Photoinduced 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.

Relation of acrylic acid polymerization behavior in deep eutectic solvent to water content: Computer simulation and experiment

Polymerizable deep eutectic solvents (DES) are promising starting materials for preparation of eutectogels and hydrogels that can be applied in drug delivery, as strain sensors and various components of soft electronics. However, the understanding of relationship between the molecular structure, physicochemical properties and polymerization behavior of such systems in pure state and in their mixtures with water is not well studied yet. In this work we report the results of both computer simulation and experimental investigations for polymerizable choline chloride/acrylic acid DES and its mixtures with water. Molecular dynamics was applied to reveal the influence of water on the structure of polymerizable DES at the molecular and supramolecular levels. The diffusion coefficients of DES components with different water content were measured using NMR. The course of photoinduced polymerization of DES/water mixtures was traced using FTIR spectroscopy, while the molar mass and hydrodynamic characteristics of obtained polyacrylic acid were studied by means of static and dynamic light scattering. It was found that addition of water leads to a gradual decrease in size of the acrylic acid clusters that exist in pure DES and is accompanied by an increase in orientation mobility and diffusion coefficients of components. The maximal molar mass was obtained for the polymer prepared by polymerization of DES with 5 wt% of water. This can be attributed to the optimal combination of acrylic acid clusters size and increased mobility of components.

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.

Light-matter interaction during and post polymerization in self-written polymer waveguide integrated with optical fibers

Self-written polymer waveguide is a polymer interconnection structure often integrated with optical fibers. The structure is fabricated by photopolymerization, through which a photon beam initiates a polymerization reaction to change liquid monomer into a solid polymer. During light-matter interaction photoinitiator molecules are excited to the singlet and then to the third state to form free radicals by attaching to the adjacent monomer molecules. The free radicals in turn form polymer chains and cross-linked structures. Photo-induced polymerization leads to a raised refractive index of the monomer and forms an optical waveguide. The change is permanent to allow the process of self-focusing and self-trapping of the propagation light beam and hence guide it to the aligned optical fiber. In this article, light matter interaction during polymer waveguide fabrication and post polymerization has been investigated. A photopolymer system of acrylate-based monomer, co-initiator amine and photo initiator is used to study the absorption of the monomer mixture at the spectral range of 450–550 nm. Then photobleaching was investigated after waveguide fabrication. The optical transmission efficiency of the polymer bridge increases as absorption ceases within the polymer structure such that optical loss reduces from 1.1 dB to about 0.65 dB.

UV-Mediated Facile Fabrication of a Robust, Fully Renewable and Controllably Biodegradable Poly(lactic acid)-Based Covalent Adaptable Network.

A robust and fully biobased covalent adaptable network (CAN) that allows recyclability, biocompatibility, and controlled biodegradability is reported. The CAN was fabricated through a simple photo-cross-linking method, wherein low-molecular-weight poly(lactic acid) (∼3 kDa) was modified with end 1,2-dithiolane rings through a one-step Steglich esterification reaction with thioctic acid (TA). These incorporated 1,2-dithiolane rings undergo photoinduced ring-opening polymerization, thus enabling the cross-linking of poly(lactic acid) with abundant dynamic disulfide bonds. The resultant CAN demonstrates excellent transparency, effective UV-blocking capabilities below 320 nm, robust tensile strength (∼39 MPa), and superior dimensional stability at 80 °C, alongside attractive biocompatibility. Moreover, owing to the dynamic exchange and redox-responsiveness of disulfide bonds, the material can be recycled by hot-pressing and a reduction-oxidation process while also being capable of controllably biodegrading at the end of its lifecycle. Furthermore, it exhibits reconfigurable shape memory properties with fast recovery. This study elucidates a straightforward approach to fabricating multifunctional and sustainable polymer materials with potential applications in diverse fields such as packaging, coating, and biomedicine.

Facile Preconcentration of Cell-Free DNA in Human Plasma by Ion-Specific Poly Ionic Sorbents Featuring an Anion Exchange Mechanism.

The expanding horizon of diagnostic and therapeutic applications involving nucleic acids (NA) requires novel tools for purification, including minimal sample preparation. In this work, thin-film microextraction devices featuring five poly ionic sorbents were examined as anion exchange extraction phases for the rapid purification of NAs. Each sorbent is composed of a nonionic cross-linker and a methacrylate monomer containing a core tetra-alkyl ammonium moiety with an alkyl, anionic, or cationic residue. Extraction devices were produced through the application of the prepolymer sorbent mixture onto a functionalized nitinol metal support followed by photoinduced free-radical polymerization. The miniaturized extraction devices (10 mm × 3.5 mm) were directly immersed into aqueous samples to isolate NAs via electrostatic interactions with the polycation. The ammonium methacrylate (AMA) monomer containing a propyl trimethylammonium group (AMA-C3N(CH3)3) exhibited the highest affinity for DNA, with 80 ± 10% of DNA being isolated. Recovery of DNA from the sorbents required the introduction of ions in an aqueous solution to exchange the anionic biopolymer from the polycationic moiety. An investigation of three anion species revealed that the AMA-C3N(CH3)3 sorbent showed the highest recoveries, with the perchlorate anion producing a preconcentration factor of 4.36 ± 0.86 while requiring only 250 mM NaClO4. A directly compatible quantitative polymerase chain reaction assay was developed to quantify the recovery of spiked DNA with lengths of 830, 204, and 98 base pairs in heat-treated human plasma. The AMA-C3N(CH3)3 sorbent was uninhibited by the complex human plasma matrix and enabled high preconcentration factors for the spiked DNA at a biologically relevant concentration of 10 pg/mL. While Qiagen's circulating cell-free DNA MinElute extraction kit enabled higher preconcentration of all analytes, the methodology described in this work requires fewer steps, less user intervention, and minimal equipment requirements to isolate DNA, making it more amenable for high-throughput and low resource applications.

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.

Microencapsulation of phase change materials (PCMs) at low temperature using a novel thin film UV reactor

Phase-change materials (PCMs) have shown great promise for energy management in buildings and gained attention in the field of sustainable and energy-efficient construction. However, to fully utilize PCMs, their proper containment is vital. In this study, a photo-induced polymerization process using a new thin film UV reactor at room temperature for PCM microencapsulation in polymer shells of different acrylate-based monomers was investigated. Four different acrylate-based monomers were investigated: namely, methyl methacrylate (MMA), ethyl acrylate (EAA), butyl acrylate (BAA), and tert-butyl acrylate (TBMA). Commercial Rubitherm’s RT21 PCM (Tpeak,melting ∼ 21 °C and ΔH = 123 kJ/kg) and Irgacure® 819 as a photosensitive initiator were used. When MMA or EAA were used, scanning electron microscopy (SEM) images revealed smooth surfaces of PCM microcapsules (m-PCMs) with a hemispherical shape. While m-PCMs with rough surfaces, buckles, and dimples were found when BAA and TBMA were applied. The results showed that the highest levels of microencapsulation efficiency, yield, and PCM content were observed for MMA and EAA samples. The TBMA sample shows low values of microencapsulation efficiency and yield (about 29.1 and 53.4 %, respectively). Furthermore, results showed that adding cross-linking agents to the recipe has had multiple favourable effects. It has mitigated sub-cooling, increased PCM content, improved microencapsulation efficiency, and boosted the overall yield of PCM. In conclusion, the current work will contribute to the development of a microencapsulation technology of PCMs that overcomes the shortcomings of long time and high temperature needed in the present traditional microencapsulation procedure.

A Smart Window with Passive Radiative Cooling and Switchable Near-Infrared Light Transmittance via Molecular Engineering.

Smart windows with synergetic light modulation have heightened demands for applications in smart cars and novel buildings. However, improving the on-demand energy-saving efficiency is quite challenging due to the difficulty of modulating sunlight with a broad bandwidth in an energy-saving way. Herein, a smart window with switchable near-infrared light transmittance and passive radiative cooling is prepared via a monomer design strategy and photoinduced polymerization. The effects of hydrogen bonds and fluorine groups in acrylate monomers on the electro-optical properties as well as microstructures of polymer-dispersed liquid crystal films have been systematically studied. Some films show a high contrast ratio of 90.4 or a low threshold voltage (Vth) of 2.0 V, which can be roll-to-roll processed in a large area. Besides, the film has a superior indoor temperature regulation ability due to its passive radiative cooling and controllable near-infrared light transmittance properties. Its radiative cooling efficiency is calculated to be 142.69 W/m2 and NIR transmittance could be switched to below 10%. The introduction of a carboxylic monomer and fluorinated monomer into the system endows the film with a highly efficient temperature management capability. The film has great potential for applications in fields such as flexible smart windows, camouflage materials, and so on.

Robust Miniemulsion PhotoATRP Driven by Red and Near-Infrared Light.

Photoinduced polymerization techniques have gathered significant attention due to their mild conditions, spatiotemporal control, and simple setup. In addition to homogeneous media, efforts have been made to implement photopolymerization in emulsions as a practical and greener process. However, previous photoinduced reversible deactivation radical polymerization (RDRP) in heterogeneous media has relied on short-wavelength lights, which have limited penetration depth, resulting in slow polymerization and relatively poor control. In this study, we demonstrate the first example of a highly efficient photoinduced miniemulsion ATRP in the open air driven by red or near-infrared (NIR) light. This was facilitated by the utilization of a water-soluble photocatalyst, methylene blue (MB+). Irradiation by red/NIR light allowed for efficient excitation of MB+ and subsequent photoreduction of the ATRP deactivator in the presence of water-soluble electron donors to initiate and mediate the polymerization process. The NIR light-driven miniemulsion photoATRP provided a successful synthesis of polymers with low dispersity (1.09 ≤ Đ ≤ 1.29) and quantitative conversion within an hour. This study further explored the impact of light penetration on polymerization kinetics in reactors of varying sizes and a large-scale reaction (250 mL), highlighting the advantages of longer-wavelength light, particularly NIR light, for large-scale polymerization in dispersed media owing to its superior penetration. This work opens new avenues for robust emulsion photopolymerization techniques, offering a greener and more practical approach with improved control and efficiency.

Use of pyridine derivatives as inhibitor/retarding agent for photoinduced cationic polymerization of epoxides

In this study, the cationic photopolymerization of epoxy controlled by pyridine derivative was investigated. Two pyridines were selected in order to explore the impact of the associated pKa and the amine steric hindrance on the polymerization. The inhibition, the polymerization rate, the heat flow and the conversion during dark polymerization were found to be affected depending of the pyridine derivative structure. Two mechanisms seem to be involved. 1) During the initiation step, the proton is trapped by pyridine derivative, a fact which delays the polymerization reaction, because of less growing chains and lower exothermicity. 2) During the propagation reaction, an interaction between the oxonium ion and the pyridine derivative takes place, which results in a decrease of the rate of polymerization. These two mechanisms depend on the concentration, but also on the associated pKa and on the steric hindrance of the amine, which allows a tailorable control over the cationic polymerization kinetics.

Precise Regulation in Chain-Edge Structural Microenvironments of 1D Covalent Organic Frameworks for Photocatalysis.

Covalent organic frameworks (COFs) constitute a promising research topic for photocatalytic reactions, but the rules and conformational relationships of 1D COFs are poorly defined. Herein, the chain edge structure is designed by precise modulation at the atomic level, and the 1D COFs bonded by C, O, and S elements is directionally prepared for oxygen-tolerant photoinduced electron transfer-atom transfer radical polymerization (PET-ATRP) reactions. It is demonstrated that heteroatom-type chain edge structures (─O─, ─S─) lead to a decrease in intra-plane conjugation, which restricts the effective transport of photogenerated electrons along the direction of the 1D strip. In contrast, the all-carbon type chain edge structure (─C─) with higher intra-plane conjugation not only reduces the energy loss of photoexcited electrons but also enhances the carrier density, which exhibits the optimal photopolymerization performance. This work offers valuable guidance in the exploitation of 1D COFs for high photocatalytic performance. This work offers valuable guidance in the exploitation of 1D COFs for high photocatalytic performance.

Penta-Methine Cyanine IRTs: Enabling NIR or Visible Photoinduced Polymerization of Acrylate and Thiol–Ene for Preparation of Polychromatic and Color-Changing Polymers

Penta-Methine Cyanine IRTs: Enabling NIR or Visible Photoinduced Polymerization of Acrylate and Thiol–Ene for Preparation of Polychromatic and Color-Changing Polymers

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.

Hybrid deterministic and stochastic approach for dynamic simulation of photoinduced atom-transfer radical polymerization processes with microscopic resolution

Among the various polymerization mechanisms available for producing polymers, photoinduced atom-transfer radical polymerization (photoATRP) stands out as a promising technique. By utilizing light as an external stimulus, photoATRP facilitates the production of well-defined polymers with precise distributions. The demand for advanced polymeric materials synthesis necessitates a deep understanding of polymer chains at the molecular level. As molecular weight distribution (MWD) is a key quality index of polymers, developing models with embedded MWD information holds significance for process design and optimization tasks. In this work, an accelerated hybrid deterministic and stochastic approach is proposed for simulating dynamic photoATRP processes. The proposed approach demonstrates computational efficiency and flexibility, enabling precise predictions for the evolution of both macroscopic and microscopic properties of polymers. An application to a batch photoATRP system model is presented to illustrate the validity and performance of the proposed hybrid approach.

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.

Photoinduced Metal-Free Atom Transfer Radical Polymerization for the Modification of Cellulose with Poly(N-isopropylacrylamide) to Create Thermo-Responsive Injectable Hydrogels.

Photoinduced metal-free ATRP has been successfully applied to fabricate thermo-responsive cellulose graft copolymer (PNIPAM-g-Cell) using 2-bromoisobuturyl bromide-modified cellulose as the macroinitiator. The polymerization of N-isopropylacrylamide (NIPAM) from cellulose was efficiently activated and deactivated with UV irradiation in the presence of an organic-based photo-redox catalyst. Both FTIR and 13C NMR analysis confirmed the structural similarity between the obtained PNIPAM-g-Cell and that synthesized via traditional ATRP methods. When the concentration of the PNIPAM-g-Cell is over 5% in water, it forms an injectable thermos-responsive hydrogel composed of micelles at 37 °C. Since organic photocatalysis is a metal-free ATRP, it overcomes the challenge of transition-metal catalysts remaining in polymer products, making this cellulose-based graft copolymer suitable for biomedical applications. In vitro release studies demonstrated that the hydrogel can continuously release DOX for up to 10 days, and its cytotoxicity indicates that it is highly biocompatible. Based on these findings, this cellulose-based injectable, thermo-responsive drug-loaded hydrogel is suitable for intelligent drug delivery systems.

Antimony-Based Halide Perovskite Nanoparticles as Lead-Free Photocatalysts for Controlled Radical Polymerization.

Metal halide perovskites have emerged as versatile photocatalysts to convert solar energy for chemical processes. Perovskite photocatalyzed polymerization draws special attention due to its straightforward synthesis process and the ability to create advanced perovskite-polymer nanocomposites. Herein, this work employs Cs3Sb2Br9 perovskite nanoparticles (NPs) as a lead-free photocatalyst for light-controlled atom transfer radical polymerization (ATRP). Cs3Sb2Br9 NPs exhibit high reduction potential and interact with electronegative bromide initiator with Lewis acid Sb sites, enabling efficient photoinduced reduction of initiators and controlled polymerization under blue light irradiation. Methacrylate monomers with various functional groups are successfully polymerized, and the resulting polymer showcased a dispersity (Đ) as small as 1.27. The living nature of polymerization is confirmed by high chain end fidelity and kinetic studies. Moreover, Cs3Sb2Br9 NPs serve as heterogeneous photocatalysts, demonstrating recyclability and reusability for up to four cycles. This work presents a promising approach to overcome the limitations of lead-based perovskites in photoinduced controlled radical polymerization, offering a sustainable and efficient alternative for the synthesis of well-defined polymeric materials.