Reversible Addition-fragmentation Chain Transfer Reaction Research Articles

Poly(acrylated epoxidized soybean oil)‐modified carbon nanotubes and their application in epoxidized soybean oil‐based thermoset composites

AbstractPoly(acrylated epoxidized soybean oil) (PAESO) has been grafted on the surface of multiwalled carbon nanotubes (MWCNTs) by reversible addition–fragmentation chain‐transfer reaction (RAFT). MWCNTs–PAESO as reinforcement has been successfully applied to prepare epoxidized soybean oil/maleopimaric‐based thermosetting composites with good dispersion through probe ultrasonic treatment in ethyl acetate. Micromorphology analyses on composites by transmission electron microscopy and scanning electron microscopy show that MWCNTs–PAESO has better dispersion stability in both ethyl acetate and epoxy matrix and better interface bonding effect with cured matrix, resulting in more uniformly and separately dispersed behavior than hydroxylated multiwalled carbon nanotubes. Correspondingly, by the method of molecular dynamics simulation, it is verified that the nonbond energy and van der Waals force of CNTs–PAESO in solvent can be relatively reduced, and that CNTs–PAESO possesses higher binding energy with matrix compared with CNTsOH. Therefore, MWCNTs–PAESO and PAESO have synergistic enhancement on the mechanical properties of composites demonstrated by rheology testing and dynamic mechanical analysis. The appropriate amount of MWCNTs–PAESO loading at 0.15 wt% can increase the glass transition temperature (Tg) of thermoset from 83.8 to 96.3°C, resulting in the improvement of both mechanical and thermal properties. These results show that surface‐grafting MWCNTs with homologous polymer can effectively increase the interfacial compatibility between matrix and MWCNTs, thereby improving the thermal and mechanical properties of composites.

Covalent Decoration of MoS2 Platforms by Silver Nanoparticles through the Reversible Addition–Fragmentation Chain Transfer Reaction

Two-dimensional nanomaterials decorated by metal nanoparticles have gained great interest, due to their potential applications in different areas ranging from electrochemical sensing to photothermal therapy. However, metal nanoparticles that are noncovalently immobilized on the surface of two-dimensional nanomaterials can be dissociated from their surface in the complex mediums. This challenge can be overcome by covalent attachment of nanoparticles to the surface of these platforms. In this work, MoS2 sheets are decorated by silver nanoparticles (AgNPs) through a reversible addition-fragmentation chain transfer (RAFT) reaction. Reactive centers were created on the surface of freshly exfoliated MoS2 and a two-dimensional platform with the ability of initiating the RAFT reaction was obtained. Afterwards, silver nanoparticles with acrylamide functionality were synthesized and attached on the surface of MoS2 sheets by the RAFT reaction. MoS2-AgNPs hybrids were characterized by different spectroscopy and microscopy methods as well as thermal and elemental analyses, and then they were used for the electrochemical determination of dipyridamole in aqueous solution. Taking advantage of the straightforward synthesis and the possible MoS2-AgNPs distance adjustment, a variety of hybrid systems with unique physicochemical and optoelectronic properties can be constructed by using this method.

Photoresponsive dynamic covalent bond based on addition–fragmentation chain transfer of allyl selenides

A new dynamic covalent bond allyl selenide that can undergo a reversible addition–fragmentation chain transfer reaction under ultraviolet irradiation.

PET-RAFT single unit monomer insertion of β-methylstyrene derivatives: RAFT degradation and reaction selectivity.

Reversible addition-fragmentation chain transfer (RAFT) single unit monomer insertion (SUMI) of β-methylstyrene derivatives into diverse RAFT agents presented fast reaction kinetics, but significant degradation of the SUMI products occurred due to a hydrogen abstraction reaction. Fortunately, such degradation can be suppressed through appropriate design of initial RAFT agents attributed to effective chain transfer and selective photoactivation.

Studies on non-gelatinous & thermo-responsive chitosan with the N-isopropylacrylamide by RAFT methodology for control release of levofloxacin

The non-gelatinous and thermo-responsive properties were introduced in chitosan by incorporating the chain of poly(N-isopropylacrylamide) via reversible addition-fragmentation chain transfer (RAFT) polymerization. To achieve this, the reaction was carried out at 80 °C by modifying the chitosan(CS) with RAFT agent as a macroinitiator (CS-RAFT), where the amine group of CS was protected with phthalic anhydride and then reacted with 4-cyano-4-[(dodecyl sulfanyl thiocarbonyl)sulfanyl]-pentanoic acid (CDSTSP) to form CS-RAFT agent. Further, the addition of NIPAAm chains onto CS-RAFT was carried out in N,N′-dimethylformamide (DMF) solvent by using 2,2′-azobisisobutyronitrile (AIBN) as an initiator in N2 atmosphere. The controlled addition of NIPAAm chains on to CS was confirmed by 1H NMR spectroscopy, further, a kinetic study was performed to get the characteristic features of the RAFT reaction. The product was characterized by 1H NMR, FT-IR, UV–Visible spectroscopy, XRD, SEM, and TGA analyses. The product in aqueous solution showed LCST at 2.0 mg/mL on 33 ± 0.1 °C. Further, beads were prepared with the sodium alginate and loaded the water-soluble levofloxacin drug (60% w/w loading was achieved). The drug delivery process was studied in-vitro at 37 ± 0.1 °C & pH 7.4, which shown controlled release of drug up to 32 h and it was 71% of the loaded levofloxacin.

Modeling and Observer-Based Monitoring of RAFT Homopolymerization Reactions

Reversible addition–fragmentation chain–transfer (RAFT) polymerization of methyl methacrylate (MMA) is modeled and monitored using a multi-rate multi-delay observer in this work. First, to fit the RAFT reaction rate coefficients and the initiator efficiency in the model, in situ 1 H nuclear magnetic resonance (NMR) experimental data from small-scale (<2 mL) NMR tube reactions is obtained and a least squares optimization is performed. 1 H NMR and size exclusion chromatography (SEC) experimental data from large-scale (>400 mL) reflux reactions is then used to validate the fitted model. The fitted model accurately predicts the polymer properties of the large-scale reactions with slight discordance at late reaction times. Based on the fitted model, a multi-rate multi-delay observer coupled with an inter-sample predictor and dead time compensator is designed, to account for the asynchronous multi-rate measurements with non-constant delays. The multi-rate multi-delay observer shows perfect convergence after a few sampling times when tested against the fitted model, and is in fair agreement with the real data at late reaction times when implemented based on the experimental measurements.

Synthesis of Bioacrylic Polymers from Dihydro-5-hydroxyl furan-2-one (2H-HBO) by Free and Controlled Radical Polymerization.

In this work, dihydro-5-hydroxyl furan-2-one (2H-HBO), a renewable-sourced chemical containing the hydroxyl functionality, is converted into its acrylic counterpart for the first time through a green chemical procedure using methacrylic anhydride. This newly synthesized acrylic monomer is able to be polymerized using different techniques such as bulk, solution, and emulsion polymerization. The ability of this monomer to copolymerize with other commercially available acrylates is studied using emulsion polymerization techniques. The pendent lactone ring remains unopened during polymerization and the new monomer is able to copolymerize with other acrylates such as methyl methacrylate and styrene. Reversible addition-fragmentation chain transfer reaction emulsion polymerization is also studied with the same monomer, leading to a steady conversion (∼60%) with a low polydispersity of 1.06. The homopolymer produced from such an emulsion polymerization shows a higher molecular weight than that produced from other methods, with a glass transition temperature of around 105 °C. This demonstrates the potential of this monomer as an interesting, green replacement for methyl methacrylate in certain fields of application.

Graft polymer synthesis by RAFT transfer‐to

ABSTRACTThe synthesis of graft polymers via controlled polymerization techniques has enabled the facile modification of the surface properties of a variety of substrates. Three grafting methods are typically highlighted in the literature: grafting‐to, grafting‐from, and grafting‐through. However, a fourth method exists when grafting is conducted using reversible addition‐fragmentation chain transfer (RAFT) polymerization, which we refer to as transfer‐to. Transfer‐to differs from the other grafting strategies in the types of structural defects and impurities that arise during polymerization. This review addresses important considerations when conducting RAFT transfer‐to, including RAFT chain transfer agent selection, monomer structure, and reaction conditions. In addition, we highlight key mechanistic differences between grafting‐from and transfer‐to and their effects on the structure and sample composition of the resulting graft polymers. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 2865–2876

One-, two-, and three-dimensional hierarchical self-assembly of non-amphiphilic low-entropy chains from nanotubes to nanoribbons and porous net-sheets

The association of some small molecules such as benzene and phthalimide with non-amphiphilic homopolymeric low-entropy chains such as PVAc, PVA, PVP, and PNIPAM has been realized by reversible addition–fragmentation chain transfer reaction (RAFT) method.

Observed Photoenhancement of RAFT Polymerizations under Fume Hood Lighting.

Given the recent findings of exogenous radical initiator/catalyst-free reversible addition-fragmentation chain transfer (RAFT) radical polymerization under both UV and visible light irradiation, the effect of standard laboratory lighting conditions (fluorescent tube lights) on traditional RAFT reactions, that is, those conducted in the presence of a thermally activated radical initiator, remains unknown. This is investigated in the current study, where a significant "photoenhancement" is observed for most cases under typical RAFT reaction conditions, indicating that fume hood lights can contribute to the generation of radicals in RAFT reactions. Given the observed emission spectrum of a typical fluorescent light source, the photoenhancement is proposed to occur through a visible light activation pathway. These findings are crucial for ensuring maximum reproducibility of controlled polymerizations conducted in the presence of typical sources of irradiation encountered in a standard chemical laboratory.

Modeling of RAFT Polymerization Processes Using an Efficient Monte Carlo Algorithm in Julia

A kinetic Monte Carlo model of a reversible addition–fragmentation chain transfer (RAFT) process is presented. The algorithm has been developed and implemented in Julia for the three main RAFT theories under current discussion (slow fragmentation, intermediate radical termination, and intermediate radical termination with oligomers). Julia is a modern programming language designed to achieve high performance in numerical and scientific computing. Thanks to a careful optimization of the code, it is possible to simulate a RAFT reaction scheme in short computing times for any of the three theories. The code is benchmarked against other programming languages (MATLAB, Python, FORTRAN, and C), showing that Julia presents advantages for this particular system. The model offers an efficient method for predicting average properties and molecular weight distributions of the polymer species, including the bivariate molecular weight distribution of the intermediate two-arm adduct. The proposed model can also be emplo...

Chemically Bonded Polyacrylamide via Thiol-Ene Click Chemistry as Separation Materials for Hydrophilic Interaction Liquid Chromatography

Abstract Thiol-ene click chemistry was applied to immobilize polyacrylamide onto alkenyl-modified silica to prepare a novel stationary phase for hydrophilic interaction liquid chromatography. Polyacrylamide was synthesized by reversible addition-fragmentation chain transfer reaction. Alkenyl functionalities were introduced onto the silica by the reaction of silica with the reaction product of 3-isocyanate opropyl trimethoxy silane, allylamine and pyridine in toluene to obtain alkenyl-modified silica (EUS, E-thiol-ene, U-urea, S-silica). The alkenyl-modified silica was then reacted with polyacrylamide in methanol at 55 °C for 48 h in the presence of 2,2-azo diisobutyl amidine hydrochloride to prepare a novel stationary phase (TE-UPAM, TE-thiol-ene, U-urea, PAM-polyacrylamide), for hydrophilic interaction liquid chromatography. This new stationary phase “TE-UPAM” was characterized by element analysis and infrared spectra, and the results showed that, compared with EUS, the carbon content of TE-UPAM increased and the characteristic peaks of multiple amide existed at 1636 and 1570 cm −1 . The effects of water content, salt concentration and pH of the mobile phase on the retention time of polar compounds were investigated. The results showed that the retention time of polar compounds decreased with the increase of water content. In contrast with acidic polar compounds, the retention time of neutral and basic polar compounds increased with the increase of salt concentration, and the retention time of basic polar compounds decreased with the decrease of pH value in the range of 3.3–4.8. The novel stationary phase behaved better than traditional silica stationary phase in the separation of uridine and bases. In addition, good separation of oligosaccharides by the novel stationary phase was also achieved, indicating great potential in the separation of polar compounds.

Well-defined nanostructured surface-imprinted polymers for highly selective magnetic separation of fluoroquinolones in human urine.

The construction of molecularly imprinted polymers on magnetic nanoparticles gives access to smart materials with dual functions of target recognition and magnetic separation. In this study, the superparamagnetic surface-molecularly imprinted nanoparticles were prepared via surface-initiated reversible addition-fragmentation chain transfer (RAFT) polymerization using ofloxacin (OFX) as template for the separation of fluoroquinolones (FQs). Benefiting from the living/controlled nature of RAFT reaction, distinct core-shell structure was successfully constructed. The highly uniform nanoscale MIP layer was homogeneously grafted on the surface of RAFT agent TTCA modified Fe3O4@SiO2 nanoparticles, which favors the fast mass transfer and rapid binding kinetics. The target binding assays demonstrate the desirable adsorption capacity and imprinting efficiency of Fe3O4@MIP. High selectivity of Fe3O4@MIP toward FQs (ofloxacin, pefloxacin, enrofloxacin, norfloxacin, and gatifloxacin) was exhibited by competitive binding assay. The Fe3O4@MIP nanoparticles were successfully applied for the direct enrichment of five FQs from human urine. The spiked human urine samples were determined and the recoveries ranging from 83.1 to 103.1% were obtained with RSD of 0.8-8.2% (n = 3). This work provides a versatile approach for the fabrication of well-defined MIP on nanomaterials for the analysis of complicated biosystems.

RAFT Polymerization of Vinyl Esters: Synthesis and Applications

This article is the first comprehensive review on the study and use of vinyl ester monomers in reversible addition fragmentation chain transfer (RAFT) polymerization. It covers all the synthetic aspects associated with the definition of precision polymers comprising poly(vinyl ester) building blocks, such as the choice of RAFT agent and reaction conditions in order to progress from simple to complex macromolecular architectures. Although vinyl acetate was by far the most studied monomer of the range, many vinyl esters have been considered in order to tune various polymer properties, in particular, solubility in supercritical carbon dioxide (scCO2). A special emphasis is given to novel poly(vinyl alkylate)s with enhanced solubilities in scCO2, with applications as reactive stabilizers for dispersion polymerization and macromolecular surfactants for CO2 media. Other miscellaneous uses of poly(vinyl ester)s synthesized by RAFT, for instance as a means to produce poly(vinyl alcohol) with controlled characteristics for use in the biomedical area, are also covered.

Stress relaxation of trithiocarbonate-dimethacrylate-based dental composites

ObjectivesTo reduce polymerization-induced shrinkage stress while maintaining mechanical properties, reversible addition-fragmentation chain transfer (RAFT)-capable functional groups were incorporated into a photopolymerizable dimethacrylate-based dental composite. We hypothesize that the incorporation of trithiocarbonate-based RAFT functional groups into conventional dimethacrylate dental resins will reduce polymerization stress. MethodsA trithiocarbonate dimethacrylate (TTCDMA) monomer, capable of undergoing radical-mediated RAFT, is mixed with 70wt% BisGMA (bisphenylglycidyl dimethacrylate) and compared to a conventional dental resin comprised of TEGDMA (triethylene glycol dimethacrylate) and 70wt% BisGMA. The shrinkage stress and methacrylate conversion were simultaneously measured during polymerization. The fracture toughness and elastic modulus were measured to evaluate the effect of the TTCDMA monomer on the mechanical properties. All the materials used herein were evaluated as a composite, including 75wt% silica fillers. ANOVA (CI 95%) was conducted to assess the differences between the means. ResultsThe TTCDMA composite exhibited a 65% stress reduction compared with TEGDMA–BisGMA though the reaction rate was slower than the conventional dental composite, owing to the additional RAFT reaction. The fracture toughness and elastic modulus of the TTCDMA-based composite were not significantly different than in the TEGDMA-based composite, while the Tg was decreased by 30°C to 155±2°C. SignificanceDespite only replacing the reactive-diluent, significant and dramatic stress reduction was observed while maintaining the elastic modulus and fracture toughness. This new RAFT-capable monomer shows great promise to replace the reactive diluent in BisGMA-based dental materials. Formulation optimization and further exploration of other RAFT-capable functional groups will provide further stress reduction in dental materials.

Probing the RAFT Process Using a Model Reaction between Alkoxyamine and Dithioester

A small-molecular model reaction was designed to probe the reversible addition–fragmentation chain transfer (RAFT) process. In this reaction, alkoxyamine releases radicals that react in situ with dithioester through the RAFT process, generating new radicals through the fragmentation of the intermediate radical. The new radicals can be trapped by free 2,2,6,6-tetramethyl-piperidinyl-N-oxyl radicals (TEMPO) from homolysis of alkoxyamine. The overall reaction is the crossover of the leaving groups between alkoxyamine and dithioester. The advantage of this model as a probe of the RAFT process is that it does not involve polymerization-related elementary reactions such as initiation, propagation, and chain length dependent termination. The kinetics of the model reaction were measured using high-performance liquid chromatography, and then fitted by Monte Carlo simulation to estimate rate coefficients. The obtained rate coefficients of addition for various dithioesters fell into a narrow range of 107–108 L mol–1 s–1, whereas the rate coefficient of fragmentation was model-dependent. It was also found that a significant fraction of the dithioester was consumed by an unspecified additional mechanism. A tentative explanation is proposed in which the intermediate radical undergoes a secondary RAFT reaction with dithioesters, forming a secondary intermediate that serves as a radical reservoir.

Microstructure Evolution and Monomer Partitioning in Reversible Addition−Fragmentation Chain Transfer Microemulsion Polymerization

Small-angle neutron scattering (SANS) studies of reversible addition-fragmentation chain transfer (RAFT) microemulsion polymerizations of butyl acrylate and 2-ethylhexyl acrylate with the RAFT agent methyl- 2-(O-ethylxanthyl)propionate (MOEP) allow the observed rate retardation to be attributed to slow fragmentation of the macro-RAFT radical. Microemulsion polymerization allows the RAFT mechanism to be investigated in the absence of termination reactions so that the cause of the rate retardation frequently observed in both homogeneous and heterogeneous polymerizations may be isolated. However, the concentration of monomer at the locus of polymerization (Cmon ) must be known as a function of conversion before a mechanistic study of the RAFT reaction can be completed. SANS is uniquely capable of probing the evolving microstructure of both the micelles and polymer particles during the polymerization. Cmon then can be calculated by combining this microstructural information with material balances on the components of the microemulsion.

Living Radical Polymerization of Isoprene via the RAFT Process

The control over the polymerization of isoprene via reversible addition−fragmentation chain transfer (RAFT) is reported. The effects of RAFT agent, reaction temperature, and monomer concentration over molecular weight control and reaction kinetics were investigated. The optimized conditions were used to produce block copolymers of isoprene with styrene and tert-butyl acrylate.