FI Catalysts Research Articles

Deciphering the role of FI catalyst’s C3 substituent on the non-isothermal crystallization kinetics of nascent disentangled UHMWPE

UH1 - UH4 were accessed using tetra-fluorinated phenoxy-imine catalysts (FI catalysts) with linear (allyl, n-propyl, 1-propenyl) or more steric demanding (isopropyl) C3 substituents ortho to the phenoxy-oxygen atom. To get a better understanding of the non-isothermal crystallization kinetics of these nascent ultra-high molecular weight polyethylenes (UHMWPEs), their thermo-rheological properties are investigated. Through the application of annealing-crystallization-melting thermal analysis and isoconversional method, it is verified that the samples are nascent disentangled UHMWPEs with higher crystallization rates compared to the commercial UHMWPE (CUH). The molar fraction of nascent entangled crystals and/or degree of supercooling have a significant influence on the non-isothermal crystallization kinetics of nascent disentangled UHMWPEs. Finally, under a lower supercooling, the electron-donating property and steric hindrance of C3 substituent strongly affect the synthesis and architecture of polyolefin which in turn has a specific non-isothermal crystallization kinetics.

DFT insight into metals and ligands substitution effects on reactivity of phenoxy-imine catalysts for ethylene polymerization

The reaction mechanism of ethylene (ET) polymerization catalyzed by the phenoxy-imine (FI) ligands using DFT calculations was studied. Among five possible isomers, isomer A which has an octahedral geometry and a (cis-N/trans-O/cis-Cl) arrangement is the most stable pre-reaction Ti-FI dichloride complex. The isomer A can be activated by MAO to form the active catalyst and the active form was used for the study of the mechanism for Ti-FI. The second ethylene insertion was found to be the rate-determining step of the catalyzed ethylene polymerization. To examine the effect of group IVB transition metals (M = Ti, Zr, Hf) substitutions, calculated activation energies at the rate-determining step (EaRDS) were compared, where values of EaRDS of Zr < Hf < Ti agree with experiments. Moreover, we examined the effect of substitution on (O, X) ligands of the Ti-phenoxy-imine (Ti-1) based catalyst. The results revealed that EaRDS of (O, N) > (O, O) > (O, P) > O, S). Hence, the (O, S) ligand has the highest potential to improve the catalytic activity of the Ti-FI catalyst. We also found the activation energy to be related to the Ti-X distance. In addition, a novel Ni-based FI catalyst was investigated. The results indicated that the nickel (II) complex based on the phenoxy-imine (O, N) ligand in the square-planar geometry is more active than in the octahedral geometry. This work provides fundamental insights into the reaction mechanism of M − FI catalysts which can be used for the design and development of M − FI catalysts for ET polymerization.

Nitrogen doped carbon coated Mo modified TiO2 nanowires (NC@MTNWs-FI) with functionalized interfacial as advanced PtRu catalyst support for methanol electrooxidation

A strategy combining hydrothermal in-situ pre-carbonization coating and interfacial functionalization is proposed to prepare the nitrogen doped carbon coated Mo modified one-dimensional TiO2 nanowires (NC@MTNWs-FI) with functionalized interfacial core-shell structure as advanced carriers for PtRu nanoparticles towards methanol electrooxidation. Mo functional doping and chitosan pre-carbonization occur simultaneously on the surface of TiO2 nanowires (TNWs), resulting in a special concentric multilayer one-dimensional (1D) structure with TiO2 core, Mo functionalized interface and an outer N-doped carbon layer. The mass activity of the prepared PtRu/NC@MTNWs-FI catalyst is increased to 1.23 A mg−1 Pt for methanol electrooxidation, which is 2 times higher than that of the unmodified supported catalyst (PtRu/NC@TNWs) and the stability is increased by 15.9%. In addition, it is 2.24 times higher than that of the PtRu/C catalyst and the stability is increased by 23.2%. This excellent catalytic performance is attributed to the synergistic electron donating effect of the Mo functionalized interface and the nitrogen doped carbon layer on the supported PtRu as well as the stronger anchoring effect. This work reveals a new method for designing highly active and stable electrocatalytic support materials for the development of fuel cells.

Fabrication of C@Mo Ti1−O2−δ nanocrystalline with functionalized interface as efficient and robust PtRu catalyst support for methanol electrooxidation

Abstract A core shell structured C@MoxTi1-xO2-δ nanocrystal with a functionalized interface (C@MTNC-FI) was fabricated via the hydrothermal method with subsequent annealing derived from tetrabutyl orthotitanate. The formation of anatase TiO2 was inhibited by the simultaneous presence of the hydrothermal etching/regrowth process, infiltration of Mo dopants and carbon coating, which endows the C@MTNC-FI with an ultrafine crystalline architecture that has a Mo-functionalized interface and carbon-coated shell. PtRu nanoparticles (NPs) were supported on C@MTNC-FI by employing a microwave-assisted polyol process (MAPP). The obtained PtRu/C@MTNC-FI catalyst has 2.68 times higher mass activity towards methanol electrooxidation than that of the un-functionalized catalyst (PtRu/C@TNC) and 1.65 times higher mass activity than that of PtRu/C catalyst with over 25% increase in durability. The improved catalytic performance is due to several aspects including ultrafine crystals of TiO2 with abundant grain boundaries, Mo-functionalized interface with enhanced electron interactions, and core shell architecture with excellent electrical transport properties. This work suggests the potential application of an interface-functionalized crystalline material as a sustainable and clean energy solution.

Influence of the Fragmentation of POSS-Modified Heterogeneous Catalyst on the Formation of Chain Entanglements

The fluorinated bis(phenoxyimine)Ti complexes (FI catalyst) are immobilized onto the polyhedral oligomeric silsesquioxane (POSS)-modified silica for the preparation of ultrahigh molecular weight polyethylene (UHMWPE) with a weakly entangled state. The POSSs can assemble to spherical nanoaggregates with an average size of 60 nm, which can serve as isolators to separate the active species and growing chains. The weakly entangled UHMWPE is prepared with an exceptional activity owing to this isolation. The evolution of entanglements for polymer chains is studied based on the fragmentation of catalytic particles. It is evidenced by the results of polymerization and characterization that 30 min of polymerization is the critical time for the entire fragmentation of catalytic particles. Importantly, this fragmentation leads to a rupture of the reacted environment which is established by the POSS nanoaggregates. Further polymerization will synthesize the UHMWPE with more entangled density.

Designing polyethylene characteristics by modification of the support for FI catalyst

Fumed silica was modified with octadecyl groups at different Cl:OH ratios (0:100, 20:80, 50:50 and 80:20) and used as support to immobilize an FI Ti-based catalyst. The supported catalysts were evaluated for ethylene polymerization and the effects of the organic ligands on the surface of the support, and the polymerization temperature in the reaction medium was examined. The resulting polymers have molecular weights higher than 1 million gmol−1, which is typical of ultrahigh molecular weight polyethylene (UHMWPE). The organic group appears to act as a modifier (horizontal spacer) around the active sites, thus affecting the activity and kinetics of the catalyst.

Pressure-Sensitive Supported FI Catalyst for the Precise Synthesis of Uni- and Bimodal Polyethylene

Pressure-sensitive phenoxy-imine titanium catalyst (FI-catalyst) was successfully synthesized by covalently immobilizing it on the surface of functionalized polystyrene (PS) nanoparticles, which acted as a support and a giant ligand simultaneously. The supported catalyst shows high catalytic activities in ethylene polymerization. Utilizing this catalyst, a serious of unimodal polyethylenes with tailored molecular weights ranging from 2 000 000 to 300 000 were produced under various reaction pressures and temperatures. Particularly, when the polymerization pressure was shifted during the reaction, the ethylene polymer with bimodal molecular weight distribution was successfully synthesized in only a single reactor. Differential scanning calorimetry analysis of the resultant polyethylene revealed a large difference between crystallinities at the first and second heating cycles, indicating that the synthesized polyethylene is of low entanglement.

Activity of phenoxy-imine titanium catalysts in ethylene polymerization: A quantum chemical approach

The mechanism of ethylene polymerization on phenoxy-imine (FI) titanium catalysts was studied theoretically to identify the major factors affecting the catalytic activity. Geometry optimizations of FI ligands, octahedral titanium dichloride complexes, active cationic species, and their π‐complexes with ethylene as well as calculations of the energy profile of chain propagation were performed at the BP86-D3 level. We found that the calculated energy gaps between frontier orbitals (HOMO and LUMO) in the active cations of the catalysts correlate with the experimental activity values. High activities of FI catalysts with α‐Cumyl groups were attributed to smaller HOMO-LUMO gaps due to hyperconjugation between π-systems of α‐Cumyl and (N‐aryl)salicylaldimine moieties in the active cations. The correlation provides a qualitative estimate of the catalytic activity for further design of new FI titanium complexes.

UHMWPE/SBA-15 nanocomposites synthesized by in situ polymerization

Different nanocomposites have been attained by in situ polymerization based on ultra-high molecular weight polyethylene (UHMWPE) and mesoporous SBA-15, this silica being used for immobilization of the FI catalyst bis [N-(3-tert-butylsalicylidene)-2,3,4,5,6-pentafluoroanilinato] titanium (IV) dichloride and as filler as well. Two distinct approaches have been selected for supporting the FI catalyst on the SBA-15 prior polymerization. A study on polymerization activity of this catalyst has been performed under homogenous conditions and upon heterogenization. A study of the effect of presence of mesoporous particles and of the immobilization method is also carried out. Moreover, the thermal characterization, phase transitions and mechanical response of some pristine UHMWPEs and UHMWPE/SBA-15 materials have been carried out. Relationships with variations on molar mass, impregnation method of catalyst and final SBA-15 content have been established.

Immobilization of isolated FI catalyst on polyhedral oligomeric silsesquioxane-functionalized silica for the synthesis of weakly entangled polyethylene.

Polyhedral oligomeric silsesquioxanes (POSSs) were adsorbed on methylaluminoxane-activated silica for the immobilization of fluorinated bis(phenoxyimine)Ti complexes (FI catalyst). These POSSs have been characterized as horizontal spacers isolating the active sites and hindering the chain overlap in polymerization. The heterogeneous catalyst exhibits considerable activity in the synthesis of weakly entangled polyethylene.

Activation of a Bis‐(Phenoxyimine) Titanium (IV) Catalyst Using Different Aluminoxane Co‐Catalysts

SummaryThe activation of a bis‐phenoxyimine catalyst based on titanium (IV) using different aluminoxanes (MAO, PMAO and MMAO12) has been studied. The effect of a co‐catalyst modifier (BHT) used in combination with the MAO has been also tested. In particular, the effect of the activation time between the catalyst and the different aluminoxanes has been taken into consideration. On increasing the activation time between catalyst and the different aluminoxanes and TMA‐free MAO, differences in the catalyst activities have been observed. UHMWPEs having a reduced number of entanglements have been synthesized activating the FI catalyst with MAO and TMA‐free MAO. The obtained reactor powders can be solid‐state processed below the melting temperature in order to obtain high modulus/high tenacity tapes used for body armor and vehicle protection applications.

Influence of Polyhedral Oligomeric Silsesquioxane Structure on the Disentangled State of Ultrahigh Molecular Weight Polyethylene Nanocomposites during Ethylene in Situ Polymerization

Three kinds of polyhedral oligomeric silsesquioxane (methyl-POSS, cyclohexyl-POSS, and phenyl-POSS) were chosen to adsorb [3-tert-Bu-2-O-C6H3CH═N(C6F5)]2TiCl2 catalyst (FI catalyst) in order to synthesize ultrahigh molecular weight polyethylene (UHMWPE)/POSS nanocomposites according ethylene in situ polymerization. It was shown that the characteristic of “living’’ polymerization of the FI catalyst would be maintained when alkyl-POSS was incorporated. However, the presence of alkyl-POSS could decay the catalyst activity. The incorporation of alkyl-POSS led to an increase of the crystallinity and the lamellar thickness of nascent UHMWPE, as observed by differential scanning calorimetry. This indicated that the alkyl-POSS would be used as a nucleating agent during the chain growth procedure. Interestingly, all the nanocomposites exhibited low starting storage modulus values which was a reflection of disentangled structure in the nascent UHMWPE nanocomposites. However, polymer chains were prior to entanglemen...

Novel Ni-based FI catalyst for ethylene polymerization

Novel nickel based FI catalysts with different ligands from well known salicylaldehyde imine ligand, to naphthoxy-imine ligand were designed, synthesized, and characterized. The effect of synthesized ligand on ethylene polymerization was investigated. Extensive experimentations have been carried out using the nickel catalysts after activation with methylaluminoxane (MAO) to study the ethylene polymerization behavior of the prepared catalysts comparably. Substituents on the arene moiety and/or the backbone of the ligand influence the activities of the active sites of the catalyst during the polymerization. Therefore, not only polymerization behavior varied, but also versatile products regarding molecular weight, crystallinity and melting point were obtained. The crystallinities and melting points of the polymer obtained at the temperatures of 10, 30 and 60°C were 58%, 39%, and 14% and 130, 97 and 88°C respectively.

Highly active self-immobilized FI-Zr catalysts in a PCP framework for ethylene polymerization.

A series of zirconium-based porous coordination polymers (PCPs) containing FI catalysts in the frameworks have been developed and studied as catalysts for ethylene polymerization. These PCPs exhibit good catalytic activities and long life times, producing polyethylenes with high molecular weights and bimodal molecular weight distribution in the form of particles.

Crystallization behavior of ultrahigh‐molecular‐weight polyethylene/polyhedral oligomeric silsesquioxane nanocomposites prepared by ethylene in situ polymerization

ABSTRACTA [3‐t‐Bu‐2‐OC6H3CHN(C6F5)]2TiCl2 catalyst (bis(phenoxyimine)titanium dichloride complex – FI catalyst) was immobilized on disilanolisobutyl polyhedral oligomeric silsesquioxane (OH‐POSS) to prepare ultrahigh molecular‐weight polyethylene (UHMWPE)/polyhedral oligomeric silsesquioxane (POSS) nanocomposites during ethylene in situ polymerization. The dispersion state of POSS in the UHMWPE matrix was characterized by X‐ray diffraction measurements and transmission electron microscopy. It was shown that the OH‐POSS achieved uniformed dispersion in the UHMWPE matrix, although its polarity was unmatched. The isothermal and nonisothermal crystallization behavior of the nanocomposites was investigated by means of differential scanning calorimetry. The crystallization rate of the nanocomposites was enhanced because of the incorporation of POSS during the isothermal crystallization. POSS acted as a nucleus for the initial nucleation and the subsequent growth of the crystallites. For nonisothermal studies, POSS showed an increase in the crystallinity. The crystallization rate of the nanocomposites decreased because the presence of POSS hindered the crystal growth. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40847.

FI Catalysts for Olefin Oligomerization and Polymerization: Production of Useful Olefin-Based Materials by Unique Catalysis

This contribution highlights the uniqueness of FI catalysts (phenoxy-imine ligated group 4 metal complexes) for olefin coordination insertion catalysis. FI catalysts possess characteristic structural and electronic features that are different from those of group 4 metallocene catalysts. These special features in turn initiate versatile catalytic properties that result in useful olefin-based materials some of which have already been commercialized.

Disentangled UHMWPE/POSS nanocomposites prepared by ethylene in situ polymerization

[3-t-Bu-2-O-C6H3CHN(C6F5)]2TiCl2 catalyst (FI catalyst) was immobilized on disilanolisobutyl POSS to synthesize disentangled ultra-high molecular weight polyethylene (UHMWPE)/POSS nanocomposites during ethylene in situ polymerization. The presence of POSS significantly influenced the polymerization properties of the FI catalyst active centers. It was shown that the characteristic of “living” polymerization of the FI catalyst was retarded. Furthermore, disilanolisobutyl POSS is dispersed uniformly in the UHMWPE matrix with particles size of only several tens nanometers. Interestingly, the incorporation of the POSS into nascent UHMWPE matrix led to a strong interaction between the POSS particles and the UHMWPE chains, resulting in an increased density of entangled chains, as reflected by rheological test. Moreover, the crystallinity and the lamellae thickness of nascent UHMWPE increased upon increasing POSS loading, as observed by differential scanning calorimetry. It suggested that the POSS particles would be presented as a nucleating agent. Finally, the thermal stability and the hydrophilic property of the nanocomposites were improved due to the incorporation of POSS particles.

A Catalyst for One‐step Isoparaffin Production via Fischer–Tropsch Synthesis: Growth of a H‐Mordenite Shell Encapsulating a Fused Iron Core

AbstractFused iron (FI), is a general Fischer–Tropsch synthesis (FTS) catalyst and can be used to convert syngas (CO+H2) into normal hydrocarbons. The syntheses of HZSM‐5 or H‐β zeolite‐shell encapsulated catalysts for FTS have been reported previously, however, conventional zeolite‐shell synthesis generally employs an organic template, which is neither economic nor environmentally benign. Here we report the synthesis, without using an organic template, of a millimeter‐sized defect‐free capsule catalyst covered by a MOR zeolite shell (thickness of 23 μm) on FI pellets. The capsule catalyst (HMOR/FI) exhibited excellent performance for FTS, greatly increasing the selectivity of middle isoparaffins. Compared with the pure FI catalyst, the CO conversion of the HMOR/FI capsule catalyst increased remarkably and the iso/n ratio was almost 8 times that of the pure FI catalyst. This report provides an effective route to synthesize a capsule catalyst, which can reduce costs effectively and is also more environmentally benign than the current conventional zeolite‐shell synthesis.

Synthesis and Application of FI Catalyst for Ethylene Polymerization

A FI (phenoxy-imine) Zr-based catalyst of bis[1-[(2,6-diisopropylphenyl)imino]methyl-3,6-ditertbutyl-2-naphtholato]zirconium(IV) dichloride was prepared by changing the ligand from salicylaldehyde imine ligand which is used for well known FI catalysts to 2-hydroxynaphthalene-1-carbaldehyde imine ligand and used for polymerization of ethylene. Replacement of the phenoxy-group by naphtholato-group does not provide any spatial difficulties in the ortho-position to oxygen, but introduction of the bulky alkyl substitution groups at the ortho position of the naphthoxy-oxygen and on phenyl ring on the N dramatically enhanced the activity of the catalyst, as well as viscosity average molecular weight (Mv) of the obtained polymer. The prepared catalyst could produce a high molecular weight polyethylene under the polymerization conditions used. The optimum activity of the catalyst was obtained at the reaction temperature of 40°C. Activity of the catalyst was continuously increased with increasing MAO concentration and monomer pressure and no optimum activity was observed in the range studied. Crystallinity and melting point of the obtained polymer were between 55–65% and 125–135°C, respectively. A molecular weight distribution of 1.55–2.75 was obtained under the polymerization condition used and the polydispersity was broadened with the time. The activity of the catalyst was not sensitive to the hydrogen concentration. However, higher amount of hydrogen could slightly increase the activity of the catalyst.

Living syndiospecific polymerization of propylene promoted by C 1 -symmetric titanium complexes activated by dried MAO

A series of C-1-symmetric titanium complexes with both salicylaldiminato and beta-enaminoketonato as the ligands have been synthesized and investigated as the catalysts for propylene polymerization. In the presence of dried methylaluminoxane (dMAO), the complex with bulky substituent tert-butyl ortho to alkyl oxygen can promote living polymerization of propylene with improved catalytic activity at ambient temperature, producing high molecular weight syndiotactic polypropylenes (rrrr 90.2%) with narrow molecular weight distributions (M-w/M-n = 1.071.22), via a propagation of 1,2-insertion of monomer and chain-end control of stereoselectivity. The propagation of polymer chain is completely different from that mediated by FI catalysts (the titanium complexes with phenoxy-imine chelate ligands) which favor 2,1-insertion of monomer. The interaction between a fluorine and a beta-hydrogen of a growing polymer chain, negligible chain transfer to monomer and dMAO without any free AlMe3 were responsible for the achievement of living propylene polymerization. The substituent ortho to alkyl oxygen determined the stereo structure of the resultant polypropylene. In the case of less steric congested complexes with two nonequivalent coordination positions, the growing polymer chain might swing back to the favorite coordination position (site-epimerization), forming m dyads regioirregular units. (c) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 50: 638-648, 2012