Reversible Addition-fragmentation Chain Transfer Research Articles

Multifunctional composite materials of rGO with RAFT initiated polymers with terminal amine or protonated amine functionalities for chemical eliminations HCHO and acidic pollutants at ambient conditions

In this paper, the contribution of self-assembled composite material of bifunctional polymer prepared by RAFT polymerization and rGO to the removal of low concentration HCHO and acids from air were systematically studied. Experimental results demonstrate that the condensation reaction between HCHO and the protonated amino group at the terminal of the rGO-py-pAMHS-NH3+-ph chain effectively can eliminate HCHO chemically, resulting in the release of H2O as the sole by-product following oxime bonds formation. rGO alone is incapable of chemically removing gaseous HCHO, but when combined with the py-pAMHS-NH3+-ph, efficient HCHO conversion can be achieved, well elucidating the remarkable HCHO removal capability via rGO-py-pAMHS-NH3+-ph. The HCHO chemical removal performance of composite is evaluated by a self-made device at the 1000 mL/min N2 velocity under 25 °C and 50 % RH and it is found that 206.41 mg of HCHO can be removed in approximately 4 h by using 1.0 g of rGO-py-pAMHS-NH3+-ph. In addition, cycling experiments demonstrate the rGO-py-pAMHS-NH3+-ph possesses good durability. We also find that the rGO-py-pAMHS-NH2-ph has the ability to remove acids when the terminal protonated amino groups have been converted into amine functionalities. This green and zero-carbon emission methodology for chemical removal of HCHO degradation and acid pollutants could provide valuable reference for developing other efficient strategies to remove other pollutants such as VOCs etc.

Light-Controlled Cationic RAFT Polymerization of Vinyl Ethers Using N-Arylacridinium Photocatalysts

Light-Controlled Cationic RAFT Polymerization of Vinyl Ethers Using <i>N</i>-Arylacridinium Photocatalysts

Photo‐controllable cationic homopolymerization and random copolymerization of vinyl ethers based on iridium salt photocatalyst

AbstractTemporal control of chain growth is a central challenge for photoinitiated active polymerization. In this work, we introduced an iridium salt complex‐based catalyst system to achieve fine temporal control of the chain growth process. By electrochemical analysis, compared with the pyran salt photocatalyst, it was found that the iridium salt complex could promote the chain transfer of active species to reversible addition‐fragmentation chain transfer polymerization (RAFT) reagent, thereby generating dormant species, which provided the possibility of time control of the polymerization process. Using this catalytic system, we successfully achieved homopolymerization of vinyl ethers with different substituents and random copolymerization with isobutyl vinyl ethers, which is not only pointed the way for broadening the monomer selection in the future, but also provided an innovative way to prepare new functionalized materials.

Influence of Polymer Side Chain Size and Backbone Length on the Self-Assembly of Supramolecular Polymer Bottlebrushes.

Hydrogen bonds are a versatile tool for creating fibrous, bottlebrush-like assemblies of polymeric building blocks. However, a delicate balance of forces exists between the steric repulsion of the polymer chains and these directed supramolecular forces. In this work we have systematically investigated the influence of structural parameters of the attached polymers on the assembly behaviour of benzene trisurea (BTU) and benzene tris(phenylalanine) (BTP) conjugates in water. Polymers with increasing main chain lengths and different side chain sizes were prepared by reversible addition-fragmentation chain-transfer (RAFT) polymerization of hydroxyethyl acrylate (HEA), tri(ethylene glycol) methyl ether acrylate (TEGA) and oligo(ethylene glycol) methyl ether acrylate (OEGA). The resulting structures were analyzed using small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). Both BTU and BTP formed fibres with PHEA attached, but a transition to spherical morphologies was observed at degrees of polymerisation (DP) of 70 and above. Overall, the main chain length appeared to be a dominating factor in inducing morphology transitions. Increasing the side chain size generally had a similar effect but mainly impeded any aggregation as is the case of POEGA. Interestingly, BTP conjugates still formed fibres, suggesting that the stronger intermolecular interactions can compensate partially for the steric repulsion.

Synthesis of block macro-CTAs by HNTs@Cu-catalyzed click reaction: Suitable CTAs for synthesizing multiblock polymers via RAFT polymerization

Multiblock copolymer macrochain-transfer agents (MBP-CTAs) can be used to synthesize MBPs in one pot via reversible addition-fragmentation chain-transfer (RAFT) polymerization. MBP-CTAs can be efficiently synthesized via a copper-catalyzed azide-alkyne cycloaddition reaction. However, traditional purification methods cannot sufficiently purify MBP-CTAs, resulting in the failure of RAFT. In this study, it was discovered that using a supported catalytic system, namely, Cu@A-HNTs, inhibited the connection between Cu and S. The residual Cu content in the MBP-CTA was successfully reduced to a low level (7.88 µg/mg). Then, hydrophilic and hydrophobic MBPs were synthesized through RAFT polymerization using the MBP-CTAs. Subsequently, multiblock copoly(methyl methacrylate-b-butyl methacrylate-CTA)s (PMMA-b-PBMA-c-CTA)s were successfully prepared. The MBP-CTAs and MBPs were characterized using ultraviolet–visible spectroscopy, 1H nuclear magnetic resonance, size-exclusion chromatography, matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry, differential scanning calorimetry measurements and uniaxial tensile tests. The results of performance testing of PMMA-b-PBMA-c-CTAs demonstrated that their fracture stress and strain significantly increased comparing with that of PMMA-b-CTAs.

Streamlining the Generation of Advanced Polymer Materials Through the Marriage of Automation and Multiblock Copolymer Synthesis in Emulsion.

Synthetic polymers are of paramount importance in modern life - an incredibly wide range of polymeric materials possessing an impressive variety of properties have been developed to date. The recent emergence of artificial intelligence and automation presents a great opportunity to significantly speed up discovery and development of the next generation of advanced polymeric materials. We have focused on the high-throughput automated synthesis of multiblock copolymers that comprise three or more distinct polymer segments of different monomer composition bonded in linear sequence. The present work has exploited automation to prepare high molar mass multiblock copolymers (typically>100,000 g mol-1) using reversible addition-fragmentation chain transfer (RAFT) polymerization in aqueous emulsion. A variety of original multiblock copolymers have been synthesised via a Chemspeed robot, exemplified by a multiblock copolymer comprising thirteen constituent blocks. Moreover, libraries of copolymers of randomized monomer compositions (acrylates, acrylamides, methacrylates, and styrenes), block orders, and block lengths were also generated, thereby demonstrating the robustness of our synthetic approach. One multiblock copolymer contained all four monomer families listed in the pool, which is unprecedented in the literature. The present work demonstrates that automation has the power to render complex and laborious syntheses of such unprecedented materials not just possible, but facile and straightforward, thus representing the way forward to the next generation of complex macromolecular architectures.

Poly(amino acid)-based drug delivery nanoparticles eliminate Methicillin resistant Staphylococcus aureus via tunable release of antibiotic

Bacterial infections threaten public health, and novel therapeutic strategies critically demand to be explored. Herein, poly(amino acid) (PAA)-based drug delivery nanoparticles (NPs) were designed for eliminating Methicillin resistant Staphylococcus aureus (MRSA) via tunable release of antibiotic. Using N-acryloyl amino acids (valine, valine methyl ester, aspartic acid, serine) as monomers, four kinds of amphiphilic PAAs were synthesized via photoinduced electron/energy transfer–reversible addition fragmentation chain-transfer (PET-RAFT) polymerization and were further assembled into nano-sized delivery systems. Their assemble behavior was drove mainly by hydrophobic/hydrophilic interaction, which determined the particle size, efficacy of drug loading and release; but numerous hydrogen bonding (HB) interaction also played an important role in regulating morphologies of the NPs and enriching drug-binding capacity. By changing the HB- and hydrophobic-interaction of the PAAs, the particle sizes (240.7 nm-302.7 nm), the drug loading efficiency (9.57%-19.76%), and the Rifampicin (Rif) release rate (49.6%-69.7%) of the PAA-based NPs could be tunable. Specially, the antimicrobial properties of the Rif-loaded NPs are found to be related to the release of Rif, which was determined by its hydrophobic interaction with hydrophobic blocks and HB interaction with hydrophilic blocks. These studies provide a new outlook for the design of delivery systems for the therapy of bacterial infection.

Preparation of diblock copolymer nano-assemblies by ultrasonics assisted ethanol-phase polymerization-induced self-assembly

Assemblies are widely used in biomedicine, batteries, functional coatings, Pickering emulsifiers, hydrogels, and luminescent materials. Polymerization-induced self-assembly (PISA) is a method for efficiently preparing particles, mainly initiated thermally. However, thermally initiated PISA usually requires a significant amount of time and energy. Here, we demonstrate the preparation of nano-assemblies with controllable morphologies and size using ultrasound (20 kHz) assisted ethanol-phase RAFT-PISA in three hours. Using poly (N, N-dimethylaminoethyl methacrylate) as the macromolecular reversible addition-fragmentation chain transfer agent (PDMA-CTA) to control the nucleating monomer benzyl methacrylate (BzMA), we obtained nano-assemblies with different morphologies. With the length of hydrophobic PBzMA block growth, the morphologies of the assemblies at 15 wt% solid content changed from spheres to vesicles, and finally to lamellae; the morphologies of the assemblies at 30 wt% changed from spheres micelles to short worms, then vesicles, and finally to large compound vesicles. With the same targeted degree of polymerization, nano-assemblies having a 30 wt% solid content display a more evolved morphology. The input of ultrasonic energy makes the system have higher surface free energy, results the mass fraction interval of solventphilic blocks (fhydrophilic) corresponding to the formation of spherical micelles is expanded from fhydrophilic > 45 % to fhydrophilic > 31 % under ultrasound and the fhydrophilic required to form worms, vesicles, and large composite vesicles decreases in turn. It is worth noting that the fhydrophilic interval of worms prepared by ultrasonics assisted PISA gets larger. Overall, the highly green, externally-regulatable and fast method of ultrasonics assisted PISA can be extended to vastly different diblock copolymers, for a wide range of applications.

Solvent effect on the self-assembly of polyisobutylene-based glycopolymers

Investigation of polymeric conformations in different solvents is critical because block copolymer solution morphology is not only associated with the architecture but also with its characteristic features which depend upon the solvent polarity. A series of double hydrophobic diblock copolymers comprising polyisobutylene (PIB) segment and varying sugar pendant units have been prepared by a combination of living cationic and reversible addition-fragmentation chain transfer (RAFT) polymerizations. After the deprotection of the acetate from sugar pendants, the synthesized water-soluble amphiphilic block copolymers showed morphological transformations in both aqueous and organic media. A conformational transition due to a change in solvent polarity from polar protic to nonpolar was supported by 1H NMR spectroscopy. The dynamic light scattering (DLS) experiments demonstrated that the hydrodynamic diameters of aggregates varied with solvent polarity. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) evidenced the morphological changes from micellar to tubular orientation. Finally, the self-assembly behavior of PIB-based glycopolymers due to changes in solvent polarity is proposed.

Phenanthroline Derived N-Doped Carbon Dots as Robust Metal-Free Photocatalysts for PET-RAFT Polymerization and Polymerization-Induced Self-Assembly.

Metal-free organic photocatalysts for photo-mediated reversible deactivation radical polymerization (photo-RDRP) are witnessed to make increasing advancement in the precise synthesis of polymers. However, challenges still exist in the development of high-efficiency and environmentally sustainable carbon dots (CDs)-based organocatalysts. Herein, N-doped CDs derived from phenanthroline derivative (Aphen) are prepared as metal-free photocatalysts for photoinduced electron transfer reversible addition-fragmentation chain transfer (PET-RAFT) polymerization. The introduction of phenanthroline structure enhances the excited state lifetime of CDs and expands the conjugated length of their internal structure to enable the light-absorption to reach green light region, thereby enhancing photocatalytic activity. The as-designed CDs exhibit unprecedented photocatalytic capacity in photopolymerization even in large-volume reaction (100mL) with high monomer conversion and narrow polymer dispersity (Mw/Mn < 1.20) under green light. The photocatalytic system is compatible with PET-RAFT polymerization of numerous monomers and the production of high molecular weight polyacrylate (Mn >250000) with exquisite spatiotemporal control. Above results confirm the potential of CDs as photocatalyst, which has not been achieved with other CDs catalysts used in photo-RDRP. In addition, the construction of fluorescent polymer nanoparticles using CDs as both photocatalyst and phosphor through photoinitiated polymerization-induced self-assembly (Photo-PISA) technology is successfully demonstrated for the first time.

Gem-bisphosphonic acid-based double hydrophilic block copolymers: RAFT synthesis and comparative assembly with gadolinium ions for the formation of MRI contrast agents

The synthesis of double hydrophilic block copolymers (DHBCs) with one block containing bisphosphonic acid groups was performed by aqueous RAFT polymerization with two approaches, either starting from a PEO-based macro-chain transfer agent (macro-CTA) or by chain extension of a RAFT-capped bisphosphonic acrylate homopolymer with oligo(ethylene glycol) methyl ether acrylate (OEGA). By complexation with gadolinium and europium ions, these polymers are prone to form hybrid polyionic complexes (HPICs) as evidenced by mono- and multi-angle DLS, TEM and luminescence measurements. The obtained HPICs showed better chemical stability at low pH values compared to previously reported counterparts based on carboxylic and monophosphonic acid groups (i.e., PEO-b-PAA and PEO-b-PVPA respectively). Due to their high relaxivity values, the proposed HPICs show potential as contrast agents for magnetic resonance imaging (MRI).

Synthesis via Reversible Addition–Fragmentation Chain Transfer Polymerization and Deep Control Property of Amphiphilic Self-assembled Poly(ethylene oxide)-block-polystyrene

Synthesis via Reversible Addition–Fragmentation Chain Transfer Polymerization and Deep Control Property of Amphiphilic Self-assembled Poly(ethylene oxide)-<i>block</i>-polystyrene

Synthesis and Thermo-Responsive Behavior of Poly(N-isopropylacrylamide)-b-Poly(N-vinylisobutyramide) Diblock Copolymer.

Thermo-responsive diblock copolymer, poly(N-isopropylacrylamide)-block-poly(N-vinylisobutyramide) was synthesized via switchable reversible addition-fragmentation chain transfer (RAFT) polymerization and its thermal transition behavior was studied. Poly(N-vinylisobutyramide) (PNVIBA), a structural isomer of poly(N-isopropylacrylamide) (PNIPAM) shows a thermo-response character but with a higher lower critical solution temperature (LCST) than PNIPAM. The chain extension of the PNVIBA block from the PNIPAM block proceeded in a controlled manner with a switchable chain transfer reagent, methyl 2-[methyl(4-pyridinyl)carbamothioylthio]propionate. In an aqueous solution, the diblock copolymer shows a thermo-responsive behavior but with a single LCST close to the LCST of PNVIBA, indicating that the interaction between the PNIPAM segment and the PNVIBA segment leads to cooperative aggregation during the self-assembly induced phase separation of the diblock copolymer in solution. Above the LCST of the PNIPAM block, the polymer chains begin to collapse, forming small aggregates, but further aggregation stumbled due to the PNVIBA segment of the diblock copolymer. However, as the temperature approached the LCST of the PNVIBA block, larger aggregates composed of clusters of small aggregates formed, resulting in an opaque solution.

Preparation of acrylate-cationic monomer block copolymers by RAFT and their flotation oil removal properties

With the development of oilfields, the liquid volume of oily wastewater gets larger. Thus, more efficient flotation agents must be developed. In this regard, cationic polyacrylates with amphiphilic structures are potentially efficient flotation agents. Many studies have explored the effect of monomer type on flotation performance. However, there is a lack of investigations on the effect of block sequences on flotation performance. In this paper, acrylates (including methyl acrylate (MA) and ethyl acrylate (EA)) and cationic monomers (including acryloxyethyl trimethyl ammonium chloride (DAC), methylacryloxyethyl trimethyl ammonium chloride (DMC) and acryloxyethyl benzyl dimethyl ammonium chloride (DBC)) were used as raw materials, random, diblock and triblock copolymers were prepared through free radical polymerization and reversible addition-fragmentation chain transfer (RAFT) polymerization. The effect of the copolymer sequence on flotation performance was studied, and triblock copolymer P(DBC-b-MA-b-DBC) had better flotation performance than those of other copolymers. The synthesis conditions of P(DBC-b-MA-b-DBC) were successively optimized using the single-factor and response surface methods, and the optimal synthesis conditions were obtained as follows: monomer concentration of 51 wt%, the first section m(DBC): the second section m(MA): the third section m(DBC) = 1.5:1:1.5, initiator concentration of 0.28 wt%, reaction time of each section of 2 h, and reaction temperature of 73 °C. Under flotation temperature of 25 °C, P(DBC-b-MA-b-DBC) concentration of 70 mg/L, aeration flow rate of 2.0 L/min and flotation time of 10 min, the oil removal of oily wastewater with initial oil content of 822 mg/L reached 96.5 %. The results of the study can provide reference for the research and development of oily wastewater treatment agents.

A self-cascade terpolymer platform for amplified chemo-chemodynamic therapy with synergistic immunogenic cell death enhancement

Chemodynamic therapy, which relies on the generation of cytotoxic radicals, can be amplified by a nanoplatform that produces hydroxyl radicals while also compromising natural radical scavenging mechanisms. For this purpose, a well-defined amphiphilic terpolymer, poly(oligo(ethylene glycol) monomethyl ether methacrylate)-block-poly(N,N-dimethyl aminoethyl methacrylate-statistical-monomer bearing ferrocene graft via azobenzene linker) (POEGMA-b-P(DMAEMA-st-(M-Azo-Fc), denoted as PAzo-Fc) is prepared by a consecutive reversible addition-fragmentation chain transfer (RAFT) polymerization technique, and is further used for doxorubicin (DOX) encapsulation to afford DOX-loaded stabilized nanomicelles, DOX@PAzo-Fc with an average hydrodynamic diameter of 86.0 nm. DOX@PAzo-Fc shows a self-cascade property for amplified CDT. That is, Azo cleavage-induced glutathione (GSH) depletion alleviates reactive oxygen species (ROS) scavenging. Together with the DOX-enhanced hydrogen peroxide generation, the Fc-mediated Fenton reaction is boosted for enhanced CDT. More importantly, the resulting amplified cascade chemo-chemodynamic therapy exerts a synergistic immunogenic cell death (ICD) enhancement effect for effective cancer immunotherapy, which further resulted in a high tumor inhibition rate of 87.8 % in murine tumor models. The uniqueness of this study is the construction of a minimalist nanoplatform based on M-Azo-Fc units for amplified CDT via simultaneously producing hydroxyl radicals and compromising natural radical scavenging mechanisms. Overall, this self-cascade terpolymer platform fabricated herein offers a facile yet robust approach for advanced combinatory cancer therapy with great potential for clinical translations.

Chiral polymer brush growth on magnetic nanoparticles under ambient conditions

Magnetic nanoparticles (MNPs) grafted with functional polymers were prepared via surface-initiated reversible addition-fragmentation chain transfer polymerization using oxygen (O2-SI-RAFT polymerization) under ambient conditions. Two types of monomers, a charged monomer and a chiral monomer, were used in this study. The successfully prepared polymer-coated MNPs could be easily separated using a bar magnet. The modified MNPs were characterized by various analytical methods, including zeta potential determination, spectroscopic analyses, magnetic hysteresis, transmission electron microscopy, and elemental composition analysis by energy-dispersive X-ray spectroscopy. Circular dichroism spectroscopy analysis showed that chiral polymers grown from the MNPs have mirror images, confirming that chiral properties can be conferred on MNPs via O2-SI-RAFT polymerization.

Fast-relaxing hydrogels with reversibly tunable mechanics for dynamic cancer cell culture

The mechanics of the tumor microenvironment (TME) significantly impact disease progression and the efficacy of anti-cancer therapeutics. While it is recognized that advanced in vitro cancer models will benefit cancer research, none of the current engineered extracellular matrices (ECM) adequately recapitulate the highly dynamic TME. Through integrating reversible boronate-ester bonding and dithiolane ring-opening polymerization, we fabricated synthetic polymer hydrogels with tumor-mimetic fast relaxation and reversibly tunable elastic moduli. Importantly, the crosslinking and dynamic stiffening of matrix mechanics were achieved in the absence of a photoinitiator, often the source of cytotoxicity. Central to this strategy was Poly(PEGA-co-LAA-co-AAPBA) (PELA), a highly defined polymer synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization. PELA contains dithiolane for initiator-free gel crosslinking, stiffening, and softening, as well as boronic acid for complexation with diol-containing polymers to give rise to tunable viscoelasticity. PELA hydrogels were highly cytocompatible for dynamic culture of patient-derived pancreatic cancer cells. It was found that the fast-relaxing matrix induced mesenchymal phenotype of cancer cells, and dynamic matrix stiffening restricted tumor spheroid growth. Moreover, this new dynamic viscoelastic hydrogel system permitted sequential stiffening and softening to mimic the physical changes of TME.

Flavylium-Containing Stimuli-Responsive RAFT Polymers: Synthesis and Enhanced Stability

Flavylium-Containing Stimuli-Responsive RAFT Polymers: Synthesis and Enhanced Stability

Streamlining the Generation of Advanced Polymer Materials Through the Marriage of Automation and Multiblock Copolymer Synthesis in Emulsion

AbstractSynthetic polymers are of paramount importance in modern life ‐ an incredibly wide range of polymeric materials possessing an impressive variety of properties have been developed to date. The recent emergence of artificial intelligence and automation presents a great opportunity to significantly speed up discovery and development of the next generation of advanced polymeric materials. We have focused on the high‐throughput automated synthesis of multiblock copolymers that comprise three or more distinct polymer segments of different monomer composition bonded in linear sequence. The present work has exploited automation to prepare high molar mass multiblock copolymers (typically&gt;100,000 g mol−1) using reversible addition‐fragmentation chain transfer (RAFT) polymerization in aqueous emulsion. A variety of original multiblock copolymers have been synthesised via a Chemspeed robot, exemplified by a multiblock copolymer comprising thirteen constituent blocks. Moreover, libraries of copolymers of randomized monomer compositions (acrylates, acrylamides, methacrylates, and styrenes), block orders, and block lengths were also generated, thereby demonstrating the robustness of our synthetic approach. One multiblock copolymer contained all four monomer families listed in the pool, which is unprecedented in the literature. The present work demonstrates that automation has the power to render complex and laborious syntheses of such unprecedented materials not just possible, but facile and straightforward, thus representing the way forward to the next generation of complex macromolecular architectures.

Single-step synthesis of methacrylate monoliths with well-defined mesopores

Polymeric networks with permanent porosity are versatile substrate materials for surface processes. The chemistry as well as textural properties, such as pore size, pore shape and pore volume of a porous material, determine its ability to interact with a target compound, the accessibility of the porous structure and its efficiency. In this paper, a one-step approach to obtain mesoporous methacrylate monoliths by reversible addition-fragmentation chain transfer (RAFT) polymerization is presented. The controlled polymerization mechanism is essential for the obtainment of a mesoporous polymer network as it promotes low ‘degree of polymerization’ of the growing chains, a delay in the onset of phase separation and favors inter-with respect to intra-crosslinking processes. By varying the components and composition of the polymerization mixture, control over the pore size and volume were achieved, allowing the design of customized mesoporous polymers with moderate polarity.