Functional Vinyl Research Articles

Vinyl-Group-Anchored Covalent Organic Framework for Promoting the Photocatalytic Generation of Hydrogen Peroxide.

The artificial photosynthesis of H2O2 from water and oxygen using semiconductor photocatalysts is attracting increasing levels of attention owing to its green, environmentally friendly, and energy-saving characteristics. Although covalent organic frameworks (COFs) are promising materials for promoting photocatalytic H2O2 production owing to their structural and functional diversity, they typically suffer from low charge-generation and -transfer efficiencies as well as rapid charge recombination, which restricts their use as catalysts for photocatalytic H2O2 production. Herein, we report a strategy for anchoring vinyl moieties to a COF skeleton to facilitate charge separation and migration, thereby promoting photocatalytic H2O2 generation. This vinyl-group-bearing COF photocatalyst exhibits a H2O2-production rate of 84.5 μmol h-1 (per 10 mg), which is ten-times higher than that of the analog devoid of vinyl functionality and superior to most reported COF photocatalysts. Both experimental and theoretical studies provide deep insight into the origin of the improved photocatalytic performance. These findings are expected to facilitate the rational design and modification of organic semiconductors for use in photocatalytic applications.

Vinyl‐Group‐Anchored Covalent Organic Framework for Promoting the Photocatalytic Generation of Hydrogen Peroxide

AbstractThe artificial photosynthesis of H2O2 from water and oxygen using semiconductor photocatalysts is attracting increasing levels of attention owing to its green, environmentally friendly, and energy‐saving characteristics. Although covalent organic frameworks (COFs) are promising materials for promoting photocatalytic H2O2 production owing to their structural and functional diversity, they typically suffer from low charge‐generation and ‐transfer efficiencies as well as rapid charge recombination, which restricts their use as catalysts for photocatalytic H2O2 production. Herein, we report a strategy for anchoring vinyl moieties to a COF skeleton to facilitate charge separation and migration, thereby promoting photocatalytic H2O2 generation. This vinyl‐group‐bearing COF photocatalyst exhibits a H2O2‐production rate of 84.5 μmol h−1 (per 10 mg), which is ten‐times higher than that of the analog devoid of vinyl functionality and superior to most reported COF photocatalysts. Both experimental and theoretical studies provide deep insight into the origin of the improved photocatalytic performance. These findings are expected to facilitate the rational design and modification of organic semiconductors for use in photocatalytic applications.

Total synthesis of (+)-oridamycins A and B.

We have accomplished a unified strategy to achieve the structurally intriguing indolosesquiterpene alkaloids with diverse biological activity, xiamycin A (1a), xiamycin A methyl ester (1b) and oridamycins A (2a), and B (2b), which possesses a complex 6/6/6/5/6-fused pentacyclic skeleton bearing a carbazole moiety fused with a highly functionalized trans-decalin motif. Lewis acid-mediated epoxy-ene cyclization establishes the required pentacyclic scaffold with the installation of the four contiguous stereogenic centers. Further oxidative cleavage of the vinyl functionality, followed by successive functional group interconversions, completed the total synthesis of the indolosesquiterpene alkaloids.

Synthetic Studies toward the C1–C12 Fragment of Amphidinolide U

AbstractAmphidinolide U is a cytotoxic marine macrolide isolated from Amphidinium sp., sharing 75% of the amphidinolide C backbone. We report here a synthetic study of the C1–C12 fragment of amphidinolide U. The C6–C12 pattern was built using consecutive regioselective ring opening of epoxides, a directed reaction to control newly formed stereogenic centers. In parallel, the C1–C5 moiety was constructed by taking advantage of a symmetrical diol. Attempts to cross-couple the C1–C5 and C6–C12 fragments by using a Suzuki cross-coupling reaction led to poor conversion rates. The same transformation on a close substrate model used during past studies on the total synthesis of amphidinolides F and C2 was successful. These contrasting results could be explained by a presumed steric hindrance of the protecting group adjacent to the vinyl function involved in the cross-coupling reaction. Our investigations will stimulate the optimization of C(sp2)–C(sp3) cross-coupling reactions with bulky substrates, with the aim of achieving a total synthesis of amphidinolide U.

Performance of new nanocomposites based on graphene-grafted-poly(itaconic acid-co-TRIM) via photoiniferter, thermal vinyl functionalization, and physical mixture as electrochemical sensing platforms for illicit drug determination

Graphene-functional polymer nanocomposites-based sensors have been used as platforms for the voltammetric sensing of a wide range of molecules. However, different strategies can be used to stablish the integration/interface between the graphene and the functional polymer. Therefore, in this work, the performance of new nanocomposites based on graphene (GO and rGO) grafted with poly(itaconic acid-co-TRIM) prepared by controlled-radical polymerization via photoiniferter [named GO-poly(IA-co-TRIM)-iniferter and rGO-poly(IA-co-TRIM)-iniferter] and free-radical polymerization via thermal vinyl functionalization as platforms [named GO-VTMS-poly(IA-co-TRIM) and rGO-VTMS-poly(IA-co-TRIM)] for voltametric sensing of mephedrone (4-MMC) was evaluated. In addition, the physical mixtures of GO/poly(IA-co-TRIM) and rGO/poly(IA-co-TRIM) were also investigated for sensor preparation. Characterization of materials was performed by FT-IR, X-ray diffraction, Raman spectroscopy, SEM, TEM, TGA, and nitrogen adsorption/desorption measurements. For sensor preparation, nanocomposite suspensions were drop-casted on the surface of a glassy carbon electrode (GCE). No cathodic peak current for mephedrone was observed when using unmodified GCE, while a pronounced analytical signal was achieved when modifying the GCE with the physical mixture of GO and poly(IA-co-TRIM). The synergic effect of GO and the itaconic acid in the poly(IA-co-TRIM) in the physical mixture explains the higher adsorption of mephedrone on the surface of the sensor when compared to the other methods evaluated. A linear analytical curve (0.25 to 10.0 µmol L−1, R2 = 0.99) was obtained with limit of detection of 0.22 μmol L−1. 4-MMC determination was not influenced by the presence of caffeine, benzocaine, paracetamol, cocaine, and ethylone. The method was applied in simulated seized street samples, with accuracy assessed by HPLC-DAD as well as in synthetic urine samples, yielding recovery values from 95.8 to 103.9%.

How Nanoparticles Modify Adsorbed Proteins: Impact of Silica Nanoparticles on the Hemoglobin Active Site.

The adsorption of proteins on surfaces has been studied for a long time, but the relationship between the structural and functional properties of the adsorbed protein and the adsorption mechanism remains unclear. Using hemoglobin adsorbed on silica nanoparticles, we have previously shown that hemoglobin's affinity towards oxygen increases with adsorption. Nevertheless, it was also shown that there were no significant changes in the quaternary and secondary structures. In order to understand the change in activity, we decided in this work to focus on the active sites of hemoglobin, the heme and its iron. After measuring adsorption isotherms of porcine hemoglobin on Ludox silica nanoparticles, we analyzed the structural modifications of adsorbed hemoglobin by X-ray absorption spectroscopy and circular dichroism spectra in the Soret region. It was found that upon adsorption, there were modifications in the heme pocket environment due to changes in the angles of the heme vinyl functions. These alterations can explain the greater affinity observed.

A Cobalt-Containing Polysilane as an Effective Solid-State Catalyst for the Hydrosilylation of Alkenes

A cobalt-containing polysilane was readily obtained from the treatment of poly(monohydro)silane with Co2(CO)8 at 60 °C. The resulting polysilane-supported cobalt catalyst (Co/Si catalyst) acts as a solid-state catalyst that exhibits good catalytic performance toward the hydrosilylation of various alkenes with hydrosiloxanes, such as 1,1,1,3,3-pentamethyldisiloxane. Suitable alkenes for this catalysis include functionalized alkenes such as allyl glycidyl ether and vinylsiloxanes as well as multiply functionalized alkenes such as triallylisocyanurate. The Co/Si catalyst can be recycled multiple times, and recycling is accomplished by simple centrifugation. It is noteworthy that this Co/Si system also catalyzes the modification of a silicone fluid and cross-linking between poly(monohydro)siloxanes and polysiloxanes that bear vinyl functionalities to afford silicone polymers, which are industrially important reactions.

Plasma-Enhanced Molecular Layer Deposition of Phosphane–Ene Polymer Films

A vapor-phase molecular layer deposition (MLD) process generating phosphorus-rich phosphane–ene polymer networks was adapted from known solution-phase methods and successfully used in a commercial atomic layer deposition tool. By using plasma-enhanced MLD on Si/SiO2 and Al2O3 substrates, film deposition was carried out with a commercially available primary phosphine, iBuPH2, paired with a known volatile cyclic siloxane precursor, tetramethyltetravinylcyclotetrasiloxane (D4Vinyl). The deposition process used radicals generated by an Ar plasma source to facilitate P–H addition to vinyl functionalities on D4Vinyl which yielded a growth per cycle of 0.6–2.0 Å, generating 10–120 nm films as determined by atomic force microscopy and scanning electron microscopy measurements. Characterization of the films were carried out using X-ray photoelectron spectroscopy, and oxygen scavenging capabilities were studied using a quartz crystal microbalance, showing an uptake of oxygen by a 12 nm depth of a freshly deposited polymer film.

The dual behaviour of β-vinylporphyrins in the presence of α,α′-dioxothiones

α,α′-Dioxothione react with meso-tetraarylporphyrins bearing vinyl functionalities as a heterodienophiles or as a heterodienes. The dual behaviour is dependent on the absence or on the presence of a metal ion on the porphyrin inner core.

Thermally latent vinyl crosslinking of polymers via sulfoxide chemistry

Radical crosslinking reactions utilizing vinyl functionality are widely used to fabricate polymeric networks for bulk and surface applications. Here, we report a thermally latent vinyl crosslinking of polymers involving sulfoxide chemistry for the first time. Polymers with sulfoxide-protected methacrylate moieties are prepared via free-radical polymerization. These moieties are deprotected by a thermal process and transformed into methacrylate functional groups. The crosslinking behaviors of the protected polymers are investigated using an oscillatory rheometer in the presence of a radical initiator. The behavior strongly depended on the formation of methacrylate species in polymer chains. The thermally latent crosslinking approach introduces a novel method for the stepwise and systematic construction of polymeric networks that can potentially be applied in dual-curing or patterning processes.

Glycerol-based enzymatically synthesized renewable polyesters: Control of molecular weight, degree of branching and functional endgroups

The catalytic specificity of Lipase B from Candida antarctica (CALB) has been exploited to achieve specific terminal groups for the synthesis of glycerol poly(ester)s. This permits the preparation of glycerol-derived macromers able to undergo further reactions/chemical modifications for customization as functional systems and building blocks for polymer synthesis. Poly(glycerol adipate) based macromers with different terminal structures were achieved from the reaction between glycerol and divinyl adipate by varying the stoichiometry (from equimolar to 1.5 and 3.0 excess either of glycerol or divinyl adipate) and amount of catalyst (1 and 3 wt%). In the course of polymerization, transesterification and hydrolysis reactions occur over vinyl functionalities that result in acid endgroups. Thus, the resulting macromers are either terminated with hydroxyl groups and/or acid groups and/or vinyl groups. Therefore, an understanding of how acid functionality appears (from vinyl groups hydrolysis) and its quantification under various conditions may provide an opportunity for the design of synthetic strategies to avoid acid production and obtain the desired structures. Endgroup analysis was carried out using 1H NMR and 13C NMR spectroscopies and MALDI-TOF spectrometry. Mainly linear hydroxyl and vinyl-terminated macromers were obtained with high efficiency without significant hydrolysis of the chain ends (for vinyl terminated).

Microwave‐assisted alcoholysis of silicone rubber waste with geraniol for effective elastomer damping

AbstractThe first step in the mainstream end‐of‐life management of discarded silicone‐rubber‐based composite insulators involves grinding and modification of them into fine silicone rubber powders (SRPs). However, significant knowledge gaps have prevented researchers from developing direct efficient surface treatments for SRPs that do not involve time‐consuming and multi‐step processes. Herein, we report a straightforward method for the efficient modification of discarded SRPs through a microwave‐assisted alcoholysis process. Specifically, the siloxane moieties of the SRPs were cleaved using nucleophilic geraniol as a modifier, thereby facilitating the introduction of abundant alkoxysilyl groups on SRPs surface. During sulfur crosslinking, the intrachain vinyl functionalities of the modified SRPs co‐crosslinked with the rubber matrix via sulfur bridges, thereby improving the dispersion state of the SRPs and the interfacial adhesion between the SRPs and the rubber matrix. Accordingly, even for a high SRP loading (200 phr, parts per hundreds of gum), the mechanical performance of the resulting systems, and in particular the tensile strength and extensibility were significantly higher than those of the rubber matrix. Moreover, the interfacial adhesion of the resulting systems was improved, and the resulting systems presented remarkable damping performance (tan δ ≥ 0.3) over a broad temperature range (≥80°C).

Tricyclic 6–8–6 laddersiloxanes derived from all-cis-tetravinylcyclotetrasiloxanolate: Synthesis, characterization and reactivity

A straightforward, efficient and scalable (gram scale) route to an unprecedented 6–8–6 laddersiloxane 3 bearing four vinyl groups on the cyclotetrasiloxane T4 unit is reported. Compound 3 was fully characterized by multinuclear NMRs, mass spectrometry, and its structure was determined by X-ray crystallography. The reactivity of the vinyl functions was next explored and hydrosilylations of 3 were successfully achieved with three different silanes in the presence of a small amount of Pt catalyst (0.025 mol% of Pt per vinyl function) in each case. The resulting laddersiloxanes were isolated in high yields (76 to 99%) after straightforward work-ups and fully characterized. With its high thermal stability (Td5 = 372 °C) and chemical versatility, 3 thus appears as a promising precursor for building hybrid materials.

Enhanced mechanical properties of porous silicone composites prepared by silane surface functionalization of hollow silica particles

In this study, mechanical and thermomechanical properties of porous silicone composites with various contents of hollow silica particles, treated by vinyltrimethoxysilane (VTMS) as a silane coupling agent, were investigated using tensile and dynamic mechanical analysis. Series of silicone composites with non-modified hollow silica particles as a reference were also prepared for comparative study. The surface characteristics of VTMS-modified hollow silica particles were analyzed using FT-IR spectroscopy. The vinyl function groups on VTMS-modified hollow silica particles led to a chemical bonding to silicone matrix, resulting in reinforcing the mechanical properties of the silicone composites. Tensile modulus of porous silicone composites without the surface modification of silica particles could be predicted by Einstein and Guth/Gold equations, implying the hydrodynamic reinforcement contribution. On the other hand, considerable improvement in the tensile modulus of silicone composites was achieved by strong interfacial adhesion created by chemical bonding on the surface of VTMS-modified hollow silica particles.

Enhancing the solvent resistance and thermomechanical properties of thermoplastic acrylic polymers and composites via reactive hybridisation

This work demonstrates the use of an engineering thermoplastic, poly(phenylene ether) (PPE) to enhance the solvent resistance and thermomechanical properties of liquid acrylic resin-based composites by a reactive hybridisation route. Oligomeric PPE with vinyl functionality was employed to attain chemical reactivity between the two constituents during the in-situ polymerisation process. Both unreinforced polymer blends and glass fibre-reinforced composites were studied; physical insights into the polymer structure and properties were obtained through complementary spectroscopic analysis, thermal analysis and microscopy. Spectroscopic analysis revealed the formation of multi-component mixtures in the blends, containing both CDCl3-soluble and -insoluble constituents, with the latter likely corresponding to a reacted acrylic/PPE species. These findings show that incorporating reactive PPE into a reactive acrylic resin to produce a hybrid-matrix system is a simple, yet effective strategy towards enhancing solvent resistance (mass retention: 98% – PPE-modified; 72% – unmodified), while simultaneously enhancing the glass transition temperature (+9%) in acrylic-matrix composites.

Determining Michael Acceptor Reactivity from Kinetic, Mechanistic, and Computational Analysis for the Base-catalyzed Thiol-Michael Reaction.

A combined experimental and computational study of the reactivities of seven commonly used Michael acceptors paired with two thiols within the framework of photobase-catalyzed thiol-Michael reactions is reported. The rate coefficients of the propagation (kP), reverse propagation (k-P), chain-transfer (kCT), and overall reaction (koverall) were experimentally determined and compared with the well-accepted electrophilicity parameters of Mayr and Parr, and DFT-calculated energetics. Both Mayr's and Parr's electrophilicity parameters predict the reactivities of these structurally varying vinyl functional groups well, covering a range of overall reaction rate coefficients from 0.5 to 6.2 s-1. To gain insight into the individual steps, the relative energies have been calculated using DFT for each of the stationary points along this step-growth reaction between ethanethiol and the seven alkenes. The free energies of the individual steps reveal the underlying factors that control the reaction barriers for propagation and chain transfer. Both the propagation and chain transfer steps are under kinetic control. These results serve as a useful guide for Michael acceptor selection to design and predict thiol-Michael-based materials with appropriate kinetic and material properties.

Fluorinated cobalt catalysts and their use in forming narrowly dispersed polyethylene waxes of high linearity and incorporating vinyl functionality

The depicted cobalt catalysts bearingortho-fluorine and fluorinatedortho-benzhydryl substituents displayed a preference for forming highly linear PE waxes; DFT studies have been used to probe this selectivity.

Selectively Depolymerizable Polyurethanes from Unsaturated Polyols Cleavable by Olefin Metathesis.

This communication describes a novel series of linear and crosslinked polyurethanes (PUs) and their selective depolymerization under mild conditions. Two unique polyols are synthesized bearing unsaturated units in a configuration designed to favor ring-closing metathesis (RCM) to five- and six-membered cycloalkenes. These polyols are co-polymerized with toluene diisocyanate to generate linear PUs and trifunctional hexamethylene- and diphenylmethane-based isocyanates to generate crosslinked PUs. The polyol design is such that the RCM reaction cleaves the backbone of the polymer chain. Upon exposure to dilute solutions of Grubbs' catalyst under ambient conditions, the PUs are rapidly depolymerized to low molecular weight, soluble products bearing vinyl and cycloalkene functionalities. These functionalities enable further re-polymerization by traditional strategies for polymerization of double bonds. It is anticipated that this general approach can be expanded to develop a range of chemically recyclable condensation polymers that are readily depolymerized by orthogonal metathesis chemistry.

Thermoplastic hybrid-matrix composite prepared by a room-temperature vacuum infusion and in-situ polymerisation process

This work explores a novel route for the fabrication of hybrid-matrix composites based on a recently developed liquid thermoplastic acrylic resin. This resin was modified using a poly(phenylene ether) (PPE) oligomer with vinyl functionality. Glass fibre-reinforced laminates based on acrylic and PPE-modified acrylic matrices were produced by a room-temperature vacuum infusion and in-situ polymerisation process. Comparative assessments of their mechanical performance and mode-I interlaminar fracture behaviour revealed enhanced matrix ductility, transverse flexural properties and initiation fracture toughness. Crazing was identified as the dominant mechanism for improved resistance to crack initiation.

Indium(III) Catalyzed Reactions of Vinyl Azides and Indoles.

Indium trichloride catalyzes the reaction of vinyl azides with unfunctionalized indoles to give vinyl indoles. This is the first example of displacement of the azide group by a carbon nucleophile while preserving the vinyl function. The protocol employs very mild reaction conditions and offers excellent yields of diverse 3-vinyl indoles. It is amenable to gram scale. Access to a library of 3,3'-bis(indolyl)methanes through condensation of vinyl azides with 2 equiv of an indole is demonstrated.