Catalytic Polymerization Research Articles

Manipulating pre-equilibria in olefin polymerization catalysis: backbone-stiffening converts a living into a highly active salan-type catalyst

Stiffening the catalyst backbone of a slow salan-type catalyst converts it into a highly active indanosalan catalyst, producing highly isotactic PP with an activity rivalling the most productive known salan-catalyst, with much higher MW capability.

Triisobutylaluminium-promoted formation of lanthanide hydrides.

Discrete lanthanide(III) isobutylaluminates Ln[N(SiMe3)2](HAliBu3)(AliBu4) (Ln = La, Pr, Nd) are obtained from Ln[N(SiMe3)2]3 and triisobutylaluminium (TIBA). Nd[N(SiMe3)2](HAliBu3)(AliBu4) reacts with crown ether to give the ion pair [Nd(18-c-6){N(SiMe3)2}(HAliBu3)][AliBu4], featuring a strong Nd-H interaction in the solid state. The equimolar reaction of La[N(SiMe3)2](HAliBu3)(AliBu4) with fluorene resulted in the concomitant formation of [(μ-fluorenyl)3La2(μ-H)(HAliBu3)2] and (fluorenyl)2La[N(SiMe3)2]. [(μ-Fluorenyl)3La2(μ-H)(HAliBu3)2] features fluorenyl ligands with a μ-η6:η6 coordination around the hydrido-bridged dilanthanum core motif. The reported complexes are the first crystallographically characterized, ancillary ligand-free lanthanide(III) tetraisobutylaluminates, and display potential model systems for Ziegler-type polymerization catalysis.

A DFT-metadynamics study disclosing key properties of ring-opening polymerization catalysts to produce polyethercarbonate polyols from cyclic ethylene carbonate as part of an emerging CCU technology.

The ring opening polymerization of cyclic carbonates made from epoxide and CO2 to CO2-containing polymers constitutes an emerging technology of particular industrial interest. Considering the reaction of ring-opening polymerization of cyclic ethylene carbonate to produce polyethercarbonate polyols, several types of catalysts were tested experimentally and mechanistic pathways were proposed, but a detailed analysis of structure property relationship including the CO2-liberation pathways is still lacking. This contribution is using computational methods to investigate reported benchmark catalysts with the lead structure AxMyOz (A: alkali metal or alkyl, M: main group element or transition metal) that are particularly approved as effiecient catalysts for industrial purpose. Employing DFT-metadynamics simulations, free energy surfaces (FESs) for the key-steps in the catalytic polymerization of cyclic ethylene carbonate (cEC) are generated. Important structural criteria and characteristics of the catalysts that influence the catalytic performance and (side)reaction pathways are determined. It turns out that less nucleophilicity of the catalyst anion and more labile cations remain major criteria for prohibiting CO2 liberation during polymerization. The key learnings of this contribution currently serve as a basis to develop the next generation of catalysts to bring this emerging carbon capture and use (CCU) technology into industrial application.

Asymmetric Catalytic Polymerization: Advances and Challenges

Asymmetric Catalytic Polymerization: Advances and Challenges

Unexpected Effect of Catalyst’s Structural Symmetry on the Branching Microstructure of Polyethylene in Late Transition Metal Polymerization Catalysis

Unexpected Effect of Catalyst’s Structural Symmetry on the Branching Microstructure of Polyethylene in Late Transition Metal Polymerization Catalysis

Microenvironment Modulation of Metal-Organic Frameworks (MOFs) for Coordination Olefin Oligomerization and (co)Polymerization.

The majority of commercial polyolefins are produced by coordination polymerization using early or late transition metal catalysts. Molecular catalysts containing these transition metals (Ti, Zr, Cr, Ni, and Fe, etc.) are loaded on supports for controlled polymerization behavior and polymer morphology in slurry or gas phase processes. Within the last few years, metal-organic frameworks (MOFs), a class of unique porous crystalline materials constructed from metal ions/clusters and organic ligands, have been designed and utilized as excellent supports for heterogeneous polymerization catalysis whose high density and uniform distribution of active sites would benefit the modulations of molecular weight distributions of high-performance olefin oligomers and (co)polymers. Impressive efforts have been made to modulate the microenvironment surrounding the active centers at the atomic level for improved activities of MOFs-based catalysts and controlled selectivity of olefin insertion. This review aims to draw a comprehensive picture of MOFs for coordination olefin oligomerization and (co)polymerization in the past decades with respect to different transition metal active centers, various incorporation sites, and finally microenvironment modulation. In consideration of more efforts are needed to overcome challenges for further industrial and commercial application, a brief outlook is provided.

Nanoconfinement-enhanced Fenton-like polymerization via hollow hetero-shell carbon for reducing carbon emissions in organic wastewater purification

Lower reaction speed and excessive oxidant inputs impede the removal of contaminants from water via the advanced oxidation processes based on peroxymonosulfate. Herein, we report a new confined catalysis paradigm via the hollow hetero-shell structured CN@C (H-CN@C), which permits effective decontamination through polymerization with faster reaction rates and lower oxidant dosage. The confined space structures regulated the CN and CO and electron density of the inner shell, which increased the electron transfer rate and mass transfer rate. As a result, CN in H-CN@C-10 reacted with peroxymonosulfate in preference to CO to generate singlet oxygen, improving the second-order reaction kinetics by 503 times. The identification of oxidation products implied that bisphenol AF could effectively remove by polymerization, which could reduce carbon dioxide emissions. These favorable properties make the nanoconfined catalytic polymerization of contaminants a remarkably promising nanocatalytic water purification technology.

A Thermodynamic Simulation Package for Catalytic Polyolefin Reactors: Development and Applications

AbstractA thermodynamic simulation package is developed for the catalytic polymerization of olefins in autoclave slurry, loop slurry, gas‐phase, and autoclave solution reactors. The number of components in the reactors may vary from two to six. The simulator uses the Sanchez–Lacombe theory, one of the major thermodynamic models in the polymer industry. Step‐by‐step instructions on how to specify the system, derive and solve the resulting nonlinear equations, and estimate the required thermodynamic properties are given. The software is used to describe ethylene/1‐hexene copolymerizations with hydrogen in different reactors under industrial conditions. These simulations demonstrate why thermodynamic effects must be included in olefin polymerization models.

Photoresponsive thiourea and urea catalysts for ring‐opening polymerization of L‐lactide

AbstractStimulus responsive catalysts have received increasing attention. Photoresponsive catalytic polymerization is particularly attractive because the noninvasive and versatile nature of light. Most photoresponsive ROP catalytic systems exhibit low activities, allowing ROP to be completed within several hours to 10 h. In this contribution, a series of (thio)ureas bearing dithienylcyclopentene optical molecular switch moiety are designed, synthesized, and characterized. The photoresponsive effects in (thio)urea/alkoxide mediated ROP of L‐lactide are investigated. These catalysts allow the ROP reactions of L‐lactide to be completed within a few minutes to 1 h and the resulting polyesters have narrow molecular weight distributions. The dithienylcyclopentene moiety allows photoisomerization to be completed within 1 min. The catalytic activity of the ROP catalyst can be altered by the photoisomerization of the dithienyl cyclopentene moiety by exposure to ultraviolet or visible light, respectively.

Practical Route for Catalytic Ring-Opening Metathesis Polymerization.

Norbornene derivatives are typical monomers for ring-opening metathesis polymerization (ROMP) for synthesizing highly functional polymers. However, the lack of catalytic methods, that is, the lack of readily available chain transfer agents (CTAs) for these monomers has been a significant cost limitation when large-scale syntheses are required. Here, we report commercially available styrene and its derivatives as efficient regioselective CTAs for the catalytic synthesis of metathesis polymers requiring up to 1000 times less ruthenium than in classical ROMP experiments. The molecular weight of the synthesized polymers was controlled by the monomer-to-CTA ratio. Low molecular weight ROMP polymers known for their antimicrobial properties were also synthesized on a gram scale in this report. Polymers were characterized by SEC, 1H NMR spectroscopy, and isotopically resolved MALDI-TOF MS. This approach describes a greener, more cost-effective, and eco-friendly methodology for the preparation of metathesis-based materials on the multigram scale.

Macrochain Transfer Agents for Catalytic Ring-Opening Metathesis Polymerization.

A monosubstituted 1,3-diene derivative attached to a polymer is demonstrated to act as a macrochain transfer agent in catalytic ring-opening metathesis polymerization. PEG- and PLA-based macrochain transfer agents were synthesized in a few steps and were characterized using NMR spectroscopy, size exclusion chromatography (SEC) and matrix-assisted laser desorption/ionization-time-of-flight (MALDI-ToF) mass spectrometry. Poly(l-lactide) based diblock copolymer, poly(ethylene glycol)-based diblock, and triblock (ABA type) copolymers of varied chain lengths were prepared catalytically in a one-pot approach via metathesis polymerization. Block copolymers were characterized by SEC and showed monomodal molecular weight distributions. Moreover, DOSY NMR spectroscopy further proved the block microstructures of the synthesized polymers.

Ti-iminocarboxylate catalyzed polymerization of ethylene to highly crystalline, disentangled, ultrahigh molecular weight polyethylene

Disentangled ultrahigh molecular weight polyethylene (d-UHMWPE) is a niche, highly sought-after, and an emerging class of polyethylene. However, the synthesis of d-UHMWPE is uncommon and is equally challenging. Here, we report a Ti-iminocarboxylate complex that produces d-UHMWPE under ambient polymerization conditions. Treatment of tetrakis(dimethylamido-titanium) [Ti(NMe2)4] with 2-((4-methoxybenylidene)amino)benzoic acid produced a novel titanium complex Cat.1 [bis-dimethylamido-Ti-(bis-iminocarboxylate)]. The identity of Cat.1 was unambiguously ascertained using a combination of 1-2D NMR spectroscopy and mass analysis. Cat.1 was activated using various cocatalysts, and MMAO (modified methylaluminoxane) outperformed the others. Screening of polymerization parameters suggested an Al/Ti ratio of 1000, 4 bar ethylene pressure, 35 °C temperature, and a polymerization time of 30 min as the optimal condition. Under the optimized polymerization conditions, Cat.1 polymerizes ethylene to ultrahigh molecular weight polyethylene with a weight average molecular weight (Mw) of 2.5 × 106 g/mol. The thermal behavior of the thus prepared material disclosed a highly crystalline [crystallinity χ (DSC) 96 %], strictly linear polyethylene. Detailed thermal analysis of the nascent polyethylene using a specifically designed DSC method revealed the existence of a high melting peak at 139–140 °C, which is a hallmark of disentangled UHMWPE. Thus, a homogeneous, single-site ethylene polymerization catalyst has been developed, which upon activation with MMAO produced highly crystalline d-UHMWPE.

Facile preparation of PHEMA hydrogel induced via Tannic Acid-Ferric ions for wearable strain sensing

As an important component of flexible electronic devices, strain sensing hydrogels have attracted extensive attention in the field of wearable sensors. However, the hydrogel matrix has some problems such as weak mechanical strength, lack of adhesion and poor performance stability. Herein, an ionic conductive poly (hydroxyethyl methacrylate) (PHEMA) hydrogel with good toughness and adhesion strength was prepared which was initiated by dynamic REDOX reaction of phenolic hydroxyl group and metal ions. The resulting PHEMA/ tannic acid (TA)-Fe hydrogel exhibits high flexibility (2227% elongation at break) and excellent adhesion properties (238 kPa on pig skin) due to the presence of TA and Fe3+ ion. Rheological results demonstrated self-healing performance of the hydrogels, and cyclic compression experiments displayed the hydrogels exhibit very good fatigue resistance. Furthermore, the hydrogel showed well strain sensing ability under different stretch and compress conditions and could maintain the stability performance for at least 100 cycles within 100% strain. Therefore, the PHEMA/TA-Fe hydrogels prepared with a simple and convenient redox catalytic polymerization method possess great potential to be used in flexible electronic devices.

12-Vertex closo-3,1,2-Ruthenadicarbadodecaboranes with Chelate POP-Ligands: Synthesis, X-ray Study and Electrochemical Properties

A class of so-called POP ligands (Xanthos, NiXantphos, DPEphos) are of a great interest to the coordination chemistry due to their wide P-M-P bite angles and ability to show either κ2- or κ3-binding modes. Such κ2–κ3-rearrangement is valuable for catalytic application and internal stabilization of intermediates. To widen the scope of ruthenium-based catalysts for Atom Transfer Radical Polymerization (ATRP) two new approaches to the synthesis of closo-ruthenacarboranes with aforementioned POP ligands were developed and six new 17-e (3,3-(POP)-3-Cl-closo-3,1,2-RuC2B9H11; 2, 4, 7) and 18-e (3,3-(POP)-3-NCCH3-closo-3,1,2-RuC2B9H11; 3, 5, 8) clusters were synthesized and characterized by means of NMR or ESR spectroscopy, MALDI mass-spectrometry and single crystal X-ray diffraction studies. The unique 18-e complex of Ru(II) with dioxygen ligand 3,3-(DPEphos)-3-(η2-O2)-closo-3,1,2-RuC2B9H11 (9) was isolated and characterized by X-ray diffraction. It was shown that aforementioned POP ligands coordinate to ruthenium by two phosphorus atoms in a κ2-fashion. The performed electrochemical studies have shown reversible Ru(II)-Ru(III) transition making the complexes suitable for application in catalysis of polymerization. The test experiments on methyl methacrylate (MMA) polymerization indicate the proceeding of the process in according with an ATRP mechanism.

Photoactive Copper Complexes: Properties and Applications.

Photocatalyzed and photosensitized chemical processes have seen growing interest recently and have become among the most active areas of chemical research, notably due to their applications in fields such as medicine, chemical synthesis, material science or environmental chemistry. Among all homogeneous catalytic systems reported to date, photoactive copper(I) complexes have been shown to be especially attractive, not only as alternative to noble metal complexes, and have been extensively studied and utilized recently. They are at the core of this review article which is divided into two main sections. The first one focuses on an exhaustive and comprehensive overview of the structural, photophysical and electrochemical properties of mononuclear copper(I) complexes, typical examples highlighting the most critical structural parameters and their impact on the properties being presented to enlighten future design of photoactive copper(I) complexes. The second section is devoted to their main areas of application (photoredox catalysis of organic reactions and polymerization, hydrogen production, photoreduction of carbon dioxide and dye-sensitized solar cells), illustrating their progression from early systems to the current state-of-the-art and showcasing how some limitations of photoactive copper(I) complexes can be overcome with their high versatility.

Advances on Controlled Chain Walking and Suppression of Chain Transfer in Catalytic Olefin Polymerization

Advances on Controlled Chain Walking and Suppression of Chain Transfer in Catalytic Olefin Polymerization

SETDB1 regulates microtubule dynamics.

SETDB1 is a methyltransferase responsible for the methylation of histone H3-lysine-9, which is mainly related to heterochromatin formation. SETDB1 is overexpressed in various cancer types and is associated with an aggressive phenotype. In agreement with its activity, it mainly exhibits a nuclear localization; however, in several cell types a cytoplasmic localization was reported. Here we looked for cytoplasmic functions of SETDB1. SETDB1 association with microtubules was detected by immunofluorescence and co-sedimentation. Microtubule dynamics were analysed during recovery from nocodazole treatment and by tracking microtubule plus-ends in live cells. Live cell imaging was used to study mitotic kinetics and protein-protein interaction was identified by co-immunoprecipitation. SETDB1 co-sedimented with microtubules and partially colocalized with microtubules. SETDB1 partial silencing led to faster polymerization and reduced rate of catastrophe events of microtubules in parallel to reduced proliferation rate and slower mitotic kinetics. Interestingly, over-expression of either wild-type or catalytic dead SETDB1 altered microtubule polymerization rate to the same extent, suggesting that SETDB1 may affect microtubule dynamics by a methylation-independent mechanism. Moreover, SETDB1 co-immunoprecipitated with HDAC6 and tubulin acetylation levels were increased upon silencing of SETDB1. Taken together, our study suggests a model in which SETDB1 affects microtubule dynamics by interacting with both microtubules and HDAC6 to enhance tubulin deacetylation. Overall, our results suggest a novel cytoplasmic role for SETDB1 in the regulation of microtubule dynamics.

Mesophase pitch production from fluorine-pretreated FCC decant oil

• Effect of fluorine treatment over FCC-DO for mesophase formation firstly suggested. • Reaction mechanism of mesophase formation by fluorination was suggested. • Fluorine promoted radical polymerization of FCC-DO to form heavy mesophase nuclei. • The amount of hydrogen donating species also increased after the fluorination. • Pitch from fluorinated DO had higher mesophase yield than pitch from pristine DO. Petroleum residue oil-based mesophase pitch production suffers from its low yield of mesophase. There have been continuous efforts, such as catalyst-assisted reactions and multistep heat treatments, to produce high-purity mesophase pitch. However, most of these techniques have difficulties with the processability. In this study, we suggest a novel fluorine pretreatment of fluid catalytic cracking (FCC) decant oil for mesophase pitch (MP) production. The effects of fluorine pretreatment on FCC decant oil were evaluated with mass spectrometry (MS) and their hydrogen donating ability. Subsequently, the MPs from pristine pitches with fluorine pretreatment were intensively compared in terms of structural, thermal, and chemical characteristics. From these results, it was found that fluorine pretreatment helps mesophase formation by catalytic radical polymerization but does not cause coking and does not require posttreatment. It was found that the fluorination method can also provide an effective method for generating MP by increasing the hydrogen donating ability (HDA) fraction. We believe that the results of this work could inspire new insights into MP production.

Photoresponsive α‐Diimine Nickel Modulated Ethylene (Co)Polymerization†

Comprehensive SummaryBeyond the single ligand electronic and/or steric modifications, external stimuli are a useful tool for modulating catalytic polymerization reactions. Light stands out from external stimuli, but the corresponding photoresponsive transition metal catalysts are significantly rare for olefin polymerization due to the difficult synthesis. In this contribution, in consideration of the key role of steric shielding on the axial sites, we installed four concerted azobenzene moieties into symmetrically terphenyl‐based α‐diimine Ni(II) complexes to prepare photoresponsive catalysts, which were applied to ethylene polymerization and copolymerization with polar monomer. Via the trans‐cis isomerization of azobenzene‐functionalized Ni(II) catalysts in dark or under UV light, catalytic activity, polymer molecular weight, branching density, incorporation of co‐monomer, and even the ratio of branching pattern were significantly modulated in ethylene (co)polymerizations. This photo‐controlled strategy behaved an opposite influence between ethylene polymerization and copolymerization, in terms of catalytic activity and polymer molecular weight. As a result, slightly branched ultrahigh molecular weight polyethylenes and high molecular weight functionalized polyethylenes were produced at ambient conditions.

Polymeric multimaterials by photochemical patterning of crystallinity.

An organized combination of stiff and elastic domains within a single material can synergistically tailor bulk mechanical properties. However, synthetic methods to achieve such sophisticated architectures remain elusive. We report a rapid, facile, and environmentally benign method to pattern strong and stiff semicrystalline phases within soft and elastic matrices using stereo-controlled ring-opening metathesis polymerization of an industrial monomer, cis-cyclooctene. Dual polymerization catalysis dictates polyolefin backbone chemistry, which enables patterning of compositionally uniform materials with seamless stiff and elastic interfaces. Visible light-induced activation of a metathesis catalyst results in the formation of semicrystalline trans polyoctenamer rubber, outcompeting the formation of cis polyoctenamer rubber, which occurs at room temperature. This bottom-up approach provides a method for manufacturing polymeric materials with promising applications in soft optoelectronics and robotics.