Propylene Polymerization Catalysts Research Articles

Synthesis of High-Molecular-Weight Polypropylene Elastomer by Propylene Polymerization Using α-Diimine Nickel Catalysts.

The α-diimine late transition metal catalyst represents a new strategy for the synthesis of atactic polypropylene elastomer. Taking into account the properties of the material, enhancing the molecular weight of polypropylene at an elevated temperature through modifying the catalyst structure, and further increasing the activity of α-diimine catalyst for propylene polymerization, are urgent problems to be solved. In this work, two α-diimine nickel(II) catalysts with multiple hydroxymethyl phenyl substituents were synthesized and used for propylene homopolymerization. The maximum catalytic activity was 5.40 × 105 gPP/molNi·h, and the activity was still maintained above 105 gPP/molNi·h at 50 °C. The large steric hindrance of catalysts inhibited the chain-walking and chain-transfer reactions, resulting in polypropylene with high molecular weights (407~1101 kg/mol) and low 1,3-enchainment content (3.57~16.96%) in toluene. The low tensile strength (0.3~1.0 MPa), high elongation at break (218~403%) and strain recovery properties (S.R. ~50%, 10 tension cycles) of the resulting polypropylenes, as well as the visible light transmittance of approximately 90%, indicate the characteristics of the transparent elastomer.

MgCl2-Supported Ziegler–Natta Catalysts for Propene Polymerization: Before Activation

MgCl₂-Supported Ziegler–Natta Catalysts for Propene Polymerization: Before Activation

The role of organoaluminum and electron donors in propene insertion on the Ziegler-Natta catalyst.

Alkyl aluminium plays a primary role in activating Ti within Ziegler-Natta (ZN) catalysts for propylene polymerization. We performed density functional calculations to explore the additional roles of AlEt3 and AlEt2Cl, in conjunction with diisobutyl phthalate (DIBP) internal donor and dicyclopentyl dimethoxysilane (DCPDMS) external donor, to enhance the stereoselectivity of propene insertion. Based on our calculated adsorption energies on the (MgCl2)13/TiCl2iBu cluster model for the ZN catalyst, the presence of DIBP on the cluster essentially facilitated AlEt2Cl adsorption while AlEt2Cl also promoted the adsorption of DIBP. The reaction between AlEt3 and DIBP on the cluster led to the extraction of DIBP, creating an available site for DCPDMS adsorption. While the stereoselectivity, represented by the difference in the activation energies between 1,2-re and 1,2-si insertions of propene, was negligible on the cluster containing only DIBP, it became significant on the clusters containing both AlEt2Cl and DIBP (and DCPDMS). AlEt2Cl plays a pivotal role in imposing steric effects near the Ti active site, thereby increasing stereoselectivity. Our findings suggest the importance of including AlEt2Cl alongside DIBP (and DCPDMS) in the ZN cluster model to investigate stereoselective propene insertion. Considering AlEt2Cl adsorption and AlEt3 reaction with internal donors is essential in developing Ziegler-Natta catalysts.

The Interplay of Backbone Stiffening and Active Pocket Design in Bis(phenolate-ether) Zr/Hf Propene Polymerization Catalysts

The Interplay of Backbone Stiffening and Active Pocket Design in Bis(phenolate-ether) Zr/Hf Propene Polymerization Catalysts

Effect of novel amido ester internal donor on the performance of Ziegler-Natta catalyst for propylene polymerization

Various classes of molecules like diethers, succinates, diesters, amido esters are currently being used as internal donors on MgCl2 supported titanium catalysts for isotactic polypropylene as an alternative to phthalate donors owing to their potential health risk laid down by REACH legislation. In the present paper, design and synthesis of a few novel amido ester internal donors with single chiral center (7–11) by mimicking the model amido ester 3 having two chiral centers; and their catalyst preparation method were described. Further preliminary polymerization tests with newly synthesized donor molecules were investigated and results revealed that by structurally mimicking 3 with one chiral center and also with varied substitutional patterns in ester/amido moiety decline the polypropylene activity as well as isotacticity. These donor molecules are ineffective for appropriate coordination on MgCl2 sites on inducing steric hindrance for improved isotacticity; nevertheless also induces poisoning effect for the active Ti centers leading to catalyst fouling in many cases.

Alkene polymerization reactions with catalysts based on acetylacetonate complexes of vanadium and titanium: effect of cocatalyst

AbstractAlkene polymerization reactions were studied with three catalyst systems containing complexes of vanadium and titanium with the acetylacetonate ligand (V(acac)3, VO(acac)2, Ti(acac)2Cl2) and a binary activator, a combination of Al(C2H5)2Cl and Mg(C4H9)2 at an [Al]:[Mg] molar ratio of ca 3. All three catalysts are highly active in ethylene homopolymerization reactions. They copolymerize ethylene and 1‐hexene to random, compositionally uniform products with 1‐hexene content of up to 20–25%. The Ti(acac)2Cl2–Al(C2H5)2Cl/Mg(C4H9)2 combination is also an effective catalyst for propylene polymerization to an essentially atactic product. Gel permeation chromatography analysis showed that all the studied M(acac)n–Al(C2H5)2Cl/Mg(C4H9)2 catalysts contain several types of active centers which differ in the average molecular weight of polymer material they produce. © 2021 Society of Industrial Chemistry.

Rigid Postmetallocene Catalysts for Propylene Polymerization: Ligand Design Prevents the Temperature-Dependent Loss of Stereo- and Regioselectivities

Rigid Postmetallocene Catalysts for Propylene Polymerization: Ligand Design Prevents the Temperature-Dependent Loss of Stereo- and Regioselectivities

Sustainable rosin acid ester as internal electron donors in Ziegler-Natta catalysts for synthesis of isotactic polypropylene with high melt flow rate

In this contribution, novel bio-derived rosin acid ester compounds have been developed and used as internal electron donors to prepare MgCl2 supported titanium catalysts for propylene polymerization. The results of the polymerization showed that tri-n-amyl maleate, triiso-amyl maleate and tri-n-heptyl maleate as internal electron donors in Ziegler-Natta catalysts all have high polymerization activity and stereoregularity. In particular, the Ziegler-Natta catalyst with tri-n-amyl maleate as the internal electron donor has the highest activity (up to 33.4 kgPP·gCat−1·h−1) for propylene polymerization and the isotacticity of polypropylene is as high as 96.8% determined by 13C NMR. Simultaneously, the obtained polypropylene with a relatively broad molecular weight distribution of 9.0 and melt flow rate of 160.3 g/10 min, which is beneficial to processing and has practical industrial application value when used as the basic material of melt blown cloth for medical mask.

Ansa-Zirconocene Catalysts for Isotactic-Selective Propene Polymerization at High Temperature: A Long Story Finds a Happy Ending

Absolute rigidity is rare in the "soft" world of organometallics. Here we introduce two cyclopenta[a]triptycyl ansa-zirconocene catalysts for isotactic-selective propene polymerization, designed by means of an integrated high-throughput experimentation/quantitative structure-activity relationship modeling approach. An ultrarigid ligand precisely wrapped around the Zr center enforces an enzyme-like lock and key fit, effectively hampering undesired reactive events, even at high temperature. Stereodefective units are hardly detectable by 13C NMR in the polymer produced at 120 °C; this corresponds to an enantioselectivity exceeding 6-7 kcal/mol: i.e., less than 1 propene misinsertion every 4000 (and at room temperature, one every ∼40000!).

Preparation of MgCl2-Supported Ziegler-Natta Catalysts via New Surfactants Emulsion for Propylene Polymerization

This article describes a MgCl2-supported Ziegler-Natta catalyst for propylene polymerization prepared via an in situ emulsion technique with new surfactants. The effect of preparation conditions such as the TiCl4/toluene molar ratio, TiCl4-contacting temperature, amount of phthaloyl dichloride, stirring rate, mixing time of TiCl4/toluene with the Mg complex, and the n-butyl chloride loading was investigated in detail. Scanning electron microscopy and laser particle size analyzer measurements showed that the catalyst particles exhibit a perfectly spherical shape, narrow particle size distribution, and low fine powder content. Energy-dispersive X-ray spectrometry indicated that the Ti, Mg, and Cl elements were evenly distributed throughout the particles. Powder X-ray diffraction measurements indicated the presence of δ-MgCl2 in the catalyst, and FTIR and GC-MS studies confirmed the presence of in situ formed di(ethylhexyl)phthalate (DEHP). Bulk polymerization of propylene using the catalyst was studied, and it was found that the catalyst displayed high activity, high bulk density with high stereospecificity, and excellent hydrogen sensitivity. The polymer produced by the catalyst has a narrow particle size distribution with a low fine powder content.

Titanium-magnesium catalysts for propylene polymerization: Study of interrelations between composition, structure and activity

Propylene polymerization titanium-magnesium catalysts (TMCs) were synthesized from different magnesium compounds with diphenylketone (DPK) as the internal donor. The catalysts differed by an order of magnitude and more in the content of titanium and donor, activity, specific surface area and pore size. Sizes of MgCl2 crystallites with 110 or 104 lateral cuts were calculated from the Ti/Mg and DPK/Mg values. For highly active TMCs the composition, XRD and specific surface area were in agreement with the MgCl2 crystallites with 104 lateral cuts, TiCl4 adsorption on one magnesium ion and elongated in the 001 direction. For low-activity TMCs obtained by reacting Mg with BuCl, the sizes of MgCl2 crystallites in different directions were close. Activity of the catalysts was inversely proportional to the crystallite size calculated from the TMC composition. This dependence was preserved for the catalysts obtained via the substitution of ketone by phthalate.

Progress in propylene homo- and copolymers using advanced transition metal catalyst systems

Recent progress on advanced transition metal catalysts for propylene polymerization and copolymerization are reviewed.

Synthesis of Titanium–Magnesium Catalysts for Propylene Polymerization: Substitution of Ketones by Dibutyl Phthalate

Titanium-magnesium catalysts (TMCs) of propylene polymerization have been synthesized in the presence of ketones as internal donors. The molar ratio of titanium chloride to ketone in TMCs was found to depend on the structure of ketone. The composition and catalytic properties of the synthesized TMCs in propylene polymerization were significantly different from those of TMCs prepared without ketone. The TMCs were synthesized by replacing ketones with a stereoregulating donor dibutyl phthalate (DBP, DBP/Mg = 0.05 mol/mol). It was shown that ketones were substituted by phthalate; the crystallite size of MgCl2 (~6.5 nm in the 110 direction) did not change. The data on the molar ratio Ti/donor = 2 for different donors (ketone, phthalate) and the same MgCl2 crystallites are consistent with the predominance of 104 lateral cuts. The catalytic properties of the substituted catalysts are almost independent of the type of ketone used and are close to those of the standard TMC obtained with phthalate alone (DBP/Mg = 0.2 mol/mol) during the formation of MgCl2. Therefore, ketones, like esters, are involved in the formation of magnesium chloride. Their subsequent substitution by phthalate allows synthesis of TMCs with high activity and stereospecificity.

{Cyclopentadienyl/Fluorenyl}-Group 4 ansa-Metallocene Catalysts for Production of Tailor-Made Polyolefins.

The development of new metallocene-based polymerization catalysts and innovative processes derived thereof still constitutes a challenge for the manufacturing of polyolefinic materials with tailored properties (e. g. particular microstructure or topology, ultra-high molecular weight, high melting transition, and their combinations) for contemporary commercial applications. This personal account summarizes our continuing endeavors to advance the family of industry-relevant stereoselective propylene polymerization catalysts based on C1 -symmetric group 4 ansa-metallocenes incorporating multi-substituted fluorenyl-cyclopentadienyl {Cp/Flu} ligands. Within the framework of this project, valuable structural and catalytic data, harvested both for neutral metallocenes and for metallocenium ion-pairs, have been used for rational design of more efficient catalytic systems, reluctant towards side reactions, and for providing new stereoregular value-added polymer materials.

A Formulation Protocol with Pyridine to Enable Dynamic Nuclear Polarization Surface-Enhanced NMR Spectroscopy on Reactive Surface Sites: Case Study with Olefin Polymerization and Metathesis Catalysts.

Dynamic nuclear polarization surface-enhanced NMR spectroscopy (DNP-SENS) has emerged as a powerful characterization tool in material chemistry and heterogeneous catalysis by dramatically increasing, by up to 2 orders of magnitude, the NMR signals associated with surface sites. DNP-SENS mostly relies on using exogenous polarizing agents (PAs), typically dinitroxyl radicals, to boost the NMR signals. However, the PAs may interact with the surface or even react with surface sites, thus leading to loss or quenching of DNP enhancements. Herein, we describe the development of a DNP-SENS formulation that allows broadening the application of DNP-SENS to samples containing highly reactive surface sites, namely a Ziegler-Natta propylene polymerization catalyst, a sulfated zirconia-supported metallocene, and a silica-supported cationic Mo alkylidene. The protocol consists of adsorbing pyridine prior to the DNP formulation (TEKPol/TCE). The addition of pyridine not only preserves the PAs and thereby restores the DNP enhancement but also allows probing Lewis/Brønsted acid surface sites that are often present on these catalysts.

Structure‐Activity Relationships for Bis(phenolate‐ether) Zr/Hf Propene Polymerization Catalysts

A series of 20 bis(phenolate‐ether) ligands, in combination with Zr and Hf, was tested for performance in propene polymerization, focusing on molecular weight, stereoregularity and regioregularity of the resulting polymer. Ligand variation covers length of the aliphatic linker between the ligand halves, as well as steric bulk of the groups ortho to the phenolate oxygen. The linker length has a dramatic effect on MW: two‐carbon linkers produce oligomers (Mn < 2.5 kDa) while three‐ and four‐carbon linkers generate much higher MW (Mn typically 50–500 kDa). Stereoselectivity can be tuned using large, flat substituents in the o‐phenolate position; tuning of regioselectivity is much harder. Hf catalysts are slower than their Zr analogs and do not work well with MAO/BHT (BHT = 2,6‐di‐tert‐butyl‐4‐methylphenol); they are generally more selective (MW, stereo and regio). Density functional calculations agree fairly well with observed selectivities, supporting the involvement of a fac/fac coordinated active species. These O4 catalysts are considerably more flexible than e.g. metallocenes, making accurate prediction of PP microstructure a significant challenge.

Sequential immobilization of ansa-hafnocene complexes for propene polymerization

We report the immobilization of the ultrarigid ansa-hafnocene complexes rac-[Me2Si(Ind*)2HfCl2] (rac-1; Ind* = 7-(3′,5′-Di-tert-butylphenyl)-4-methoxy-2-methylindenyl) on silica as hetereogeneous catalysts for propene polymerization. A sequential three-step synthesis on the siliceous surface led to pre-catalysts of the generalized structure SiO2–Si(Ind*)2HfCl2, which possess the silylene bridge of the substituted bis(indenyl) ligand directly attached to the surface. The immobilized pre-catalysts show very poor performance in the polymerization of propene, independent on the reaction conditions and the employed silica. Based on the results, we suggest that the close proximity of the catalyst to the surface combined with the steric congestion provoked by the ligand prevents a continuous polymerization, most likely due to a blockage of the catalytically active sites with growing polymer.

Ansa-Metallocenes Bearing 4-(N-Azolyl)-2-methylindenyl and Related Ligands: Development of Highly Isoselective Catalysts for Propene Polymerization at Higher Temperatures

A series of Me2Si-bridged bis(2-Me-indenyl) ansa-zirconocenes containing N-pyrrolyl, N-indolyl, N-carbazolyl, and P-dibenzophospholyl substituents in position 4 of the indenyl moieties has been synthesized. Pd-catalyzed arylation of the azoles with 4-Br-2-Me-indene was used to synthesize the respective 4-(N-azolyl)indenes. 4-(P-Dibenzophospholyl)indene was obtained in high yield by reaction of 5-Cl-dibenzophosphole with (2-Me-inden-4-yl)MgBr. Some of the synthesized zirconocenes were characterized by X-ray crystallography. The rac-zirconocenes were tested in propylene polymerization in the presence of MAO or perfluoroarylborate activators. At 100 °C, the zirconocene rac-Me2Si[2-Me-4-(N-carbazolyl)indenyl]2ZrCl2/MAO afforded highly crystalline isotactic polypropylene with reasonable molecular weight (318 kDa) and a Tm value of 157 °C determined by a remarkably low total number of stereo- and regioerrors, which makes it one of the most isoselective catalysts for high-temperature propylene polymerization.

Effect of internal donors on the performance of Ti-Mg catalysts in propylene polymerization: Donor introduction during or after MgCl2 formation

Propylene polymerization catalysts with different internal donors (ID) are synthesized by two methods: (1) a standard method with ID introduction during formation of MgCl2 by reacting Mg(OEt)2 with TiCl4, and (2) the introduction of ID on MgCl2 already formed in the presence of butyl acetate (the substitution method). 1,3-diether, dibutyl phthalate (DBP) and pentane-2,4-diol-dibenzoate (PDDB) are used as ID. Catalysts prepared with the same ID by both methods slightly differ in their composition, activity and stereospecificity (the content of xylene soluble polypropylene (PP) fraction). But the catalyst active sites produce PP, whose properties (melt flow index, MFI, and molecular-weight distribution as Mw/Mn) depend on ID in the same manner for both methods of catalyst synthesis. Hence, the effect of ID on the catalyst active sites is not related with the effect of ID on the formation of MgCl2 crystallites with different cuts.

Modification of Si/Mg Composite Supported Ziegler- Natta Ti-based Catalysts for Propylene Polymerization Using the Third Metal Elements

Modification of Si/Mg Composite Supported Ziegler- Natta Ti-based Catalysts for Propylene Polymerization Using the Third Metal Elements