Effect of Borate Cocatalysts toward Activity and Comonomer Incorporation in Ethylene Copolymerization by Half-Titanocene Catalysts in Methylcyclohexane
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ABSTRACT:
SUBMITTER: Kitphaitun S
PROVIDER: S-EPMC9955119 | biostudies-literature | 2022 Aug
REPOSITORIES: biostudies-literature
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Project description:A family of half-titanocene complexes bearing π,π-stacked aryloxide ligands and their catalytic performances towards ethylene homo-/co- polymerizations were disclosed herein. All the complexes were well characterized, and the intermolecular π,π-stacking interactions could be clearly identified from single crystal X-ray analysis, in which a stronger interaction could be reflected for aryloxides bearing bigger π-systems, e.g., pyrenoxide. Due to the formation of such interactions, these complexes were able to highly catalyze the ethylene homopolymerizations and copolymerization with 1-hexene comonomer, even without any additiveson the aryloxide group, which showed striking contrast to other half-titanocene analogues, implying the positive influence of π,π-stacking interaction in enhancing the catalytic performances of the corresponding catalysts. Moreover, it was found that addition of external pyrene molecules was capable of boosting the catalytic efficiency significantly, due to the formation of a stronger π,π-stacking interaction between the complexes and pyrene molecules.
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Project description:Ethylene/polar monomer coordination copolymerization offers an attractive way of making functionalized polyolefins. However, ethylene copolymerization with industrially relevant short chain length alkenoic acid remain a big challenge. Here we report the efficient direct copolymerization of ethylene with vinyl acetic acid by tetranuclear nickel complexes. The protic monomer can be extended to acrylic acid, allylacetic acid, ω-alkenoic acid, allyl alcohol, and homoallyl alcohol. Based on X-ray analysis of precatalysts, control experiments, solvent-assisted electrospray ionization-mass spectrometry detection of key catalytic intermediates, and density functional theory studies, we propose a possible mechanistic scenario that involves a distinctive vinyl acetic acid enchainment enabled by Ni···Ni synergistic effects. Inspired by the mechanistic insights, binuclear nickel catalysts are designed and proved much more efficient for the copolymerization of ethylene with vinyl acetic acid or acrylic acid, achieving the highest turnover frequencies so far for both ethylene and polar monomers simultaneously.
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Project description:The self-assembled multinuclear PdII complexes {(Li-OPOOMe2)PdMe(4-5-nonyl-pyridine)}4Li2Cl2 (C, Li-OPOOMe2 = PPh(2-SO3Li-4,5-(OMe)2-Ph)(2-SO3--4,5-(OMe)2-Me-Ph)), {(Zn-OP-P-SO)PdMe(L)}4 (D, L = pyridine or 4-tBu-pyridine, [OP-P-SO]3- = P(4-tBu-Ph)(2-PO32--5-Me-Ph)(2-SO3--5-Me-Ph)), and {(Zn-OP-P-SO)PdMe(pyridine)}3 (E) copolymerize ethylene and vinyl fluoride (VF) to linear copolymers. VF is incorporated at levels of 0.1-2.5 mol% primarily as in-chain -CH2CHFCH2- units. The molecular weight distributions of the copolymers produced by D and E are generally narrower than for catalyst C, which suggests that the Zn-phosphonate cores of D and E are more stable than the Li-sulfonate-chloride core of C under copolymerization conditions. The ethylene/VF copolymerization activities of C-E are over 100 times lower and the copolymer molecular weights (MWs) are reduced compared to the results for ethylene homopolymerization by these catalysts.
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Project description:The aim of this work is to investigate the influence of the ethanol content of adducts on the catalytic behavior of related Ziegler-Natta (ZN) catalysts in propylene homo- and copolymerizations (with 1-hexene comonomer) in terms of activity, isotacticity, H2 response, and comonomer incorporation. For this purpose, three MgCl2.nEtOH adducts with n values of 0.7, 1.2, and 2.8 were synthesized and used in the synthesis of related ZN catalysts. The catalysts were thoroughly characterized using XRD, BET, SEM, EDX, N2 adsorption-desorption, and DFT techniques. Additionally, the microstructure of the synthesized (co)polymers was distinguished via DSC, SSA, and TREF techniques. Their activity was found to enhance with the adduct's ethanol content in both homo- and copolymerization experiments, and the increase was more pronounced in homopolymerization reactions in the absence of H2. Furthermore, the catalyst with the highest ethanol content provided a copolymer with a lower isotacticity index, a shorter meso sequence length, and a more uniform distribution of comonomer within the chains. These results were attributed to the higher total surface area and Ti content of the corresponding catalyst, as well as its lower average pore diameter, a larger proportion of large pores compared to the other two catalysts, and its spherical open bud morphology. It affirms the importance of catalyst/support ethanol-content control during the preparation process. Then, molecular simulation was employed to shed light on the iso-specificity of the polypropylene produced via synthesized catalysts.
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Project description:Multicomponent supramolecular polymers are a versatile platform to prepare functional architectures, but a few studies have been devoted to investigate their noncovalent synthesis. Here, we study supramolecular copolymerizations by examining the mechanism and time scales associated with the incorporation of new monomers in benzene-1,3,5-tricarboxamide (BTA)-based supramolecular polymers. The BTA molecules in this study all contain three tetra(ethylene glycol) chains at the periphery for water solubility but differ in their alkyl chains that feature either 10, 12 or 13 methylene units. C10BTA does not form ordered supramolecular assemblies, whereas C12BTA and C13BTA both form high aspect ratio supramolecular polymers. First, we illustrate that C10BTA can mix into the supramolecular polymers based on either C12BTA or C13BTA by comparing the temperature response of the equilibrated mixtures to the temperature response of the individual components in water. Subsequently, we mix C10BTA with the polymers and follow the copolymerization over time with UV spectroscopy and hydrogen/deuterium exchange mass spectrometry experiments. Interestingly, the time scales obtained in both experiments reveal significant differences in the rates of copolymerization. Coarse-grained simulations are used to study the incorporation pathway and kinetics of the C10BTA monomers into the different polymers. The results demonstrate that the kinetic stability of the host supramolecular polymer controls the rate at which new monomers can enter the existing supramolecular polymers.
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Project description:Vanadium complexes bearing naphthalene-bridged nitrogen-sulfonate ligand ([ê²(N,O)-8-(PhN)-1-naphthalenesulfonato]VOCl (1a) and [ê²(N,O)-8-(PhN)-1-naphthalenesulfonato]VCl₂ (1b)) were synthesized. Activated by ethylaluminium sesquichloride (EASC) and in the presence of ethyl trichloroacetate (ETCA) as reactivator, complexes 1a and 1b showed activities of up to 39.1 kg polymer (mol V)-1 h-1, affording the copolymers with high molecular weights (Mw up to 28 × 10⁴) and narrow molecular weight distributions (Mw/Mn ~ 3.0) as well as high propylene incorporation of up to 49.4%. Compared to the traditional VOCl₃ system, these complexes exhibited higher propylene incorporation ability and higher catalytic activities especially at high polymerization temperatures of 50 °C and above. Determined by DSC and 13C NMR, the copolymers obtained with 1a and 1b had more random structures than that with the VOCl₃ system.
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Project description:In order to increase the thermal stability of olefin polymerization precatalysts, new titanium(IV) complexes with diolate ligands differing in the degree of steric hindrances were synthesized from readily available precursor (±)camphor. The structures of the complexes 1-2 were established by X-ray diffraction. Complexes 1-4 in the presence of an activator {EtnAlCl3-n + Bu2Mg} catalyzed the synthesis of UHMWPE with an Mv up to 10 million and a productivity of up to 3300 kg/molTi·atm·h. The obtained polymers are obviously characterized by a low density of macromolecular entanglement, which makes it possible to use the solid-phase method for their processing. The mechanical characteristics of the oriented UHMWPE films had a breaking strength up to 2.7 GPa and an elastic modulus of up to 151 GPa. The precatalysts 1-4 were also active in ethylene/1-octene copolymerization. The comonomer content was in the range of 1.4-4.6 mol%. The use of a rigid linker and an increase in the steric load of the diolate complexes ensured the thermal stability of the catalytic system in the range of 50-70 °C.
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Project description:Synthesizing functionalized polyethylenes via ethylene coordination copolymerization with fundamental low-cost vinyl polar monomers provides a very attractive approach. However, it is also very challenging as the functional group (FG) to be introduced onto the polyolefin chain is directly derived from the corresponding vinyl polar monomers (CH2 = CH-FG), which often cause catalyst poisoning due to the FG coordination to active metal center and β-X elimination during catalysis, etc. It is especially true for the synthesis of cyano-functionalized polyethylenes (PEs) via ethylene/acrylonitrile copolymerization, which can only rely on Pd catalysis with low activity. Here we present an approach utilizing binuclear Ni catalysis for ethylene/acrylamide copolymerization and the synthesis of cyano-functionalized PEs (>99%) with great activity up to 4.1 × 106 g/(mol cat·h). Extensive polymer characterizations (NMR, GPC, model experiments, etc) confirm significant chain transfer and the conversion of amide to nitrile during catalysis. Mechanistic investigations, including comprehensive control experiments, deuterium labeling and computational studies, support an isomerization-mediated chain transfer polymerization (ICTP) mechanistic pathway, which include tandem acrylamide enchainment, amido group conversion into CN group, and active catalyst regeneration by Et2AlCl. Catalyst poisoning could be largely circumvented by this catalyst system.
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Project description:Melt memory effects in polymer crystallization have attracted much attention in the past few years. Although progress has been made in understanding how the chemical structure of polymers can affect melt memory, there are still some knowledge gaps. In this work, we study how incorporating a second comonomer unit that is partially included in the crystalline unit cell affects the melt memory effect of the major component in a random isodimorphic copolymer for the first time. This second comonomer unit depresses the melting temperature of the homopolymer, reduces the crystallinity, and distorts the crystalline unit cell. However, its effect on the stability of self-nuclei and the production of melt memory has not been studied so far. To this aim, we have selected poly[(butylene succinate)-ran-(ε-caprolactone)] random copolyesters PBS-ran-PCL that are isodimorphic, i.e., they exhibit a pseudoeutectic point. This point separates the formation of BS-rich crystals from CL-rich crystals as a function of composition. The results reveal that the melt memory effect of these isodimorphic copolymers is strongly reduced with the incorporation of even very small amounts of comonomer unit (i.e., 1 molar %). This indicates that the incorporation of a second comonomer unit in the polymer chain disrupts the intermolecular interactions present between the chain segments in the crystal lattice of the major component and reduces the capacity of the material to produce self-nuclei. This reduction is more drastic for copolymers in which the second comonomer unit is mostly rejected from the crystalline phase. Contrary to olefin-based copolymers, for copolyesters, the second comonomer unit eases the process to reach an isotropic melt state upon melting. This work reveals the impact of introducing comonomer units on the melt memory effect in isodimorphic random copolyesters.
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