Chain Growth Process Research Articles

Oxygen-initiated radical ring-opening polymerization of macrocyclic allylic sulfides under ambient conditions

Although radical ring-opening polymerization (ROP) is a powerful approach for synthesizing polymers with diverse backbone structures, the intrinsic oxygen sensitivity of radicals challenges the ability to perform these polymerizations under air conditions. Here, we reported a novel oxygen-initiated radical ROP of macrocyclic allylic sulfides that can efficiently proceed under an air atmosphere, enabling the construction of sulfur-containing polymers with moderate to high molecular weights. The versatility of this approach was further demonstrated by copolymerizing macrocyclic allylic sulfides with vinyl monomers to create degradable vinyl polymers under ambient conditions. Density functional theory calculations revealed that the quenching of radicals by oxygen in the chain-growth process was kinetically disfavored, thereby allowing the polymerization to be compatible with oxygen. This work will further advance applications of radical ROP in diverse fields by enhancing its tolerance towards oxygen.

Photo‐controllable cationic homopolymerization and random copolymerization of vinyl ethers based on iridium salt photocatalyst

AbstractTemporal control of chain growth is a central challenge for photoinitiated active polymerization. In this work, we introduced an iridium salt complex‐based catalyst system to achieve fine temporal control of the chain growth process. By electrochemical analysis, compared with the pyran salt photocatalyst, it was found that the iridium salt complex could promote the chain transfer of active species to reversible addition‐fragmentation chain transfer polymerization (RAFT) reagent, thereby generating dormant species, which provided the possibility of time control of the polymerization process. Using this catalytic system, we successfully achieved homopolymerization of vinyl ethers with different substituents and random copolymerization with isobutyl vinyl ethers, which is not only pointed the way for broadening the monomer selection in the future, but also provided an innovative way to prepare new functionalized materials.

A gradient micromechanical model to explore flexoelectric copolymers via stochastic chain growth

Flexoelectric sensors respond with an electric polarization when they are subjected to inhomogeneous deformation. When these are based on polymeric materials, the electro-mechanical coupling relates to the loss of microstructural symmetries of the polar polymer chains. The object of this work is to explore the mechanisms that induce flexoelectricity in soft (co)polymers via a micromechanical model that explicitly considers the spatial composition distribution of polymer chains. To this end, we analyze the deformation of the Arruda–Boyce 8-chain cell under inhomogeneous deformation and its influence on the overall polarization resulting from the polar monomers. Cells with random-walk chains and tailored degree of entanglement feed Monte Carlo simulations to inform an effective chain dipole that drives the flexoelectric polarization. Homogeneous stretch/compression of the cell accompanying bending deformation reinforce the flexoelectric response. In addition, we focus on stochastic chain-growth processes and the insertion of different types of polar monomers within a same chain. Here, we introduce a model where reactivity ratios of real copolymerization reactions control the resulting flexoelectric coupling. Since the framework allows to relate the effective flexoelectric polarization to any structural isomer distribution, it is especially convenient to model copolymers. Overall, the model is proposed as a versatile framework to explore the intricacies of flexoelectric (co)polymers and to foster the design of flexoelectric devices from real manufacturing parameters.

Titelbild: Chiral Supramolecular Multiblock Copolymerization Accompanying Chirality Transfer in Heterostructures via Living Chain Growth (Angew. Chem. 25/2023)

The copolymerization of kinetically trapped states of tetraphenylethylene containing glycine (TPE-G) and/or D-/L-alanine moieties leads to the formation of supramolecular multi-blocks copolymers, such as B-A-B, A-B-A-B-A, and C-B-A-B-C patterns (BCPs; tri- and penta-blocks) by a chain-growth process. The chirality of the supramolecular BCPs was not only successfully controlled by the chiral seed, but it also transferred to an achiral component during the chain-growth polymerization, as reported Sung Ho Jung, Jong Hwa Jung et al. in their Research Article (e202300913).

Cover Picture: Chiral Supramolecular Multiblock Copolymerization Accompanying Chirality Transfer in Heterostructures via Living Chain Growth (Angew. Chem. Int. Ed. 25/2023)

The copolymerization of kinetically trapped states of tetraphenylethylene containing glycine (TPE-G) and/or D-/L-alanine moieties leads to the formation of supramolecular multi-blocks copolymers, such as B-A-B, A-B-A-B-A, and C-B-A-B-C patterns (BCPs; tri- and penta-blocks) by a chain-growth process. The chirality of the supramolecular BCPs was not only successfully controlled by the chiral seed, but it also transferred to an achiral component during the chain-growth polymerization, as reported Sung Ho Jung, Jong Hwa Jung et al. in their Research Article (e202300913).

MOF-Derived Ru1Zr1/Co Dual-Atomic-Site Catalyst with Promoted Performance for Fischer-Tropsch Synthesis.

Cobalt-based catalysts have been widely used for Fischer-Tropsch synthesis (FTS) in industry; however, achieving rational catalyst design at the atomic level and thereby a higher activity and more long-chain-hydrocarbon products simultaneously remain an attractive and difficult challenge. The dual-atomic-site catalysts with unique electronic and geometric interface interactions offer a great opportunity for exploiting advanced FTS catalysts with improved performance. Herein, we designed a Ru1Zr1/Co catalyst with Ru and Zr dual atomic sites on the Co nanoparticle (NP) surface through a metal-organic-framework-mediated synthesis strategy which presents greatly enhanced FTS activity (high turnover frequency of 3.8 × 10-2 s-1 at 200 °C) and C5+ selectivity (80.7%). Control experiments presented a synergic effect between Ru and Zr single-atom site on Co NPs. Further density functional theory calculations of the chain growth process from C1 to C5 revealed that the designed Ru/Zr dual sites remarkably lower the rate-limiting barriers due to the significantly weakened C-O bond and promote the chain growth processes, resulting in the greatly boosted FTS performance. Therefore, our work demonstrates the effectiveness of dual-atomic-site design in promoting the FTS performance and provides new opportunities for developing efficient industrial catalysts.

Fabrication of Transition Metal (Mn, Co, Ni, Cu)‐Embedded Faveolate ZnFe2O4 Spinel Structure with Robust CO2 Hydrogenation into Value‐added C2+ Hydrocarbons

AbstractCO2 hydrogenation is the most efficient way to achieve the goal of “Carbon Neutral,” and the transition metals (Mn, Co, Ni, Cu)‐embedded faveolate ZnFe2O4 were fabricated and then evaluated with a CO2 hydrogenation test. The systematic investigation of the effect of the introduced transition metals on the catalytic performance revealed that the activity was influenced by the surface structure, especially by the surface Fe−C percentages. The introduction of Zn could increase CO2 adsorption, thus promoting the reverse water gas shift (RWGS) reaction, which is considered the first step during CO2 hydrogenation. The surface Fe−C species played a significant role during the Fischer‐Tropsch (F−T) synthesis, specific to the carbon chain growth process. Among all catalysts, Co‐doped ZnFe2O4 exhibited the highest surface Fe−C percentage; therefore, it exhibited the optimal CO2 conversion, C2+ selectivity, C2‐C4 space‐time yield, and olefin/paraffin ratio, which were 42.12 %, 81.26 %, 34.64 %, and 40.25 %, respectively. Furthermore, the introduced Co species can also act as active sites to enhance the activation and dissociation of CO2, as confirmed by theoretical adsorption calculations.

Mechanism-Guided Design of Chain-Growth Click Polymerization Based on a Thiol-Michael Reaction.

The development of chain-growth click polymerization is challenging yet desirable in modern polymer chemistry. In this work, we reported a novel chain-growth click polymerization based on the thiol-Michael reaction. This polymerization could be performed efficiently under ambient conditions and spatiotemporally regulated by ultraviolet light, allowing the synthesis of sulfur-containing polymers in excellent yields and high molecular weights. Density functional theory calculations indicated that the thiolate addition to the Michael acceptor is the rate-determining step, and introducing the phenyl group could facilitate the chain-growth process. This polymerization is a new type of chain-growth click polymerization, which will provide a unique approach to creating functional polymers.

Insights into the Fischer–Tropsch mechanism on χ-Fe5C2(510) based on the hydrogen coverage effect

Investigating the mechanism of the Fischer–Tropsch synthesis is beneficial for modifying catalysts, which would result in an improved catalyst performance. However, theoretical calculations have mainly focused on several key elementary reactions and have thus provided fragmented information. Here, we select χ-Fe5C2(510) as representative facet and consider the elementary reactions on as comprehensively as possible via the density-functional theory (DFT)-based kinetic Monte Carlo (kMC) method to generate the fine structure of the Fischer–Tropsch mechanism. The results reveal that the CO activation mechanism is divided into cyclical pathways and termination pathways. The chain growth process and chain dissociation process coexist in the Fischer-Tropsch synthesis while the former follows the CO insertion mechanism, and the latter follows the carbide mechanism. The product methane and ethylene are produced major from the intermediates which are generated in the chain dissociation process rather than the chain grown process as the article reported before. The deep interpretation of the Fischer–Tropsch mechanism from the fine structure could be the guidance to experimentalists in mechanism verification or catalyst design.

Abatement of Aromatic Contaminants from Wastewater by a Heat/Persulfate Process Based on a Polymerization Mechanism.

A novel approach to the abatement of pollutants consisting of their conversion to separable solid polymers is explored by a heat/persulfate (PDS) process for the treatment of high-temperature wastewaters. During this process, a simultaneous decontamination and carbon recovery can be achieved with minimal use of PDS, which is significantly different from conventional degradation processes. The feasibility of this process is demonstrated by eight kinds of typical organic pollutants and by a real coking wastewater. For the treatment of the selected pollutants, 30.2-91.9% DOC abatement was achieved with 24.8-91.2% carbon recovery; meanwhile, only 5.2-47.0% of PDS was consumed compared to a conventional degradation process. For the treatment of a real coking wastewater, 71.0% DOC abatement was achieved with 66.0% carbon recovery. With phenol as a representative compound, our polymerization-based heat/PDS process is applicable in a wide pH range (3.5-9.0) with a carbon recovery of >87%. Both SO4•- and HO• can be initiators for polymerization, with different contribution ratios under various conditions. Phenol monomers are semioxidized to form phenolic radicals, which are polymerized via chain transfer or chain growth processes to form separable solid phenol polymers, benzenediol polymers, and cross-linked polymers.

Fluorine and hydroxyl containing unsymmetrical a-diimine Ni (II) dichlorides with improved catalytic performance for ethylene polymerization

A series of new tailored a-diimine Ni (II) complexes (Ni-OH, Ni-FOH, Ni-PhOH, and Ni-PhFOH) containing bulky ortho-N-aryl groups with various dibenzhydryl substitutes was successfully synthesized, characterized and applied in ethylene polymerization. The a-diimine ligands and Ni (II) complexes were characterized by 1H, 19F, and 13C NMR, elemental analysis, and high resolution electrospray ionization mass spectrometry (ESI-HRMS). The X-ray crystallographic study of metal complexes Ni-OH, Ni-FOH, and Ni-PhFOH revealed their distorted tetrahedral geometry. An unsymmetrical steric-enhancement design approach was employed to modulate the competition between the monomer insertion and the chain-walking process in ethylene polymerization. This facile design resulted in a high catalytic activity and yielded high molecular weight PE. The catalytic activity of these complexes was optimized by varying the polymerization conditions (temperature, time, and ethylene pressure), use of co-catalysts and variation of the Al/Ni ratio. When activated with modified methylaluminoxane (MMAO), these Ni complexes exhibited the activity as high as 29.1 × 106 g of PE (mol of Ni)−1 h−1), with a molecular weight of 1.81 × 106 g mol−1. Their thermal stability was well pronounced at elevated temperatures; high activity of 2.88 × 106 g of PE (mol of Ni)−1 h−1 and high molecular weight PE (0.86 × 106 g mol−1obtained at 90 °C). PEs with tunable branches and high melting points (127.5 °C) were obtained, which is a typical feature of LLDPE. The incorporation of fluorine atoms on N-aryl groups had a strong positive influence on the catalytic activity of the Ni complexes and favored the chain-growth process in the ethylene polymerization. Surprisingly, the simultaneous presence of terminal hydroxyl group in these complexes did not adversely affect their catalytic activity, while offering the possibility for covalent attachment to the solid supports for future heterogeneous polymerization.

Controlled reductive C-C coupling of isocyanides promoted by an aluminyl anion.

We report the reaction of the potassium aluminyl, K[Al(NON)] ([NON]2- = [O(SiMe2NDipp)2]2-, Dipp = 2,6-iPr2C6H3) with a series of isocyanide substrates (R-NC). In the case of tBu-NC, degradation of the isocyanide was observed generating an isomeric mixture of the corresponding aluminium cyanido-κC and -κN compounds, K[Al(NON)(H)(CN)]/K[Al(NON)(H)(NC)]. The reaction with 2,6-dimethylphenyl isocyanide (Dmp-NC), gave a C3-homologation product, which in addition to C-C bond formation showed dearomatisation of one of the aromatic substituents. In contrast, using adamantyl isocyanide Ad-NC allowed both the C2- and C3-homologation products to be isolated, allowing a degree of control to be exercised over the chain growth process. These data also show that the reaction proceeds through a stepwise addition, supported in this study by the synthesis of the mixed [(Ad-NC)2(Dmp-NC)]2- product. Computational analysis of the bonding within the homologised products confirm a high degree of multiple bond character in the exocyclic ketenimine units of the C2- and C3-products. In addition, the mechanism of chain growth was investigated, identifying different possible pathways leading to the observed products, and highlighting the importance of the potassium cation in formation of the initial C2-chain.

Customizing Polymers by Controlling Cation Switching Dynamics in Non-Living Polymerization.

Controlling the chain growth process in non-living polymerization reactions is difficult because chain termination typically occurs faster than the time it takes to apply an external trigger. To overcome this limitation, we have developed a strategy to regulate non-living polymerizations by exploiting the chemical equilibria between a metal catalyst and secondary metal cations. We have prepared two nickel phenoxyphosphine-polyethylene glycol variants, one with 2-methoxyphenyl (Ni1) and another with 2,6-dimethoxyphenyl (Ni2) phosphine substituents. Ethylene polymerization studies using these complexes in the presence of alkali salts revealed that chain growth is strongly dependent on electronic effects, whereas chain termination is dependent on both steric and electronic effects. By adjusting the solvent polarity, we can favor polymerizations via non-switching or dynamic switching modes. For example, in a 100:0.2 mixture of toluene/diethyl ether, reactions of Ni1 and both Li+ and Na+ cations in the presence of ethylene yielded bimodal polymers with different relative fractions depending on the Li+/Na+ ratio used. In a 98:2 mixture of toluene/diethyl ether, reactions of Ni2 and Cs+ in the presence of ethylene generated monomodal polyethylene with dispersity <2.0 and increasing molecular weight as the amount of Cs+ added increased. Solution studies by NMR spectroscopy showed that cation exchange between the nickel complexes and alkali cations in 98:2 toluene/diethyl ether is fast on the NMR time scale, which supports our proposed dynamic switching mechanism.

Expanding the toolbox of controlled/living branching radical polymerization through simulation-informed reaction design

•A controlled/living branching polymerization was achieved •Mechanistic studies and kinetic simulations guided the reaction optimization •Branched polymers were synthesized from a broad range of vinyl monomers Branched polymers with superior mechanical, photonic, and electrical properties have shown their growing advantages in biomedical applications, water treatment, and catalysis. Anchoring branched functional motifs onto select molecular-/nano-objects introduces structural hierarchy as well as combined and enhanced properties. To realize efficient grafting of branched functional polymers, a controlled chain-growth branching polymerization is desirable but remains underexplored. In this article, the chain-growth process was achieved by copolymerizing α-haloacrylate with conventional vinyl monomers via atom transfer radical polymerization. We conducted systematic mechanistic studies to obtain an optimal profile of the polymerization conditions, where an activator regeneration approach was employed. Assisted by kinetic simulations, a variety of vinyl monomers, including acrylates, styrene, acrylonitrile, and acrylamides, were successfully copolymerized with α-haloacrylate with high monomer conversion to produce well-defined branched polymers with tunable degrees of branching. The impact of controlled branching on the thermoresponsive properties was studied using the synthesized poly(N-isopropylacrylamide). Branched polymers with superior mechanical, photonic, and electrical properties have shown their growing advantages in biomedical applications, water treatment, and catalysis. Anchoring branched functional motifs onto select molecular-/nano-objects introduces structural hierarchy as well as combined and enhanced properties. To realize efficient grafting of branched functional polymers, a controlled chain-growth branching polymerization is desirable but remains underexplored. In this article, the chain-growth process was achieved by copolymerizing α-haloacrylate with conventional vinyl monomers via atom transfer radical polymerization. We conducted systematic mechanistic studies to obtain an optimal profile of the polymerization conditions, where an activator regeneration approach was employed. Assisted by kinetic simulations, a variety of vinyl monomers, including acrylates, styrene, acrylonitrile, and acrylamides, were successfully copolymerized with α-haloacrylate with high monomer conversion to produce well-defined branched polymers with tunable degrees of branching. The impact of controlled branching on the thermoresponsive properties was studied using the synthesized poly(N-isopropylacrylamide).

Olefin oligomerization by zirconium boratabenzene catalysts

In the present quantum chemical study, α-olefin dimerization and trimerization by zirconium boratabenzene catalysts has been studied as the single-site reactivity of group 4 metallocene catalysts has proven to be industrially important. The thermodynamics and kinetics of C=C insertion for ethylene, 1-butene, and 1-hexene as well as relevant ß-H elimination barriers have been quantified using density functional theory, using methodology previously calibrated in earlier research by the University of North Texas (UNT) and the ExxonMobil Chemical Company (EMCC) team for bis-indenyl zirconium catalysts. The insertions of the alkenes are relevant to chain growth processes, while the ß-H eliminations model chain termination. Various substituents on the boratabenzene rings were also compared to determine how these ligands change the thermodynamics and kinetics of the insertion and chain termination steps.

Aromatic stacking and the self-assembly of perylene monoimide diester homodimers

The self-assembly properties of two novel perylene monoimide diester homodimers have been investigated by concentration-dependent UV–Vis and 1H NMR titration experiments and steady-state fluorescence and SEM techniques. It was found that, as a result of different positioning of the perylene monoimide diester subunits in these structures, the cooperativity and binding-models for their chain growth processes differ significantly in dichloromethane (DCM) and dimethyl sulfoxide (DMSO) due to a change in efficiency of the π- π stacking. The mechanism of aggregation in each case was determined by the application of Goldstein–Stryer nucleation − elongation model to the concentration-dependent data. Because of different aggregation propensities of the respective monomers in DCM, scanning electron microscopy revealed different morphologies for the assemblies.

Biosensor Encapsulation via Photoinitiated Chemical Vapor Deposition (piCVD)

Thin and porous poly(hydroxyethyl acrylate) (pHEA) and poly(3,3,4,4,5,5,6,6,7,7,8,8,8-Tridecafluorooctyl acrylate) (pTFOA) encapsulating layers were successfully deposited on model electrical and optical glucose sensors via photoinitiated chemical vapor deposition (piCVD). This surface-restricted chain growth process afforded uniform coverage and strong interfacial adhesion of the resulting polymer encapsulation layers, which enabled the whole sensing area to be fully covered, even after being subjected to numerous electrochemical scanning cycles. Meanwhile, the amorphous films allowed rapid ion and analyte diffusion through themselves and, therefore, achieved quick sensing responses. Especially, pTFOA promised well-defined calibration curves with good repeatability. Furthermore, piCVD films maintained their morphology after being dehydrated and rehydrated over multiple days demonstrating their excellent stability as surface protective layers. These promising features of pHEA and pTFOA synthesized via piCVD may serve as a new encapsulating idea to be applied to various wearable sensors with different substrates and serve as a new strategy to extend the shelf life and functionality of biosensors.

Ru1Con Single-Atom Alloy for Enhancing Fischer–Tropsch Synthesis

Fischer–Tropsch synthesis (FTS) is a significant catalytic process for the production of liquid fuel and fine chemicals from natural gas-, coal-, and biomass-derived syngas. However, exploring high-performance catalysts and understanding the catalytic mechanism remain challenging. Herein, we design a Ru1Con single-atom alloy (SAA) catalyst with isolated Ru atoms anchored onto a Co nanoparticle surface through a two-dimensional confinement strategy to achieve greatly improved FTS activity (2.6 molCO molM–1 h–1) and long-chain hydrocarbon selectivity (C5+: 86.0%) at a low reaction temperature of 150 °C. A series of in situ experiments, catalytic tests, and density functional theory (DFT) calculations reveal that the Ru single-atom sites in Ru1Con SAA are more active for the FTS reaction than pure Ru and Co surfaces. This is because single-atom Ru with a much higher electronic density near the Fermi level could effectively and simultaneously decrease the rate-limiting barriers of both C–O splitting and chain growth processes. This work demonstrates the possibility of designing Ru single-atom sites to improve FTS performance and provides a deeper understanding of the strategy for developing other high-performance industrial catalysts.

Effect of process conditions on the product distribution of Fischer-Tropsch synthesis over an industrial cobalt-based catalyst using a fixed-bed reactor

A systematic study of the effects of process variables on Fischer-Tropsch synthesis product selectivity over an industrial cobalt catalyst was carried out at a broad range of industrial conditions (T = 170−215 °C, P = 1.0–5.6 MPa, H2/CO = 2.0–3.0, WHSV = 2.0–23.4 N L/g/h) using a fixed-bed reactor. Lower temperature and higher pressure were beneficial for suppressing methane formation. However, a volcano-shape of temperature versus C19+ selectivity was observed. Correlations between pressure and C19+ selectivity were closely related to the temperature. Lower space velocity and inlet H2/CO ratio had mild but positive effects on the product distribution. The unique C19+ selectivity variations with temperature and pressure indicate a complicated chain growth process that stems from different aspects of the catalyst (i.e., chain propagation, chain termination and α-olefin readsorption) with process conditions. A mechanism involving several accordant and opposite effecting factors is considered for reasonably explaining the abnormal observations and providing a few reasonable interpretations of the contradictions among the related literatures.

Polycondensation Kinetics: 1. Bifunctional Organosilicon Monomers

Polycondensation of bifunctional organosilicon monomers as a chain unbranched process includes initiation (hydrolysis of nonreactive end groups), propagation (sequential addition of monomers and bimolecular aggregation of n-mers), and termination (cyclization and entanglement of end groups in a nonreactive environment). Kinetic models of these steps with a minimum number of rate constants have been proposed. It has been shown that the chain propagation pathways involving different end groups are mixed and the competition of the chain growth and termination processes determines the molecular mass distribution of oligomers and their fractal packing in nanoscale aggregates.