Polymer-supported Ziegler–Natta catalysts. I. A preliminary study of catalyst synthesis

Polymer-supported Ziegler–Natta catalysts based on various polymer carriers were synthesized by different methods, including (1) loading TiCl₄ directly onto the polymer supports; (2) loading TiCl₄ onto the polymer supports modified by magnesium chloride (MgCl₂); (3) loading TiCl₄ onto the polymer supports modified by Grignard reagent (RMgCl); and (4) loading TiCl₄ onto the polymer supports modified by magnesium alkyls (MgR₂). The activity and kinetic features of the catalysts for ethylene polymerization were examined. Among the combinations tested, the best was found to be TiCl₄/n-Bu₂Mg.Et₃Al/poly(ethylene-co-acrylic acid) (92:8), which produced a catalyst of very high activity for ethylene polymerization. © 1994 John Wiley & Sons, Inc.     

Preparation of Polyethylene/Graphene Nanocomposites with Octadecylamine‐Modified Graphene Oxide‐MgCl‐Supported Ziegler–Natta Catalyst

In this work, an octadecylamine‐modified graphene oxide (ODA‐GO)‐MgCl‐supported Ziegler–Natta catalyst was synthesized by reacting ODA‐GO with a Grignard reagent, followed by anchoring TiCl₄ to the structure. The effect of the ODA‐GO on the catalyst morphology and ethylene polymerization behavior was examined. The resultant polyethylene (PE)/ODA‐GO nanocomposites directly mirrored the catalyst morphology by forming a layered morphology, and the ODA‐GO fillers were well dispersed in the PE matrix and showed strong interfacial adhesion with it. The resultant PE/ODA‐GO nanocomposites exhibited better thermal stability and mechanical properties than neat PE, even with a small amount of ODA‐GO added. Thus, this work provides a facile approach to the production of high‐performance PE. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 855–860     

Ethylene–hexene copolymerization by heterogeneous and homogeneous Ziegler–Natta catalysts and the “comonomer” effect

Homopolymerization of ethylene and 1-hexene and their copolymerizations were compared to investigate the influence of α-olefin on the enhancement of ethylene polymerization rate (R_p), which is often referred to as the “comonomer” effect. With the two homogeneous Ziegler–Natta catalysts, Et[Ind]₂ZrCl₂/MAO and (π-C₅H₅)₂ZrCl₂/MAO (MAO = methylaluminoxane), hexene causes reduction of R_p—in other words a negative “comonomer” effect. In the case of the high activity MgCl₂ supported TiCl₃ catalysts there is a slight positive “comonomer” effect; the R_p increases by 25 to 70% with the addition of 15 mol % of hexene. The “comonomer” effects in there catalyst systems are much smaller than that observed for the classical TiCl₃ catalyst. © 1993 John Wiley & Sons, Inc.     

Synthesis of polypropylene-co-p-methylstyrene copolymers by metallocene and Ziegler–Natta catalysts

This paper discusses the copolymerization reaction of propylene and p-methylstyrene (p-MS) via four of the best-known isospecific catalysts, including two homogeneous metallocene catalysts, namely, {SiMe₂[2-Me-4-Ph(Ind)]₂}ZrCl₂ and Et(Ind)₂ZrCl₂, and two heterogeneous Ziegler–Natta catalysts, namely, MgCl₂/TiCl₄/electron donor (ED)/AlEt₃ and TiCl₃. AA/Et₂AlCl. By comparing the experimental results, metallocene catalysts show no advantage over Ziegler–Natta catalysts. The combination of steric jamming during the consective insertion of 2,1-inserted p-MS and 1,2-inserted propylene (k₂₁ reaction) and the lack of p-MS homopolymerization (k₂₂ reaction) in the metallocene coordination mechanism drastically reduces catalyst activity and polymer molecular weight. On the other hand, the Ziegler–Natta heterogeneous catalyst proceeding with 1,2-specific insertion manner for both monomers shows no retardation because of the p-MS comonomer. Specifically, the supported MgCl₂/TiCl₄/ED/AlEt₃ catalyst, which contains an internal ED, produces copolymers with high molecular weight, high melting point, and no p-MS homopolymer. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2795–2802, 1999     

Polymerization of ethylene using a high-activity Ziegler–Natta catalyst. II. Molecular weight regulation

This article describes studies on the variables that regulate the molecular weight in ethylene polymerization using a highly active Ziegler–Natta catalyst with hydrogen for molecular weight control. The dependence of the degree of polymerization on the concentration of catalyst, cocatalyst, monomer, partial pressure of hydrogen, and temperature has been established. The rate constant for chain transfer with cocatalyst has been evaluated. © 1993 John Wiley & Sons, Inc.     

Preparation of polyethylene/lignin nanocomposites from hollow spherical lignin‐supported vanadium‐based Ziegler–Natta catalyst

In the present article, a novel hollow spherical lignin‐supported vanadium‐based Ziegler–Natta catalyst was synthesized. The active centers of the obtained catalyst well dispersed in the lignin through the SEM‐EDX analysis. The resultant catalyst was investigated in ethylene polymerization and found to exhibit remarkable catalytic activity upon activation with ethylaluminium sesquichloride cocatalyst and ethyl trichloroacetate activator. During the polymerization, the lignin was gradually exfoliated by the polymerization force arising from the propagation of ethylene chain. The resultant PE/lignin nanocomposites preformed higher thermal stability compared to virgin PE. Copyright © 2016 John Wiley & Sons, Ltd.     

Effects of Alterations to Ziegler–Natta Catalysts on Kinetics and Comonomer (1‐Butene) Incorporation

Various MgCl₂‐supported Ziegler–Natta (ZN) catalysts are synthesized with the intention to influence polymerization performance and 1‐butene incorporation in an ethylene copolymer. Modifications are introduced during different steps in the synthesis process, namely support preparation, titanation, and catalyst workup. While multiple different effects are observed upon modification, heat treatment during titanation shows the greatest impact. Increasing the heat‐treatment temperature increases polymerization activity. More importantly, the 1‐butene distribution can be shifted toward a more homogeneous profile. The amount of 1‐butene incorporated is similar to both for short‐ and for very long‐chain molecules. This behavior has so far been known only from metallocene‐based polyethylene and suggests that active sites are distributed more homogeneously in the ZN catalyst.

     

Monomer-isomerization polymerization. XXXVIII. Monomer-isomerization copolymerizations of styrene and 2-Butene with Ziegler–Natta catalyst

Monomer-isomerization copolymerizations of styrene (St) and cis-2-butene (c2B) with TiCl₃-(C₂H₅)₃Al catalyst were studied. St and c2B were found to undergo a new type of monomer-isomerization copolymerization, i.e., only isomerization of 2B to 1-butene ( 1B ) took place to give a copolymer consisting of St and 1B units. The apparent copolymerization parameters were determined to be r_st = 16.0 and r_c2b = 0.003. The parameters were changed by the addition of NiCl₂ (r_St = 8.4, r_c2b = 0.05). The copolymers containing the major amount of St units were produced easily through monomer-isomerization copolymerization of St and 2B. © 1995 John Wiley & Sons, Inc.     

Evaluation of the Initial Stages of Gas‐Phase Ethylene Polymerizations with a SiO2‐Supported Ziegler–Natta Catalyst

The very early stages of gas‐phase ethylene polymerization on an SiO₂‐supported Ziegler–Natta catalyst were studied with the help of a short‐stop reactor. The short‐stop‐reactor‐based technique was useful in studying nascent polymerization, providing insights at very short, controlled times into important phenomena regarding catalyst fragmentation and the activation and deactivation of catalyst sites that take place during the very early stages of the reaction. Experimental results indicate that the growth of the polymer chains occurs at unsteady conditions during the initial stages of the polymerization. Hydrogen has a strong influence on the initial kinetics, leading to a significant decrease of polymerization activity. Polymer crystallinity increases with the reaction time, probably due to the formation of long chains with a high degree of crystallinity.

     

Polymerization of propylene by metallocene and Ziegler–Natta mixed catalytic systems. Study of polypropylene properties

Propylene was polymerized with metallocene and Ziegler–Natta mixed-catalytic systems to obtain reactor blends of metallocene and Ziegler–Natta-derived propylene homopolymers. The two catalytic systems are able to act jointly, providing individual polymers with different melting and crystallization temperatures. Compatibility between the components of the mixed-catalytic systems and the influence of the components on the polymerization process and on the properties of the reactor blends were studied. Thermal, mechanical, viscoelastic, rheological, and optical properties of the blends were tested and compared with those of conventional polypropylene grades. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 3063–3072, 1998     

Ethylene–styrene thermoplastic copolymers prepared with supported Ziegler–Natta catalysts

The magnesium chloride supported Ziegler–Natta catalysts are able to copolymerize ethylene and styrene in conditions of high activity. Different parameters, including catalyst type, monomer ratio, temperature and Lewis bases, allow variation of the activity and reactivity ratio. The incorporation of styrene in the copolymer remains always rather limited in moles. The products obtained contain less than 20% styrene in weight, and seem very similar in structure to linear low-density polyethylenes (LLDPE) obtained with the same catalyst: the melting temperature is only about 5°C lower than that of pure polyethylene. The polymer can be fractionated by solvents in a similar manner to LLDPE, and contains a styrene-enriched fraction, but homopolystyrene production has never been observed.     

Optimization of UHMWPE/graphene nanocomposite preparation by single‐supported Ziegler‐Natta catalytic system via RSM

In this study, the preparation of ultra‐high molecular weight polyethylene/graphene nanocomposite was carried out using single‐supported Ziegler‐Natta catalyst, and the operational conditions were optimized via response surface methodology. For this purpose, the effect of 3 parameters, monomer pressure, temperature, and molar ratio of [Al] respect to [Ti] on the catalyst productivity and molecular weight of the synthesized nanocomposite polymer, was investigated using the Box‐Behnken experimental design at 3 levels. Monomer pressure, temperature, and molar ratio of [Al] respect to [Ti] were considered as independent variables and catalyst productivity and molecular weight as dependent variables. The highest catalyst productivity and molecular weight were equal to 923 (grPE/mmolTi.h) and 2.04 (million gr/mol), respectively, which were obtained under optimal reaction conditions: temperature of 60°C, pressure of 8 bar, and molar ratio of 185. Finally, in order to investigate the morphology and nanoparticle dispersion in polymer matrix, scanning electron microscope and X‐ray diffraction were used. The results indicate the homogenous dispersion of graphene nanoparticles in polymer matrix.     

Theoretical studies on the role of bridging group of CGC type ligands for the Ziegler–Natta catalysis

The potential energy surfaces of the initial reactions of ethylene polymerization with the Ziegler–Natta catalysis related to the constrained geometric catalysts (CGCs) were studied by the B3LYP density functional method. Three metals (Ti, Zr, and Hf) in the Ziegler–Natta catalysis and eight bridging groups (BH, CH₂, NH, O, AlH, SiH₂, PH, and S) between cyclopentadienyl (Cp) and NH ligands were treated. The reaction occurs through two steps as that of Kaminsky type: the first step produces the complex without a barrier and the second is the insertion of ethylene into the metal–carbon bond through the transition state. The complex formation energy for each metal system correlates linearly to the electronegativity of the bridging atom for each row atom of the periodic table except for those of the BH-bridging systems. The energies of the reactions for the BH-bridging systems could be explained with the through-bond model as the reactions of ansa-metallocenes and the π back-donation of BN double bond.     

Polymer-supported Ziegler–Natta catalysts. II. Ethylene homo- and copolymerization with TiCl4/MgR2/poly(ethylene-co-acrylic acid) catalyst

A novel polymer-supported titanium-based catalyst shows high activity and nondecaying kinetic profiles for ethylene polymerization. The presence of 1-hexene comonomer drastically increases the catalyst activity, exhibiting a similarity to the MgCl₂-supported catalysts. However, the nondecaying kinetic profiles of copolymerization distinguish this catalyst from the latter. Infrared analysis indicates that the transition metals were immobilized on the polymer support via functional groups. The effects of polymerization conditions on catalyst activity have been assessed. Characterization of the resulting polymer product by means of ¹³C-NMR, DSC, and SEM demonstrates a branch-free structure with high melting point, high crystallinity, and high molecular weight for the ethylene homopolymer. The reactivity ratios of ethylene-1-hexene copolymerization are evaluated from ¹³C-NMR analysis data. © 1994 John Wiley & Sons, Inc.     

Novel spherical Ziegler–Natta catalyst for polymerization and copolymerization. I. Spherical MgCl2 support

Spherical MgCl₂ adducts used as supports for a Ziegler–Natta catalyst for olefin polymerization were prepared by the general precipitation method. The influence of MgCl₂/EtOH (mol/mol) and the dispersion speeds on the particle size (PS) and particle size distribution (PSD) were investigated. It was found that the former played a trivial role in controlling the PS and PSD, and the latter was the key factor. In particular, the influence of ethanol on the crystal structure was further examined, with consideration given to the performance of the supported Ziegler–Natta catalyst. It was believed that the reactions between MgCl₂ and ethanol had a controlling effect on the destruction of the original anhydrous MgCl₂, which was the key point in the preparation of suitable supports for the latest generation Ziegler–Natta catalyst. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3112–3119, 2002     

Polymerization of propylene by mixed Ziegler–Natta and metallocene catalysts

The polymerization of propylene using a mixture of racemic metallocenes and Ziegler–Natta catalysts was investigated. The polypropylene was obtained as a mixture of a fine powder and beads, with the powder being absorbed partially on the beads. The relative amount of the powder can be controlled by the concentration of the metallocene. The compatibility between the components of the mixed catalytic systems and the effect of the components on the rate of polymerization and on the properties of the new polymers were studied. The metallocene system dramatically affects the melt viscosity, isotacticity and molecular weight of the polymers. The two catalytic systems are able to act jointly, producing different polymers, for which separate melting and crystallization temperatures are obtained. © 1998 John Wiley & Sons, Ltd.     

Liquid‐phase polymerization of propylene with a highly active Ziegler–Natta catalyst. Influence of hydrogen,cocatalyst, and electron donor on the reaction kinetics

This paper presents an experimental kinetic study of the polymerization of propylene in liquid monomer with a high activity catalyst. The influences of the concentration of hydrogen and the molar ratios of the catalyst, cocatalyst, and electron donor on the activation period, the maximum activity, the yield, and the decay behavior have been investigated at a temperature of 42°C using a relatively simple kinetic model. On the basis of the experimental data, the reaction rate has been modeled as a function of the hydrogen concentration, the molar ratio of cocatalyst and titanium, and the molar ratio of the electron donor and the cocatalyst. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 219–232, 1999     

Theoretical investigation of the Ziegler–Natta catalysis in heterogeneous conditions

We present ab initio calculations on the Ziegler–Natta catalysis in heterogeneous conditions. Both cluster and periodic models with different basis sets have been used to explain the chemical reactivity of the various species that are involved. In heterogeneous conditions, several parameters contribute to the catalysis: the oxidation state of the titanium atom, the structure of the titanium site, the interaction with the support, MgCl₂, and the cocatalyst, AlR₃. This article yields to a synthetic view of the catalytic activity. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002