Supported Ziegler-Natta Catalysts Research Articles

Trans‐1,4‐stereospecific copolymerization of ethylene and isoprene catalyzed by MgCl2‐supported Ziegler–Natta catalyst

ABSTRACTCopolymerization of ethylene and isoprene (Ip) catalyzed by TiCl4/MgCl2‐Al(i‐C4H9)3 catalyst was systematically studied. Homopolymer of ethylene and Ip were synthesized under the same conditions for making comparisons. Proton nuclear magnetic resonance was employed to characterize chain structure of the copolymer. Influences of Ip concentration, molar ratio of cocatalyst to Ti and reaction temperature on the copolymerization activity and copolymer chain structure were investigated. The copolymerization activity was evidently lowered by increasing Ip concentration, and the Ip content in copolymer was rather low under reaction conditions leading to higher activity. Insertions of Ip in polymer chain showed rather high regioselectivity for 1,4‐connections (>85%) and medium to high stereoselectivity for trans‐1,4‐isomer (>70%) under typical conditions, but the regio and stereoselectivities tended to decrease with decrease in Ip concentration and increase in Al/Ti ratio. Melting temperature of the copolymer decreased with increase of Ip content, indicating incorporation of Ip units in most of the copolymer chains. This work has proved feasibility of introducing small amount of Ip units with high trans‐1,4‐stereoselectivity into ethylene/isoprene copolymer chains by catalyzed copolymerization with MgCl2‐supported Ziegler–Natta catalysts. The copolymer is expected to be a promising candidate of easily degradable film or packaging materials. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 2715–2722

Synthesis, chain structures and phase morphologies of trans-1,4-poly(butadiene-co-isoprene) copolymers

High trans-1,4-poly(butadiene-co-isoprene) (TBIR) copolymers from the stereo-selective and chemo-selective copolymerization of butadiene (Bd) and isoprene (Ip) are reported with MgCl2 supported Ziegler-Natta catalyst (TiCl4/MgCl2Al(i-Bu)3). Three major components in the copolymers, separated by stepwise isothermal crystallization fractionation, consist of crystalline trans-1,4-polyisoprene (TPI) blocks and trans-1,4-polybutadiene (TPB) blocks but in varied sequence length. Unique phase morphologies with different crystalline lamellar structures are observed in these TBIR copolymers for the first time. The phase morphologies of TBIR reflecting as the discrete lamellar stacks of TPB blocks and dendrimer-shaped lamellae of TPI blocks become diverse in different components with the varied statistical monomer and comonomer unit sequence distribution. The copolymers with TPB blocks are produced in the initial polymerization stage from the active species with relatively low stereospecificity. With the stereospecificity transformation of the active species from low to high, TBIR copolymers with crystalline TPB and TPI blocks and copolymers with TPI blocks are successively formed.

Nucleation kinetics of MgCl2–ethanol adduct for the supported Ziegler–Natta catalysts with a thermodynamic approach

MgCl2–ethanol adducts play a key role in the synthesis of supported Ziegler–Natta catalysts. The morphology of the MgCl2–ethanol adducts, which is controlled by their crystallization process, can determine the structure and thus the property of the polyolefin products. Here we study the nucleation kinetics of MgCl2–ethanol adducts by measuring the metastable zone width (MSZW) and induction time at different temperatures. Supersaturation ratios used in induction time measurements were predicted by the Mixed Solvent Electrolyte (MSE) model embedded in OLI System. Nývlt′s approach was applied to determine MSZW. By the induction time measurement, the effect of temperature, and supersaturation were studied. It was found that induction time decreases as either temperature or supersaturation increases. The measured MSZW and induction time are used to estimate the nucleation kinetics of the system, and thereby distinguishing between the homogeneous and heterogeneous mechanisms. The interfacial tension and other related nucleation parameters were calculated from the induction time data. XRD and TGA indicate that the MgCl2–ethanol adduct has the stoichiometry of MgCl2·6C2H5OH.

Mechanism of internal and external electron donor effects on propylene polymerization with MgCl2‐supported Ziegler–Natta catalyst: New evidences based on active center counting

ABSTRACTTwo TiCl4/Di/MgCl2 type supported Ziegler–Natta catalysts were prepared by loading dibutylphthalate or dicyclopentyldimethoxysilane (DCPDMS) (internal donor, Di) and TiCl4 on activated δ‐MgCl2 in sequence, and a blank catalyst was prepared by loading TiCl4 on the same δ‐MgCl2 without adding Di. These catalysts have similar specific surface area and pore size distribution, thus form a suitable base for comparative studies. Propylene polymerization with the catalysts was conducted in n‐heptane slurry using triethylaluminum (TEA) as cocatalyst, and the effects of Di as well as De (external donor, in this work it was DCPDMS) on the number of active centers, the distribution of active centers among three polypropylene (PP) fractions (isotactic, medium isotactic, and atactic PP chains), and chain propagation rate constants of the PP fractions were studied by counting the number of active centers in the PP fractions using a method based on selective quench‐labeling of the propagation chains by 2‐thiophenecarbonyl chloride. When De was not added in the polymerization, introducing a phthalate type Di in the catalyst evidently changed the active center distribution by enhancing the proportion of active centers producing isotactic PP (iPP) ( ), but scarcely changed reactivities of the three groups of active centers forming the three fractions. When the De was added in the polymerization system with TiCl4/phthalate/MgCl2 catalyst, further shifting of active center distribution in favor of took place, meanwhile reactivities of the three groups of active centers also remarkably changed in favor of . Mutual effects of these changes led to overwhelming dominance of iPP production in the TiCl4/Di/MgCl2–TEA/De system (Di = phthalate, De = alkoxysilane). In contrast, though using alkoxysilane as Di also caused shifting of active center distribution in favor of when De was not added, addition of alkoxysilane De caused reverse shifting of active center distribution in favor of those producing PP of lower stereoregularity. This unfavorable change largely counteracted the reactivity changes in favor of caused by the De, rendering the catalytic system rather poor isospecificity. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46605.

MgCl2-Supported Ziegler–Natta Catalysts: a DFT-D “Flexible-Cluster” Approach to Internal Donor Adducts

A “flexible cluster” model approach to Ziegler–Natta catalysts for the production of isotactic polypropylene, allowing the use of realistically sized MgCl2 monolayer clusters (up to 38 MgCl2 units) without any constraints, was employed to investigate the formation of adducts between the MgCl2 support and three industrially relevant internal donor classes, namely phthalates, succinates, and 1,3-dimethoxypropanes. The calculated adsorption modes and thermochemical data for adducts of single-donor molecules confirmed earlier literature trends only in part. Results for adducts with multiple donor molecules, in turn, did not confirm the indications of periodic models about steric repulsion between neighboring adsorbates hampering high degrees of surface coverage; as a matter of fact, such repulsions seem to be largely traceable to unnecessary constraints inherent in periodic calculations.

Preparation of Octadecylamine-Graphene/MgCl₂-Supported Ziegler-Natta Catalyst and Its Application in Ethylene Polymerization.

A facile coagglomeration method for preparing a long alkyl chain modified graphene oxide (MGO)/MgCl2-supported Ti-based Ziegler-Natta catalyst was reported. The effects of MGO on the catalyst morphology and activity for ethylene polymerization were examined. The resultant polyethylene (PE)/MGO nanocomposites exhibited a layered morphology, with the MGO fillers being well dispersed and exhibiting strong interfacial adhesion to the PE matrix. The thermal stability and mechanical properties of the PE were significantly enhanced with the introduction of a small amount of the MGO filler. Thus, this work provides a facile approach to the production of high-performance PE.

Propylene polymerization over supported Ziegler–Natta catalysts: Effect of internal and external donors on distribution of active sites according to stereospecificity

ABSTRACTData on the content of fractions with different microtacticities for polypropylene (PP) samples produced over three catalysts [the “donor‐free” titanium–magnesium catalyst and catalysts with dibutyl phthalate and 1,3‐diether(fluorene) used as internal donors] upon polymerization in the absence/presence of an external donor (ED) have been obtained by preparative temperature rising elution fractionation method. The effect of internal and EDs on the distribution of PP fractions with different microtacticity is discussed. Data on molecular weight and thermophysical characteristics were obtained for individual fractions with different microtacticities. Correlations were found between microtacticity, molecular weight, and the melting points of these fractions. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46291.

1-Hexene polymerization with supported Ziegler-Natta catalyst: Correlation between catalyst particle fragmentation and active center distribution

1-Hexene was polymerized with a commercial MgCl2-supported Ziegler-Natta catalyst using triethylaluminum as cocatalyst at different monomer/catalyst mass ratio (mhexene/mcat = 5, 15, 30), and the number of active centers ([C*]/[Ti]) was determined by quench-labeling the catalyst with 2-thiophenecarbonyl chloride and monitoring sulfur content of the polymer. Changes of polymerization rate (Rp) and propagation rate constant (kp) with time were also determined. [C*]/[Ti] was found to increase with time for 3 − 5 folds in the first 10 min of polymerization, but the maximum [C*]/[Ti] value reached after the induction period markedly enhanced with increase of monomer/catalyst mass ratio. Gradual fragmentation of the catalyst particles in parallel with the [C*]/[Ti] increase was observed by SEM analysis. It means that a large proportion of active center precursors are inaccessible to cocatalyst and monomer at the beginning of reaction, and fragmentation of the particles by hydraulic force of the growing polymer chains leads to exposure and activation of these precursors. Raising the monomer concentration can provide larger hydraulic force to expose those active site precursors that are more tightly buried inside the catalyst particle. The polymer molecular weight distribution and related active center distribution was found to shift with increase of the monomer/catalyst ratio, meaning that there are different types of buried active center precursors, and their exposure requires different extent of particle fragmentation.

Kinetics of short‐duration ethylene–propylene copolymerization with MgCl2‐supported Ziegler–Natta catalyst: Differentiation of active centers on the external and internal surfaces of the catalyst particles

ABSTRACTEthylene–propylene copolymerization with a TiCl4/MgCl2 type ZN catalyst was conducted for different durations from 30 to 600 s, and changes of polymerization rate, concentration of active centers ([C*]) and copolymer chain structure with time were traced. The copolymerization rate decayed with time, but [C*]/[Ti] increased in the same period. This was attributed to release of more active sites through disintegration of catalyst particles by the growing polymer phase. Ethylene content of the copolymer quickly decreased in the period of 30–90 s, meaning that the active centers activated in the reaction process have stronger ability of incorporating propylene than those activated at the very beginning. The copolymer samples were fractionated into two parts, namely n‐heptane soluble fraction (random copolymer) and insoluble fraction (segmented copolymer with high ethylene content). With continuation of the copolymerization, active centers producing the random copolymer chains increased much faster than active centers producing the segmented copolymer chains, and became the dominant centers after 120 s. Consequently, proportion of the soluble fraction sharply increased with time. All these results indicate that the active centers located on the external surface of catalyst particles are highly different from those buried inside the particles. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46030.

Propylene polymerization reactions with supported Ziegler–Natta catalysts: Observing polymer material produced by a single active center

ABSTRACTMedium‐ and high‐resolution SEM analysis of several Ti‐based MgCl2‐supported Ziegler–Natta catalysts and isotactic polypropylene produced with them is carried out. Each catalyst particle, 35–55 μ in size, produces one polymer particle with an average size of 1.5–2 mm, which replicates the shape of the catalyst particle. Polymer particles contain two distinct morphological features. The larger of them are globules with Dav ∼400 nm; from 1 to 2 × 1011 globules per particle. Each globule represents the combined polymer output of a single active center. The globules consist of ∼2500 microglobules with an average size of ∼20 nm. The microglobules contain several folded polymer molecules; they are the smallest thermodynamically stable macromolecular ensembles in propylene polymerization reactions. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 3832–3841

Kinetics of short‐duration ethylene polymerization with MgCl2‐supported Ziegler–Natta catalyst: Two‐stage initiation evidenced by changes in active center concentration

ABSTRACTThe kinetics of ethylene polymerization with a TiCl4/MgCl2‐type Ziegler–Natta catalyst was studied. Changes in polymerization activity and concentration of active centers ([C*]) in the first 5 min were determined. Initiation of the active centers was found to proceed in two stages. In the first stage, [C*]/[Ti] quickly rose to about 1% in less than 30 s and then remained stable in the subsequent 60 s. Then the [C*]/[Ti] value started to increase again, forming the second buildup stage. The polymerization activity was found to change roughly in parallel with the change in [C*]/[Ti]. Changes in the polymer/catalyst particle morphology and polymer molecular weight distribution with polymerization time were studied. A mechanistic model was proposed to explain the two‐stage kinetics: initiation of active sites on the outer surface of catalyst particles takes place in the first stage, and initiation of active sites buried inside the particles takes place in the second stage. These buried sites are released when the catalyst particles are fragmented by the expanding polymer phase. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45187.

Effect of Aminosilane Compounds as External Donors on Isospecific Polymerizations of 1-Butene with MgCl2/TiCl4/DIBP Catalyst

Four aminosilane compounds were synthesized and employed as external electron donors for 1-butene polymerization with MgCl2 supported Ziegler-Natta catalyst. The four aminosilane compounds are di(piperidinyl)dimethoxysilane (DPPDMS), di(piperidinyl)- diethoxysilane (DPPDES), di(pyrrolidinyl)dimethoxysilane (DPRDMS) and di(pyrrolidinyl)- diethoxysilane (DPRDES). A detailed study has been performed on the effects of the chemical structure of different external electron donors on the catalytic efficiency, isotacticity, melting temperature and molecular weight distribution of obtained poly(1-butene). Poly(1-butene) products have been characterized with gel permeation chromatography (GPC) and differential scanning calorimetry (DSC) analysis. The results indicated that: first, aminosilane compounds with dimethoxy groups showed higher catalytic efficiency and polymers isospecificity than those of with diethoxy groups. Conversely, the aminosilane compounds with diethoxy groups were conductive to obtaining polymers with broader molecular weight distribution than those of with dimethoxy groups. Second, compared with single DPPDMS or TEOS (tetraethyl orthosilicate), DPPDMS/TEOS complex in a proper molar ratio would not only increase the catalytic efficiency and isotacticity of obtained polymers, but also broaden the molecular weight distribution of polymers. Third, the effects of other factors on catalytic efficiency and isotacticity of polymers product were also studied, including different amount of hydrogen, concentration of external donor and cocatalyst. Di(piperidinyl)dimethoxysilane (DPPDMS) was synthesized and employed as external electron donors for 1-butene polymerization with MgCl2 supported Ziegler-Natta catalyst. Compared with single DPPDMS or TEOS (tetraethyl orthosilicate), DPPDMS/TEOS complex in a proper molar ratio would not only increase the catalytic efficiency and isotacticity of obtained polymers, but also broaden the molecular weight distribution of polymers. The selection of molar ratio should depend on the requirements to the polymer.

Influence of Activation Conditions on the Gas Phase Polymerisation of Propylene

SummaryThe impact of injection conditions of a supported Ziegler Natta catalyst on the rate of polymerization of propylene in a gas phase process is investigated. It is observed that the instantaneous rate of propylene polymerization is higher if the catalyst is injected wetted with a hydrocarbon before being charged to the reactor. This is attributed to the effect of the hydrocarbon in decreasing local particle overheating for the critical initial instants of polymerization, due to lower diffusion of the monomer to the active sites and to absorption of the heat of vaporization. An enhancement of the observed initial polymerization rate is also observed with prepolymerization.

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.

Electron Paramagnetic Resonance Study of the Interaction of Surface Titanium Species with AlR3 Cocatalyst in Supported Ziegler–Natta Catalysts with a Low Titanium Content

The electron paramagnetic resonance (EPR) method was used to investigate the formation of alkylated Ti(III) species in superactive titanium–magnesium catalysts with a low titanium content during their interaction with an organoaluminum activator (AlMe3), as well as the interaction of alkylated Ti(III) surface species with carbon monoxide. EPR data on the content of alkylated Ti(III) species in these catalysts agree well with the number of Ti–R bonds that are determined after the interaction of radioactive carbon monoxide (14CO) with catalyst activated by triethylaluminum in the absence of monomer. Parameters of EPR spectra of the Ti(III) species having different structure and composition on the surface of titanium–magnesium catalysts were calculated by quantum-chemical simulations. The calculated g-values are consistent with the g-values observed in EPR spectra of the catalysts. Analysis of the literature data and results of our study made it possible to propose the parameters of EPR spectra characterizin...

Effect of Water on the Supported Ziegler–Natta Catalysts: Optimization of the Operating Conditions by Response Surface Methodology

In this study different water containing adducts, with MgCl2·nEtOH·mH2O formula, were synthesized through melt quenching method. After characterization of support samples, the final catalysts were prepared by reaction of the samples with TiCl4 and tested in slurry phase propylene polymerization. The prepared catalysts showed similar stereospecificities but different activities in polymerization experiments, so that, with increasing water amount from m = 0.0 to m = 0.4 wt%, the catalyst activity reached its maximum value of 4.62 kgPP/g Cat.h, and then by further water increase, from m = 0.4 to m = 1.0 wt%, the activity decreased. After optimizing water content, to reach the maximum efficiency of the catalytic system, optimization of the synthesis conditions was considered via response surface methodology. The studied operation conditions affecting the catalyst efficiency were volume ratio of TiCl4 to toluene (V), initial TiCl4 injection temperature (I) and TiCl4 injection time (T). Results showed that catalytic performance is strongly dependent on its preparation conditions. Analysis of variance indicated that V and I are the most effecting parameters on the catalyst activity with F-value of 39.64, and 8.12, respectively. Indeed, it was found that TiCl4 injection time had no enormous effect on the catalyst activity, but in combination with V, the injection time increment through the scrutinized range decreased the polymerization activity. The obtained model provided a promising tool for designing suitable catalysts for polypropylene production using MgCl2/TiCl4 based Ziegler–Natta catalysts. The focus of the present study is to explore how the presence of water in the adduct synthesis step affects the final ZN catalyst performance in propylene polymerization. Besides water amount, effect of important catalyst synthesis parameters on the catalytic performance was studied as well through response surface methodology.

Condensed Mode Cooling for Ethylene Polymerization: Part I. The Effect of Different Induced Condensing Agents on Polymerization Rate

The effect of commonly used induced condensing agents (ICAs) on the rate of polymerization of ethylene on a supported Ziegler–Natta catalyst in a gas‐phase process is investigated. It is observed that the instantaneous rate of ethylene polymerization is promoted in presence of all ICAs studied. This is attributed to the effect of the heavy ICAs in enhancing the local concentration of ethylene at the active polymerization sites that are dispersed within the growing polymer particles. It is found that the higher the solubility of ICA in the polymer, the greater the observed effect. It is also observed that the enhancement due to the presence of an ICA is greater during the initial phase of the polymerization. image

MgCl2‐supported TiCl4catalysts containing diethyl norbornene‐2,3‐dicarboxylate internal electron donor for 1‐butene polymerization: Effects of internal electron donor configuration

ABSTRACTThree isomeric 5‐norbornene‐2,3‐dicarboxylic acid diethyl ester (NDDE) withendo‐,exo‐, andtrans‐configuration have been synthesized and employed as internal electron donors (IED) in 1‐butene polymerization over magnesium chloride supported Ziegler–Natta catalysts. It was found that the configuration of NDDE plays a key role in tuning the catalyst activity, stereospecificity, molecular weight (MW), and polydispersity index (PDI) of resulting poly(1‐butene). The type of catalyst withcis‐5‐norbornene‐endo‐2,3‐dicarboxylic acid diethyl ester as IED shows the highest catalyst activity, while catalyst withtrans‐NDDE as IED yields the poly(1‐butene) with the highest MW and the most broad PDI. IR results showed that the NDDE withendo‐,exo‐, andtrans‐configuration have different coordination way to MgCl2, subsequently affecting the catalysts performance. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci.2014,131, 40758.

Investigating Phthalate and 1,3-Diether Coverage and Dynamics on the (104) and (110) Surfaces of MgCl2-Supported Ziegler–Natta Catalysts

In this work we present a systematic DFT analysis of the effect of surface coverage on the coordination properties of two industrial Lewis bases, dimethyl phthalate and 9,9-bis(methoxymethyl)fluorene, to the (104) and (110) surfaces of MgCl2. Further, we investigated several possible migration pathways for the migration of the Lewis bases on the same MgCl2 monolayer. Our study clearly shows that complete coverage of the Mg vacancies on the surface by coordinating dimethyl phthalate or 9,9-bis(methoxymethyl)fluorene is hampered by steric repulsion between vicinally coordinated donor molecules. Further, our study clearly indicates that both dimethyl phthalate and 9,9-bis(methoxymethyl)fluorene migration on the same MgCl2 monolayer on the (104) and (110) surfaces basically requires donor dissociation.

The role of two different internal donors (phthalate and 1,3‐diether) on the formation of surface structure in MgCl2‐supported Ziegler–Natta catalysts and their catalytic performance of propylene polymerization

ABSTRACTThe role of two different internal donors [a phthalate (diisobutylphthalate) and a 1,3‐diether (2,2‐diisobutyl‐1,3‐dimethoxypropane)] on the formation of surface structure in MgCl2‐supported Ziegler–Natta catalysts and their catalytic performance of propylene polymerization was investigated by comparing and correlating the catalyst structures and the polymerization characteristics. In the catalyst formation, the 1,3‐diether had better affinity for the MgCl2 surface than the phthalate and the 1,3‐diether generated the (110) surface more than the (104) surface while the phthalate generated both the (110) and (104) surfaces of MgCl2. With both donors introduced, the (110) and (104) surfaces were generated simultaneously, although the (110) surface was dominant due to the higher affinity via the 1,3‐diether. In addition, it seemed probable that the active sites formed on the (110) plane showed isospecific characteristics in the presence of a donor while those formed on the (104) plane could be isospecific regardless of a donor. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40536.