the polymerization medium to control the concentration of ethylene in the slurry during polymerization. Influences of the mixture composition on the polymerization behavior of ethylene, the particle size and its distribution of nascent UHMWPE, and the initial entangled state of UHMWPE were explored. Experimental results showed that as the volume fraction of heptane decreased, the viscosity of the solvent mixture increased exponentially, and ethylene solubility as well as mass transfer coefficient of ethylene in solvent decreased, which greatly affected the ethylene polymerization rate. By adjusting the volume fraction of heptane in the polymerization medium, the particle size, initial entanglement state density, and molecular weight of nascent UHMWPE will be coordinately controlled. UHMWPE with smaller particle size, lower entanglement density, and higher molecular weight can be prepared using the conventional Ziegler–Natta catalyst and polymerization medium with a lower heptane content, and its sintered UHMWPE material shows good mechanical properties.

Synthesis and properties of syndiotactic 1,2‐polybutadiene catalyzed by iron catalyst with phosphate as additive

Abstract1,2 Syndiotactic polymerization of butadiene is accessible by iron catalysts prepared from commercially available iron sources, trialkylaluminum with additional phosphate as additive. The catalyst formation is quite robust in terms of handling and stability under polymerization conditions. Activity equal to 115 kg (polymer)/mol(Fe)·h is achieved at 10,000 equiv. of monomer relative to the catalyst loading in 2 h at 50°C. The resultant polymer possesses 1,2 incorporation up to 80.2–93.1% with syndiotactic configuration (rrrr) of 40.2–85.2%. Crystallinity of polymers can be also tuned over a wide range degree from weak (2.1%) to high crystallinity (68.2%) by varying catalyst component feeding, enabling potential application as both rubber and resin. The higher activity of iron catalyst is preferred at hydrocarbon solvent n‐hexane, n‐heptane or toluene, higher temperature as well as trialkylalumium, such as tri‐iso‐butylaluminum, tri‐ethylaluminum, and tri‐methylaluminum as cocatalyst. Significant stereospecificity stability to variation for monomer concentration, type of alkylaluminum and temperature is also found. The high activity and 1,2‐stereoselectivity featured with these thermal robust iron catalysts sheds light on the significance of additive on regulating stereo‐polymerization promoted by conventional Ziegler–Natta catalysts. These features collectively could offer advantages for application in industry production of 1,2‐syndiotactic polybutadiene.

Effects of monomer length on α‐olefins polymerization using a conventional Ziegler–Natta catalyst

Abstractα‐Olefin monomers with different lengths from C4 to C10 were polymerized via a conventional Ziegler–Natta catalyst. It was found that activity of the catalyst decreases with increase in the monomer length as well as introduction of external donor. GPC results exhibited a steady decrease in molecular weight from poly1‐butene to poly1‐decene; however, PDI did not show a clear trend. Based on differential scanning calorimetry and X‐ray diffraction analyses, poly1‐butene and poly1‐decene represented crystalline structure with one and two melting points, respectively, while poly1‐hexene and poly1‐octene showed amorphous nature. The content of isotactic pentads increased from poly1‐butene to poly1‐octene, with maximum value of mmmm = 76%, but decreased again in poly1‐decene. Calculated ΔEre‐si values showed a peak by increasing monomer length which was in line with the experimental results for isotactic content.

Propylene Polymerization over MgCl2‐Supported Ziegler–Natta Catalysts Containing Tri‐Ether as the Internal Donor

ABSTRACT1‐Methoxy‐2,2‐bis(methoxymethyl)butane as a new internal donor was synthesized by the reaction of 1,1,1‐tris(hydroxymethyl)propane with sodium hydride as the base and methyl iodide as the alkyl halide. The tri‐ether compound was characterized by NMR and FTIR techniques. The MgCl2‐supported titanium catalysts were incorporated with varying amounts of 1‐methoxy‐2,2‐bis(methoxymethyl)butane as the internal donor (ID) and also without the internal donor were synthesized, and then the prepared catalysts were characterized. The concentration of titanium, magnesium, and chloride were determined by spectrophotometry and by complexometric and argentometric titration, respectively. The polymerization of propylene was carried out with the prepared catalysts in conjunction with triethylaluminum as a cocatalyst and hydrogen as a chain transfer agent, with and without cyclohexylmethyldimethoxysilane as the external donor. The effects of a new internal donor on MgCl2‐supported Ziegler–Natta catalysts for propylene polymerization were investigated, and then these results were compared to the obtained polypropylenes results, which were obtained using the conventional Ziegler–Natta catalyst containing diisobutyl phthalate as the internal donor. The highest isotacticity, melting temperature, and crystallinity degree of polypropylene were obtained using Cat‐D with an ID/Mg molar ratio equal to 0.44, and the highest catalytic activity is related to Cat‐B with an ID/Mg molar ratio equal to 0.22.The Ziegler–Natta catalysts incorporated with various ID/Mg molar ratios of 1‐methoxy‐2,2‐bis(methoxymethyl)butane were synthesized. The polymerization of propylene was carried out with the prepared catalysts. The highest catalytic activity is related to Cat‐B with an ID/Mg molar ratio equal to 0.22. The catalyst with an optimum ID/Mg molar ratio equal to 0.44 is a favorable catalyst for polymerization of propylene.

Nanocomposites and high-modulus fibers based on ultrahigh-molecular-weight polyethylene and silicates: Synthesis, structure, and properties

Nanocomposites based on ultrahigh-molecular-weight polyethylene and inorganic fillers—such as organomodified layered aluminosilicates, aerosil, and diatomite—are prepared via polymerization filling. The polymerization of ethylene was conducted in the suspension mode with the use of a conventional Ziegler-Natta catalyst, TiCl4 + Al(i-Bu)3, under mild conditions (a temperature of 30°C and a pressure of 0.1MPa). The structure and properties of the composites are studied via X-ray diffraction analysis and DSC. The polyethylene matrix features a high enthalpy, a high melting temperature (up to 143°C), a crystallinity of 70–80%, a content of the monoclinic phase of 12–15%, and a bulk density of 0.05–0.15 g/cm3; the molecular mass is (1.5–1.6) × 106. High-modulus, high-strength fibers with an elastic modulus of 25–28 GPa and a strength of 0.65–0.70 GPa are prepared via direct solvent-free molding of nascent reactor powders based on ultrahigh-molecular-weight polyethylene filled (7 wt %) with aerosol or montmorillonite modified with vinyltrimethoxysilane.

Nanocomposites based on layered silicates and ultrahigh-molecular-mass polyethylene prepared via in situ polymerization

Nanocomposites based on ultrahigh-molecular-mass PE and layered silicates are prepared via in situ polymerization. The process is conducted in the suspension mode under mild conditions with the use of a conventional Ziegler-Natta catalyst and a bifunctional complex containing a nickel oligoallene component along with a titanium component. The fillers are four types of montmorillonite: nonmodified montmorillonite and three montmorillonites modified with various organic intercalants. In their presence, the activities of the catalysts appreciably increase (by a factor of 2–3). Composites containing 10–40 wt % aluminosilicates are prepared. The structures of the polymer matrix and composites are studied via X-ray diffraction. It is found that the degree of exfoliation of the filler depends not only on its amount but also on the type of modifier and the type of catalytic system. The PE matrix with a molecular mass of (1.5–1.6) × 106 has a melting point of T m = 141–143°C, a high enthalpy of melting, and a high degree of crystallinity. The IR-spectral studies of the polymers synthesized with the bifunctional complex reveal the presence of branches in a chain, thereby suggesting the formation of linear PE with a medium density (0.938–0.946 g/cm3). Nanocomposites containing 10% aluminosilicate possess the best complex of mechanical properties relative to that of unfilled polyethylene.

Crystallizable Polyisoprene under Strain Obtained by Nd-based Catalyst

The conventional Ziegler-Natta catalyst composed of neodymium versatate (Nd(vers)3), alkylaluminum (Al( i-Bu)2H or Al( i-Bu)3) and diisobutylaluminum chloride (Al( i-Bu)2Cl) was examined in isoprene polymerization. The polymer with narrow molecular weight distribution ( Mw/ Mn < 3) can be obtained by controlling Al( i-Bu)2H amounts and component addition order. While, polyisoprene with high cis-1,4 content (> 96%), high molecular weight (> 100×104) and narrow molecular weight distribution (Mw/Mn < 2.2) is synthesized by using Al( i-Bu)3 as cocatalyst. In the meantime, the obtained polymer has crystallization behavior under strain.

Polymer‐supported heterogeneous titanium‐based Ziegler‐Natta catalyst for ethylene polymerization

AbstractReported here in, is the synthesis of polystyrene (PS)‐supported Ziegler–Natta catalyst (PS‐TiCl4) by the reaction of PS and titanium tetrachloride (TiCl4). PS was synthesized by emulsion polymerization using super critical CO2 (sc‐CO2) as a medium. Three catalysts were synthesized by varying the TiCl4/PS weight ratio in hexane medium. The resulting catalysts were characterized by Fourier transformed‐infrared spectroscopy, UV–visible spectroscopy, scanning electron microscope and energy dispersive X‐ray detector, X‐ray diffraction analysis. The acidity of the catalysts in an acetone/water solution was measured by pH meter. The thermogravimetric analysis reveals that catalysts are stable upto 150–180°C. Due to their higher degree of thermal stability these catalysts may potentially be used as a support in conventional Ziegler–Natta catalyst for ethylene polymerization. These catalysts also showed good storability and its overall catalytic productivity are found to be 3720 g PE/g Ti. The productivity of the catalysts also depended on the titanium concentration in the polymer matrix. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Poly(amic acid)‐Supported Heterogeneous Titanium‐Based Ziegler‐Natta Catalyst for Ethylene Polymerization in a Slurry Process

AbstractThe synthesis of a poly(amic acid) (PAA)‐supported Ziegler–Natta catalyst (PAA‐TiCl4) by the reaction of PAA and titanium tetrachloride (TiCl4) is reported. For ethylene polymerization, three catalysts were synthesized by varying the TiCl4/PAA weight ratio in a hexane medium. The resulting catalysts were characterized by Fourier‐transformed infrared (FT‐IR), ultraviolet (UV), scanning electron microscopy and energy dispersive x‐ray detector (SEM‐EDX), and x‐ray diffraction analysis (XRD). The acidity of the catalysts in an acetone/water solution was measured by a pH meter. Thermogravimetric analysis reveals that catalysts are stable up to 110–125°C. Because of their higher degree of thermal stability, these catalysts may potentially be used as a support in a conventional Ziegler–Natta catalyst for ethylene polymerization. Furthermore, because of the extensive reaction between the functional groups of PAA and TiCl4, the chain structure of the PAA was destroyed. The newly synthesized catalysts showed good storability, and the overall catalytic productivity is 4921 g PE/g Ti/h. A catalyst with titanium incorporation corresponding to 2.8 wt% showed the maximum activity. The productivity of the catalysts also depended on the titanium concentration in the polymer matrix. These catalysts are found to retain their catalytic activity for a long time (∼90 days), and a mild reaction condition is required for catalysis. © 2011 Wiley Periodicals, Inc. Adv Polym Techn 32: E119–E130, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/adv.20276

Single site metallorganic polymerization catalysis as a method to probe the properties of polyolefins

Single-site metallorganic catalysts for the polymerization of olefins has allowed the synthesis of new polymeric materials having molecular structures that cannot be obtained with conventional Ziegler–Natta catalysts, with exceptional control over the chain architecture, including control of the concentration of stereo- and regio-defects and efficient uniform placement of comonomeric units along the chains. The cases of isotactic and syndiotactic polypropylenes are illustrated as examples of a fine tuning of the physical and mechanical properties of polymeric materials achieved through the controlled incorporation of stereo- and regio-defects, and the rational choice of the catalytic system. Novel isotactic polypropylenes with controlled properties, intermediate between those of stiff-plastic and elastomeric materials have been produced through the design of the catalysts. For syndiotactic polypropylene, a new class of thermoplastic elastomers with finely controlled mechanical properties have been produced by using metallorganic catalysts of different stereoselectivity. Depending on the concentration of stereodefects, elastomers showing entropic or unconventional enthalpic elasticity, can be produced.

The Influence of Mixed Activators on Ethylene Polymerization and Ethylene/1-Hexene Copolymerization with Silica-Supported Ziegler-Natta Catalyst

This article reveals the effects of mixed activators on ethylene polymerization and ethylene/1-hexene copolymerization over MgCl2/SiO2-supported Ziegler-Natta (ZN) catalysts. First, the conventional ZN catalyst was prepared with SiO2 addition. Then, the catalyst was tested for ethylene polymerization and ethylene/1-hexene (E/H) co-polymerization using different activators. Triethylaluminum (TEA), tri-n-hexyl aluminum (TnHA) and diethyl aluminum chloride (DEAC), TEA+DEAC, TEA+TnHA, TnHA+ DEAC, TEA+DEAC+TnHA mixtures, were used as activators in this study. It was found that in the case of ethylene polymerization with a sole activator, TnHA exhibited the highest activity among other activators due to increased size of the alkyl group. Further investigation was focused on the use of mixed activators. The activity can be enhanced by a factor of three when the mixed activators were employed and the activity of ethylene polymerization apparently increased in the order of TEA+ DEAC+TnHA > TEA+DEAC > TEA+TnHA. Both the copolymerization activity and crystallinity of the synthesized copolymers were strongly changed when the activators were changed from TEA to TEA+DEAC+TnHA mixtures or pure TnHA and pure DEAC. As for ethylene/1-hexene copolymerization the activity apparently increased in the order of TEA+DEAC+TnHA > TEA+TnHA > TEA+DEAC > TnHA+DEAC > TEA > TnHA > DEAC. Considering the properties of the copolymer obtained with the mixed TEA+DEAC+TnHA, its crystallinity decreased due to the presence of TnHA in the mixed activator. The activators thus exerted a strong influence on copolymer structure. An increased molecular weight distribution (MWD) was observed, without significant change in polymer morphology.

Effects of comonomer content, comonomer distribution and crystallization condition on crystallinity and dimension of crystal lattice of ethylene-propylene copolymers

AbstractIn the present work, the crystallinity and dimension of crystal lattice of two series of ethylene-propylene copolymers with different propylene contents, which were prepared by a fluorinated bis(phenoxyimine) Ti catalyst (FI-EP copolymers) and a conventional Ziegler-Natta catalyst (ZN-EP copolymers), respectively, were studied. It is found that the overall propylene content and crystallization condition have more marked effects on the crystallinity of the FI-EP copolymers with a random comonomer distribution than that of the ZN-EP copolymers with a heterogeneous comonomer distribution. The dimension of a-axis of the PE crystals increases more rapidly with the overall propylene content in the FI-EP copolymers, indicating that more propylene units are included into the PE crystals, whereas the a-axis of the PE crystals remains unchanged for all the ZNEP copolymers. Quenching of the samples leads to more propylene units getting included into the PE crystals. The effects of comonomer content and crystallization condition on crystallinity and dimension of crystal lattice of FI-EP and ZN-EP copolymers can be explained in terms of their different comonomer distributions.

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 Ktrm/Kp and Ktra/Kp, and higher ratio of Ktra/Ktrm which indicates that chain transfer to cocatalyst is predominant.

Thermal fractionation and effect of comonomer distribution on the crystal structure of ethylene–propylene copolymers

In this paper the comonomer distributions of two series of ethylene–propylene copolymers with different propylene contents, which were prepared by a fluorinated bis(phenoxyimine) Ti catalyst (FI–EP copolymers) and a conventional Ziegler–Natta catalyst (ZN–EP copolymers), respectively, were characterized. It is found that the comonomer distribution of ethylene–propylene copolymers can still be characterized by thermal fractionation at a long scale, though the propylene units can be incorporated into the PE crystal lattice. The FI–EP copolymers exhibit a narrow and random comonomer distribution, whereas a broad comonomer distribution is observed for the ZN–EP copolymers. The crystal structures of the FI–EP and ZN–EP copolymers were studied by WAXD. The a-axis of the PE crystals of the FI–EP copolymers increases rapidly with propylene content, indicating that more propylene units are incorporated into the PE crystal lattice, whereas only a slight expansion in a-axis is observed for the ZN–EP copolymers. WAXD result also shows the presence of hexagonal phase in the FI–EP copolymers and the relative content of the hexagonal phase increases with the propylene content, while in the ZN–EP copolymers the hexagonal phase is negligible.

Highly cis-1,4 Selective Polymerization of Dienes with Homogeneous Ziegler−Natta Catalysts Based on NCN-Pincer Rare Earth Metal Dichloride Precursors

The first aryldiimine NCN-pincer ligated rare earth metal dichlorides (2,6-(2,6-C6H3R2N=CH)2-C6H3)LnCl2(THF)2 (Ln = Y, R = Me (1), Et (2), iPr (3); R = Et, Ln = La (4), Nd (5), Gd (6), Sm (7), Eu (8), Tb (9), Dy (10), Ho (11), Yb (12), Lu (13)) were successfully synthesized via transmetalation between 2,6-(2,6-C6H3-R2N=CH)2-C6H3Li and LnCl3(THF)(1-3.5). These complexes are isostructural monomers with two coordinating THF molecules, where the pincer ligand coordinates to the central metal ion in a kappaC:kappaN:kappaN' tridentate mode, adopting a meridional geometry. Complexes 1-6, 9-11, and 13 combined with aluminum tris(alkyl)s and [Ph3C][B(C6F5)4] established a homogeneous Ziegler-Natta catalyst system, which exhibited high activities and excellent cis-1,4 selectivities for the polymerizations of butadiene (T(p) = 25 degrees C, 99.9%; 0 degrees C, 100%) and isoprene (T(p) = 25 degrees C, 98.8%). Remarkably, such high cis-1,4 selectivity almost remained at elevated polymerization temperatures up to 80 degrees C and did not vary with the type of the central lanthanide element, however, which was influenced obviously by the ortho substituent of the N-aryl ring of the ligands and the bulkiness of the aluminum alkyls. The Ln-Al bimetallic cations were considered as the active species. These results shed new light on improving the catalytic performance of the conventional Ziegler-Natta catalysts for the specific selective polymerization of dienes.

CRYSTALLIZATION KINETICS OF ETHYLENE-PROPYLENE COPOLYMERS PREPARED BY LIVING COORDINATION POLYMERIZATION

In this paper, crystallization kinetics of a series of ethylene-propylene copolymers prepared by living polymerization coordination catalyzed by a fluorinated bis(phenoxyimine) Ti catalyst (FI-EP copolymers) was studied, and was compared with that of ethylene-propylene copolymers prepared by a conventional Ziegler-Natta catalyst (ZN-EP copolymers). It is found that, the Avrami exponent and the crystallization rate constant of the FI-EP and ZN-EP copolymer show similar dependence on crystallization temperature, but the FI-EP copolymers exhibit a larger Avrami exponent than corresponding ZN-EP copolymers at high crystallization temperature and at low propylene content level. The crystallization temperature, equilibrium melting temperature and crystallinity of the FI-EP copolymers decrease more rapidly with propylene content than those of the ZN-EP copolymers. This can be attributed to their different comonomer distributions and partially to the different molecular weight distributions at low propylene content level.

Ethylene polymerization using metallocenes supported on MgCl2/SiCl4−n (n-C6H13O)n

Metallocene complexes Cp2TiCl2, Cp2ZrCl2, Cp2Zr(N n Bu2)2, Cp2Ti(η 1-OC(O)C6H5)2 and Cp2Zr(η 1-OC(O)C6H5)2 were supported on MgCl2/SiCl4−n (n-C6H13O) n carrier and used for ethylene polymerization. The supported complexes result in highly active catalysts when treated with different aluminum alkyl-based co-catalysts. These catalysts are able of tuning the final properties of the produced polyethylenes. Mixed composites of metallocenes and conventional Ziegler–Natta catalysts supported on the same carrier were also studied. A supported zirconocene Cp2Zr(η 1-OC(O)C6H5)2 on MgCl2/SiCl4−n (n-C6H13O) n resulted in a highly active catalyst that eject control on the molecular weight, crystallinity and morphology of the resultant polyethylene.

A novel route to the synthesis of PP- g-PMMA copolymer via ATRP reaction initiated by Si–Cl bond

The copolymerization of propylene with allyldimethylsilane (ADMS) was carried out with conventional Ziegler–Natta catalyst supported on MgCl 2. The effects of the concentration of ADMS in the feed on the polymerization reaction and copolymer properties were investigated. The resulting copolymer PP- co-ADMS was chlorinated to PP–Si–Cl by refluxing the copolymer with SOCl 2 in benzene. The chlorinated copolymer was used to initiate ATRP of MMA with CuCl/PMDETA as catalyst to produce graft copolymer PP- g-PMMA, which was characterized with 1H NMR, 13C NMR, GPC and DSC. Polymer blend of iPP/PP- g-PMMA/PMMA was prepared and the results shown that PP- g-PMMA was an effective compatilizer.

Surface science of single-site heterogeneous olefin polymerization catalysts

This article reviews the surface science of the heterogeneous olefin polymerization catalysts. The specific focus is on how to prepare and characterize stereochemically specific heterogeneous model catalysts for the Ziegler-Natta polymerization. Under clean, ultra-high vacuum conditions, low-energy electron irradiation during the chemical vapor deposition of model Ziegler-Natta catalysts can be used to create a "single-site" catalyst film with a surface structure that produces only isotactic polypropylene. The polymerization activities of the ultra-high vacuum-prepared model heterogeneous catalysts compare well with those of conventional Ziegler-Natta catalysts. X-ray photoelectron spectroscopic analyses identify the oxidation states of the Ti ions at the active sites. Temperature-programmed desorption distinguishes the binding strength of a probe molecule to the active sites that produce polypropylenes having different tacticities. These findings demonstrate that a surface science approach to the preparation and characterization of model heterogeneous catalysts can improve the catalyst design and provide fundamental understanding of the single-site olefin polymerization process.

Synthesis of branched polyethylene from ethylene stock by an interference-free tandem catalysis of TiCl 4/MgCl 2 and iron catalyst

An interference-free tandem catalysis based on iron catalyst and TiCl 4/MgCl 2, activated by MAO, was used to prepare branched polyethylene by polymerization of ethylene. No obvious deactivation due to the side reaction of catalysts and cocatalysts was detected during the reaction process, which commonly existed in tandem catalytic systems based on conventional Ziegler–Natta catalysts. A series of branched polyethylene with different properties have been prepared by adjusting of reaction temperature, Fe/Ti molar ratio and the amount of MAO used. The alteration of oligomers concentration in the reaction system, by changing of reaction conditions, led to the products with different branching degrees, thus the thermal properties and molecular weight. The products obtained in toluene at lower Fe/Ti ratios exhibited better morphology than those obtained at higher Fe/Ti ratios.