Photoinduced Electron Transfer-reversible Addition-fragmentation Chain Research Articles

Perovskite Nanocrystals Initiate One‐Step Oxygen Tolerant PET‐RAFT Polymerization of Highly Loaded, Efficient Plastic Nanocomposites

AbstractLead halide perovskite nanocrystals (LHP‐NCs) incorporated within polymer matrices have emerged as promising materials for various photonic applications. However, challenges persist in achieving high‐quality nanocomposites due to low monomer conversion yields, restricted LHP‐NCs loadings, and difficulty in maintaining NCs integrity post‐polymerization. A novel protocol for synthesizing LHP‐NCs/poly(methyl methacrylate) nanocomposites in a single step via the NC‐initiated photoinduced electron transfer‐reversible addition‐fragmentation chain transfer (PET‐RAFT) method is presented. Polymerization initiation mediated by NCs surfaces under blue light enables the fabrication of homogeneous nanocomposites with NCs loadings up to 7% w/w and ≈90% monomer conversion even in the presence of oxygen. This process preserves the optical quality of the NCs and passivates NCs surface defects, resulting in nanocomposites exhibiting near unity luminescence efficiencies. The potential of this approach for producing highly loaded nanocomposites for radiation detection is validated by radioluminescence measurements showing light yield values of 6000 ph MeV−1 and fast scintillation dynamics with effective lifetime of 490 ps, showing promise for time‐of‐flight radiometry.

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.

Light-mediated intracellular polymerization.

The synthesis of synthetic intracellular polymers offers groundbreaking possibilities in cellular biology and medical research, allowing for novel experiments in drug delivery, bioimaging and targeted cancer therapies. These macromolecules, composed of biocompatible monomers, are pivotal in manipulating cellular functions and pathways due to their bioavailability, cytocompatibility and distinct chemical properties. This protocol details two innovative methods for intracellular polymerization. The first one uses 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (Irgacure 2959) as a photoinitiator for free radical polymerization under UV light (365 nm, 5 mW/cm2). The second method employs photoinduced electron transfer-reversible addition-fragmentation chain-transfer polymerization with visible light (470 nm, 100 mW/cm2). We further elaborate on isolating these intracellular polymers by streptavidin/biotin interaction or immobilized metal ion affinity chromatography for polymers tagged with biotin or histidine. The entire process, from polymerization to isolation, takes ~48 h. Moreover, the intracellular polymers thus generated demonstrate significant potential in enhancing actin polymerization, in bioimaging applications and as a novel avenue in cancer treatment strategies. The protocol extends to animal models, providing a comprehensive approach from cellular to systemic applications. Users are advised to have a basic understanding of organic synthesis and cell biology techniques.

3D Temperature-Controlled Interchangeable Pattern for Size-Selective Nanoparticle Capture.

Patterned surfaces with distinct regularity and structured arrangements have attracted great interest due to their extensive promising applications. Although colloidal patterning has conventionally been used to create such surfaces, herein, we introduce a novel 3D patterned poly(N-isopropylacrylamide) (PNIPAM) surface, synthesized by using a combination of colloidal templating and surface-initiated photoinduced electron transfer-reversible addition-fragmentation chain transfer (SI-PET-RAFT) polymerization. In order to investigate the temperature-driven 3D morphological variations at a lower critical solution temperature (LCST) of ∼32 °C, multifaceted characterization techniques were employed. Atomic force microscopy confirmed the morphological transformations at 20 and 40 °C, while water contact angle measurements, upon heating, revealed distinct trends, offering insights into the correlation between surface wettability and topography adaptations. Moreover, quartz crystal microbalance with dissipation monitoring and electrochemical measurements were employed to detect the topographical adjustments of the unique hollow capsule structure within the LCST. Tests using different sizes of PSNPs shed light on the size-selective capture-release potential of the patterned PNIPAM, accentuating its biomimetic open-close behavior. Notably, our approach negates the necessity for expensive proteins, harnessing temperature adjustments to facilitate the noninvasive and efficient reversible capture and release of nanostructures. This advancement hopes to pave the way for future innovative cellular analysis platforms.

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.

Phenanthroline Derivatives as Efficient Organic Photocatalysts for Visible‐Light‐Mediated PET‐RAFT Polymerization

Comprehensive SummaryPhenanthroline is an excellent and stable π‐electron acceptor with a large conjugated chromophore. Phenanthroline derivatives are widely used in adsorption, photodegradation, solar cells, biology, and so on. At present, there are still limited organic molecules utilized to efficiently photocatalyze reversible‐deactivation radical polymerization (RDRP). Therefore, the design of organic photocatalysts (OPCs) for RDRP remains a challenge. Herein, according to the strategy of combining the donor groups and weak acceptor groups, donor‐acceptor (D‐A) type OPCs based on phenanthroline were utilized for the first time in photoinduced electron transfer‐reversible addition‐fragmentation chain transfer (PET‐RAFT) polymerization. 1,10‐Phenanthroline‐5‐amine (Aphen) with a donor group‐amino was screened out for efficacious photo‐controlled radical polymerization under blue light for various monomers with conjugated and unconjugated structures with high monomer conversion and well‐defined narrow dispersity polymers (Đ &lt; 1.20). Controllable homo‐polymers and block copolymers were successfully realized by chain extension reaction and block copolymerization of structurally diverse monomers.

Recognition of “Oxygen-/Water-Fueled” PET-RAFT Protocol Matched to Covalent Organic Frameworks

The reactive oxygen species (ROS)-mediated photoinduced electron transfer reversible addition-fragmentation chain transfer (PET-RAFT) process is an attractive tool to enhance the oxygen tolerance of radical polymerization systems. In this paper, we investigate the relationship between the covalent organic framework (COF) structure and polymerization performance based on the O2•–/H2O system by modulating the COF at atomic and molecular levels. We combine density functional theory (DFT) calculations and experiments to clarify the “oxygen-/water-fueled” PET-RAFT polymerization mechanism and identify the key steps of the protocol. Based on the modulation of the TD-1 COF template structure, the relatively efficient charge–hole separation efficiency allows the matching of TD-2 COF and TD-3 COF with the O2•–/H2O system to achieve high-quality RAFT polymerization, providing insights into the rational design and development of catalytic systems with better performance.

Synthesis of hyperbranched polymer films via electrodeposition and oxygen-tolerant surface-initiated photoinduced polymerization

HypothesisHyperbranched polymers, not only possess higher functionality, but are also easier to prepare compared to dendrimers and dendric polymers. Combining electrodeposition and surface-initiated photoinduced electron transfer-reversible addition-fragmentation chain transfer (SI-PET-RAFT) polymerization is hypothesized to be a novel strategy for preparing hyperbranched polymer films on conductive surfaces without degassing. ExperimentsPolymer brush grafted films with four different architectures (i.e. linear, branched, linear-block-branched, and branched-block-linear) were prepared on gold-coated glass substrates using electrodeposition, followed by SI-PET-RAFT polymerization. The resulting film structure and thickness, surface topology, absorption property, and electrochemical behavior were confirmed by spectroscopy, microscopy, microbalance technique, and impedance measurement. FindingsThese hyperbranched polymer brushes were capable of forming a thicker but more uniformly covered films compared to linear polymer brush films, demonstrating that hyperbranched polymer films can be potentially useful for fabricating protective polymer coatings on various conductive surfaces.

SI-PET-RAFT in flow: improved control over polymer brush growth.

Surface-initiated photoinduced electron transfer-reversible addition-fragmentation chain transfer (SI-PET-RAFT) provides a light-dependent tool to synthesize polymer brushes on different surfaces that tolerates oxygen and water, and does not require a metal catalyst. Here we introduce improved control over SI-PET-RAFT polymerizations via continuous flow conditions. We confirm the composition and topological structure of the brushes by X-ray photoelectron spectroscopy, ellipsometry, and AFM. The improved control compared to no-flow conditions provides prolonged linear growth of the polymer brush (up to 250 nm, where no-flow polymerization maxed out <50 nm), and improved polymerization control of the polymer brush that allows the construction of diblock polymer brushes. We further show the linear correlation between the molecular weight of the polymer brush and its dry thickness by combining ellipsometry and single-molecule force spectroscopy.

Influence laws of air gap structure manipulation of covalent organic frameworks on dielectric properties and exciton effects for photopolymerization.

Boosting the dissociation of excitons is essential to enhance the photocatalytic efficiency. However, the relationship between the structure of the catalyst and the exciton effect on the photocatalytic activity is still unclear as the main problem. Here, it is proposed that as a descriptive factor, an experimentally measurable dielectric constant (εr) is available to quantitatively describe its relationship with exciton binding energy (Eb) and photocatalytic activity. With tuning the linker of covalent organic frameworks (COFs), the "air gap" structure is oriented to shrink, leading to an increased εr of COFs and a lower Eb to facilitate exciton dissociation. Meanwhile, taking "water-/oxygen-fueled" photo-induced electron transfer reversible addition-fragmentation chain transfer (PET-RAFT) polymerization as a demonstration platform, it can be seen that COFs with a small "air gap" structure have relatively superior photocatalytic activity. This provides important implications for the evolution of efficient photocatalysts.

Activity Improvement and Thermal Stability Enhancement of D-Aminoacylase Using Protein-Polymer Conjugates

In this study, the synthesis of new polymer-protein conjugates using a grafting-from strategy was performed by employing photo-induced electron transfer reversible addition-fragmentation chain transfer (PET-RAFT) polymerization. D-aminoacylase is an industrially significant enzyme for the preparation of chiral amino acids and it is coupled with reversible addition-fragmentation (RAFT) chain transfer agent (CTA) using activated ester chemistry. The effects of polymeric side chain compositions on the activity of D-aminoacylase were studied with two different polymeric side chain lengths. For this reason, two monomers, a hydrophilic N-(2-aminoethyl acrylamide) and a hydrophobic and N- (iso-butoxymethyl) acrylamide were used, respectively. It was found that modification by grafting from strategy increased the thermal stability of D-aminoacylase enzyme. Additionally, the hydrophobic monomer conjugate has been reported to increase the activity of the enzyme more than the hydrophilic monomer.

Antiviral Polymer Brushes by Visible-Light-Induced, Oxygen-Tolerant Covalent Surface Coating

This work presents a novel route for creating metal-free antiviral coatings based on polymer brushes synthesized by surface-initiated photoinduced electron transfer-reversible addition-fragmentation chain transfer (SI-PET-RAFT) polymerization, applying eosin Y as a photocatalyst, water as a solvent, and visible light as a driving force. The polymer brushes were synthesized using N-[3-(decyldimethyl)-aminopropyl] methacrylamide bromide and carboxybetaine methacrylamide monomers. The chemical composition, thickness, roughness, and wettability of the resulting polymer brush coatings were characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), water contact angle measurements, and ellipsometry. The antiviral properties of coatings were investigated by exposure to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and avian influenza viruses, with further measurement of residual viable viral particles. The best performance was obtained with Cu surfaces, with a ca. 20-fold reduction of SARS-Cov-2 and a 50-fold reduction in avian influenza. On the polymer brush-modified surfaces, the number of viable virus particles decreased by about 5-6 times faster for avian flu and about 2-3 times faster for SARS-CoV-2, all compared to unmodified silicon surfaces. Interestingly, no significant differences were obtained between quaternary ammonium brushes and zwitterionic brushes.

Synthesis of zwitterionic copolymer containing sulfobetaine and catechol for antibacterial application

• A catechol zwitterionic copolymer was handily prepared by PET-RAFT polymerization. • Polymer grafted surfaces were readily fabricated via solution deposition method. • Incorporation of catechol rendered copolymer excellent antibacterial potency. Catechol-modified zwitterionic polymers have been successfully applied for functional modification of surfaces. However, catechol derivatives synthesized by atom transfer radical polymerization (ATRP) involve complicated procedures and harsh conditions. In this study, a random copolymer P(SBMA- co -DA) (PSD) was prepared from sulfobetaine methacrylate (SBMA) and N-3,4-dihydroxybenzenethyl methacrylamide (DA) by photo-induced electron transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization technique. Staphylococcus aureus adhesion assay showed that PSD possessed similarly powerful antibacterial performance at high concentration as compared to dopamine-modified poloxamer 407, while PSBMA (PSB) exhibited no obvious antibacterial potency. We believe that the facile method will be beneficial to synthesis of catechol-containing polymers for different applications.

Binary Hybridization Strategy toward Stable Porphyrinic Zr‐MOF Encapsulated Perovskites as High‐Performance Heterogeneous Photocatalysts for Red to NIR Light‐Induced PET‐RAFT Polymerization

AbstractStable binary nanohybrids based on all‐inorganic halide perovskite encapsulated in porphyrinic Zr‐MOF (PCN‐222) are constructed for photoinduced electron transfer‐reversible addition‐fragmentation chain transfer (PET‐RAFT) polymerization. The synergistic effect of perovskite and PCN‐222 endows the photocatalyst with high‐efficiency photogenic charge carrier separation and light absorption property. CsPbI3@PCN‐222 (20%) is finally screened out as the oxygen and solvent‐resistant photocatalyst for highly efficient photo‐controlled polymerization of conjugated and unconjugated monomers under red to near infrared (NIR) light with high monomer conversion and narrow molecular weight distribution well‐defined polymers (Đ &lt; 1.20). Controllable polymers and ultrahigh molecular weight polymers (up to 1730000 g mol−1) are successfully obtained by chain extension and block copolymerization of various monomers. The constructed photocatalysts easily achieve excellent light and temporal control, and even show high MMA conversion with NIR light under a thick barrier.

Homopolymer-block-Alternating Copolymers Composed of Acrylamide Units: Design of Transformable Divinyl Monomers and Sequence-Specific Thermoresponsive Properties.

In this work, we synthesized an acrylamide-based terpolymer that is a block copolymer composed of an AB alternating copolymer and a C homopolymer. The key to the unprecedented achievement is rational design of an acrylate-acrylamide divinyl monomer carrying CF3-substituted salicylic acid ester bonds (AAm-CF3) to realize the efficient and selective cyclopolymerization as well as the quantitative transformation of the resultant cyclorepeating units. The selectivity in the cyclopolymerization and the pendant transformation ability were evaluated through reactivity ratios of the corresponding model monomers and quantitative aminolysis reactions of the model compound. The cyclopolymerization via the photoinduced electron transfer-reversible addition-fragmentation chain transfer (PET-RAFT) process with a macrochain-transfer agent and subsequent aminolysis reaction afforded the homopolymer-block-alternating copolymer. The sequence-controlled terpolymer exhibited a very unique thermal response behavior in water that was strikingly different from the corresponding sequence-uncontrolled terpolymers, such as homopolymer-block-statistical copolymers and all statistical terpolymers, despite the fact that the structure cannot be distinguished by 1H NMR.

Anti-UV and hydrophobic dual-functional coating fabrication for flame retardant polyester fabrics by surface-initiated PET RAFT technique

Inspired by the flourish of living radical polymerization (LRP), surface-initiated LPR technology shows great potential in good control and accurate tailoring of target polymer coatings. In this work, surface-initiated photoinduced electron transfer-reversible addition-fragmentation chain transfer polymerization (SI-PET-RAFT) was employed as a facile synthetic rout for the fabrication of surface-tethered polymeric brushes with anti-UV and hydrophobic properties for flame retardant polyester fabrics (FRPET). Firstly, RAFT agent 4-Cyano-4-[(dodecyl sulfanyl thiocarbonyl) sulfanyl] pentanoic acid (CDTPA) was grafted onto polydopamine (PDA) deposited FRPET, followed by the controlled growth of glycidyl methacrylate (GMA) onto polyester fabrics via SI-PET-RAFT method. Finally, benzotriazole anti-UV agents were grafted as secondary functionalization. According to SEM-EDS and XPS analysis, PGMA has been immobilized successfully onto the surface of FRPET fabrics. An efficient PET RAFT polymerization of GMA with low dispersity (Ð<1.2), temporal control, and chain-end fidelity was achieved under mild yellow light irradiation (λmax = 570 nm, 4 W/m2). It also exhibited the feasibility of polymerization under natural sunlight and oxygen tolerance. The flame retardant, UV resistant and hydrophobic properties of the treated fabrics were investigated. In the microscale combustion calorimetry test, the peak heat release rate (PHRR) effectively decreased by 59.50%. In the cone calorimetry test, the PHRR and total heat release also reduced. The melt-dripping was eliminated in the vertical flaming test and reached V-0 rating with LOI value of 28%. The UV transmittance of the fabric decreased to<4%, meeting the standard of UV resistant fabric and the water contact angle reached 125°, thus making flame retardant polyester fabric have good hydrophobicity. Besides, it also kept good durability in flame retardancy, UV shielding and water repellent. This study provides new insights into the surface engineering of photoregulated LRP techniques for multi-functional coating synthesis.

A Porphyrinic Donor-Acceptor Conjugated Porous Polymer as Highly Efficient Photocatalyst for PET-RAFT Polymerization.

Heterogeneous catalysts offer a highly desirable platform for exploring environmental-benign transformation systems, yet, they typically suffer from significant loss of catalytic efficiency compared with their homogeneous counterparts. Here, the facile synthesis of a porphyrinic conjugated porous polymer incorporated with imidazolium bromide moieties by taking advantage of the Debus-Radziszewski reaction is reported. Owing to the unique donor-acceptor structure, this heterogeneous and metal-free photocatalyst exhibits much improved catalytic activity compared with its small molecular analogs in photoinduced electron transfer reversible addition-fragmentation chain transfer (PET-RAFT) polymerization, producing polymers with narrow distribution (Đ = 1.06-1.18) and high degree of chain-end fidelity. Moreover, the heterogeneous catalyst can be easily separated at the end of polymerization by centrifugation and recycled for five independent PET-RAFT polymerizations without obvious decreases in catalytic efficiency.

Controlled Intracellular Polymerization for Cancer Treatment.

Numerous prodrugs have been developed and used for cancer treatments to reduce side effects and promote efficacy. In this work, we have developed a new photoactivatable prodrug system based on intracellular photoinduced electron transfer–reversible addition–fragmentation chain-transfer (PET–RAFT) polymerization. This unique polymerization process provided a platform for the synthesis of structure-predictable polymers with well-defined structures in living cells. The intracellularly generated poly(N,N-dimethylacrylamide)s were found to induce cell cycle arrest, apoptosis, and necroptosis, inhibit cell proliferation, and reduce cancer cell motilities. This polymerization-based “prodrug” system efficiently inhibits tumor growth and metastasis both in vitro and in vivo and will promote the development of targeted and directed cancer chemotherapy.

Rapid Online Analysis of Photopolymerization Kinetics and Molecular Weight Using Diffusion NMR.

Online, high-throughput molecular weight analysis of polymerizations is rare, with most studies relying on tedious sampling techniques and batchwise postanalysis. The ability to track both monomer conversion and molecular weight evolution in real time could underpin precision polymer development and facilitate study of rapid polymerization reactions. Here, we use a single time-resolved diffusion nuclear magnetic resonance (NMR) experiment to simultaneously study the kinetics and molecular weight evolution during a photopolymerization, with in situ irradiation inside the NMR instrument. As a model system, we used a photoinduced electron transfer reversible addition-fragmentation chain transfer (PET-RAFT) polymerization. The data allow diffusion coefficients and intensities to be calculated every 14 s from which the polymer size and monomer conversion can be extracted. Key to this approach is (1) the use of shuffled gradient amplitudes in the diffusion NMR experiment to access reactions of any rate, (2) the addition of a relaxation agent to increase achievable time resolution and, (3) a sliding correction that accounts for viscosity changes during polymerization. Diffusion NMR offers a uniquely simple, translatable handle for online monitoring of polymerization reactions.

Selective Photoactivation of Trithiocarbonates Mediated by Metal Naphthalocyanines and Overcoming Activation Barriers Using Thermal Energy.

Metal naphthalocyanines (MNcs) were demonstrated to be efficient photocatalysts to activate photoinduced electron-transfer reversible addition-fragmentation chain transfer (PET-RAFT) polymerization, enabling well-controlled polymerization of (meth)acrylates under near-infrared (λ = 780 nm) light. Owing to their lower redox potential compared to previously explored photocatalysts, the activation of trithiocarbonate RAFT agents exhibited a unique selectivity that was dependent on the nature of the R group. Specifically, MNcs were capable in activating tertiary R group trithiocarbonates, whereas no activation of the trithiocarbonate possessing a secondary R group was observed. The combination of density functional theory calculations and experimental studies have revealed new mechanistic insights into the factors governing a PET-RAFT mechanism and explained this unique selectivity of MNcs toward tertiary carbon trithiocarbonates. Interestingly, by increasing the reaction temperature moderately (i.e., ∼15 °C), the energy barrier prohibiting the photoactivation of the trithiocarbonate with a secondary R group was overcome, enabling their successful activation.