Macrocyclic polyalkenamers formed as byproducts during ring-opening metathesis polymerization (ROMP) provide valuable insight into ring-chain equilibria and secondary metathesis processes. However, the characterization of these macrocycles is often complicated by the presence of linear polymer products with identical chemical composition. Here, we present a strategy to facilitate the isolation of macrocycles generated during ROMP by modifying chain ends using enyne metathesis chemistry and introducing polar functional groups into linear polymer chains through the addition of polar monomers. The resulting polarity difference allows nonpolar macrocycles to be separated from linear polymers by using conventional silica gel chromatography. The isolated cyclic fractions were characterized by gel permeation chromatography (GPC), NMR spectroscopy, and matrix-assisted laser desorption-ionization time-of-flight mass spectrometry (MALDI-TOF MS). Using this approach, we systematically investigated how reaction parameters influence the yield and molecular weight of macrocycles in the ROMP of cyclooctadiene (COD). The methodology also enables comparative analysis of macrocycle formation in the ROMP of cyclooctene (COE), cyclopentene (CP), and norbornene (NB). These results provide a separation-based approach for studying the macrocyclic species formed during ROMP.

Bottlebrush polymers are an important class of materials which consist of side chains grafted along a linear backbone. There has been a significant effort to understand structure-property relationships of bottlebrush polymers in solution, with experiments and simulations mapping the impact of parameters such as side chain length, backbone length, and concentration. Improvements in the ability to synthetically control the graft density have resulted in greater interest in understanding how the side chain density influences polymer conformation. However, the impact of graft density on bottlebrush polymers with polynorbornene backbones, which are now ubiquitous, remains relatively unexplored. Here, we examine two sets of polynorbornene-based bottlebrush polymers with polystyrene side chains where the graft density varies between 0.4 and 1.0 side chains per norbornene repeat (i.e., 40 to 100% grafted). The solution conformation of these materials in a good solvent, toluene, is probed through small-angle neutron scattering measurements. Fitting these data with a shape-based model allows for the extraction of parameters such as the radius of gyration and the persistence length. Scaling the radius of gyration based on the Flory theory for grafted chains shows that the side chain-side chain interactions have a greater contribution to the polymer conformation compared to the side chain-backbone interactions, in agreement with results from other backbone chemistries. Additionally, there now exist literature studies rich with dilute solution studies of other chemistries, which are used to develop general scaling relationships for both the radius of gyration and the persistence length as a function of the crowding parameter (product of the side chain degree of polymerization and graft density). Several different representations of the crowding parameter are studied to emphasize the importance of the backbone chemistry to the scaling relationships and solution conformation.

Cyclic polymers are topologically interesting and envisioned as a lubricant material. However, scalable synthesis of pure cyclic polymers remains elusive. The most straightforward way is to recycle a used catalyst for the synthesis of cyclic polymers. Unfortunately, it is demanding because of the catalyst’s vulnerability and inseparability from polymers, which depreciates the practicality of the process. Here, we develop a continuous process streamlined in a circular way that polymerization, polymer separation, and catalyst recovery happen in situ, to dispense a pure cyclic polymer after bulk ring-expansion metathesis polymerization of cyclopentene. It is enabled by introducing silica-supported ruthenium catalysts and a newly-designed glassware. Also, different depolymerization kinetics of the cyclic polymer from its linear analogue is discussed. This process minimizes manual labor, maximizes security of vulnerable catalysts, and guarantees purity of cyclic polymers, thereby showcasing a prototype of a scalable access to cyclic polymers with increased reusability of precious catalysts (≥415,000 turnovers).

Cyclopolymerization is a powerful method for synthesizing polyacetylenes containing four- to seven-membered rings. However, the structure of the repeat unit only consists of mono-cycloalkene due to the single cyclization of diyne monomers. Herein, we demonstrate a novel cascade cyclopolymerization to synthesize polyacetylenes containing fused bicyclic rings from triyne monomers containing bulky dendrons via sequential cascade ring-closing metathesis. These dendrons provided solubility and stability to the rigid bicyclic polyacetylene backbone. In addition, we controlled the regioselectivity of the catalyst approach by altering its structure and synthesized polymers containing fused bicyclo[4,3,0] or [4,4,0] rings with high molecular weights of up to 120 kg mol(-1). Interestingly, the resulting polymers showed narrower band gaps (down to 1.6 eV) than polymers with mono-cycloalkene repeat units due to the planarization of the conjugated segment resulting from the fused bicyclic structure.

A concise and stereoselective total synthesis of the clinically relevant tricyclic prostaglandin D 2 metabolite (tricyclic-PGDM) methyl ester in racemic form was accomplished in eight steps from a readily available known cyclopentene-diol derivative. The synthesis features a nickel-catalyzed Ueno–Stork-type dicarbofunctionalization to generate two consecutive stereocenters, a palladium-catalyzed carbonylative spirolactonization to build the core oxaspirolactone, and a Z -selective cross-metathesis to introduce the ( Z )-3-butenoate side chain, a group challenging to introduce through traditional Wittig protocols and troublesome for the two previous total syntheses. A general Z -selective cross-metathesis protocol to construct ( Z )-β,γ-unsaturated esters was also developed that has broad functional group tolerance and high stereoselectivity. Additionally, our synthesis already accumulated 75 mg of valuable material for an 18 O-tricyclic-PGDM-based assay used in clinical settings for inflammation.

The self-assembly of poly(dimethylsiloxane)-b-poly(trimethylene carbonate) (PDMS-b-PTMC) bottlebrush block polymers was investigated under different processing conditions. Small-angle X-ray scattering (SAXS) and UV/Visible spectroscopy provided insight into the self-assembly and structure in response to heating and applied pressure. In the absence of applied pressure (i.e., before annealing), the PDMS-b-PTMC bottlebrush block polymers are white solids and adopt small, randomly oriented lamellar grains. Heating the materials to 140 °C in the absence of applied pressure appears to "lock in" the isotropic, short-range-ordered state, preventing the formation of the long-range-ordered lamellar structure responsible for photonic properties. Applying modest anisotropic pressure (3 psi) between parallel plates at ambient temperature orients the short-range lamellar grains; however, applied pressure alone does not produce long-range order. Only when the bottlebrush block polymers were heated (>100 °C) under modest pressure (3 psi) were long-range-ordered photonic crystals formed. Analysis of the SAXS data motivated analogies to liquid crystals and revealed the potential self-assembly pathway. These results provide insight into the structure and self-assembly of bottlebrush block polymers with low glass transition temperature side chains in response to different processing conditions.

Synthetic polymer leaflets in prosthetic cardiac valves hold the potential to reduce calcification and thrombus, while improving blood flow, durability, and device economics. A recently developed siloxane poly(urethane‐urea) (LifePolymer, LP) exhibits properties essential for heart valve leaflets, including low dynamic modulus, high tensile strength, minimal creep, and excellent biostability. LP's properties result from carefully designed “linked co‐macrodiol” chemistry that maximizes silicone content and virtual crosslinks between soft and hard phases. Characterization of multiple commercial batches demonstrates a robust synthesis process with minimal variation. Extensive ISO 10993–based biocompatibility testing results in no observable toxicity or other adverse reactions. An ex vivo AV shunt thrombogenicity investigation reveals nearly undetectable levels of platelet attachment and thrombus formation on LP surfaces. Chronic ovine implantation of prototype heart valves with LP leaflets shows no differences in thrombogenicity or systemic tissue response when compared to a clinically standard tissue‐based valve. Toxicological risk assessment, based on extractables and leachables analysis of LP‐based heart valves, confirms minimal toxicological risk. Lastly, 24‐week, strain‐accelerated in vivo LP biostability testing confirms previous favorable in vitro biostability findings. These studies demonstrate that this newly developed elastomer exhibits ideal biomaterial properties for the flexible leaflets of a totally synthetic heart valve replacement.

Electrochemical CO2 reduction over Cu could provide value-added multicarbon hydrocarbons and alcohols. Despite recent breakthroughs, it remains a significant challenge to design a catalytic system with high product selectivity. Here we demonstrate that a high selectivity of ethylene (55%) and C2+ products (77%) could be achieved by a highly modular tricomponent copolymer modified Cu electrode, rivaling the best performance using other modified polycrystalline Cu foil catalysts. Such a copolymer can be conveniently prepared by a ring-opening metathesis polymerization, thereby offering a new degree of freedom for tuning the selectivity. Control experiments indicate all three components are essential for the selectivity enhancement. A surface characterization showed that the incorporation of a phenylpyridinium component increased the film robustness against delamination. It was also shown that its superior performance is not due to a morphology change of the Cu underneath. Molecular dynamics (MD) simulations indicate that a combination of increased local CO2 concentration, increased porosity for gas diffusion, and the local electric field effect together contribute to the increased ethylene and C2+ product selectivity.

α-Oxygenated Z -olefins are ubiquitous in biologically active molecules and serve as versatile handles for organic synthesis, but their syntheses are often tedious and less selective. Here we report the efficient Z -selective metathesis of various terminal acrylates and allyl alcohols, which enables facile and selective construction of high value-added α-oxygenated Z -olefins from readily available feedstock chemicals. These challenging metathesis transformations are enabled by novel cyclometalated Ru-carbene-nitrate complexes bearing bulky-yet-flexible side arms, whose assembly was unlocked by new organometallic syntheses.

The efficient Z-selective cross-metathesis between acrylamides and common terminal olefins has been developed by the use of novel cyclometalated ruthenium catalysts with bulky N-heterocyclic carbene (NHC) ligands. Superior reactivity and stereoselectivity are realized for the first time in this challenging transformation, allowing streamlined access to an important class of cis-Michael acceptors from readily available feedstocks. The kinetic preference for cross-metathesis is enabled by a pivalate anionic ligand, and the origin of this effect is elucidated by density functional theory calculations.

Complexes with the formula [M(diimine)(CN-BR3)4]2-, where diimine = bipyridine (bpy), phenanthroline (phen), 3,5-trifluoromethylbipyridine (flpy), R = Ph, C6F5, and M = FeII, RuII, were synthesized and characterized by X-ray crystal structure analysis, UV-visible spectroscopy, IR spectroscopy, and voltammetry. Three highly soluble complexes, [FeII(bpy)(CN-B(C6F5)3)4]2-, [RuII(bpy)(CN-B(C6F5)3)4]2-, and [RuII(flpy)(CN-B(C6F5)3)4]2-, exhibit electrochemically reversible redox reactions, with large potential differences between the bpy0/- or flpy0/- and MIII/II couples of 3.27, 3.52, and 3.19 V, respectively. CASSCF+NEVPT2 calculations accurately reproduce the effects of borane coordination on the electronic structures and spectra of cyanometallates.

A robust synthesis of gem-dialkyl acyclic diene monomers has been developed. This route is scalable, flexible, and biorenewable, allowing for the production of a wide range of diene monomers of different lengths and different gem-dialkyl substitution starting from unsaturated esters derived from seed oils. The metathesis polymerization of these monomers and the hydrogenation of the resulting polyolefins leads to telechelic gem-dialkyl polyethylenes, which can be used as elastomers in the synthesis of polyurethanes and other block polymers.

Ru–cyclic alkyl amino carbene (Ru–CAAC) olefin metathesis catalysts perform extraordinarily in metathesis macrocyclization and ethenolysis, but previous studies have been limited to the use of five-membered CAAC (CAAC-5) ligands. In this work, we synthesized a different group of ruthenium catalysts with more σ-donating and π-accepting six-membered CAAC (CAAC-6) ligands, and their metathesis activity was probed through initiation studies, ring-closing metathesis (RCM), cross-metathesis, and ethenolysis. These catalysts display higher initiation rates than analogous Ru–CAAC-5 complexes but demonstrate lower activity in RCM and ethenolysis.

Correction for ‘Aqueous electrocatalytic CO2 reduction using metal complexes dispersed in polymer ion gels’ by Shunsuke Sato et al., Chem. Commun., 2020, DOI: 10.1039/d0cc00791a.

Drug capture is a promising technique to prevent off-target chemotherapeutic agents from reaching systemic circulation and causing severe side effects. The current work examines the viability of using immobilized aldehydes for drug-capture applications via Schiff base formation between doxorubicin (DOX) and aldehydes. Commercially available pyridoxal-5′-phosphate (VB6) was immobilized on iron oxide nanoparticles (IONPs) to capture DOX from human serum. Leaching of VB6 persisted as a primary issue and thus various aldehydes with anchoring groups such as catechol, silatrane, and phosphonate esters have been studied. The phosphonate group-based anchor was the most stable and used for further capture studies. To improve the hydrophilic nature of the aldehydes, sulfonate-containing aldehydes and polyethylene glycols (PEGs) were investigated. Finally, the optimized functionalized iron oxide particles, PEGylated-IONP, were used to demonstrate doxorubicin capture from human serum at biologically relevant temperature (37 °C), time (30 min), and concentrations (μM). The current study sets the stage for the development of potential compact dimension capture device based on surface-anchorable polymers with aldehyde groups.

Ovarian cancer survival and the recurrence rate are drastically affected by the amount of tumor that can be surgically removed prior to chemotherapy. Surgeons are currently limited to visual inspection, making smaller tumors difficult to be removed surgically. Enhancing the surgeon's ability to selectively remove cancerous tissue would have a positive effect on a patient's prognosis. One approach to aid in surgical tumor removal involves using targeted fluorescent probes to selectively label cancerous tissue. To date, there has been a trade-off in balancing two requirements for the surgeon: the ability to see maximal tumors and the ability to identify these tumors by eye while performing the surgery. The ability to see maximal tumors has been prioritized and this has led to the use of fluorophores activated by near-infrared (NIR) light as NIR penetrates most deeply in this surgical setting, but the light emitted by traditional NIR fluorophores is invisible to the naked eye. This has necessitated the use of specialty detectors and monitors that the surgeon must consult while performing the surgery. In this study, we develop nanoparticles that selectively label ovarian tumors and are activated by NIR light but emit visible light. This potentially allows for maximal tumor observation and real-time detection by eye during surgery. We designed two generations of up-converting nanoparticles that emit green light when illuminated with NIR light. These particles specifically label ovarian tumors most likely via tumor-associated macrophages, which are prominent in the tumor microenvironment. Our results demonstrate that this approach is a viable means of visualizing tumors during surgery without the need for complicated, expensive, and bulky detection equipment. Continued improvement and experimentation could expand our approach into a much needed surgical technique to aid ovarian tumor removal.

We use fac-[Re(bpy)(CO)3Cl] ([Re-Cl]) dispersed in polymer ion gel (PIG) ([Re]-PIG) to carry out electrocatalytic CO2 reduction in water. Electrolysis at -0.68 V vs. RHE in a CO2-saturated KOH and K2CO3 solution produces CO with over 90% Faradaic efficiency. The PIG electrode is readily combined with water oxidation catalysts to generate a full electrochemical cell. Additionally, we provide evidence that the PIG electrode can be implemented with other molecular catalysts.