Atom Transfer Radical Polymerization Technique Research Articles

On the way to increase osseointegration potential: Sequential SI-ATRP as promising tool for PEEK-based implant nano-engineering

In the search of the ideal bone implant material, surface initiated atom transfer radical polymerization (SI-ATRP) techniques were successfully employed to modify the polyetheretherketone (PEEK) surface with complex architecture nanolayers featuring hydrophilic poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) or poly(2-hydroxyethyl methacrylate) (PHEMA) branches. As a result, polymer layers with height up to over 300 nm were synthesized to decrease the water contact angle from 92.8° to 23.0°. In-depth analysis of layer topography, structure and elemental composition realized with atomic force microscopy (AFM), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), time-of-flight secondary ions mass spectroscopy (TOF-SIMS) and X-ray photon spectroscopy (XPS) confirmed successful surface modification. Additionally, to demonstrate the applicability of proposed PEEK functionalization, the biomineralization assay in simulated body fluid (SBF) solution was conducted. The high density of hydroxyl and amine groups in branched polymer brushes structure enhanced the rate of hydroxyapatites (HAp) formation substantially. Compared to untreated PEEK, modification with polymer brushes resulted in the creation of cauliflower-like structures with high specific surface area and Ca/P ratio equal to 1.83–1.87 for PEEK grafted with brushes composed of PHEMA backbone segment and PDMAEMA or PHEMA as block polymer branches (PEEK-g-PHEMA-g-PDMAEMA or PEEK-g-PHEMA-g-PHEMA) after 2 weeks. Finally, the process of the hydroxyapatite formation and increase of the layer thickness in a range of 14 days to 6 weeks of immersion in SBF was thoroughly visualized by scanning electron microscopy (SEM).

Surface Functionalization with Polymer Brushes via Surface-Initiated Atom Transfer Radical Polymerization: Synthesis, Applications, and Current Challenges.

Polymer brushes have received great attention in recent years due to their distinctive properties and wide range of applications. The synthesis of polymer brushes typically employs surface-initiated atom transfer radical polymerization (SI-ATRP) techniques. To realize the control of the polymerization process in different environments, various SI-ATRP techniques triggered by different stimuli have been developed. This review focuses on the latest developments in different stimuli-triggered SI-ATRP methods, such as electrochemically mediated, photoinduced, enzyme-assisted, mechanically controlled, and organocatalyzed ATRP. Additionally, SI-ATRP technology triggered by a combination of multiple stimuli sources is also discussed. Furthermore, the applications of polymer brushes in lubrication, biological applications, antifouling, and catalysis are also systematically summarized and discussed. Despite the advancements in the synthesis of various types of 1D, 2D, and 3D polymer brushes via controlled radical polymerization, contemporary challenges remain in the quest for more efficient and straightforward synthetic protocols that allow for precise control over the composition, structure, and functionality of polymer brushes. We anticipate the readers could promote the understanding of surface functionalization based on ATRP-mediated polymer brushes and envision future directions for their application in surface coating technologies.

A new starch-based adhesive material containing diblock branches for sizing cotton and cotton/polyester

A new starch macroinitiator (dibromopropyl etherified starch, DPES) with two active sites per dibromopropyl substituent, was successfully prepared and then conducted a two-step graft polymerization with EMA and AA, respectively, to prepare new grafted starch (DPES-g-poly(ethyl methacrylate)-b-poly(acrylic acid), DPES-g-PEMA-b-PAA) samples using the electron transfer atom transfer radical polymerization (ARGET ATRP) technique in an aqueous medium. The DPES-g-PEMA-b-PAA had excellent adhesion to cotton and cotton/polyester roving. As the grafting ratios increased from 0 to 9.346%, gradually promoted adhesion forces from 61.3 N to 76.8 N for cotton roving and from 91.2 N to 123.0 N for cotton/polyester roving were presented. In addition, the DPES-g-PEMA-b-PAA possessed lower film crystallinity and brittleness as well as higher viscosity compared with ATS. Based on these results, the DPES-g-PEMA-b-PAA with a total grafting ratio of 9.346% was concluded as a new adhesive material in the application of sizing cotton and cotton/polyester warps.

Aggregation‐induced emission polymers via reversible‐deactivation radical polymerization

AbstractAggregation‐induced emission (AIE) is a unique phenomenon whereby aggregation of molecules induces fluorescence emission as opposed to the more commonly known aggregation‐caused quenching (ACQ). AIE has the potential to be utilized in the large‐scale production of AIE‐active polymeric materials because of their wide range of practical applications such as stimuli‐responsive sensors, biological imaging agents, and drug delivery systems. This is evident from the increasing number of publications over the years since AIE was first discovered. In addition, the ever‐growing interest in this field has led many researchers around the world to develop new and creative methods in the design of monomers, initiators and crosslinkers, with the goal of broadening the scope and utility of AIE polymers. One of the most promising approaches to the design and synthesis of AIE polymers is the use of the reversible‐deactivation radical polymerization (RDRP) techniques, which enabled the production of well‐controlled AIE materials that are often difficult to achieve by other methods. In this review, a summary of some recent works that utilize RDRP for AIE polymer design and synthesis is presented, including (i) the design of AIE‐related monomers, initiators/crosslinkers; the achievements in preparation of AIE polymers using (ii) reversible addition–fragmentation chain transfer (RAFT) technique; (iii) atom transfer radical polymerization (ATRP) technique; (iv) other techniques such as Cu(0)‐RDRP technique and nitroxide‐mediated polymerization (NMP) technique; (v) the possible applications of these AIE polymers, and finally (vi) a summary/perspective and the future direction of AIE polymers.

A Novel Silica Hybrid Nanoparticle with Zwitterion-Functionalized Polymer Chains for Highly Efficient N-Glycan Enrichment

N-Glycosylation is one of the most common and important protein posttranslational modifications. Structural aberrations of the N-glycans branching from glycoproteins are closely related to various disease occurrences and progressions. Therefore, global systematic identification of disease-related N-glycans not only largely facilitates the understanding of their cellular functions but also promotes the development of new diagnostic and therapeutic biomarkers. However, N-glycans are low in abundance and hydrophilic, thereby hindering high-throughput, and large-scale N-glycan analysis and N-glycoproteome research. Here, a zwitterion-functionalized polymer brush-grafted silica hybrid hydrophilic material (poly-SBMA-S) was fabricated by in situ growth of polymeric [2-(methacryloyloxy)ethyl]dimethyl(3-sulfopropyl)ammonium hydroxide (SBMA) chains on porous silica particles through a surface-initiated atom transfer radical polymerization technique, and it was used as a new stationary phase for highly selective N-glycan enrichment. Human plasma demonstrated 64 N-glycans due to the densely packed polyzwitterion chains and the significantly increased coverage of hydrophilic binding sites, demonstrating the high potential of the new hydrophilic matrix in the profiling and analysis of N-glycans and other hydrophilic targets.

Hydration and dehydration behaviors of poly(N-isopropylacrylamide)-grafted silica beads

The use of poly(N-isopropyl acrylamide) (PNIPAAm) in thermoresponsive interfaces for biomedical applications has been extensively investigated. Understanding the hydration and dehydration characteristics of PNIPAAm-grafted interfaces is crucial for the development of highly functional thermoresponsive interfaces. In this study, four PNIPAAm-grafted silica beads were prepared using atom transfer radical polymerization and radical polymerization techniques, with varying amounts of PNIPAAm grafted onto the beads. These PNIPAAm-grafted silica beads were used as samples, and their hydration and dehydration behaviors were analyzed using FTIR spectroscopy. Through the analysis of FTIR spectra obtained from the PNIPAAm-grafted silica beads prepared in this study, distinct observations were made under varying relative humidity and temperature conditions. Specifically, an elevation in the peak intensity of the broad peak at 3700–3000 cm−1, associated with the O-H group of hydrated water on PNIPAAm, was noted at higher humidity levels at 10°C. This increase in humidity resulted in an amplified peak intensity at 3700–3000 cm−1, indicative of the presence of the hydrated water molecules bonded to the PNIPAAm. Concurrently, shifts in the amide I and II peaks were observed with increasing relative humidity, signifying enhanced hydration and increased hydrogen bonding to C=O and N-H groups. Conversely, increasing the temperature at relatively high humidity led to a decreased in the intensity of the broad peak at 3700–3000 cm−1; this was attributed to the dehydration of the grafted PNIPAAm and subsequent water loss. The dehydration of PNIPAAm resulted in significant peak shifts for the amide I and II peaks, indicating a decrease in hydrogen bonding with the amide group. A significant change in peak intensity and shifts were evident, underscoring PNIPAAm brush's heightened propensity for hydration. These findings confirm the effectiveness of FTIR spectroscopy as a valuable approach for studying the hydration and dehydration behaviors of thinly grafted PNIPAAm layers on substrates.

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.

Synthesis and Characterization of Spirocyclic Mid-Block Containing Triblock Copolymer

Polymers containing cyclic derivatives are a new class of macromolecular topologies with unique properties. Herein, we report the synthesis of a triblock copolymer containing a spirocyclic mid-block. To achieve this, a spirocyclic polystyrene (cPS) mid-block was first synthesized by atom transfer radical polymerization (ATRP) using a tetra-functional initiator, followed by end-group azidation and a copper (I)-catalyzed azide-alkyne cycloaddition reaction. The resulting functional cPS was purified using liquid chromatography techniques. Following the esterification of cPS, a macro-ATRP initiator was obtained and used to synthesize a poly (methyl methacrylate)-block-cPS-block-poly (methyl methacrylate) (PMMA-b-cPS-b-PMMA) triblock copolymer. This work provides a synthetic strategy for the preparation of a spirocyclic macroinitiator for the ATRP technique and as well as liquid chromatographic techniques for the purification of (spiro) cyclic polymers.

CO2 and Magnetic Dual-Responsive Microspheres That Reversibly and Selectively Capture Target Proteins under Mild Conditions

CO2-responsive polymers transform from hydrophobic to hydrophilic under a gas stimulus, which can be used to capture proteins under mild conditions; however, the selectivity is not high enough. In this work, Fe3O4 enveloped with silicon dioxide (SiO2) was prepared and grafted on poly(2-(diethylamino)ethyl methacrylate) (PDEA) through the atom transfer radical polymerization (ATRP) technique, yielding a CO2-responsive magnetic microsphere. The molecularly imprinted surface was then fabricated using poly(dopamine) (PDA) with bovine serum albumin (BSA) as a template, producing gas and magnetic dual-responsive microspheres with good selectivity, denoted as Fe3O4/SiO2/PDEA-MIP. Their chemical structure and CO2 responsiveness were confirmed. Their adsorption capacity for BSA was 55 mg g–1 under the concentration of 0.8 mg mL–1 with good reversibility. The imprinting factor (IF) reached as high as 5.73 under optimized adsorption conditions, which further makes it specifically capture the target protein from a mixture and separate the protein under gas or magnetic control. The interaction between BSA with unprotonated and protonated PDEA was theoretically studied by quantum mechanics calculations, which prove its reversibility under the CO2 stimulus. Furthermore, the circular dichroism (CD) spectra approved that the conformation of proteins remained unchanged under the CO2 stimulus, indicating that it is a moderate separation technique for proteins. This work supplied a strategy to develop highly selective and switchable materials to realize protein recognition and separation under mild conditions.

Conducting Polymer-Infused Electrospun Fibre Mat Modified by POEGMA Brushes as Antifouling Biointerface.

Biofouling on surfaces, caused by the assimilation of proteins, peptides, lipids and microorganisms, leads to contamination, deterioration and failure of biomedical devices and causes implants rejection. To address these issues, various antifouling strategies have been extensively studied, including polyethylene glycol-based polymer brushes. Conducting polymers-based biointerfaces have emerged as advanced surfaces for interfacing biological tissues and organs with electronics. Antifouling of such biointerfaces is a challenge. In this study, we fabricated electrospun fibre mats from sulphonated polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (sSEBS), infused with conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) (sSEBS-PEDOT), to produce a conductive (2.06 ± 0.1 S/cm), highly porous, fibre mat that can be used as a biointerface in bioelectronic applications. To afford antifouling, here the poly(oligo (ethylene glycol) methyl ether methacrylate) (POEGMA) brushes were grafted onto the sSEBS-PEDOT conducting fibre mats via surface-initiated atom transfer radical polymerization technique (SI-ATRP). For that, a copolymer of EDOT and an EDOT derivative with SI-ATRP initiating sites, 3,4-ethylenedioxythiophene) methyl 2-bromopropanoate (EDOTBr), was firstly electropolymerized on the sSEBS-PEDOT fibre mat to provide sSEBS-PEDOT/P(EDOT-co-EDOTBr). The POEGMA brushes were grafted from the sSEBS-PEDOT/P(EDOT-co-EDOTBr) and the polymerization kinetics confirmed the successful growth of the brushes. Fibre mats with 10-mers and 30-mers POEGMA brushes were studied for antifouling using a BCA protein assay. The mats with 30-mers grafted brushes exhibited excellent antifouling efficiency, ~82% of proteins repelled, compared to the pristine sSEBS-PEDOT fibre mat. The grafted fibre mats exhibited cell viability >80%, comparable to the standard cell culture plate controls. Such conducting, porous biointerfaces with POEGMA grafted brushes are suitable for applications in various biomedical devices, including biosensors, liquid biopsy, wound healing substrates and drug delivery systems.

A specific sensor system based on in-situ synthesis fluorescent polymers by ARGET ATRP achieving sensitive exosome detection

Exosomes, as a kind of tumor biomarker, are often found at elevated levels above normal in the blood of cancer patients, making highly sensitive exosome testing important for monitoring the development and progression of cancer. In this work, an ultra-sensitive and specific fluorescence method for exosome assays was constructed on the basis of atom transfer radical polymerization (ATRP) technique. Firstly, two recognition units, the CD63 aptamer and the EGFR antibody, can specifically bind to exosomes to form a sandwich structure, which endows the proposed sensor with excellent selectivity through two specific recognitions. Secondly, activator regenerated by electron transfer ATRP (ARGET ATRP) polymerization amplification method can introduce a huge amount of the fluorescent monomers into the sensing system, leading to a marked rise in sensitivity. Under optimal experimental conditions, a clear linear relationship between the logarithm of the fluorescence intensity and the concentration of exosomes in the range of 5 × 104 exosomes/mL to 5 × 109 exosomes/mL was obtained. The limit of detection (LOD) was as low as 11,610 exosomes/mL. Furthermore, this sensor exhibited good selectivity and stability, and excellent immunity to interference, providing a new method for the detection of exosomes. The exosome detection strategy used in this system provides a new idea for effective detection of lung cancer at an early stage.

One-step synthesis and characterization of the block-graft terpolymer via simultaneous atom transfer radical polymerization (ATRP) and ring-opening polymerization (ROP) techniques

One-step synthesis and characterization of the block-graft terpolymer via simultaneous atom transfer radical polymerization (ATRP) and ring-opening polymerization (ROP) techniques

2‐(N‐3‐Sulfopropyl‐N,N‐dimethyl ammonium)ethyl methacrylate modified graphene oxide embedded into cellulose acetate ultrafiltration membranes for improved performance

AbstractN‐(3‐sulfopropyl)‐N‐(methacryloxyethyl)‐N,N‐dimethylammonium betaine (SBMA) modified graphene oxide composite used as a filler in the fabrication of a nanocomposite cellulose acetate membrane was grafted through reverse atom transfer radical polymerization (RATRP) technique from a GO‐Br precursor. All the prepared materials (GO, GO‐Br, PSBMA@GO) were characterized using a combination of FTIR, BET, TEM, TGA, RAMAN, and XRD. The effect of different GO and PSBMA@GO contents on cellulose acetate membranes was investigated using AFM, contact angle measurements and SEM techniques. The surface hydrophilicity of the fabricated membranes increased with increasing content of PSBMA@GO filler through the water contact angle method. The relative flux of the base membrane at 900 kPa was 66.6 L.m−2.h−1 compared to that of PSBMA@GO composite membrane (0.5 wt%) at 117.67 L.m−2.h−1. The addition of the PSBMA@GO composites resulted in increased fouling resistance with high‐flux recovery (93%) and low‐overall flux decrease ratios (0.01%). Furthermore, nanocomposite membranes exhibited higher dye rejections for Congo Red (CR, 99.1% hence confirming their UF nature), methyl orange (MO, 84.2%) and methylene blue (MB, 95.3%) dyes compared with unmodified CA membranes. Overall, these nanocomposite membranes showed promising properties as potential candidates for dye removal in textile wastewater.

Expanding the use of affordable CuSO4·5H2O in ATRP techniques in homogeneous media

Advances in atom transfer radical polymerization (ATRP) are usually focused on reducing the metal catalyst concentration, using low toxicity metals or even metal-free catalysts, to minimize or avoid the contamination of polymers. In this work, the less toxic and inexpensive CuSO4·5H2O was used to replace CuBr2, the most employed metal source for ATRP, to control polymerizations under homogeneous conditions. Well-defined (Đ ≤ 1.3) hydrophobic homopolymers of poly(methyl acrylate) (PMA), poly(methyl methacrylate) (PMMA), polystyrene (PS) and poly(butyl acrylate) (PBA) were obtained in various organic solvent/water mixtures with similar control as when CuBr2 was used. The main limitation is the lower solubility of the CuSO4/L complex in pure organic solvents compared with CuBr2/L. The preparation of several hydrophilic polymers, namely poly(2-hydroxyethyl acrylate) (PHEA), poly((3-acrylamidopropyl)trimethylammonium chloride) (PAMPTMA), poly(2-hydroxyethyl acrylamide) (PHEAA), polyacrylamide (PAAm), poly(N,N-dimethylacrylamide) (PDMAA), poly(2-aminoethyl methacrylate hydrochloride) (PAMA), poly[oligo(ethylene oxide) methyl ether acrylate] (POEOA) and biorelevant block copolymers (PHEA-b-PAMPTMA and PAMPTMA-b-PHEAA) was successfully carried out in aqueous medium using different ATRP techniques. Future studies on this system will include the use of CuSO4/L complexes in several organic solvents and in heterogeneous ATRP.

Peptide-Modified Surfaces for Binding Carbamylated Proteins from Plasma.

Carbamylation of blood proteins is a common post-translational modification that occurs upon kidney dysfunction that is strongly associated with deleterious outcomes for patients treated using hemodialysis. In this study, we focused on the removal of two representative carbamylated plasma proteins, carbamylated albumin (cHSA) and fibrinogen (cFgn), through adsorption onto a surface functionalized with a specific peptide (cH2p1). Surfaces modified with poly(hydroxyethyl methacrylate) (p(HEMA)) were prepared using surface-initiated atom transfer radical polymerization (SI-ATRP) techniques and functionalized with cH2p1. cH2p1-functionalized surfaces showed selective binding toward cHSA and cFgn, compared to their native protein form, with NH-cH2p1 of superior selectivity than CO-cH2p1. The adsorption capacity of carbamylated protein on NH-cH2p1 was maintained in diluted plasma, and ultralow adsorption of native Fgn was observed. Similar to unmodified p(HEMA) surfaces, NH-cH2p1 showed a low platelet adhesion and activation, suggesting that the designed surface does not adversely affect platelets.

Enhanced Conductivity and Antibacterial Behavior of Cotton via the Electroless Deposition of Silver.

In this study, the surface-initiated atom transfer radical polymerization (SI-ATRP) technique and electroless deposition of silver (Ag) were used to prepare a novel multi-functional cotton (Cotton-Ag), possessing both conductive and antibacterial behaviors. It was found that the optimal electroless deposition time was 20 min for a weight gain of 40.4%. The physical and chemical properties of Cotton-Ag were investigated. It was found that Cotton-Ag was conductive and showed much lower electrical resistance, compared to the pristine cotton. The antibacterial properties of Cotton-Ag were also explored, and high antibacterial activity against both Escherichia coli and Staphylococcus aureus was observed.

New Photoresponsive Poly(meth)acrylates Bearing Azobenzene Moieties Obtained via ATRP Polymerization Exhibiting Liquid-Crystalline Behavior.

Here, we report our studies on photoresponsive poly(meth)acrylates containing azobenzene groups connected to a polymer backbone via a short methylene linker. A series of side-chain azobenzene polymers was synthesized via the atom transfer radical polymerization (ATRP) technique using several catalytic systems. The polymers synthesized under the optimized conditions were characterized by a narrow polydispersity (Đ ≤ 1.35), and they underwent a reversible transformation of their structure under light illumination. The fabricated polymers can store and release energy accumulated during the UV-light illumination by the thermal cis-trans isomerization of the chromophore groups. The enthalpy of the process (determined from DSC) was relatively high and equaled 61.9 J∙g−1 (17 Wh∙kg−1), indicating a high potential of these materials in energy storage applications. The liquid-crystalline behavior of the synthesized poly(meth)acrylates was demonstrated by the birefringent optical textures as observed in thin-films and X-ray scattering studies.

Photoluminescent folic acid functionalized biocompatible and stimuli-responsive nanostructured polymer brushes for targeted and controlled delivery of doxorubicin

In this work, the new photoluminescent and biocompatible folic acid (FA) conjugated stimuli-responsive nanostructured polymer brushes were designed, fabricated, and then evaluated as a doxorubicin (DOX) carrier. In this regard at first, graphene quantum dots (GQDs) were prepared through citric acid (CA) pyrolysis. In the following, the functionalization of GQDs with 3-aminopropyltriethoxysilane (APTS) and then α-bromoisobutyryl bromide (BIB) obtained the GQDs-Br, which have the ability to acts as a nano-based initiator. Subsequently, the N-isopropylacrylamide (NIPAM) and acrylated β-cyclodextrin (Ac-β-CD) monomers grown from the GQDs-Br surface as a block copolymer (GQDs-PNIPAM-co-PβCD) via atom transfer radical polymerization (ATRP) technique. Eventually, the conjugation with FA achieved the photoluminescent nanostructure copolymer brushes with targeted drug delivery capability (GQDs-PNIPAM-co-PβCD@FA). The synthesized samples were characterized through various characterization techniques. DOX was loaded via several possible interactions on GQDs-PNIPAM-co-PβCD@FA. The in vitro DOX release test exhibited 12% of DOX release in the simulated environment with the physiological condition while 43% of DOX released in the simulated cancer cells condition; confirm the pH sensitivity of the carrier. The in vitro biological tests displayed good stability, biodegradability, and biocompatibility of the prepared nanostructure. As well as, the higher efficiency of DOX@GQDs-PNIPAM-co-PβCD@FA in MDA-MB 231 cells killing compared to A 549 cells revealed the targeted drug delivery. The results demonstrated that the fabricated nanosystem could be a hopeful candidate for targeted breast cancer therapy with the inherent potential of imaging.

Surface Functionalization of Graphene Oxide with Polymer Brushes for Improving Thermal Properties of the Polymer Matrix

In this work, polymethyl methacrylate (PMMA) and polystyrene (PS) with controlled structures would be grafted on graphene material. The hybrid materials were prepared by coating graphene oxide (GO) with polydopamine (PDA) as a reactive underlayer and reducing agent, subsequently, surface-initiated polymerization of monomers (methyl methacrylate, styrene) based on the activators regenerated electron transfer atom transfer radical polymerization (ARGET-ATRP) technique. The polymer brush-modified graphene materials were then incorporated into the PMMA or PS matrix to get polymer nanocomposites with better thermal properties. The results of Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and thermal gravimetric analysis (TGA) demonstrated that PMMA and PS chains were successfully anchored on the surfaces of functionalized GO sheets. The influence of the grafted polymer brush-modified GO on thermal stability of PMMA and PS was investigated by a simultaneous thermal analyzer. Thermal conductivity of the polymer nanocomposite was determined by a conductive calorimeter. The results showed that thermal stability, glass transition temperature ( T g ), and thermal conductivity of the polymer nanocomposites were obviously improved compared with pure PMMA or PS.

Making ATRP More Practical: Oxygen Tolerance.

Atom-transfer radical polymerization (ATRP) is a well-known technique for the controlled polymerization of vinyl monomers under mild conditions. However, as with any other radical polymerization, ATRP typically requires rigorous oxygen exclusion, making it time-consuming and challenging to use by nonexperts. In this Account, we discuss various approaches to achieving oxygen tolerance in ATRP, presenting the overall progress in the field.Copper-mediated ATRP, which we first discovered in the late 1990s, uses a CuI/L activator that reversibly reacts with the dormant C(sp3)-X polymer chain end, forming a X-CuII/L deactivator and a propagating radical. Oxygen interferes with activation and chain propagation by quenching the radicals and oxidizing the activator. At ATRP equilibrium, the activator is present at a much higher concentration than the propagating radicals. Thus, oxidation of the activator is the dominant inhibition pathway. In conventional ATRP, this reaction is irreversible, so oxygen must be strictly excluded to achieve good results.Over the last two decades, our group has developed several ATRP techniques based on the concept of regenerating the activator. When the oxidized activator is continuously converted back to its active reduced form, then the catalytic system itself can act as an oxygen scavenger. Regeneration can be accomplished by reducing agents and photo-, electro-, and mechanochemical stimuli. This family of methods offers a degree of oxygen tolerance, but most of them can tolerate only a limited amount of oxygen and do not allow polymerization in an open vessel.More recently, we discovered that enzymes can be used in auxiliary catalytic systems that directly deoxygenate the reaction medium and protect the polymerization process. We developed a method that uses glucose oxidase (GOx), glucose, and sodium pyruvate to very effectively scavenge oxygen and enable open-vessel ATRP. By adding a second enzyme, horseradish peroxidase (HPR), we managed to extend the role of the auxiliary enzymatic system to generating carbon-based radicals and changed ATRP from an oxygen-sensitive to an oxygen-fueled reaction.While performing control experiments for the enzymatic methods, we noticed that using sodium pyruvate under UV irradiation triggers polymerization without the presence of GOx. This serendipitous discovery allowed us to develop the first oxygen-proof, small-molecule-based, photoinduced ATRP system. It has oxygen tolerance similar to that of the enzymatic methods, exhibits superior compatibility with both aqueous media and organic solvents, and avoids problems associated with purifying polymers from enzymes. The system was able to rapidly polymerize N-isopropylacrylamide, a challenging monomer, with a high degree of control.These contributions have substantially simplified the use of ATRP, making it more practical and accessible to everyone.