Effect of Tertiary Amines on the Photoinduced Electron Transfer-Reversible Addition–Fragmentation Chain Transfer (PET-RAFT) Polymerization

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 (100 mL) 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 >250 000) 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.

One-pot Formulation of Cationic Oligochitosan Coated Nanoparticles via Photo- Polymerization Induced Self-Assembly

During last few decades, oligochitosan (OCS)-coated nanoparticles have received great interest for nanomedicine, food and environment applications. However, their current formulation techniques are time-consuming with multi-synthesis/purification steps and sometimes require the use of organic solvents, crosslinkers and surfactants. Herein, we report a facile and rapid one-pot synthesis of OCS-based nanoparticles using photo-initiated reversible addition fragmentation chain transfer polymerization-induced self-assembly (Photo-RAFT PISA) under UV-irradiation at room temperature. To achieve this, OCS was first functionalized by a chain transfer agent (CTA) resulting in a macromolecular chain transfer agent (OCS-CTA), which will act as a reactive electrostatic/steric stabilizer. Owing to its UV-sensitivity, OCS-CTA was then used as photo-iniferter to initiate the polymerization of 2-hydroxypropyl methacrylate (HPMA) in aqueous acidic buffer, resulting in OCS-g-PHPMA amphiphilic grafted copolymers which self-assemble into nano-objects. Transmission electron microscopy and light scattering analysis reveal formation of spherical nanostructures.

Mimicking Charged Host-Defense Peptides to Tune the Antifungal Activity and Biocompatibility of Amphiphilic Polymers

Invasive fungal infections impose a substantial global health burden. They cause more than 1.5 million deaths annually and are insufficiently met by the currently approved antifungal drugs. Antifungal peptides are a promising alternative to existing antifungal drugs; however, they can be challenging to synthesize, and are often susceptible to proteases in vivo. Synthetic polymers which mimic the properties of natural antifungal peptides can circumvent these limitations. In this study, we developed a library of 29 amphiphilic polyacrylamides with different charged units, namely, amines, guanidinium, imidazole, and carboxylic acid groups, representative of the natural amino acids lysine, arginine, histidine, and glutamic acid. Ternary polymers incorporating primary ammonium (lysine-like) or imidazole (histidine-like) groups demonstrated superior activity against Candida albicans and biocompatibility with mammalian cells compared to the polymers containing the other charged groups. Furthermore, a combination of primary ammonium, imidazole, and guanidinium (arginine-like) within the same polymer outperformed the antifungal drug amphotericin B in terms of therapeutic index and exhibited fast C. albicans-killing activity. The most promising polymer compositions showed synergistic effects in combination with caspofungin and fluconazole against C. albicans and additionally demonstrated activity against other clinically relevant fungi. Collectively, these results indicate the strong potential of these easily producible polymers to be used as antifungals.

Amide-Containing Bottlebrushes via Continuous-Flow Photoiniferter Reversible Addition-Fragmentation Chain Transfer Polymerization: Micellization Behavior

Herein, a series of ternary amphiphilic amide-containing bottlebrushes were synthesized by photoiniferter (PI-RAFT) polymerization of macromonomers in continuous-flow mode using trithiocarbonate as a chain transfer agent. Visible light-mediated polymerization of macromonomers under mild conditions enabled the preparation of thermoresponsive copolymers with low dispersity and high yields in a very short time, which is not typical for the classical reversible addition-fragmentation chain transfer process. Methoxy oligo(ethylene glycol) methacrylate and alkoxy(C12-C14) oligo(ethylene glycol) methacrylate were used as the basic monomers providing amphiphilic and thermoresponsive properties. The study investigated how modifying comonomers, acrylamide (AAm), methacrylamide (MAAm), and N-methylacrylamide (-MeAAm) affect the features of bottlebrush micelle formation, their critical micelle concentration, and loading capacity for pyrene, a hydrophobic drug model. The results showed that the process is scalable and can produce tens of grams of pure copolymer per day. The unmodified copolymer formed unimolecular micelles at temperatures below the LCST in aqueous solutions, as revealed by DLS and SLS data. The incorporation of AAm, MAAm, and N-MeAAm units resulted in an increase in micelle aggregation numbers. The resulting bottlebrushes formed uni- or bimolecular micelles at extremely low concentrations. These micelles possess a high capacity for loading pyrene, making them a promising choice for targeted drug delivery.

Biofilm heterogeneity-adaptive photoredox catalysis enables red light-triggered nitric oxide release for combating drug-resistant infections

The formation of biofilms is closely associated with persistent and chronic infections, and physiological heterogeneity such as pH and oxygen gradients renders biofilms highly resistant to conventional antibiotics. To date, effectively treating biofilm infections remains a significant challenge. Herein, we report the fabrication of micellar nanoparticles adapted to heterogeneous biofilm microenvironments, enabling nitric oxide (NO) release through two distinct photoredox catalysis mechanisms. The key design feature involves the use of tertiary amine (TA) moieties, which function as sacrificial agents to avoid the quenching of photocatalysts under normoxic and neutral pH conditions and proton acceptors at acidic pH to allow deep biofilm penetration. This biofilm-adaptive NO-releasing platform shows excellent antibiofilm activity against ciprofloxacin-resistant Pseudomonas aeruginosa (CRPA) biofilms both in vitro and in a mouse skin infection model, providing a strategy for combating biofilm heterogeneity and biofilm-related infections.

Emulsion-Directed Synthesis of Poly-Porphyrin Nanoparticles as Heterogeneous Photocatalysts for PET-RAFT Polymerization

Heterogeneous photocatalysts have attracted extensive attention in photo-induced electron transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization due to their remarkable advantages such as easy preparation, tunable photoelectric properties, and recyclability. In this study, zinc (II) 5,10,15,20-tetrakis(4-aminophenyl)porphyrin (ZnTAPP)-based poly-porphyrin nanoparticles (PTAPP-Zn) are constructed by an emulsion-directed approach. It is investigated as a heterogeneous photocatalyst for PET-RAFT polymerization of various methacrylate monomers under visible light exposure, and the reactions show refined polymerization control with high monomer conversions. Furthermore, it is demonstrated that the PTAPP-Zn nanoparticles with the larger pore size enhance photocatalytic activity in PET-RAFT polymerization. In addition, the capabilities of oxygen tolerance and temporal control are demonstrated and PTAPP-Zn particles can be easily recycled and reused without an obvious decrease in catalytic efficiency.

Latest Advances in Highly Efficient Dye-Based Photoinitiating Systems for Radical Polymerization

Light-activated polymerization is one of the most important and powerful strategies for fabrication of various types of advanced polymer materials. Because of many advantages, such as economy, efficiency, energy saving and being environmentally friendly, etc., photopolymerization is commonly used in different fields of science and technology. Generally, the initiation of polymerization reactions requires not only light energy but also the presence of a suitable photoinitiator (PI) in the photocurable composition. In recent years, dye-based photoinitiating systems have revolutionized and conquered the global market of innovative PIs. Since then, numerous photoinitiators for radical polymerization containing different organic dyes as light absorbers have been proposed. However, despite the large number of initiators designed, this topic is still relevant today. The interest towards dye-based photoinitiating systems continues to gain in importance, which is related to the need for new initiators capable of effectively initiating chain reactions under mild conditions. In this paper we present the most important information about photoinitiated radical polymerization. We describe the main directions for the application of this technique in various areas. Attention is mainly focused on the review of high-performance radical photoinitiators containing different sensitizers. Moreover, we present our latest achievements in the field of modern dye-based photoinitiating systems for the radical polymerization of acrylates.

Ultrafast Visible-Light-Induced ATRP in Aqueous Media with Carbon Quantum Dots as the Catalyst and Its Application for 3D Printing

Photoinduced atom transfer radical polymerization (ATRP) has been proved to be a versatile technique for polymer network formation. However, the slow polymerization rates of typical ATRP limited its application in the field of additive manufacturing (3D printing). In this work, we introduced carbon quantum dots (CQDs) for the first time to the ATRP in aqueous media and developed an ultrafast visible-light-induced polymerization system. After optimization, the polymerization could achieve a high monomer conversion (>90%) within 1 min, and the polydispersity index (PDI) of the polymer was lower than 1.25. This system was then applied as the first example of ATRP for the 3D printing of hydrogel through digital light processing (DLP), and the printed object exhibited good dimensional accuracy. Additionally, the excellent and stable optical properties of CQDs also provided interesting photoluminescence capabilities to the printed objects. We deduce this ATRP mediated 3D printing process would provide a new platform for the preparation of functional and stimuli-responsive hydrogel materials.

Rational Design of Photocatalysts for Controlled Polymerization: Effect of Structures on Photocatalytic Activities

Over the past decade, the use of photocatalysts (PCs) in controlled polymerization has brought new opportunities in sophisticated macromolecular synthesis. However, the selection of PCs in these systems has been typically based on laborious trial-and-error strategies. To tackle this limitation, computer-guided rational design of PCs based on knowledge of structure-property-performance relationships has emerged. These rational strategies provide rapid and economic methodologies for tuning the performance and functionality of a polymerization system, thus providing further opportunities for polymer science. This review provides an overview of PCs employed in photocontrolled polymerization systems and summarizes their progression from early systems to the current state-of-the-art. Background theories on electronic transitions are also introduced to establish the structure-property-performance relationships from a perspective of quantum chemistry. Typical examples for each type of structure-property relationships are then presented to enlighten future design of PCs for photocontrolled polymerization.

Photoinduced Cascade C-N/C═O Bond Formation from Bromodifluoroalkyl Reagents, Amines, and H2O via a Triple-Cleavage Process

A green, sustainable, and straightforward method for the synthesis of unsymmetrical oxalamides via photoinduced C-N/C═O bond formation of bromodifluoroacetamide, amine, and H₂O through a triple-cleavage process has been developed. In addition, this approach also provides access to the known bioactive compounds, and a feasible reaction mechanism is proposed. Moreover, the advantages of this transformation, including mild reaction conditions, a broad substrate scope, and operational simplicity, make this protocol attractive for further applications.

Photoluminescent and visual determination of ibandronic acid using a carbon dots/AgInS2 quantum dots ratiometric sensing platform

A sensing platform combining carbon dots (CDs, with blue emission) and thiomalic acid (TMA)-capped AgInS₂ quantum dots (QDs, with orange emission) was developed aiming the photoluminescence (PL) ratiometric determination of ibandronic acid (IBAN), a bisphosphonate pharmaceutical. The ternary AgInS₂ QDs were used for IBAN probing, undergoing a concentration-related PL quenching in its presence, whilst the PL of CDs remained practically unaffected due to its chemical inertness towards the antiresorptive drug, provided an intrinsic self-reference fluorophore. In addition, a visual sensing approach was also proposed, employing for the first time ternary QDs. This relied on RGB images acquired by means of a digital camera and seek the development of a rapid IBAN screening test. The developed sensing platforms were employed for IBAN determination in samples with pharmaceutical interest providing good results, in accordance to the reported IBAN levels, and obtaining recovery values between 98 and 103%.

Dual Enhancement of Carrier Generation and Migration on Au/g-C3N4 photocatalysts for High-Efficient Broadband PET-RAFT Polymerization

Photo-induced electron/energy transfer RAFT (PET-RAFT) polymerization can produce well-defined polymers with spatio-temporal control. Semiconductor graphitic carbon nitride (g-C3N4) as thermally and chemically stable photocatalyst, has achieved PET-RAFT method under UV-irradiation...

Reusable polymer brush-based photocatalysts for PET-RAFT polymerization

Fluorescein polymer-brush functionalized glass beads synthesize polymers via photoelectron reversible addition fragmentation chain transfer (PET-RAFT) polymerization. These shelf stable heterogeneous catalysts can be recycled after simple filtration.

Random and Diblock Thermoresponsive Oligo(ethylene glycol)-Based Copolymers Synthesized via Photo-Induced RAFT Polymerization

Amphiphilic random and diblock thermoresponsive oligo(ethylene glycol)-based (co)polymers were synthesized via photoiniferter polymerization under visible light using trithiocarbonate as a chain transfer agent. The effect of solvent, light intensity and wavelength on the rate of the process was investigated. It was shown that blue and green LED light could initiate RAFT polymerization of macromonomers without an exogenous initiator at room temperature, giving bottlebrush polymers with low dispersity at sufficiently high conversions achieved in 1-2 h. The pseudo-living mechanism of polymerization and high chain-end fidelity were confirmed by successful chain extension. Thermoresponsive properties of the copolymers in aqueous solutions were studied via turbidimetry and laser light scattering. Random copolymers of methoxy- and alkoxy oligo(ethylene glycol) methacrylates of a specified length formed unimolecular micelles in water with a hydrophobic core consisting of a polymer backbone and alkyl groups and a hydrophilic oligo(ethylene glycol) shell. In contrast, the diblock copolymer formed huge multimolecular micelles.

Dextran-Coated Latex Nanoparticles via Photo-RAFT Mediated Polymerization Induced Self-Assembly

Polysaccharide coated nanoparticles represent a promising class of environmentally friendly latex to replace those stabilized by small toxic molecular surfactants. We report here an in situ formulation of free-surfactant core/shell nanoparticles latex consisting of dextran-based diblock amphiphilic copolymers. The synthesis of copolymers and the immediate latex formulation were performed directly in water using a photo-initiated reversible addition fragmentation chain transfer-mediated polymerization induced self-assembly strategy. A hydrophilic macromolecular chain transfer-bearing photosensitive thiocarbonylthio group (eDexCTA) was first prepared by a modification of the reducing chain end of dextran in two steps: (i) reductive amination by ethylenediamine in the presence of sodium cyanoborohydride, (ii) then introduction of CTA by amidation reaction. Latex nanoparticles were then formulated in situ by chain-extending eDexCTA using 2-hydroxypropyl methacrylate (HPMA) under 365 nm irradiation, leading to amphiphilic dextran-b-poly(2-hydroxypropyl methacrylate) diblock copolymers (DHX). Solid concentration (SC) and the average degree of polymerization - Xn-- of PHPMA block (X) were varied to investigate their impact on the size and the morphology of latex nanoparticles termed here SCDHX. Light scattering and transmission electron microscopy analysis revealed that SCDHX form exclusively spherical nano-objects. However, the size of nano-objects, ranging from 20 nm to 240 nm, increases according to PHPMA block length.

Direct Access to Polysaccharide-Based Vesicles with a Tunable Membrane Thickness in a Large Concentration Window via Polymerization-Induced Self-Assembly

Polymersomes are multicompartmental vesicular nano-objects obtained by self-assembly of amphiphilic copolymers. When prepared in the aqueous phase, they are composed of a hydrophobic bilayer enclosing water. Although such fascinating polymeric nano-objects have been widely reported with synthetic block copolymers, their formation from polysaccharide-based copolymers remains a significant challenge. In the present study, the powerful platform technology known as polymerization-induced self-assembly was used to prepare in situ pure vesicles from a polysaccharide-grafted copolymer: dextran-g-poly(2-hydroxypropyl methacrylate) (Dex-g-PHPMA). The growth of the PHPMA grafts was performed with a dextran-based macromolecular chain transfer agent in water at 20 °C using photomediated reversible addition fragmentation chain transfer polymerization at 405 nm. Transmission electron microscopy, cryogenic electron microscopy, small-angle X-ray scattering, atomic force microscopy, and dynamic light scattering revealed that amphiphilic Dex-g-PHPMA_{X = 100-300} (X is the targeted average degree of polymerization, X_n̅, of each graft at full conversion) exhibit remarkable self-assembly behavior. On the one hand, vesicles were obtained over a wide range of solid concentrations (from 2.5% to 13.5% w/w), which can facilitate posterior targeting of such rare morphology. On the other hand, the extension of X_n̅ induces an increase in the vesicle membrane thickness, rather than a morphological evolution (spherical micelles to cylinders to vesicles).

Modern trends in controlled synthesis of functional polymers: fundamental aspects and practical applications

Major trends in controlled radical polymerization (CRP) or reversible-deactivation radical polymerization (RDRP), the most efficient method of synthesis of well-defined homo- and copolymers with specified parameters and properties, are critically analyzed. Recent advances associated with the three classical versions of CRP: nitroxide mediated polymerization, reversible addition-fragmentation chain transfer polymerization and atom transfer radical polymerization, are considered. Particular attention is paid to the prospects for the application of photoinitiation and photocatalysis in CRP. This approach, which has been intensively explored recently, brings synthetic methods of polymer chemistry closer to the light-induced processes of macromolecular synthesis occurring in living organisms. Examples are given of practical application of CRP techniques to obtain industrially valuable, high-tech polymeric products.

The bibliography includes 429 references.

Reversible Deactivation Radical Polymerization: From Polymer Network Synthesis to 3D Printing

3D printing has changed the fabrication of advanced materials as it can provide customized and on-demand 3D networks. However, 3D printing of polymer materials with the capacity to be transformed after printing remains a great challenge for engineers, material, and polymer scientists. Radical polymerization has been conventionally used in photopolymerization-based 3D printing, as in the broader context of crosslinked polymer networks. Although this reaction pathway has shown great promise, it offers limited control over chain growth, chain architecture, and thus the final properties of the polymer networks. More fundamentally, radical polymerization produces dead polymer chains incapable of postpolymerization transformations. Alternatively, the application of reversible deactivation radical polymerization (RDRP) to polymer networks allows the tuning of network homogeneity and more importantly, enables the production of advanced materials containing dormant reactivatable species that can be used for subsequent processes in a postsynthetic stage. Consequently, the opportunities that (photoactivated) RDRP-based networks offer have been leveraged through the novel concepts of structurally tailored and engineered macromolecular gels, living additive manufacturing and photoexpandable/transformable-polymer networks. Herein, the advantages of RDRP-based networks over irreversibly formed conventional networks are discussed.

Photocatalytic intramolecular radical cyclization involved synergistic SET and HAT: synthesis of 3,3-difluoro-γ-lactams

A mild and metal-free protocol for visible-light induced intramolecular radical cyclization of N-allyl(propargyl)-2-bromo-2,2-difluoro-N-arylacetamide has been developed.

Experimental validation of eosin-mediated photo-redox polymerization mechanism and implications for signal amplification applications

When eosin-mediated, photo-redox polymerization is used to amplify signals in biosensing, oxygen has dual, opposing roles.

Enlightening advances in polymer bioconjugate chemistry: light-based techniques for grafting to and from biomacromolecules

Photochemistry has revolutionized the field of polymer-biomacromolecule conjugation. Ligation reactions necessitate biologically benign conditions, and photons have a significant energy advantage over what is available thermally at ambient temperature, allowing for rapid and unique reactivity. Photochemical reactions also afford many degrees of control, specifically, spatio-temporal control, light source tunability, and increased oxygen tolerance. Light-initiated polymerizations, in particular photo-atom-transfer radical polymerization (photo-ATRP) and photoinduced electron/energy transfer reversible addition-fragmentation chain transfer polymerization (PET-RAFT), have been used for grafting from proteins, DNA, and cells. Additionally, the spatio-temporal control inherent to light-mediated chemistry has been utilized for grafting biomolecules to hydrogel networks for many applications, such as 3-D cell culture. While photopolymerization has clear advantages, there are factors that require careful consideration in order to obtain optimal control. These factors include the photocatalyst system, light intensity, and wavelength. This Perspective aims to discuss recent advances of photochemistry for polymer biomacromolecule conjugation and potential considerations while tailoring these systems.

Role of External Field in Polymerization: Mechanism and Kinetics

The past decades have witnessed an increasing interest in developing advanced polymerization techniques subjected to external fields. Various physical modulations, such as temperature, light, electricity, magnetic field, ultrasound, and microwave irradiation, are noninvasive means, having superb but distinct abilities to regulate polymerizations in terms of process intensification and spatial and temporal controls. Gas as an emerging regulator plays a distinctive role in controlling polymerization and resembles a physical regulator in some cases. This review provides a systematic overview of seven types of external-field-regulated polymerizations, ranging from chain-growth to step-growth polymerization. A detailed account of the relevant mechanism and kinetics is provided to better understand the role of each external field in polymerization. In addition, given the crucial role of modeling and simulation in mechanisms and kinetics investigation, an overview of model construction and typical numerical methods used in this field as well as highlights of the interaction between experiment and simulation toward kinetics in the existing systems are given. At the end, limitations and future perspectives for this field are critically discussed. This state-of-the-art research progress not only provides the fundamental principles underlying external-field-regulated polymerizations but also stimulates new development of advanced polymerization methods.

3D printing and growth induced bending based on PET-RAFT polymerization

We demonstrated a method for PET-RAFT growth induced bending of a 3D printed strip using visible light, where the growth on one side of the strip causes stress and the strip bends accordingly to reach a more comfortable position.

Self-assembly of amphiphilic copolymers containing polysaccharide: PISA versus nanoprecipitation, and the temperature effect

The self-assembly methods and the temperature have a considerable impact on the morphology of the resulting nanoobjects in the case of amphiphilic glycopolymers.

A Versatile 3D and 4D Printing System through Photocontrolled RAFT Polymerization

Reversible addition-fragmentation chain-transfer (RAFT) polymerization is a valuable tool for synthesizing macromolecules with controlled topologies and diverse chemical functionalities. However, the application of RAFT polymerization to additive-manufacturing processes has been prevented due to the slow polymerization rates of typical systems. In this work, we developed and optimized a rapid visible (green) light mediated RAFT polymerization process and applied it to an open-air 3D printing system. The reaction components are non-toxic, metal free and environmentally friendly, which tailors these systems toward biomaterial fabrication. The inclusion of RAFT agent in the photosensitive resin provided control over the mechanical properties of 3D printed materials and allowed these materials to be post-functionalized after 3D printing. Additionally, photoinduced spatiotemporal control of the network structure provided a one-pass approach to 4D printed materials. This RAFT-mediated 3D and 4D printing process should provide access to a range of new functional and stimuli-responsive materials.