Photoinduced Atom Transfer Radical Polymerization Research Articles

Efficient Oxygen-Accelerated Near-Infrared Photoinduced Atom Transfer Radical Polymerization Mediated with S-Scheme Heterojunction Photocatalyst Composed of Lead-Free Halide Perovskite Encapsulated into Metal–Organic Framework

Efficient Oxygen-Accelerated Near-Infrared Photoinduced Atom Transfer Radical Polymerization Mediated with S-Scheme Heterojunction Photocatalyst Composed of Lead-Free Halide Perovskite Encapsulated into Metal–Organic Framework

Riboflavin‐Catalyzed Photoinduced Atom Transfer Radical Polymerization

AbstractThe photoATRP of methyl acrylate (MA) is investigated using riboflavin (RF) and CuBr2/Me6TREN as a dual catalyst system under green LED irradiation (λ ≈ 525 nm). Both RF and CuBr2/Me6TREN enhanced oxygen tolerance, enabling effective ATRP in the presence of residual oxygen. High molar mass polymers (up to Mn ≈ 129 000 g·mol−1) with low dispersity (Đ ≤ 1.16) are prepared, and chain‐end fidelity is confirmed through successful chain extension. The molecular masses of the obtained polymer increased linearly with conversion and showed high initiation efficiency. Mechanistic studies by laser flash photolysis reveal that the predominant activator generation mechanism is reductive quenching of RF by Me6TREN (83%, under [CuBr2]/[Me6TREN] = 1/3 condition), supported by polymerization kinetics and thermodynamic calculations.

ATRP with ppb Concentrations of Photocatalysts.

In atom transfer radical polymerization (ATRP), dormant alkyl halides are intermittently activated to form growing radicals in the presence of a CuI/L/X-CuII/L (activator/deactivator) catalytic system. Recently developed very active copper complexes could decrease the catalyst concentration to ppm level. However, unavoidable radical termination results in irreversible oxidation of the activator to the deactivator species, leading to limited monomer conversions. Therefore, successful ATRP at a low catalyst loading requires continuous regeneration of the activators. Such a regenerative ATRP can be performed with various reducing agents under milder reaction conditions and with catalyst concentrations diminished in comparison to conventional ATRP. Photoinduced ATRP (PhotoATRP) is one of the most efficient methods of activator regeneration. It initially employed UV irradiation to reduce the air-stable excited X-CuII/L deactivators to the activators in the presence of sacrificial electron donors. Photocatalysts (PCs) can be excited after absorbing light at longer wavelengths and, due to their favorable redox potentials, can reduce X-CuII/L to CuI/L. Herein, we present the application of three commercially available xanthene dyes as ATRP PCs: rose bengal (RB), rhodamine B (RD), and rhodamine 6G (RD-6G). Even at very low Cu catalyst concentrations (50 ppm), they successfully controlled PhotoATRP. Well-defined polymers with preserved livingness were prepared under green LED irradiation, with subppm concentrations ([PC] ≥ 10 ppb) of RB and RD-6G or 5 ppm of RD. Interestingly, these PCs efficiently controlled ATRP at wavelengths longer than their absorption maxima but required higher loadings. Polymerizations proceeded with high initiation efficiencies, yielding polymers with narrow molecular weight distributions and high chain-end fidelity. UV-vis, fluorescence, and laser flash photolysis studies helped to elucidate the mechanism of the processes involved in the dual-catalytic systems, comprising parts per million of Cu complexes and parts per billion of PCs.

Synthesis of a perovskite surface-coated polymer brush by photo-induced atom transfer radical polymerization

Lead halide perovskite nanocrystals (PNCs) are expected to be applied in the field of optoelectronics due to their color tunability, high color purity, and near-unity photoluminescence quantum yields. Moreover, the construction of nanocomposite structures with functional polymers has been reported to improve the material stability as well as the ordered structure with high orientation and periodicity. In this study, we demonstrated the synthesis of polymethyl methacrylate (PMMA) on the PNCs by surface-initiated polymerization. We synthesized PMMA polymer brushes by photo-induced atom transfer radical polymerization (p-ATRP) after coordinating the initiator on the PNC surface. We succeeded in obtaining PMMA-PNCs with a degree of polymerization of 21. Moreover, thermal stability tests showed that PMMA-PNCs achieved improved thermal stability compared to pristine-PNCs. This work can provide guidance for developing polymer brush-PNCs via surface-initiated polymerization.

Fabrication of POSS-centered polyester network as high anti-chlorine and anti-fouling separation layer of membrane via successive Photo-ATRP and interfacial polymerization for molecular separation

The incorporation of polyhedral oligomeric sesquisiloxane (POSS), a distinctive nanoparticle, into the membrane separation layer represents an effective strategy for enhancing the chlorine resistance of membranes. This modification contributes to both the durability of the membrane and its separation efficiency. However, POSS is easy to agglomerate, which affects the separation performance of the membrane. In this paper, POSS-centered polyhydroxy polymer (OMEPOSS-P(GMA-NMDG)) was synthesized via photo-induced atom transfer radical polymerization and used as water-soluble monomer to prepare polyester separation layer on porous substrates through interfacial polymerization with trimelanoyl chloride. The obtained POSS-centered polyester membrane exhibits a high dye removal rate exceeding 99 %, and it can realize the screening of dye molecules with different molecular weight and different charge. Notably, the membrane demonstrates excellent chlorine resistance, maintaining effective separation efficiency after exposure to sodium hypochlorite solutions at concentrations of 10 000 ppm for 96 h and 1000 ppm for 7 days. It is worth noting that the membrane showed high anti-fouling performance. This method provides a useful guideline for the development of chlorine-resistant and anti-fouling separation membranes.

Exploiting Photoinduced Atom Transfer Radical Polymerizations with Boron-Dopant and Nitrogen-Defect Synergy in Carbon Nitride Nanosheets.

Graphitic carbon nitrides (g-C3N4) possess various benefits as heterogeneous photocatalysts, including tunable bandgaps, scalability, and chemical robustness. However, their efficacy and ongoing advancement are hindered by challenges like limited charge-carrier separation rates, insufficient driving force for photocatalysis, small specific surface area, and inadequate absorption of visible light. In this study, boron dopants and nitrogen defects synergy are introduced into bulk g-C3N4 through the calcination of a blend of nitrogen-defective g-C3N4 and NaBH4 under inert conditions, resulting in the formation of BCN nanosheets characterized by abundant porosity and increased specific surface area. These BCN nanosheets promote intermolecular single electron transfer to the radical initiator, maintaining radical intermediates at a low concentration for better control of photoinduced atom transfer radical polymerization (photo-ATRP). Consequently, this method yields polymers with low dispersity and tailorable molecular weights under mild blue light illumination, outperforming previous reports on bulk g-C3N4. The heterogeneity of BCN enables easy separation and efficient reuse in subsequent polymerization processes. This study effectively showcases a simple method to alter the electronic and band structures of g-C3N4 with simultaneously introducing dopants and defects, leading to high-performance photo-ATRP and providing valuable insights for designing efficient photocatalytic systems for solar energy harvesting.

Well-defined non-symmetric NHC-iron(III) catalyst for photoinduced atom-transfer radical polymerization of methyl methacrylate

Photoinduced atom transfer radical polymerization (photo-ATRP) has emerged as a prominent technique in contemporary polymer chemistry, offering a potent means to create precisely structured materials. Well-defined catalysts are essential for controlling the growth of polymers with reproducible results; however, most photo-ATRP catalytic systems involve mixing the metal salt with the ligand. Herein we present a well-defined iron(III) based photo-ATRP catalyst bearing bidentate NHC ligand, 3-Methyl-1-phenyl-1H-3,1-benzimidazol-3-ium iodide (Pmb). The [FeBr(Pmb)2] was successfully synthesized and fully characterized by FTIR, UV–Vis, and EPR spectroscopic studies, elemental analysis, MALDI-TOF mass spectrometry, and computational studies. [FeBr(Pmb)2] was employed as the catalyst for photo-ATRP of methyl methacrylate (MMA) under ultraviolet light irradiation (365 nm). The catalytic activity of [FeBr(Pmb)2] in the photo-ATRP of MMA was evaluated under different conditions using EBPA as the initiator. The polymerizations showed robust activity, yelding in polymers with controlled molecular weights and a narrow molecular weight distribution (MWD). Remarkably, this was achieved with low catalysts loading (102.6 ppm), mainly at the molar ratio [MMA]/[EBPA]/[Fe] = 200/1/0.04. Well-defined polyMMA was synthesized and temporal control over photo-ATRP was successfully demonstrated through “on/off” experiments. For example, photo-ATRP of MMA with a molar ratio of [200/1/0.04] after 12 h at T = 25 °C in bulk resulted in PMMA with a polydispersity (Ð) of 1.15 at 50 % monomer conversion.

Visible-light-induced ATRP under high-pressure: synthesis of ultra-high-molecular-weight polymers.

In this study, a high-pressure-assisted photoinduced atom transfer radical polymerization (p ≤ 250 MPa) enabled the synthesis of ultra-high-molecular-weight polymers (UHMWPs) of up to 9 350 000 and low/moderate dispersity (1.10 < Đ < 1.46) in a co-solvent system (water/DMSO), without reaction mixture deoxygenation.

Recent Advances on Metal-Free Quantum Dots as Green Photocatalysts for Photoinduced Atom Transfer Radical Polymerization

Recent Advances on Metal-Free Quantum Dots as Green Photocatalysts for Photoinduced Atom Transfer Radical Polymerization

Catechol-formaldehyde resin microspheres@UiO-66-NH2@ CdS core-shell nanohybrids as robust visible-light photocatalyst for multifunctional applications

Well-defined zirconium based metal-organic frameworks (MOFs) coated polymer core-shell nanohybrid (CFR@MOF) was constructed using catechol formaldehyde resin (CFR) microspheres as a support, followed by encapsulating CdS nanoparticles (NPs) into MOF (UiO-66-NH2) shell layers to obtain CFR@UiO-66-NH2@CdS nanohybrids to enhance visible photosensitization for multifunctional photocatalytic applications including organic pollutant degradation, water disinfection and photoinduced atomic transfer radical polymerization (photoATRP). The CFR microspheres with a regular spherical morphology (200–400 nm) provided a versatile initial platform for the growth of MOF shells through mononuclear coating. The impact of different loadings of CdS NPs incorporated into CFR@UiO-66-NH2 shells on photocatalytic performance was systematically investigated. CFR@UiO-66-NH2 @CdS demonstrated robust dye degradation and antibacterial ability. Especially, a remarkable inhibitory efficiency of 99.99 % and 99.7 % was achieved for S. aureus and E. coli, with a low photocatalyst dosage (100 μg/mL) under visible light. Furthermore, by combining CFR@UiO-66-NH2@CdS with CuBr2/L catalysts, a high-efficiency red-light triggered photoredox catalytic polymerization system was established in photoinduced atom transfer radical polymerization (photoATRP), achieving high conversion rate (>90 %) for various monomers in a short time.

Fabrication of well-defined lignin-derived elastomers by atom transfer radical polymerization and Diels-Alder reaction towards sustainable, super-tough and high temperature-resistant hot-melt adhesives

Hot-melt adhesives synthesized from sustainable resource have attracted increasing attention in fields of home decoration, handicraft production, automotive industries, etc., due to their free of volatile organic compounds (VOCs) and environmentally friendly advantages. However, it is still challenging to fabricate super-tough and heat-resistant hot-melt adhesives with utilization of the inherited properties of sustainable resource as feedstock. Herein, a combination of photoinduced metal-free atom transfer radical polymerization (ATRP) and Diels-Alder (DA) reaction was applied to prepare lignin-derived elastomers for super-tough and high temperature-resistant hot-melt adhesives. Firstly, photoinduced metal-free ATRP of lauryl methacrylate (LMA) derived from fatty acids and furfuryl methacrylate (FMA) derived from furfural, were employed to fabricate sustainable well-defined multi-arm lignin-graft copolymers bearing furfuryl groups with the aid of lignin based macro-initiator (L-Br). The photoinduced metal-free ATRP in this work could be activated and deactivated by an “ON–OFF” ultraviolet (UV) light switch, and successfully achieved the precise control over the molecular weight and composition of lignin-graft copolymers. Then, Diels-Alder (DA) reaction was applied to functionalize the lignin-graft copolymers with dynamic crosslinked network and obtain the lignin-derived elastomers. Benefiting from the multi-arm structure and the dynamic crosslinked network, these lignin-derived elastomers exhibited favorable mechanical property, thermal stability, shape memory, self-healing and recycled properties. In addition, the lignin-derived elastomers could be used as hot-melt adhesives and their lap shear strengths could reach 5.95 MPa, while being bonded with aluminum plates. Moreover, the steel plate bonded with lignin-derived elastomers could remain stable even at 100 °C. We believe that this work will offer a new approach for designing lignin-derived elastomers towards sustainable, strong, super-tough and high-temperature-resistant hot-melt adhesives.

Red-Light-Driven Atom Transfer Radical Polymerization for High-Throughput Polymer Synthesis in Open Air.

Photoinduced reversible-deactivation radical polymerization (photo-RDRP) techniques offer exceptional control over polymerization, providing access to well-defined polymers and hybrid materials with complex architectures. However, most photo-RDRP methods rely on UV/visible light or photoredox catalysts (PCs), which require complex multistep synthesis. Herein, we present the first example of fully oxygen-tolerant red/NIR-light-mediated photoinduced atom transfer radical polymerization (photo-ATRP) in a high-throughput manner under biologically relevant conditions. The method uses commercially available methylene blue (MB+) as the PC and [X-CuII/TPMA]+ (TPMA = tris(2-pyridylmethyl)amine) complex as the deactivator. The mechanistic study revealed that MB+ undergoes a reductive quenching cycle in the presence of the TPMA ligand used in excess. The formed semireduced MB (MB•) sustains polymerization by regenerating the [CuI/TPMA]+ activator and together with [X-CuII/TPMA]+ provides control over the polymerization. This dual catalytic system exhibited excellent oxygen tolerance, enabling polymerizations with high monomer conversions (>90%) in less than 60 min at low volumes (50-250 μL) and high-throughput synthesis of a library of well-defined polymers and DNA-polymer bioconjugates with narrow molecular weight distributions (Đ < 1.30) in an open-air 96-well plate. In addition, the broad absorption spectrum of MB+ allowed ATRP to be triggered under UV to NIR irradiation (395-730 nm). This opens avenues for the integration of orthogonal photoinduced reactions. Finally, the MB+/Cu catalysis showed good biocompatibility during polymerization in the presence of cells, which expands the potential applications of this method.

Regulating Charge Carrier Dynamics in Stable Perovskite Nanorods for Photo-Induced Atom Transfer Radical Polymerization.

Semiconducting nanocrystals have attracted world-wide research interest in artificial photosynthesis due to their appealing properties and enticing potentials in converting solar energy into valuable chemicals. Compared to 0D nanoparticles, 1D nanorods afford long-distance charge carriers separation and extended charge carriers lifetime due to the release of quantum confinement in axial direction. Herein, stable CsPbBr3 nanorods of distinctive dimensions are crafted without altering their properties and morphology via grafting hydrophobic polystyrene (PS) chains through a post-synthesis ligand exchange process. The resulting PS-capped CsPbBr3 nanorods exhibit a series of enhanced stabilities against UV irradiation, elevated temperature, and polar solvent, making them promising candidates for photo-induced atom transfer radical polymerization (ATRP). Tailoring the surface chemistry and dimension of the PS-capped CsPbBr3 nanorods endows stable, but variable reaction kinetics in the photo-induced ATRP of methyl methacrylate. The trapping-detrapping process of photogenerated charge carriers lead to extended lifetime of charge carriers in lengthened CsPbBr3 nanorods, contributing to a facilitated reaction kinetics of photo-induced ATRP. Therefore, by leveraging such stable PS-capped CsPbBr3 nanorods, the effects of surface chemistry and charge carriers dynamics on its photocatalytic performance are scrutinized, providing fundamental understandings for designing next-generation efficient nanostructured photocatalyst in artificial photosynthesis and solar energy conversion.

Oxygen Tolerance during Surface-Initiated Photo-ATRP: Tips and Tricks for Making Brushes under Environmental Conditions.

Achieving tolerance toward oxygen during surface-initiated reversible deactivation radical polymerization (SI-RDRP) holds the potential to translate the fabrication of polymer brush-coatings into upscalable and technologically relevant processes for functionalizing materials. While focusing on surface-initiated photoinduced atom transfer radical polymerization (SI-photoATRP), we demonstrate that a judicious tuning of the composition of reaction mixtures and the adjustment of the polymerization setup enable to maximize the compatibility of this grafting technique toward environmental conditions. Typically, the presence of O2 in the polymerization medium limits the attainable thickness of polymer brushes and causes the occurrence of "edge effects", i.e., areas at the substrates' edges where continuous oxygen diffusion from the surrounding environment inhibits brush growth. However, the concentrations of the Cu-based catalyst and "free" alkyl halide initiator in solution emerge as key parameters to achieve a more efficient consumption of oxygen and yield uniform and thick brushes, even for polymerization mixtures that are more exposed to air. Precise variation of reaction conditions thus allows us to identify those variables that become determinants for making the synthesis of brushes more tolerant toward oxygen, and consequently more practical and upscalable.

RNA-Polymer Hybrids via Direct and Site-Selective Acylation with the ATRP Initiator and Photoinduced Polymerization.

Combining synthetic polymers with RNA paves the way for creating RNA-based materials with non-canonical functions. We have developed an acylation reagent that allows for direct incorporation of the atom transfer radical polymerization (ATRP) initiator into both short synthetic oligoribonucleotides and natural biomass RNA extracted from torula yeast. The acylation was performed in a quantitative yield. The resulting initiator-functionalized RNAs were used for grafting polymer chains from the RNA by photoinduced ATRP, resulting in RNA-polymer hybrids with narrow molecular weight distributions. The RNA initiator was used for the polymerization of oligo(ethylene oxide) methyl ether methacrylate, poly(ethylene glycol) dimethacrylate, and N-isopropylacrylamide monomers, resulting in RNA bottlebrushes, hydrogels, and stimuli-responsive materials. This approach, readily applicable to both post-synthetic and nature-derived RNA, can be used to engineer the properties of a variety of RNA-based macromolecular hybrids and assemblies providing access to a wide variety of RNA-polymer hybrids.

Monte Carlo simulation of photoinduced atom-transfer radical polymerization for dynamic microscopic properties

Atom-transfer radical polymerization (ATRP) is a powerful and versatile technique for the synthesis of well-defined polymers with precise control over the molecular weight and architecture. Photoinduced ATRP (photoATRP) is a variant of ATRP based on the transfer of radical polymers through a photochemical process, offering numerous benefits over traditional ATRP, including reduced environmental impact and improved polymer yields. Monte Carlo (MC) simulation is an attractive tool for simulating photoATRP, enabling one to predict microscopic properties of the polymers. In this work, a dynamic Monte Carlo (DMC) model is developed for the photoATRP processes at microscopic resolution. The dependency information of individual chains’ length on the radical, dormant, and dead polymers is captured. Furthermore, the polymerization process simulation of photoATRP systems based on the developed DMC method for temporal control over polymer growth is established. Several facets on the enhancement of temporal control are investigated under the condition of light intermittency.

Gelation in Photoinduced ATRP with Tuned Dispersity of the Primary Chains.

We investigated gelation in photoinduced atom transfer radical polymerization (ATRP) as a function of Cu catalyst loading and thus primary chain dispersity. Using parallel polymerizations of methyl acrylate with and without the addition of a divinyl crosslinker (1,6-hexanediol diacrylate), the approximate values of molecular weights and dispersities of the primary chains at incipient gelation were obtained. In accordance with the Flory-Stockmayer theory, experimental gelation occurred at gradually lower conversions when the dispersity of the primary chains increased while maintaining a constant monomer/initiator/crosslinker ratio. Theoretical gel points were then calculated using the measured experimental values of dispersity and initiation efficiency. An empirical modification to the Flory-Stockmayer equation for ATRP was implemented, resulting in more accurate predictions of the gel point. Increasing the dispersity of the primary chains was found not to affect the distance between the theoretical and experimental gel points and hence the extent of intramolecular cyclization. Furthermore, the mechanical properties of the networks, such as equilibrium swelling ratio and shear storage modulus showed little variation with catalyst loading and depended primarily on the crosslinking density.

Rose bengal-mediated photoinduced atom transfer radical polymerization for high sensitivity detection of target DNA

Convenient and sensitive detection of biomolecules is of utmost importance in the field of early disease screening. In this study, a Rose Bengal-Mediated photoinduced atom transfer radical polymerization (photoATRP) method was used to achieve highly sensitive detection of target DNA (tDNA). The tDNA was specifically recognized using PNA with terminal modified sulfhydryl groups, and the initiator α-bromophenylacetic acid (BPAA) was attached to the electrode surface via a phosphate-Zr4+-carboxylate acid structure. Under the excitation of blue light, rose bengal (RB) acts as a photocatalyst, β-nicotinamide adenine dinucleotide (NADH) as an electron donor, and ferrocenylmethyl methacrylate (FMMA) as a monomer to activate the photoATRP reaction and generate a large number of electroactive polymer chains on the electrode surface. Under optimal conditions, the method can be used for the quantitative analysis of tDNA in the concentration range of 1–105 fM (R2 = 0.994) with a limit of detection (LOD) of 0.115 fM. This metal-free mediated photoATRP biosensor, with low cost and environmental friendliness, has great potential in the field of highly sensitive biomolecule detection.

Metal-free Photochemically Mediated ATRP for Ultrasensitive Quantification of CYFRA 21–1 for Detection of Early Stage Non-Small Cell Lung Cancer

A convenient electrochemiluminescence (ECL) biosensor for sensitive detecting CYFRA 21–1 via metal-free photoinduced atom transfer radical polymerization (photo-ATRP) strategy was constructed for the first time. The CYFRA 21–1 antigen was modified on the Au electrode surface by constructing a sandwich type antibody-antigen-antibody immune system, which could achieve high selectivity through twice specific recognition. Photo-ATRP, which can avoid the use of heavy metal catalysts, and control the polymerization reaction by turning the light on and off, was activated by the photoredox catalyst Esion Y (EY) upon 470 nm blue light (24 V/15 W) irradiation. Whereafter, a large number of luminol binding sites were generated, which resulted in significant signal amplification. Under the optimal experimental conditions, the biosensor displayed an ideal linear relationship in the range from 10 fg ml−1 to 1 ng ml−1 with a low detection limit of 5.8 fg ml−1, which can realize the trace detection of CYFRA 21–1. Furthermore, the prepared ECL biosensor exhibited specific selectivity, outstanding stability and reproducibility. This ECL sensing systems highlighted the advances of using metal-free photo-ATRP signal amplification strategy in the developments of highly efficient and environmentally friendly immunosensors for CYFRA 21–1 detection.

Tailoring Charge Separation at Meticulously Engineered Conjugated Polymer/Perovskite Quantum Dot Interface for Photocatalyzing Atom Transfer Radical Polymerization.

In stark contrast to conventional organic ligand-capped counterparts, the ability to create stable metal halide perovskite nanocrystals strongly tethered with conjugated polymers (CPs) represents an important endeavor toward tailoring charge carrier dynamics at their interface that critically underpins applications of this unique class of all semiconducting, organic-inorganic nanomaterials for optoelectronics. This, however, has yet to be largely explored. Herein, we report, for the first time, the unraveling of efficient charge separation at judiciously designed CP/perovskite quantum dot (QD) interface for photoinduced atom transfer radical polymerization (p-ATRP). Such scrutiny is rendered by in situ crafting an array of monodisperse, highly stable, CP-ligated perovskite QDs with precisely controlled dimensions of each constituent via capitalizing on unimolecular, amphiphilic starlike block copolymers as nanoreactors. The intimate and permanent surface tethering of CPs imparts remarkable thermal, photo, and polar solvent stabilities of CP-ligated perovskite QDs. More importantly, they manifest efficient interfacial charge separation with a profound dependence on the length of ligated CPs and the size of perovskite QDs. The outstanding structural stabilities and charge separation characteristic enable CP-ligated perovskite QDs as robust photocatalysts for p-ATRP of a wide selection of monomers with stable and controllable reaction kinetics, also depending crucially on the length of CPs and the size of perovskite QDs. In principle, an exciting variety of CP-ligated, uniform perovskite QDs with virtually unlimited material choice of both markedly improved stabilities and tunable electronic band alignments can be readily accessed by exploiting the amphiphilic starlike block copolymer nanoreactor strategy for use in photodetectors, sensors, and LEDs, among other areas.