Living Radical Polymerization Research Articles

Cellular Internalization and Exiting Behavior of Zwitterionic 4-Armed Star-Shaped Polymers.

The zwitterionic phospholipid polymer poly(2-methacryloyloxyethyl phosphorylcholine-co-n-butyl methacrylate) (PMB) is amphiphilic copolymer, and it has been reported to directly penetrate cell membranes and have good cytocompatibility. Conventional PMBs are linear-type random copolymers that are polymerized by a free radical polymerization technique. In contrast, star-shaped polymers, or simple branched-type polymers, have unique properties compared to the linear types, for example, a viscosity based on the effect of the excluded volume. In this study, a branched architecture was introduced into a PMB molecular structure, and a 4-armed star-shaped PMB (4armPMB) was synthesized by an atom transfer radical polymerization (ATRP) technique known as living radical polymerization. Linear-type PMB was also synthesized using ATRP. The effects of the polymer architecture on cytotoxicity and cellular uptake were investigated. Both 4armPMB and LinearPMB were successfully synthesized, and these polymers were verified to be water soluble. Pyrene fluorescence in the polymer solution indicated that the architecture had no effect on the behavior of the polymer aggregates. In addition, these polymers caused no cytotoxicity or cell membrane damage. The 4armPMB and LinearPMB penetrated into the cells after a short incubation period, with similar rates. In contrast, the 4armPMB showed a quicker back-diffusion from the cells than that of LinearPMB. The 4armPMB showed fast cellular internalization and exiting behaviors.

Tailoring Polymerization Controllability and Dispersity through a Photoswitchable Catalyst Strategy.

Modulating on-demand polymerization is a challenge in synthetic macromolecules. Herein, tailoring polymerization controllability and dispersity during single-electron transfer mediated living radical polymerization (SET-LRP) of MMA was achieved. Hexaarylbiimidazole (HABI) was employed as a photoswitchable catalyst, allowing reversible control of catalytic activity between an active and inactive state. In the presence of HABI and with light on (active state), controlled SET-LRP of MMA followed first-order kinetics, resulting in polymers with narrow molecular weight distribution. In contrast, polymerization responded to light and reverted to their original uncontrolled state with light off (inactive state). Therefore, repeatable resetting polymerization could be easily performed. The key to photomodulating dispersity is to use an efficient molecular switch to tailor the breadths of dispersity. Besides, the mechanism of HABI-mediated SET-LRP with switchable ability is proposed. This article is protected by copyright. All rights reserved.

Where is the induction from? Effect of disproportionation and comproportionation in Cu(0)-mediated reversible deactivation radical polymerization

There is a controversial debate about the mechanism of reversible deactivation radical polymerization (RDRP) in the presence of Cu(0). Two mechanism models have been proposed - supplemental activator and reducing agent atom transfer radical polymerization (SARA ATRP) and single-electron transfer living radical polymerization (SET-LRP), however, they are contradictory to each other, and neither of them are able to fully explain experimental phenomenon in the Cu(0)-mediated RDRP process, especially a period of slow addition i.e., induction period occurs under certain reaction conditions. In this work, the induction phenomenon and its underlying mechanism was explored and clarified by using different catalyst systems (CuI, Cu(0), Cu(0)&CuII) and different initiator systems i.e., EBriB (ethyl α-bromoisobutyrate), EBrP (ethyl 2-bromopropionate), MBrP (methyl 2-bromopropionate) and MClP (methyl 2-chloropropionate). New insights on the roles of different copper species and their mutual conversion kinetics were provided. It is proved that the appearance/absence of the induction period is due to the difference in the relative concentrations of CuI and CuII accumulated at the early stage of the reaction. Moreover, the disproportionation and comproportionation co-exist in the Cu(0)-mediated RDRP system and play an essential role in establishing the equilibrium among different copper species (Cu0, CuI and CuII) at the early reaction stage.

Correlation between Self-Folding Behavior of Amphiphilic Polymers and Their Molecular Flexibility.

Self-folding behavior of amphiphilic polymers in aqueous environments mimics the structures of biomacromolecules (e.g., proteins). Since both the three-dimensional structure (static) and the molecular flexibility (dynamic) of a protein are essential for its biological functions, the latter should be considered when designing synthetic polymers that are intended to mimic proteins. Herein, we investigated the correlation between the self-folding behavior of amphiphilic polymers and their molecular flexibility. We synthesized amphiphilic polymers by subjecting N,N-dimethylacrylamide (hydrophilic) and N-benzylacrylamide (hydrophobic) to living radical polymerization. Polymers containing 10, 15, and 20 mol % of N-benzylacrylamide demonstrated self-folding behavior in an aqueous phase. The spin-spin relaxation time (T2) of the hydrophobic segments decreased with the percent collapse of the polymer molecules, indicating that mobility was restricted by the self-folding behavior. Furthermore, comparison of the polymers with random and block sequences revealed that the mobility of hydrophobic segments was not affected by the component of the local segments.

Rare earth–cobalt bimetallic catalysis mediates stereocontrolled living radical polymerization of acrylamides

Rare earth–cobalt bimetallic catalysis mediates stereocontrolled living radical polymerization of acrylamides

On the Absence of Cyclic Structures in Branched Polystyrenes Synthesized by Living Three-Dimensional Radical Polymerization in the Medium of a Deteriorating Thermodynamic Quality Solvent

Branched polystyrenes are synthesized by the radical copolymerization of styrene and divinylbenzene with reversible inhibition (in the presence of 2,2,6,6-tetramethylpiperidine-1-oxyl) under deteriorating thermodynamic quality of the solvent. The resulting polymers are studied by size-exclusion chromatography combined with static light scattering, ozonolysis, NMR spectroscopy, and differential scanning calorimetry. The branched polymers synthesized by living radical polymerization are characterized by lower intrinsic viscosity values than their linear analogs. Kuhn–Mark–Houwink parameters for these polymers in a tetrahydrofuran solution (а = 0.29) confirm the nonlinear architecture of macromolecules and a high content of pendant double bonds comparable in the order of magnitude with their theoretical content in the absence of the cyclization reaction indicate their branched structure. The glass transition temperature of the branched polystyrenes is 20–35°С lower than the glass transition temperature of the linear polystyrene.

Novel electrochemical sensing platform basing on di-functional stimuli-responsive imprinted polymers for simultaneous extraction and determination of metronidazole

A novel magnetic-controlled electrochemical sensor has been fabricated by combined photo-responsive surface molecular imprinted polymers (P-SMIPs) and electrochemical sensor. In particular, the P-SMIPs were obtained by living radical polymerization of photo-responsive functional monomer onto the magnetic Fe3O4 modified multi-walled carbon nanotubes nanocomposites. The magnetic glassy carbon electrode was introduced to make the anchoring and removal of P-SMIPs onto the magnetic-controlled glassy carbon electrode easy to manipulate. Driven by UV/vis light, the platform performs releasing and absorption of metronidazole basing on conformational variations of the photo-responsive monomer at the receptor sites part in the P-SMIPs. This process can be tested by the photo-responsive variations of metronidazole electrochemical signal. As the consequence, extracting of P-SMIPs sensor can be conveniently triggered by the controllable UV light intervention measure, leading to effectively improve in both analytes mass transfer rate to the receiving media and extraction efficiency. The experimental result indicated that the excellent recoveries of metronidazole were varied between 77.9% and 89.9% with RSDs ≤4.87% in the biological samples. Therefore, the P-SMIPs sensor shows satisfactory potential in reusable extractions that can be recycled several times with no significant loss of activity, and this utilization strategy can be extended to other analytes, achieving manifold applications of pharmaceutical and environmental.

Synthesis of High Molecular Weight Polymers by Organocatalyzed Living Radical Polymerization and Self‐Assembly Behavior

Back Cover: In article 2300005, Keling Hu, Yongjun Zhang, and co-workers demonstrate an organocatalyzed living radical polymerization method for high molecular weight polymers (HMWPs), yielding well-defined HMWPs in a metal-free and sulfur-free manner. This technique is rather mild and crucial for eliminating the persistent radical effect and dramatically improving livingness of propagation radicals, enabling HMWPs without the need of exogenous initiator or harsh equipment.

Synthesis of High Molecular Weight Polymers by Organocatalyzed Living Radical Polymerization and Self-Assembly Behavior.

A mild organocatalyzed living radical polymerization method is studied for high molecular weight polymers (HMWPs), yielding low-dispersity linear and star polymers (Đ = Mw /Mn = 1.03-1.28) up to Mn = 3.9 × 105 and monomer conversion = 80%, where Mn and Mw are the number- and weight-average molecular weights, respectively. Even at high degrees of polymerization (DPs > 2000), this technique still features excellent control over molecular weights and Đ values, indicating the living character. The macroinitiators prepared at DP = 2000 are subsequently used for block polymerizations at high DPs (>2000) with functional methacrylates, yielding linear A-B diblock, linear B-A-B triblock, and 3-arm star A-B diblock copolymers, suggesting the excellent block efficiency of macroinitiators synthesized at a high DP value (=2000). This mild organocatalyzed living radical polymerization technique can enhance the livingness of propagation radicals and kinetic chain length at high monomer conversions for monomers with moderate propagation rate coefficients (kp s), reduce the persistent radical effect as much as possible, and hence enable HMWPs without the presence of metal catalyst, exogenous initiator, or harsh equipment. The obtained amphiphilic block copolymers present unique microphase separation behavior, and hold great potential in advanced materials applications, for example, thermosensitive nanocarriers.

Catalytic effect of DMSO in metal‐catalyzed radical polymerization mediated by disproportionation facilitates living and immortal radical polymerizations

AbstractDMSO, an interesting solvent for copper‐catalyzed living radical polymerization (LRP) mediated by disproportionation, does not exhibit the greatest disproportionation of Cu(I)X into Cu(0) and Cu(II)X2. Under suitable conditions, DMSO provides 100% conversion and absence of termination, facilitating the development of complex‐architecture methodologies by living and immortal polymerizations. The mechanism yielding this level of precision is being investigated. Here we compare Cu(0)‐wire‐catalyzed LRP of methyl acrylate mediated by disproportionating ligands tris(2‐dimethylaminoethyl)amine, Me6‐TREN, tris(2‐aminoethyl)amine, TREN, and Me6‐TREN/TREN = 1/1 in presence of eight disproportionating solvents, some more efficient than DMSO in disproportionation. Unexpectedly, we observed that all solvents increased the rate of polymerization when monomer concentration decreased. This reversed trend from that of conventional LRPs demonstrates catalytic effect for disproportionating solvents. Above a certain concentration, the classic concentration‐rate dependence was observed. The external order of reaction of the apparent rate constant of propagation, kpapp on solvent concentration demonstrated the highest order of reaction for the least disproportionating DMSO. Of all solvents investigated, DMSO has the highest ability to stabilize Cu(0) nanoparticles and therefore, yields the highest activity of Cu(0) nanoparticles rather than their greatest concentration. The implications of the catalytic effect of solvent in this and other reactions were discussed.

Adhesive Gel System Growable by Reversible Addition–Fragmentation Chain Transfer (RAFT) Polymerization

Gel materials are materials with high elasticity that deform when stressed and then return to their original shapes once the stress is removed. Gel materials are expected to be used in artificial living tissues, soft robotics, sensors, and so on. On the other hand, humans grow and change their bodies and characteristics over time. In this research, we developed an adhesive gel system that can grow and change its characteristics like our humans after adhesion through reversible addition–fragmentation chain transfer (RAFT) polymerization, a class of living radical polymerization. The adhesive joint grown by RAFT polymerization had higher adhesive strength than the non-RAFT-polymerized adhesive joint and a function, i.e., thermal responsiveness of adhesive strength. The environment around us changes over time. These growable adhesive gel systems should enable us to use gel materials for a long time while adapting their structures and characteristics to environmental changes.

Thermoresponsive star-shaped polymer with heteroarm type with methacrylates: preparation by living radical polymerization method and its topological effect

Thermoresponsive star-shaped polymer with heteroarm type with methacrylates was prepared by living radical polymerization method with ruthenium catalyst. The effect of the arm structures was also investigated.

Synthesis and Application of Amphiphilic Block Copolymer

The amphiphilic di- and tri-block copolymer is widely used to solve many seemingly intractable problems in our lives. They have the potential to help curing the cancel and some of them already in clinical application. Besides, it can work as a stabilizer of dispersions to disperse insoluble substance in certain solvents to make the substance work better. After decades of scientists’ exploring, the living polymerization have been frequently used in living polymerization. In addition, the simple and efficient methods laying the foundation of the various application of amphiphilic di/tri-block copolymer. In this research, the living radical polymerization, such as reversible deactivation radical polymerization (RDRP) and ring-opening metathesis polymerization (ROMP), are mentioned. And the living anionic polymerization is the main approach synthesize a diverse of different block copolymers, where the reaction mechanism is further discussed in this research. After analyzing the properties of amphiphilic di- and tri-block copolymer to find why it can be used for drug delivery and as a stabilizer of dispersions, some applications for amphiphilic di- and tri-block copolymers will be introduced. With such advanced synthesis methods, however, the application of amphiphilic block copolymer is mainly in drug delivery. As a result, there might be some potential applications for amphiphilic di- and tri-block copolymer.

Colloidal Crystals of Charged-Polymer-Brush-Decorated Hybrid Particles in Low-Polarity Solvents

Colloidal crystals are self-assembled systems that are suitable as models for studying crystallization; they are also attractive as nanostructures with a periodic arrangement of materials that have different refractive indices. Here, we present a method of constructing colloidal crystals in an organic solvent using charged-polymer-brush-decorated core-shell-type hybrid particles synthesized by surface-initiated living radical polymerization. The core-shell-type hybrid particles consisted of a silica particle core surrounded by a shell of polymer brushes obtained by the polymerization of methyl methacrylate and a small amount of a cationic monomer, [2-(methacryloyloxy)ethyl]trimethylammonium chloride. When the core-shell-type hybrid particles were dispersed in a low-polarity solvent with a dielectric constant of ∼11, colloidal crystals formed when the particle volume fraction exceeded a certain threshold, and remarkably, the interparticle distance in the colloidal crystal reached more than several micrometers under certain colloidal crystallization conditions. The colloidal crystallization behavior depended upon the surface charge density of the hybrid particles, ionic strength of the suspension, and dielectric constant of the solvent. The proposed method to construct colloidal crystals using electrostatic interactions between charged polymer brushes will promote the development of systems exhibiting particle self-assembly.

Well-Defined pH-Sensitive Self-Assembled Triblock Copolymer-Based Crosslinked Micelles for Efficient Cancer Chemotherapy

Delivery of chemotherapeutics to cancer cells using polymeric micelles is a promising strategy for cancer treatment. However, limited stability of micelles, premature drug release and off-target effect are the major obstacles that restrict the utilization of polymeric micelles as effective drug delivery systems. In this work, we addressed these issues through the innovative design of targeted pH-sensitive crosslinked polymeric micelles for chemotherapeutic delivery. A well-defined triblock copolymer, poly(ethylene glycol)-b-poly(2-hydroxyethyl methacrylate)-b-poly(butyl acrylate) (PEG-b-PHEMA-b-PBA), was synthesized by living radical polymerization, and then modified by using 4-pentenoic anhydride to incorporate pendant crosslinkable alkene groups in the middle block. The resulting copolymer underwent self-assembly in aqueous solution to form non-crosslinked micelles (NCMs). Subsequently, intramicellar thiol-ene crosslinking was performed by using 1,4-butanediol bis(3-mercaptopropionate) to give crosslinked micelles (CMs) with pH-sensitive crosslinks. The targeted CM (cRGD-DOX10-CM5) was readily prepared by using tumor-targeting ligand cyclo(Arg-Gly-Asp-D-Phe-Cys) (cRGD) together with the 1,4-butanediol bis(3-mercaptopropionate) during the crosslinking step. The study of cumulative DOX release revealed the pH-sensitive feature of drug release from these CMs. An in vitro MTT assay revealed that NCMs and CMs are biocompatible with MCF 10A cells, and the samples exhibited significant therapeutic efficiency as compared to free DOX. Cellular uptake studies confirmed higher uptake of cRGD-DOX10-CM5 by MCF 10A cancer cells via cRGD-receptor-mediated endocytosis as compared to the corresponding analogues without cRGD. These results indicate that such pH-responsive crosslinked PEG-b-PHEMA-b-PBA-based micelles are therapeutically effective against cancer cells and hold remarkable promise to act as smart drug delivery systems for cancer therapy.

Hydrogen bond-containing oligomer as a facile interfacial mediator in rubber/silica composites

Silica is one of the most important reinforcements in the rubber industry due to its indispensable applications in green tires. However, the significant difference in polarity between conventional diene rubber and silica generally results in poor silica dispersion and, hence, considerably compromises the overall performance of the composites. Herein, a poly (hydroxyethyl methacrylate) oligomer was synthesized via living radical polymerization using disulfiram as an iniferter. Upon thermal activation, the oligomer can further divide into macroradicals that are capable of directly grafting onto the unsaturated moieties in the rubber skeleton. Therefore, the pendant ester and hydroxyl functionalities can interact with silanol groups on the silica surface through interfacial hydrogen bonding, which significantly improves the interfacial interaction and facilitates the dispersion of silica. Accordingly, incorporating a small amount of oligomer (less than 3.5 wt%) can achieve a remarkable improvement in the tensile modulus and rolling and wet skid resistances of the obtained composites. We envisage that the present reactive oligomer can provide an effective strategy toward in situ modification of the rubber skeleton, which also has significant potential to optimize the static and dynamic performance of rubber/silica composites for tire tread applications.

Preparation of a magnetocaloric dual-response SiO2-based green nano-emulsifier by an SET-LRP method and evaluation of its properties

In recent years, intelligent nano-emulsifiers have received extensive attention in various fields. In this study, core–shell–shell nanoparticles (Fe3O4@SiO2@PNIPAM) showing magnetic and thermal responsiveness have been successfully prepared as a green nano-emulsifier by single-electron-transfer living radical polymerization (SET-LRP). The emulsifying properties of Fe3O4@SiO2@PNIPAM with different PNIPAM contents in toluene/water systems and the magnetic and thermal responsiveness of Pickering emulsions have been mainly investigated. The research shows that when the content of PNIPAM is higher, Fe3O4@SiO2@PNIPAM has the strongest emulsifying power and the Pickering emulsion is the most stable. After applying a magnet field outside the emulsion, Fe3O4@SiO2@PNIPAM nanoparticles can be separated rapidly, which leads to emulsion demulsification. When the temperature is above the low critical solution temperature (LCST), the PNIPAM chain shrinks and the Pickering emulsion is demulsified. When the temperature returns below the LCST, the emulsion is emulsified again, and a stable emulsion can still be formed. Therefore, the Pickering emulsion made by Fe3O4@SiO2@PNIPAM as an intelligent and efficient green nano-emulsifier can be converted between emulsified state and demulsified state by the control of magnetic field and temperature. These provide a wide range of ideas for Pickering emulsion recycling, industrial oil-containing wastewater separation and enhanced oil recovery.

Production and 3D Printing of a Nanocellulose-Based Composite Filament Composed of Polymer-Modified Cellulose Nanofibrils and High-Density Polyethylene (HDPE) for the Fabrication of 3D Complex Shapes

This work aims to produce a 3D-printable bio-based filament composed of high-density polyethylene (HDPE) and chemically modified cellulose nanofibrils. Printing using HDPE as a raw material is challenging due to its massive shrinkage and warping problems. This paper presents a new method to overcome those difficulties by enhancing the mechanical properties and achieving better print quality. This was achieved using modified cellulose nanofibrils (CNFs) as fillers. Firstly, CNF was converted to a CNF-based macroinitiator through an esterification reaction, followed by a surface-initiated single-electron transfer living radical polymerization (SI-SET-LRP) of the hydrophobic monomer stearyl acrylate. Poly stearyl acrylate-grafted cellulose nanofibrils, CNF-PSAs, were synthesized, purified and characterized with ATR-FTIR, 13C CP-MAS NMR, FE-SEM and water contact angle measurements. A composite was successfully produced using a twin-screw extruder with a CNF-PSA content of 10 wt.%. Mechanical tests were carried out with tensile testing. An increase in the mechanical properties, up to 23% for the Young’s modulus, was observed. A morphologic analysis also revealed the good matrix/CNF compatibility, as no CNF aggregates could be observed. A reduction in the warping behavior for the composite filament compared to HDPE was assessed using a circular arc method. The 3D printing of complex objects using the CNF-PSA/HDPE filament resulted in better print quality when compared to the object printed with neat HDPE. Therefore, it could be concluded that CNF-PSA was a suitable filler for the reinforcement of HDPE, thus, rendering it suitable for 3D printing.

Construction of pH-responsive nanoplatform from stable magnetic nanoparticles for targeted drug delivery and intracellular imaging

Currently, developing responsive hydrophobic drug delivery systems centered on magnetic nanoparticles is a promising approach for the efficient delivery of hydrophobic drugs to living cells. Here, an efficacious designed strategy was proposed to construct pH-responsive nanoplatform for targeted hydrophobic drug delivery based on the formation of surface-anchored targeting molecules on the surface of Fe3O4 @C via single electron transfer living radical polymerization (SET-LRP) method. First, we prepared polymer-modified Fe3O4 @C using 4-vinylphenylboronic acid (VB) and polyethylene glycol methyl ether methacrylate (PEGMA) as polymerized monomers and confirmed that Fe3O4 @C-VB-PEGMA had high biocompatibility and low cytotoxicity. Next, we prepared curcumin-containing Fe3O4 @C-VB-PEGMA-Cur nanoplatform with an encapsulation efficiency for Cur as high as 67.7%. Furthermore, the nanoplatform not only displayed pH-responsive release behaviors of Cur under different pH values (pH=7.2, 6.5, 5.4), but also can be effectively targeted into HepG2 cells. More importantly, the nanoplatform also exhibited effectively inhibiting the growth of HepG2 cells and continuously intracellular imaging by the targeted releasing of loaded Cur. It is envisaged that these findings are a step forward in the construction of pH-responsive platform as a tool for clinical hydrophobic drug delivery.

Pd-Mediated Light-Controlled Living Radical Polymerization of Methyl Acrylate

Abstract The radical polymerization of methyl acrylate in the presence of a palladium dimer complex and ethyl iodoacetate as an initiator under photoirradiation conditions led to the formation of poly(methyl acrylate) having good Ð values. The polymerization could be controlled by switching the light on and off, exhibiting living characteristics. We propose that such α-Pd polyesters could function as dormant species, which would allow a pair of transient α-keto radicals and persistent Pd radicals to be generated upon photoirradiation.