Ring-Opening Metathesis Polymerization with the Second Generation Hoveyda–Grubbs Catalyst: An Efficient Approach toward High-Purity Functionalized Macrocyclic Oligo(cyclooctene)s

Highly Tunable Metal-Free Ring Opening Polymerization of Glycidol into Various Controlled Topologies Catalyzed by Frustrated Lewis Pairs

Controlling the topology of a polymer is essential in determining its physical properties and processing. Even after numerous studies, obtaining a diverse array of topologies, particularly within the framework of...

Bioactive Synthetic Polymers

Synthetic polymers are omnipresent in society as textiles and packaging materials, in construction and medicine, among many other important applications. Alternatively, natural polymers play a crucial role in sustaining life and allowing organisms to adapt to their environments by performing key biological functions such as molecular recognition and transmission of genetic information. In general, the synthetic and natural polymer worlds are completely separated due to the inability for synthetic polymers to perform specific biological functions; in some cases, synthetic polymers cause uncontrolled and unwanted biological responses. However, owing to the advancement of synthetic polymerization techniques in recent years, new synthetic polymers have emerged that provide specific biological functions such as targeted molecular recognition of peptides, or present antiviral, anticancer, and antimicrobial activities. In this review, the emergence of this generation of bioactive synthetic polymers and their bioapplications are summarized. Finally, the future opportunities in this area are discussed.

Facile synthesis of norbornene–ethylene–vinyl acetate/vinyl alcohol multiblock copolymers by the olefin cross-metathesis of polynorbornene with poly(5-acetoxy-1-octenylene)

New norbornene−ethylene–vinyl acetate/vinyl alcohol multiblock copolymers are synthesized via the olefin cross-metathesis reaction of polynorbornene with poly(5-acetoxy-1-octenylene) followed by CC bond hydrogenation and acetoxy group deprotection.

Living Polymerization Caught in the Act: Direct Observation of an Arrested Intermediate in Metathesis Polymerization

Understanding the stability and reactivity of the propagating species is critical in living polymerization. Therefore, most living olefin metathesis polymerizations require the stabilization of the catalyst by coordination of external ligands containing Lewis basic heteroatoms, e.g., phosphines and pyridines. However, in some cases, chemists postulated that the propagating metal carbene could also be stabilized by olefin chelation. Here, we disclose that stable 16-electron olefin-chelated Ru carbenes play a key role in previously reported living/controlled ring-opening metathesis polymerization of endo-tricyclo[4.2.2.0^2,5]deca-3,9-diene and cyclopolymerization of 1,8-nonadiynes using Grubbs catalysts. We successfully isolated these propagating species during polymerization and confirmed their olefin-chelated structures using X-ray crystallography and NMR analysis. DFT calculations and van 't Hoff plots from the equilibrium between olefin-chelated Ru carbenes and 3-chloropyridine (Py)-coordinated carbenes revealed that entropically favored olefin chelation overwhelmed enthalpically more stable Py-coordinated Ru carbenes at room temperature. Therefore, olefin chelation stabilized the propagating species and slowed down the propagation relative to initiation, thereby lowering polydispersity. This finding provides a deeper understanding of the olefin metathesis polymerization mechanism using Grubbs catalysts and offers clues for designing new controlled/living polymerizations.

Oligo(ethylene glycol) Length Effect of Water-Soluble Ru-Based Olefin Metathesis Catalysts on Reactivity and Removability

A study of reaction kinetics and removal efficiency of a family of ruthenium (Ru)-based olefin metathesis catalysts containing ethylene-glycol-oligomer-tethered N-heterocyclic carbene (NHC) ligands has been carried out, with a focus on variation of ethylene glycol oligomer length. The length of ethylene glycol oligomer was precisely defined by sequential addition of repeating units. Due to the dual solubility of ethylene glycol oligomer, the produced catalyst was highly soluble in both aqueous and organic solvents (dichloromethane). In aqueous solution, the polarity increase with longer ethylene glycol oligomers enhanced the reactivity in homogeneous solution. The length of ethylene glycol oligomer did not significantly affect olefin metathesis rate in organic solution. Yet the removal efficiency of catalyst strongly relies on the length of ethylene glycol oligomer. A longer ethylene glycol oligomer demonstrated better catalyst removal efficiency. The tested catalyst removal method was aqueous extraction from organic solution using its higher water solubility property compared to its lower organic solvent (dichloromethane) solubility property. The results obtained from the aqueous extraction catalyst removal method demonstrated similar and/or better removal rates compared to previously reported host-guest catalyst removal methods.

Immobilized Grubbs catalysts on mesoporous silica materials: insight into support characteristics and their impact on catalytic activity and product selectivity

The ideal support characteristics for immobilization of the Hoveyda–Grubbs 2 catalyst were defined in the metathesis of cyclooctene and the reaction mechanism to cyclic oligomers was unraveled.

Depolymerization of 1,4-polybutadiene by metathesis: high yield of large macrocyclic oligo(butadiene)s by ligand selectivity control

Herein, we demonstrate a practical high yield preparation of large macrocyclic oligo(butadiene)s, preferably the C16 to C44 fraction, from commercial 1,4-polybutadiene by exploring intramolecular backbiting using a series of commercially available Ru catalysts.