Ziegler-Natta Catalytic Systems Research Articles

Negative comonomer effect induced by TiCl3-like clusters in MgCl2-based Ziegler-Natta catalysts

The comonomer effect of ethylene/α-olefin copolymerization in the Ziegler-Natta (Z-N) catalytic system, remaining largely elusive and less understood at the molecular level, has been of huge industrial importance and absorbing research interest for decades. Herein, four catalysts with similar physical structures but different polymerization activities and comonomer effects were synthesized by using n-butanol in combination with different secondary electron donors. By tracking catalyst formation, it was found that altering the secondary donor changes the ν(O-H) stability and in turn the MgCl2 facet growth, to influence the polymerization activity. In situ diffuse reflectance Ultraviolet–visible spectra show that different types of active Ti centers are in function in the ethylene polymerization and the ethylene/1-butene copolymerization. Tracing further the microscopic structures of active species upon triethylaluminium (TEA) activation by using Extended X-ray Absorption Fine Structure, it is found that: (i) for the catalysts with negative comonomer effect, the enhanced donor migration promotes the aggregation of active species and leads to the formation of TiCl3-like clusters; (ii) by contrast, for the catalysts with positive comonomer effect, the less mobile donors hinder the aggregation of active species, thus inducing the formation of isolated Ti3+ sites. Our work reveals an evident correlation between the active center and the comonomer effect, which may be strongly modified by the aggregation of the former.

Isoprene Polymerization in the Presence of Phosphate Catalytic Systems Based on a Mixture of Neodymium and Gadolinium Salts

Coordination polymerization of isoprene in the presence of Ziegler–Natta catalytic systems based on a mixture of neodymium and gadolinium bis(2-ethylhexyl) phosphates at the neodymium/gadolinium molar ratios of 25/75, 50/50, and 75/25 was studied. These catalytic systems exhibit high catalytic activity in isoprene polymerization, equal to that of the catalytic system based on neodymium bis(2-ethylhexyl) phosphate. The influence of the Nd/Gd ratio on the molecular-mass characteristics and microstructure of the polymers obtained was examined. The kinetic parameters of the isoprene polymerization using catalytic systems based on a mixture of neodymium and gadolinium salts were determined. The possibility of using such systems in the synthesis of stereoregular cis-1,4-polyisoprene with the optimum level of molecular masses was demonstrated

In-situ polymerization of silica/polyethylene using bisupported Ziegler-Natta catalyst of nanosilica/BOM/TiCl4/TEAL: Study of thermo-mechanical properties system

• Preparation of silica/PE nanocomposite using a bisupported Ziegler-Natta catalytic system. • The nanosilica/BOM/TiCl 4 /TEAL was characterized by TEM, FTIR, BET, and SEM analysis. • The thermal properties of the nanocomposites were studied by DSC and TG analysis (TGA). The physical and chemical properties of silica-supported Ziegler-Natta catalysts industrially important for polyethylene/silica production. Polyethylene (PE)/silica nanocomposites were prepared through in-situ polymerization using a bisupported Ziegler-Natta catalytic system. Since the silica and nanosilica-supported Ziegler-Natta catalysts have shown low efficiency in the ethylene polymerization. This problem was solved through the prepared bisupported catalyst in this study. This approach includes the preparation and utilization of a bisupported nanosilica/BOM/TiCl 4 /TEAL catalytic system in which nanosilica and BOM (butyl octyl magnesium) were used as conjugate supports and also TEAL (triethyl aluminum) was as an activator. It was found that the performance of the nanosilica-BOM bisupported catalyst was efficient in the ethylene polymerization towards the preparation of the PE/silica nanocomposites. Hydrogen was applied to control the molecular weight of the nanocomposites. An unusual polymerization behavior was observed in the presence of hydrogen. The nanocomposites were not soluble in any solvent. The nanostructure of the resulting PE/silica nanocomposites was characterized by transmission electron microscopy (TEM), FTIR, BET, and SEM. The thermal properties of the nanocomposites were studied by differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA).

Coordinative Chain Transfer Polymerization of Sustainable Terpene Monomers Using a Neodymium-Based Catalyst System.

The present investigation involves the coordinative chain transfer polymerization (CCTP) of biobased terpenes in order to obtain sustainable polymers from myrcene (My) and farnesene (Fa), using the ternary Ziegler–Natta catalyst system comprising [NdV3]/[Al(i-Bu)2H]/[Me2SiCl2] and Al(i-Bu)2H, which acts as cocatalyst and chain transfer agent (CTA). The polymers were produced with a yield above 85% according to the monomeric consumption at the end of the reaction, and the kinetic examination revealed that the catalyst system proceeded with a reversible chain transfer mechanism in the presence of 15–30 equiv. of CTA. The resulting polyterpenes showed narrow molecular weight distributions (Mw/Mn = 1.4–2.5) and a high percent of 1,4-cis microstructure in the presence of 1 equiv. of Me2SiCl2, having control of the molecular weight distribution in Ziegler–Natta catalytic systems that maintain a high generation of 1,4-cis microstructure.

Quantification of oxygenates, sulphides, thiols and permanent gases in propylene. A multiple linear regression model to predict the loss of efficiency in polypropylene production on an industrial scale

This research developed a new methodology using a gas chromatograph, a pulsed discharge helium ionization detector (PDHID), and two mass spectrometric (MSD) detectors. The detectors worked simultaneously, using 8 columns and 7 valves. This new proposal for simultaneous analysis, with a single injection and analysis time of 36 min, allowed the quantification of 10 oxygenated compounds (alcohols, ketones and carboxylic acids), 3 permanent gases, 3 sulphides and 4 thiols, which are aggressive inhibitors of the Ziegler-Natta catalytic systems. The RSD (n=6) for repeatability of the peak area of the 20 compounds analyzed, and the retention time were less than 0.59 and 0.23% respectively. The RSD (n=6) for intermediate precision for the peak area was less than 0.85% and, for the retention time, less than 0.35%. 95% of the inhibitors analyzed showed relative errors inter and intra-day less than 3%. The inhibitors detected and quantified were: formic acid (2 to 45.32 ppm), acetic acid (1 to 25.32 ppm), acetone (5 to 72.67 ppm), methanol (1 to 39.93 ppm), isopropyl alcohol (2 to 74.88 ppm), ethanol (0.1 to 57.51 ppm), 1-propanol (0.1 to 92.36 ppm), 1-butanol (5 to 92.36 ppm), 2-butanol (5 to 95.15 ppm), tert-butanol (5 to 90.22 ppm), CO2 (0.5 to 5.0 ppm), CO (0.002 to 5.049 ppm), O2 (0.5 to 6.5 ppm), CH3(CH2)3SH (0.025 to 2.238 ppm), CH3CH2SH (0.025 to 1.595 ppm), COS (0.025 to 1.477 ppm), CH3SH (0.025 to 1.223 ppm), CH3(CH2)2SH (0.025 to 1.880 ppm), CS2 (0.025 to 1.929 ppm), H2S (0.025 to 0.847 ppm) and tert-butylmercaptan (0.025 to 2.283 ppm). These compounds generated reductions of between 5 and 20% in polypropylene production, representing losses of several million dollars. Therefore, a multilinear regression model was developed to predict this percentage of production loss in a fluidized bed reactor, based on the quantified inhibitors. The model has a correlation coefficient of 0.91 and a standard deviation of 1.12, allowing comparisons between actual and predicted experimental values. P values are less than 0.05, indicating that each inhibitor has a statistically significant effect on the model.

Halide-free neodymium phosphate based catalyst for highly cis-1,4 selective polymerization of dienes.

Neodymium-based Ziegler–Natta type catalytic systems are known to produce polydienes with high cis-1,4 content. It is generally believed that in Ziegler–Natta catalytic systems, a halide or pseudohalide, whether in the catalyst itself or a separate source, is required for the success of the polymerization. In this work, we have synthesized an unusual halide-free neodymium diethyl phosphate catalyst for diene polymerization. This neodymium complex combined with triisobutylaluminum (TIBA), formed a binary catalytic system and was used to polymerize β-myrcene. The catalytic system displays high stereospecificity and produces poly(β-myrcene) with 96% cis-1,4 content and a relatively narrow molecular weight distribution (Mw/Mn = 1.80). Also, kinetic studies indicated the catalytic system gives a pseudo-living polymerization. The block copolymer poly(β-myrcene)-b-poly(isoprene) was successfully synthesized by sequential monomer addition, further demonstrating the pseudo-living nature of polymerization with the neodymium diethyl phosphate catalyst.

Insights into the Formation Process of Yttrium–Aluminum Bimetallic Alkyl Complexes Supported by a Bulky Phosphazene Ligand

The reaction of the yttrium dialkyl precursor [N[Ph2PNC6H3(iPr)2]2Y(CH2SiMe3)2] (1) with more than 3 equiv of trimethylaluminum or triethylaluminum afforded the dinuclear heterometallic complexes N[Ph2PNC6H3(iPr)2]2Y{(μ-R)2AlR2}R (R = Me (2), Et (3)). When trimethylaluminum loading was reduced to 2 equiv, the same reaction gave the product N[Ph2PNC6H3(iPr)2]2Y{(μ-Me)2(μ-CH2SiMe3)AlMe}Me (4), with quite a different bonding mode. All of these complexes were characterized by NMR spectra, X-ray crystallography, and elemental analysis. We elucidated the step-reaction mechanism between the yttrium dialkyl complex based on bulky phosphazene ligand and trialkylaluminum, which might shed new light on the formation process of active species in organoaluminum-dependent Ziegler–Natta catalytic systems.

Synthesis of highly isotactic poly 1-hexene using Fe-doped Mg(OEt)2/TiCl4/ED Ziegler–Natta catalytic system

In this article, polymerization of 1-hexene with FeCl3-doped Mg(OET)2/TiCl4/electron donor (ED) catalytic system is presented. For this purpose, first a number of TiCl4 catalysts supported on Mg(OEt)2 and Fe-doped Mg(OEt)2 supports were prepared with ethylbenzoate or dibutylphthalate as the internal EDs. After successive catalysts synthesis, they were employed in 1-hexene polymerization using cyclohexyl methyl dimethoxysilane as external ED as well as without it. The catalysts activity and molecular weight distribution (MWD) of poly 1-hexenes (PHs) were influenced strongly by both FeCl3 doping and donor presence so that a remarkable increase in the catalyst activity was seen in doped catalysts. Deconvolution of MWD curves revealed that increase in the type of active centers by introducing FeCl3 into the support should be responsible for the broadening of MWD of PHs. 13CNMR analysis indicated that while isotacticity does not change considerably by Fe doping, EDs increase its amount as high as 8–21%. Second, the stereoselective behavior of active Ti species in doped and undoped catalysts was fully explored by molecular modeling using density functional theory (DFT) method. Finally, with the aid of rheological measurements, the processability of polymers were evaluated and then the gel permeation chromatography (GPC) results were approved through the values obtained from model fitting as well as changes in moduli crossover modulus.

Periodic DFT study of the donor interactions with the MgCl2surface in the Ziegler–Natta catalytic system

Using periodic DFT, the present study evaluated the interactions of donors with MgCl2surfaces. The selected donors included 1,3-dimethoxy-2,2-dimethylpropane, dimethoxydimethylsilane, and dimethyl phthalate.

Polymerization of conjugated dienes with a homogeneous Ziegler–Natta catalytic system based on a carbon-bridged bis(phenolate) yttrium alkyl complex

1,3-Diene polymerization with some controllable characteristics was carried out and catalyzed by a triisobutylaluminum modified MAO activated complex [(EDBP)Y(CH2SiMe3)(THF)3].

Highly Isotactic Poly(N-butenyl-carbazole): Synthesis, Characterization, and Optical Properties

The synthesis of isotactic poly(N-butenyl-carbazole) (i-PBK) by using homogeneous isospecific Ziegler-Natta catalytic system is reported. The achieved polymer is crystalline and shows, to DSC and X-ray analysis, two distinct crystalline phases.i-PBK FTIR spectrum and X-ray diffraction pattern are compared with those of poly(N-vinylcarbazole) (PVK). The observed differences are tentatively associated with higher flexibility of thei-PBK chains due to the alkylene group connecting the carbazole group to the main chain.i-PBK optical properties are also compared with those of PVK and isotactic poly(N-pentenyl-carbazole) (i-PPK), a higher homologue ofi-PBK recently used as emitting layer in organic light emitting diodes (OLEDs) showing white light emission. The close similarity of the fluorescence spectra ofi-PBK andi-PPK is a promising basis for optical applications of this polymer.

Preparation and Characterization of UHMWPE/Graphene Nanocomposites Using Bi-Supported Ziegler-Natta Polymerization

Ultrahigh-molecular-weight polyethylene (UHMWPE)/graphene nanocomposites with molecular weights as high as 3 × 106 g/mol were prepared via in situ polymerization using a bi-supported Ziegler-Natta catalytic system. Effects of [Al]/[Ti] molar ratio, temperature, monomer pressure, and polymerization time on productivity of the catalyst have been investigated. Increasing [Al]/[Ti] molar ratio from 128 to 320, increased productivity from 1667 g PE/mmol Ti.h to maximum value which was 2420 g PE/mmol Ti.h. Further [Al]/[Ti] ratio decreased the productivity. Reaction temperature effect investigation reveals that the optimal activity was obtained at 60°C. the polymerization productivity increases with monomer pressure and decreased with polymerization time. Morphological information was determined by using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Obtained results show that graphene layers in these nanocomposites were completely exfoliated and dispersed uniformly in the polyethylene matrix while no nanoparticle cluster has been formed.

In situ preparation and property investigation of polypropylene/fumed silica nanocomposites

We present the preparation of polypropylene (PP)/fumed silica (FS) nanocomposites via in situ polymerization in this article. The approach includes preparation and utilization of a bisupported Ziegler–Natta catalytic system in which magnesium ethoxide and FS are used as conjugate supports of the catalyst. Catalyst preparation and polymerization processes are carried out in the slurry phase and under argon atmosphere. Scanning electron microscopy images show a good dispersion of the FS throughout the PP matrix. Results from differential scanning calorimetry reveal that the crystallization temperature of prepared nanocomposites increases by increasing FS loading. Also, crystal content of nanocomposites increases as the FS concentration increases up to 3.48 wt%. Nanocomposites containing <3.14 wt% of nanoparticles do not show considerable change in their melting point where with more increment in filler concentration, melting temperature slightly increases. Thermogravimetric analysis shows a considerable improvement in the thermal stability of PP/FS nanocomposites compared to pure PP. Rheological studies indicate that the incorporation of FS into PP matrix results in increment in storage modulus, loss modulus, and complex viscosity of polymeric matrix, particularly in low frequency region. By increasing FS loading, the PP/FS nanocomposites show a transition from liquid‐like to solid‐like viscoelasticity behavior depicting microstructural changes in their structures. POLYM. COMPOS., 35:37–44, 2014. © 2013 Society of Plastics Engineers

How Well Can DFT Reproduce Key Interactions in Ziegler–Natta Systems?

AbstractThe performance of density functional theory in reproducing some of the main interactions occurring in MgCl2‐supported Ziegler–Natta catalytic systems is assessed. Eight model systems, representatives of key interactions occurring in Ziegler–Natta catalysts, are selected. Fifteen density functionals are tested in combination with two different basis sets, namely, TZVP and cc‐pVTZ. As a general result, we found that the best performances are achieved by the PBEh1PBE hybrid generalized gradient approximation (GGA) functional, but also the cheaper PBEh GGA functional gives rather good results. The failure of the popular B3LYP and BP86 functionals is noticeable.magnified image

Reversible coordinative chain transfer polymerization of isoprene and copolymerization with ε-caprolactone by neodymium-based catalyst

Coordinative chain transfer polymerization (CCTP) of isoprene was investigated by using the typical Ziegler–Natta catalytic system [Nd(Oi-Pr)3/Al(i-Bu)2H/Me2SiCl2] with Al(i-Bu)2H as cocatalyst and chain transfer agent (CTA). The catalyst system exhibited high catalytic efficiency for the reversible CCTP of isoprene and yielded 6–8 polymer chains per Nd atom due to the high chain transfer ability of Al(i-Bu)2H. The narrow molecular weight distribution (Mw/Mn = 1.22–1.45) of the polymers, the good linear relationship between the Mn and yield of the polymer, and the feasible seeding polymerization of isoprene indicated the living natures of the catalyst species. Moreover, the living Nd-polyisoprene active species could further initiate the ring-opening polymerization of polar monomer (ε-caprolactone) to afford an amphiphilic block copolymer consisting of cis-1,4-polyisoprene and poly(ε-caprolactone) with controllable molecular weight and narrow molecular weight distribution.

Preparation of ultrahigh‐molecular‐weight polyethylene/carbon nanotube nanocomposites with a Ziegler–Natta catalytic system and investigation of their thermal and mechanical properties

AbstractIn this research, ultrahigh‐molecular‐weight polyethylene (UHMWPE)/multiwalled carbon nanotube (MWCNT) nanocomposites with different nanotube concentrations (0.5, 1.5, 2.5, and 3.5 wt %) were prepared via in situ polymerization with a novel, bisupported Ziegler–Natta catalytic system. Magnesium ethoxide [Mg(OEt)2] and surface‐functionalized MWCNTs were used as the support of the catalyst. Titanium tetrachloride (TiCl4) accompanied by triethylaluminum constituted the Ziegler–Natta catalytic system. Preparation of the catalyst and the polymerization were carried out in the slurry phase under an argon atmosphere. Support of the catalyst on the MWCNTs was investigated with Fourier transform infrared spectroscopy. The results confirmed the interaction between the catalyst and the MWCNT hydroxyl groups. Intrinsic viscosity measurements showed an ultrahigh molecular weight in the produced samples. Scanning electron microscopy images confirmed the good dispersion of MWCNTs throughout the polyethylene (PE) matrix. The crystallization behavior of the samples was examined with differential scanning calorimetry. Its results showed that the crystal content of the samples increased with increasing MWCNT concentration up to 1.5 wt %. The same trend was observed for the crystallization temperature, whereas the melting temperature did not change with increasing MWCNT concentration up to 1.5 wt %, but it decreased beyond this concentration. In addition, thermogravimetric analysis results showed that the addition of MWCNTs noticeably improved all of the investigated thermal stability factors of the UHMWPE/MWCNT nanocomposites compared to those of pure PE. The results obtained from tensile testing revealed significant increases in the Young's modulus, yield stress, and ultimate tensile strength. This indicated a tremendous improvement in the mechanical properties of the PE/MWCNT nanocomposites compared to those of pure PE. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci 125:453–461, 2012

XPS study of Al‐Alkyl effect on Ziegler–Natta catalytic system

X‐ray photoelectron spectroscopy was performed on Ziegler–Natta catalysts to elucidate the effect of aluminum alkyl compounds (Al‐Alkyl) on TiClx/MgCl2/THF catalytic system. Chemical structure and element composition changes of catalysts were studied and various reduction activity of Al‐alkyl on catalysts was identified in different processes. The analytical results indicate that XPS is an acceptable method to measure titanium valence in Al‐alkyl‐ZN catalysts with a proper sample protection method. The XPS results demonstrate that the Al‐alkyl treatment of ZN catalysts could influence the chemical state of titanium dramatically. In Method A, the valence of Ti was reduced to Ti3+ partially, and the contents of Ti3+ increased with the increasing amount of DC, but Ti2+ was absent. With same amount of Al%, combination of DC and THA has better reduction effect than DC with Method B. Copyright © 2011 John Wiley & Sons, Ltd.

Kinetic modeling of slurry propylene polymerization using a heterogeneous multi-site type Ziegler–Natta catalyst

The semi-batch slurry polymerization of propylene using a heterogeneous multi-site type Ziegler–Natta catalytic system was studied. A simple kinetic model including initiation, propagation, spontaneous chain transfer, chain transfer to hydrogen, chain transfer to monomer and chain transfer to cocatalyst, and spontaneous deactivation was developed to predict instantaneous rates of polymerization and average molecular weights of final products. Estimation of kinetic parameters was performed using online measurements of polymerization rate and end of batch measurements of average molecular weights. The multivariable nonlinear optimization problem was solved using the Nelder–Mead simplex method for three different site types at three levels of temperatures. The model predicts that the propagation reaction has a lower activation energy than chain transfer reactions which leads to a decrease of molecular weight at elevated temperatures. The deactivation reaction has a higher activation energy than the propagation reaction, which results in decreasing the final rate of polymerization at higher temperatures.

Activity of butadiene polymerization centers at in situ formation of titanium catalysts

Directional action on the activity of macromolecule propagation centers and their typical set in synthesis of stereoregular polydienes in the presence of polycentered Ziegler-Natta catalytic systems allows control over the molecular characteristics of the polymers obtained and over the service characteristics of products thereof.

Ziegler-Natta catalytic systems

A calorimetric investigation on the reactions of TiCl4 with phthalates in 1,1,2,2-tetrachloroethane (TCE) is presented in order to better understand the complex interactions present in Ziegler-Natta catalytic systems. The Lewis bases diethyl isophthalate (L1), diethyl terephthalate (L2) and the ortho-isomer diethylphthalate (L3), have been chosen to study how the substituent positions could influence the energy and the stoichiometry of the complexation reactions.