Ring-opening Metathesis Polymerization Research Articles

Catalytic Syntheses of Thiol-End-Functionalized ROMP Polymers.

Thiol-functionalized polymers have become a crucial class of materials due to their distinct chemical properties and versatile reactivity, leading to a broad spectrum of applications. Herein, we report the straightforward syntheses of a wide range of thiol-end-functionalized ring-opening metathesis polymerization (ROMP) polymers exploiting our previously reported catalytic ROMP mechanisms using suitable chain transfer agents. All the synthesized polymers were characterized via SEC, 1H NMR spectroscopy and MALDI-ToF mass spectrometry techniques. Furthermore, the existence of thiol groups on the polymer chains was verified through the well-established thiol coating reaction on gold nanoparticle surfaces. We believe this method of synthesizing thiol-end-functionalized ROMP polymers (using a reduced amount of ruthenium metal compared to conventional living ROMP) will be of great importance to materials science and biochemical research.

Mechanistic Insights into the cis-Selective Catalytic Ring-Opening Metathesis Polymerization.

Cis-selective ring-opening metathesis polymerization (ROMP) with the commercial Grubbs "nitrato catalyst" has shown promise for synthesizing stereoregular materials, but it comes with the drawback of losing control over the molecular weight due to the poor initiation rate of the catalyst and the need for stoichiometric ruthenium complex loading. To address these issues, we developed a chain transfer polymerization method that allows for the catalytic synthesis of polymers while controlling the degree of polymerization. This allowed us to produce shorter polymers with exceptional chain-end control. Analysis of the polymers revealed a novel double monomer addition mechanism for this catalyst. MALDI-ToF mass spectrometric measurements showed that when using small monomers like norbornene, the polymer chains contained only odd numbers of monomers. In contrast, the polymerization of norbornene-imide-type monomers shows a major distribution with odd numbers of monomers along with a minor distribution of even numbers. This unique distribution of polymer chain types had not been previously observed in ROMP. We explain this phenomenon by the chiral nature of the catalyst that yields two isomeric catalytic species with dissimilar reactivities toward monomer and chain transfer agents.

Full on-device manipulation of olefin metathesis for precise manufacturing.

Olefin metathesis, as a powerful metal-catalysed carbon-carbon bond-forming method, has achieved considerable progress in recent years. However, the complexity originating from multicomponent interactions has long impeded a complete mechanistic understanding of olefin metathesis, which hampers further optimization of the reaction. Here, we clarify both productive and hidden degenerate pathways of ring-closing metathesis by focusing on one individual catalyst, using a sensitive single-molecule electrical detection platform. In addition to visualizing the full pathway, we found that the conventionally unwanted degenerate pathways have an unexpected constructive coupling effect on the productive pathway, and both types of pathway can be regulated by an external electric field. We then pushed forward this ability to ring-opening metathesis polymerization involving more interactive components. With single-monomer-insertion-event resolution, precise on-device synthesis of a single polymer was achieved by online manipulation of monomer insertion dynamics, intramolecular chain transfer, stereoregularity, degree of polymerization and block copolymerization. These results offer a comprehensive mechanistic understanding of olefin metathesis, exemplifying infinite opportunities for practical precise manufacturing.

Ring-opening metathesis polymerization of Norbornene-derived cyclic olefins using Iminomethyl-hydroxyl-ligated tungsten Complexes: Fast reaction and tunable cis/trans selectivity

Ring-opening metathesis polymerization of Norbornene-derived cyclic olefins using Iminomethyl-hydroxyl-ligated tungsten Complexes: Fast reaction and tunable cis/trans selectivity

Polyalkenamers as Drop-In Additives for Ring-Opening Metathesis Polymerization: A Promising Upcycling Paradigm.

We report a distinct strategy to upcycle waste polyalkenamers such as polybutadiene into new, performance-advantaged materials by using them as drop-in additives for ring-opening metathesis polymerization (ROMP). The polyalkenamers serve as competent chain-transfer agents in ROMPs of common classes of cyclic olefin monomers, facilitating good molecular weight control, allowing low Ru catalyst loadings, and enabling efficient incorporation of the polyalkenamer into the synthesized polymeric material. We successfully demonstrate ROMP using model polyalkenamers and translate these learnings to leverage commercial polybutadiene and acrylonitrile butadiene styrene (ABS) as chain transfer agents for ROMP copolymerizations. Critically, our strategy is shown to be highly efficient and operationally simple, quantitatively incorporating the polyalkenamer and inheriting aspects of its thermomechanical performance. Our results highlight a promising pathway for the upcycling of polyalkenamers and provide an alternative to existing deconstruction and functional upcycling strategies.

Ring-Opening Metathesis Polymerization of Thianorbornenes.

A series of exo-7-thiabicyclo[2.2.1]hept-5-ene-2,3-dicarboximides were synthesized and polymerized using Schrock's catalyst, 2,6-diisopropylphenylimidoneophylidene molybdenum(VI) bis(hexafluoro-tert-butoxide). The ring-opening metathesis polymerization (ROMP) reactions were found to proceed in a controlled manner, enabling chain extensions and tuning of polymer molecular weight. The polymers were characterized using size exclusion chromatography (SEC) as well as spectroscopic (NMR, FT-IR), thermal (TGA, DSC), and optical techniques. The physical, chemical, and optical properties of the polymers were found to be affected by the embedded sulfur atoms and the pendant substituents. Copolymers with norbornene were also synthesized and characterized. Treatment of a poly(thianorbornene) with potassium hydroxide led to ring-opening hydrolysis and afforded a derivative that was soluble in aqueous media.

B(C6F5)3 Co-Catalyst Promotes Unconventional Halide Abstraction from Grubbs I to Enhance Reactivity and Limit Decomposition.

Ruthenium based Grubbs metathesis has become a commonplace reaction for synthetic chemists. Development of new generations of catalysts evolving from Grubbs I (GI) have led to greater stability, functional group compatibility, and superior reactivities. However, these advancements lead to increased costs. To this end, we report here how the addition of the commercially available tris(pentafluorophenyl)borane Lewis acid, which has become a common place catalyst in its own right, leads to enhanced reactivity of GI. Moreover, the increased reactivity arises via halide abstraction rather than traditional phosphine dissociation, providing ring-opening metathesis polymerization products that are divergent from those synthesized without the Lewis acid cocatalyst.

Hydrazine‐Catalysed Ring‐Opening Metathesis Polymerization Of Cyclobutenes

AbstractMaterials formed by the ring‐opening metathesis polymerization (ROMP) of cyclic olefins are highly valued for industrial and academic applications but are difficult to prepare free of metal contaminants. Here we describe a highly efficient metal‐free ROMP of cyclobutenes using hydrazine catalysis. Reactions can be initiated via in situ condensation of a [2.2.2]‐bicyclic hydrazine catalyst with an aliphatic or aromatic aldehyde initiator. The polymerizations show living characteristics, achieving excellent control over molecular weight, low dispersity values, and high chain‐end fidelity. Additionally, the hydrazine can be used in substoichiometric amounts relative to the aldehyde chain‐end while maintaining good control over molecular weight and low dispersity values, indicating that a highly efficient chain transfer mechanism is occurring.

Preparation of poly(endo-norbornene derivatives) with ultra-high molecular weight by combining ROMP and acyclic metathesis reaction

Endo-norbornene derivatives are much cheaper and more accessible. However, it is difficult to prepare endo-polynorbornenes with ultra-high molecular weight (UHMW) by ring opening metathesis polymerization (ROMP) owing to the low activity. The molecular weight of poly(endo-NB-2OH)n could only reach to 309.1 kg mol−1 for 24 h via ROMP. While, UHMW poly(endo-NB-2OH)m was prepared by combining ROMP and acyclic metathesis reaction in much shorter time. The effects of residual monomer, amount of H2SO4, concentration, temperature and reaction time were investigated in depth. The UHMW P(endo-NB-2OH)m (Mn =2645.5 kg mol−1, PDI = 1.74) could be obtained at 80 °C for 5 min with H2SO4/G3 as 10/1 and concentration of 0.1 M. Moreover, UHMW P(endo-NBI-OH)m(Mn =1114.2 kg mol−1, PDI = 1.95) was also successfully prepared by this method. However, the H2SO4/G3 should increase to 30/1, and reacted for 45 min owing to the steric resistance of the cyclic dicarboximide. For P(exo-NBI-OH)n with lower activity, reaction time should prolong to 3 h to obtain UHMW P(exo-NBI-OH)m(Mn =1716.7 kg mol−1, PDI = 1.93). Finally, UHMW P(endo-NB-2alkyne)m, P(endo-NBI-alkyne)m, and P(exo-NBI-alkyne)m were successfully prepared via post-modification. Acyclic metathesis reaction is a robust and universal reaction to prepare other functional UHMW polynorbornenes, especially for the UHMW endo-polynorbornenes, which could not be prepared by ROMP efficiently.

Synthesis of Reduction-Sensitive Brush-Arm Star Polymers via Combined Ring-Opening Metathesis Polymerization–Atom Transfer Radical Polymerization and Controlled-Release Properties

Synthesis of Reduction-Sensitive Brush-Arm Star Polymers via Combined Ring-Opening Metathesis Polymerization–Atom Transfer Radical Polymerization and Controlled-Release Properties

Exploring the ring-opening metathesis polymerization process by kinetic Monte Carlo simulation

Investigating the kinetics of polymerization reactions is a powerful tool to obtain information for the engineering design of such processes. It provides insights into how the relative rates of elementary reactions which influence both the kinetics of the reactions and thus characteristics of the products as well, particularly when the reaction parameters of these reactions are unknown. Among polymerization processes, ring-opening metathesis polymerization (ROMP) has gained broad academic and industrial interest, due to its mild conditions to obtain a wide range of polymer products. In this study, kinetic Monte Carlo simulation was applied to reveal the effect of the elementary reactions of ROMP on the kinetics and product distribution. Both the propagation and the cross-metathesis reactions were considered, with the latter leading to the formation of various types of macrospecies whose population levels were also monitored. Relevant tendencies were observed regarding how the variations in the reaction parameters of the elementary reactions of this polymerization process, such as reaction probabilities, monomer addition method, catalyst-to-monomer ratio, and reaction time, affect the kinetics of the polymerization process and the product distributions. These variations also influence the key macromolecular parameters of the resulting polymeric materials, including chain length distribution (CLD), population levels, and polymer functionalities. The results of this study indicate that this simulation technique is a valuable tool for mapping the tailoring possibilities of modifying the reaction parameters of ROMP to achieve desired properties. These properties include number average molecular weight, polydispersity, chain end functionality, and macrocycle-free products.

A "Bottom-Up" Strategy for High-Performance Benzocyclobutene (BCB)-Subnanometer Inorganic Nanocomposites.

Developing benzocyclobutene (BCB) nanocomposites with ultra-small inorganic sizes represents a formidable challenge, although it offers great potential to produce materials with customizable structural and rich functional properties. In this study, we present a "bottom-up" design strategy for creating cross-linked benzocyclobutene (BCB) nanocomposites with highly dispersed nanodomains, such as organoalkoxysilane. This approach leverages ring-opening metathesis polymerization (ROMP) and thermally induced cycloaddition reactions to embed oligomeric silsesquioxanes, achieving a unique molecular structure with promising low-dielectric applications. The synthesis involves organoalkoxysilane and BCB as pendant groups of polynorbornenes that are covalently integrated. Additionally, the methoxyl groups of linear polymers could be further hydrolyzed under acidic conditions, and BCB groups could undergo thermal-induced ring-opening at high temperatures and Diels-Alder addition between themselves and vinyl groups, respectively. Fourier transform infrared (FTIR) spectroscopy analyses suggested the presence of ladder or network structures and high-resolution transmission electron microscopy (HRTEM) images presented the well-dispersed inorganic clusters, facilitating excellent dielectric properties with a dielectric constant (Dk) of 2.25 and a dissipation factor (Df) of 2.27 × 10-4. Compared with previously reported low-Dk materials, the cured nanocomposites also exhibited a significantly balanced enhancement of their comprehensive properties. This molecular bottom-up strategy provided a simple and universal method for constructing BCB-inorganic nanocomposites featuring a subnanometer inorganic structure, paving the way for future investigation into new classes of polymer-inorganic nanocomposites with a low Dk.

Degradable polyolefins prepared by integration of disulfides into metathesis polymerizations with 3,6-dihydro-1,2-dithiine.

Disulfide-containing polyolefins were synthesized by ring-opening metathesis polymerization (ROMP) of the 6-membered disulfide-containing cyclic olefin, 3,6-dihydro-1,2-dithiine, which was prepared by ring-closing metathesis of diallyl disulfide. This approach facilitated the production of disulfide-containing unsaturated polyolefins as copolymers with disulfide monomer units embedded within a poly(cyclooctene) or poly(norbornene) framework. The incorporation of disulfides into the polymer backbone imparts redox responsiveness and enables polymer degradation via chemical reduction or thiol-disulfide exchange. This ROMP copolymerization strategy yielded both linear polyolefins, as well as bottlebrush polymers, with degradable segments, thereby broadening the scope of responsive polymer architectures synthesized by ROMP.

Allylic Epoxides Increase the Strain Energy of Cyclic Olefin Monomers for Ring-Opening Metathesis Polymerization.

Ring-opening metathesis polymerization (ROMP) is an effective method for synthesizing functional polymers, but since the technique typically relies on high ring strain cyclic olefins, the most common monomers are norbornene derivatives. The reliance on one class of monomer limits the obtainable properties of ROMP polymers. In this work, we investigate new bicyclic monomers synthesized via epoxidation of commercial dienes. DFT estimates of these monomers' ring strains suggests a significant increase in strain for cyclic olefins containing allylic epoxides. We found that the eight-membered (3,4-COO) and five-membered (CPO) cyclic olefins were particularly effective for ROMP. CPO was of especially intriguing due to its excellent polymerizability when compared to the limited reactivity of other five-membered rings. Unlike polynorbornenes, the resulting polymers of both monomers displayed glass transition temperatures well below room temperature. Interestingly, poly(3,4-COO) showed both high stereo- and regioregularity while poly(CPO) showed little regularity. Both polymers could be readily modified via post-polymerization ring-opening of the reactive allylic epoxides. With a high epoxide density in poly(CPO), CPO is an exciting new ROMP monomer that is easily synthesized, can be polymerized to high conversion at room temperature, and may be facilely modified to yield a wide range of functional materials.

Allylic Epoxides Increase the Strain Energy of Cyclic Olefin Monomers for Ring‐Opening Metathesis Polymerization

Ring‐opening metathesis polymerization (ROMP) is an effective method for synthesizing functional polymers, but since the technique typically relies on high ring strain cyclic olefins, the most common monomers are norbornene derivatives. The reliance on one class of monomer limits the obtainable properties of ROMP polymers. In this work, we investigate new bicyclic monomers synthesized via epoxidation of commercial dienes. DFT estimates of these monomers’ ring strains suggests a significant increase in strain for cyclic olefins containing allylic epoxides. We found that the eight‐membered (3,4‐COO) and five‐membered (CPO) cyclic olefins were particularly effective for ROMP. CPO was of especially intriguing due to its excellent polymerizability when compared to the limited reactivity of other five‐membered rings. Unlike polynorbornenes, the resulting polymers of both monomers displayed glass transition temperatures well below room temperature. Interestingly, poly(3,4‐COO) showed both high stereo‐ and regioregularity while poly(CPO) showed little regularity. Both polymers could be readily modified via post‐polymerization ring‐opening of the reactive allylic epoxides. With a high epoxide density in poly(CPO), CPO is an exciting new ROMP monomer that is easily synthesized, can be polymerized to high conversion at room temperature, and may be facilely modified to yield a wide range of functional materials.

Bioinspired, Carbohydrate-Containing Polymers Efficiently and Reversibly Sequester Heavy Metals.

Water scarcity and heavy metal pollution are significant challenges in today's industrialized world. Conventional heavy metal remediation methods are often inefficient and energy-intensive, and produce chemical sludge. To address these issues, we developed a bioinspired, carbohydrate-containing polymer system for efficient and selective heavy metal removal. Using ring opening metathesis polymerization, we synthesized polymers bearing amphiphilic glucuronate side chains capable of selectively binding heavy metal cations in mixed media. In samples containing high concentrations of heavy metals (>550 ppb), these polymers rapidly form a filterable precipitate upon metal capture, reducing the concentration of cation to <1.5 ppb within 3 min, as measured by inductively coupled plasma mass spectrometry. This system effectively removes cadmium ions from highly contaminated solutions to levels below the Agency for Toxic Substances and Disease Registry limit for Cd2+ in drinking water and selectively removes both Cd2+ and Pb2+ from lake water spiked with trace amounts of metal. Acidification triggers protonation of the glucuronate groups, releasing the heavy metals and resolubilizing the polymer. This capture-and-release process can be repeated over multiple cycles without loss of binding capacity. As such, this study introduces a novel class of recyclable materials with pH-responsive properties, offering potential for applications in water remediation and beyond.

Enhancing CO2 Transport Across the PEG/PPG-Based Crosslinked Rubbery Polymer Membranes with a Sterically Bulky Carbazole-Based ROMP Comonomer.

A series of poly(ethylene glycol)-block-poly(propylene glycol) (PEG/PPG)- and 5,6-di(9H-carbazol-9-yl)isoindoline-1,3-dione (2CZPImide)-based crosslinked rubbery polymer membranes, denoted as PEG/PPG-2CZPImide (x:y), are prepared from the norbornene-functionalized PEG/PPG oligomer (NB-PEG/PPG-NB) and 2-(bicyclo[2.2.1]hept-5-en-2-ylmethyl)-5,6-di(9H-carbazol-9-yl)isoindoline-1,3-dione (2CZPImide-NB) via ring-opening metathesis polymerization (ROMP). The molar ratio (x:y) of the NB-PEG/PPG-NB (x) to 2CZPImide-NB (y) monomers is varied from 10:1 to 6:1. X-ray diffraction (XRD), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), and pure gas permeability studies reveal that the comonomer 2CZPImide-NB successfully increases the d-spacing among the crystalline PEG/PPG segments, hence enhancing the diffusivity of gases through the membranes. The synthesized membranes exhibit good CO2 separation performance, with CO2 permeabilities ranging from 311.1 to 418.1 Barrer and CO2/N2 and CO2/CH4 selectivities of 39.4-52.0 and 13.4-16.0, respectively, approaching the 2008 Robeson upper bound. Moreover, PEG/PPG-2CZPImide (6:1), displaying optimal CO2 permeability and CO2/N2 and CO2/CH4 selectivities, shows long-term stability against physical aging and plasticization resistance up to 20 days and 10 atm, respectively.

Hydrazine-Catalysed Ring-Opening Metathesis Polymerization Of Cyclobutenes.

Materials formed by the ring-opening metathesis polymerization (ROMP) of cyclic olefins are highly valued for industrial and academic applications but are difficult to prepare free of metal contaminants. Here we describe a highly efficient metal-free ROMP of cyclobutenes using hydrazine catalysis. Reactions can be initiated via in situ condensation of a [2.2.2]-bicyclic hydrazine catalyst with an aliphatic or aromatic aldehyde initiator. The polymerizations show living characteristics, achieving excellent control over molecular weight, low dispersity values, and high chain-end fidelity. Additionally, the hydrazine can be used in substoichiometric amounts relative to the aldehyde chain-end while maintaining good control over molecular weight and low dispersity values, indicating that a highly efficient chain transfer mechanism is occurring.

Mixed matrix membrane for hydrogen separation enhanced by Oxacalix[4]arene-Containing porous organic polymers

The mixed matrix membranes (MMMs) have great potential for industrial H2 enhancement applications. However, some challenges remain to incorporate the nanoporous architectures with industrial processable polymers. In this work, a macrocyclic cavitand from oxacalix[4]arene was integrated into porous polymers via a facile ring-opening-metathesis polymerization (ROMP), the resulting BIT-POP-20 was added to polysulfone matrix to make novel MMMs with different mass ratios. These membranes improved gas permeation rate for CO2, H2 and He, compared with pristine polysulfone, and high H2/N2 selectivity of 105 was achieved. This huge improved H2/N2 separation performances were due to the nanoporous gas passages through the open supramolecular cavities. This work presents an interesting example in designing MMMs using intrinsic macrocyclic cavity in porous polymer backbone that helps increase their performances in gas separations.

Organelle-Targeting Polymer Dots Exhibiting Thermally Activated Delayed Fluorescence for Subcellular Imaging.

Selective imaging of specific subcellular structures provides valuable information about the cellular microenvironment. Materials exhibiting thermally activated delayed fluorescence (TADF) are rapidly emerging as metal-free probes with long-lived emission for intracellular time-gated imaging applications. Polymers incorporating TADF emitters can self-assemble into luminescent nanoparticles, termed polymer dots (Pdots), and this strategy enables them to circumvent the limitations of commercial organelle trackers and small molecule TADF emitters. In this study, diblock copolymers comprised of a hydrophilic block containing organelle-targeting monomers and a hydrophobic TADF-active block were synthesized by ring-opening metathesis polymerization (ROMP). Oxanorbornene-based monomers incorporating morpholine and triphenylphosphonium groups for lysosome and mitochondria targeting, respectively, were also synthesized. ROMP by sequential addition yielded well-defined diblock copolymers with dispersities <1.28. To analyze the effect of tuning the hydrophilic corona on cellular viability and uptake, we prepared Pdots with poly(ethylene glycol) (PEG) and bis-guanidinium (BGN) coronas, resulting in limited and efficient cellular uptake, respectively. Red-emissive Pdots with BGN-based coronas and organelle-targeting functionality were obtained with quantum yields up to 12% in water under air. Colocalization analysis confirmed that lysosome and mitochondria labeling in live HeLa cells was accomplished within 2 h of incubation, affording Pearson's correlation coefficients of 0.37 and 0.70, respectively. The potential application of these Pdots for time-resolved imaging is highlighted by a proof of concept using time-gated spectroscopy, which effectively separates the delayed emission of the TADF Pdots from the background autofluorescence of biological serum.