Logic-Controlled Radical Polymerization with Heat and Light: Multiple-Stimuli Switching of Polymer Chain Growth via a Recyclable, Thermally Responsive Gel Photoredox Catalyst

Combining photocontrolled-cationic and anionic-group-transfer polymerizations using a universal mediator: enabling access to two- and three-mechanism block copolymers

An ongoing challenge in polymer chemistry is accessing diverse block copolymers from multiple polymerization mechanisms and monomer classes. One strategy to accomplish this goal without intermediate compatibilization steps is the use of universal mediators. Thiocarbonyl thio (TCT) functional groups are well-known mediators to combine radical with either cationic or anionic polymerization, but a sequential cationic-anionic universal mediator system has never been reported. Herein, we report a TCT universal mediator that can sequentially perform photocontrolled cationic polymerization and thioacyl anionic group transfer polymerization to access poly(ethyl vinyl ether)-block-poly(thiirane) polymers for the first time. Thermal analyses of these block copolymers provide evidence of microphase separation. The success of this system, along with the established compatibility of radical polymerization, enabled us to further chain extend the cationic-anionic diblock using radical polymerization of N-isopropylacrylamide. The resulting terpolymer represents the first example of a triblock made from three different monomer classes incorporated via three different mechanisms without any end-group modification steps. The development of this simple, sequential synthesis using a universal mediator approach opens up new possibilities by providing facile access to diverse block copolymers of vinyl ethers, thiiranes, and acrylamides.

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.

Nucleic Acid-Binding Dyes as Versatile Photocatalysts for Atom-Transfer Radical Polymerization

Nucleic acid-binding dyes (NuABDs) are fluorogenic probes that light up after binding to nucleic acids. Taking advantage of their fluorogenicity, NuABDs have been widely utilized in the fields of nanotechnology and biotechnology for diagnostic and analytical applications. We demonstrate the potential of NuABDs together with an appropriate nucleic acid scaffold as an intriguing photocatalyst for precisely controlled atom-transfer radical polymerization (ATRP). Additionally, we systematically investigated the thermodynamic and electrochemical properties of the dyes, providing insights into the mechanism that drives the photopolymerization. The versatility of the NuABD-based platform was also demonstrated through successful polymerizations using several NuABDs in conjunction with diverse nucleic acid scaffolds, such as G-quadruplex DNA or DNA nanoflowers. This study not only extends the horizons of controlled photopolymerization but also broadens opportunities for nucleic acid-based materials and technologies, including nucleic acid-polymer biohybrids and stimuli-responsive ATRP platforms.

Universal Strategy for Inorganic Nanoparticle Incorporation into Mesoporous Liquid Crystal Polymer Particles

Developing inorganic-organic composite polymers necessitates a new strategy for effectively controlling shape and optical properties while accommodating guest materials, as conventional polymers primarily act as  carriers that transport inorganic substances. Here, a universal approach is introduced utilizing mesoporous liquid crystal polymer particles (MLPs) to fabricate inorganic-organic composites. By leveraging the liquid crystal phase, morphology and optical properties are precisely controlled through the molecular-level arrangement of the host, here monomers. The controlled host material allows the synthesis of inorganic particles within the matrix or accommodation of presynthesized nano-inorganic particles, all while preserving the intrinsic properties of the host material. This composite material surpasses the functional capabilities of the polymer alone by sequentially integrating one or more inorganic materials, allowing for the incorporation of multiple functionalities within a single polymer particle. Furthermore, this approach effectively mitigates the drawbacks associated with guest materials resulting in a substantial enhancement of composite performance. The presented approach is anticipated to hold immense potential for various applications in optoelectronics, catalysis, and biosensing, addressing the evolving demands of the society.

Growth kinetics and morphology characterization of binary polymeric fluid under random photo-illumination

We present a comprehensive study using dissipative particle dynamics simulations to investigate phase separation kinetics (PSK) in three-dimensional (3d) polymeric fluids under random photo-illumination. We consider two scenarios: polymer blends with active radicals at one end of each immiscible chain and block copolymer (BCP) melts with photosensitive bonds linking incompatible blocks. The phase separation (PS) is induced by temperature quench of the initial homogeneously mixed system. Simultaneously, the system experiences random photo-illumination, simulated by two concurrent random events: (a) the recombination of active radicals in polymer blends and (b) the breaking of photosensitive bonds in BCP chains. Variations in the bond-breaking probability, Pb, mimic the change in light intensity. The length scale follows power law growth, R(t) ∼ tϕ, where ϕ represents the growth exponent. Increasing Pb results in a gradual transition in growth kinetics from micro-PS to macro-PS, accompanied by corresponding transition probabilities for both systems. Micro-PSK dominates the evolution process at low Pb values. The scaling functions exhibit data overlap for most scaled distances, indicating the statistical self-similarity of evolving patterns. Our study enhances the understanding of PSK in polymeric fluids, revealing the impact of photosensitive bonds and active radicals. Furthermore, it suggests the potential for designing novel polymeric materials with desired properties.

Near-Infrared Light and Acid/Base Dual-Regulated Polymerization Utilizing Imidazole-Anion-Fused Perylene Diimides as Photocatalysts

This work presents the first example of acid/base-responsive and near-infrared (NIR)-absorbing photocatalysts based on imidazole-anion-fused perylene diimide chromophores. The photocatalysts were in situ generated by deprotonation of imidazole-fused perylene diimide under an alkaline environment. NIR (λ = 730 nm, 128 mW/cm2) photoinduced atom transfer radical polymerization (ATRP) was implemented, exhibiting high efficiency and excellent livingness under ppm level of photocatalysts (15 ppm relative to monomer) and Cu(II) complex (10 ppm relative to monomer) concentrations. The method showed capabilities to polymerize behind opaque barriers (i.e., paper and pig skin) and under aerobic condition. Notably, this work demonstrated a dual temporal control of polymerization by adding weak base/acid and switching NIR light on/off. The polymerization can even be halted by bubbling CO2 and was then fully recovered by adding triethylamine. The NIR photoATRP of acrylamide monomers in aqueous solution was also performed, which can be regulated by the change of pH.

Photocatalytic ATRP Depolymerization: Temporal Control at Low ppm of Catalyst Concentration

A photocatalytic ATRP depolymerization is introduced that significantly suppresses the reaction temperature from 170 to 100 °C while enabling temporal regulation. In the presence of low-toxicity iron-based catalysts and under visible light irradiation, near-quantitative monomer recovery could be achieved (up to 90%), albeit with minimal temporal control. By employing ppm concentrations of either FeCl2 or FeCl3, the depolymerization during the dark periods could be completely eliminated, thus enabling temporal control and the possibility to modulate the rate by simply turning the light "on" and "off". Notably, our approach allowed preservation of the end-group fidelity throughout the reaction, could be carried out at high polymer loadings (up to 2M), and was compatible with various polymers and light sources. This methodology provides a facile, environmentally friendly, and temporally regulated route to chemically recycle ATRP-synthesized polymers, thus opening the door for further opportunities.

Cooperative and Orthogonal Switching in the Solid State Enabled by Metal-Organic Framework Confinement Leading to a Thermo-Photochromic Platform

Cooperative behavior and orthogonal responses of two classes of coordinatively integrated photochromic molecules towards distinct external stimuli were demonstrated on the first example of a photo-thermo-responsive hierarchical platform. Synergetic and orthogonal responses to temperature and excitation wavelength are achieved by confining the stimuli-responsive moieties within a metal-organic framework (MOF), leading to the preparation of a novel photo-thermo-responsive spiropyran-diarylethene based material. Synergistic behavior of two photoswitches enables the study of stimuli-responsive resonance energy transfer as well as control of the photoinduced charge transfer processes, milestones required to advance optoelectronics development. Spectroscopic studies in combination with theoretical modeling revealed a nonlinear effect on the material electronic structure arising from the coordinative integration of photoresponsive molecules with distinct photoisomerization mechanisms. Thus, the reported work covers multivariable facets of not only fundamental aspects of photoswitch cooperativity, but also provides a pathway to modulate photophysics and electronics of multidimensional functional materials exhibiting thermo-photochromism.

Lamp vs Laser: A Visible Light Photoinitiator That Promotes Radical Polymerization at Low Intensities and Cationic Polymerization at High Intensities

A visible light absorbing anthraquinone derivative 1-tosyloxy-2-methoxy-9,10-anthraquinone (QT) mediates both cationic and radical polymerizations depending on the intensity of visible light used. A previous study showed that this initiator generates para-toluenesulfonic acid through a stepwise, two-photon excitation mechanism. Thus, under high-intensity irradiation, QT generates acid in sufficient quantities to catalyze the cationic ring-opening polymerization of lactones. However, under low-intensity (lamp) conditions, the two-photon process is negligible, and QT photooxidizes DMSO, generating methyl radicals which initiate the RAFT polymerization of acrylates. This dual capability was utilized to switch between radical and cationic polymerizations to synthesize a copolymer using a one-pot procedure.

Switchable DNA Photocatalysts for Radical Polymerization Controlled by Chemical Stimuli

Polymerization catalysts that activate in response to specific chemical triggers offer spatial and temporal control over polymer synthesis, facilitating the development of responsive materials and custom polymer coatings. However, existing catalysts switch their activity through mechanisms that are not generalizable to chemically diverse stimuli. To approach the level of control exhibited in biological polymer synthesis, switchable polymerization catalysts need to be configurable for activation in response to diverse chemical stimuli. Here, we combine synthetic photocatalysts with conformation-switching DNA aptamers to create polymerization catalysts that respond to diverse chemical stimuli. We use the secondary structure of DNA to bring a photocatalyst and quencher dye into proximity, turning off photocatalysis. The DNA structure can be precisely designed to change conformation in response to a molecular trigger, moving the photocatalyst far from the quencher and activating photocatalysis. We show these photocatalysts can initiate free-radical polymerization to form bulk hydrogels in response to complementary DNA, a metal ion (Zn2+), or small molecules (glucose and hydrocortisone). We demonstrate the biocompatibility of these switchable photocatalysts by triggering their activation on the surface of yeast cells. Finally, we perform reversible-deactivation radical polymerization through photoinduced electron/energy transfer reversible addition-fragmentation chain-transfer in a dual-stimulus manner, in which catalytic activity is regulated reversibly by photoirradiation and the conformational state of the DNA catalyst. These results demonstrate that DNA conformational changes triggered by chemically diverse stimuli can regulate the activity of radical polymerization photocatalysts. This platform offers new capabilities in spatially and temporally controlled polymer synthesis, with potential applications in diagnostics, sensing, and environmentally responsive materials.

Temperature- and pH-Responsive Polymeric Photocatalysts for Enhanced Control and Recovery

The emergence of heterogeneous photocatalysis has facilitated redox reactions with high efficiency, without compromising the recyclability of the photocatalyst. Recently, stimuli-responsive heterogeneous photocatalytic materials have emerged as a powerful synthetic tool, with simple and rapid recovery, as well as an enhanced dynamic control over reactions. Stimuli-responsive polymers are often inexpensive and easy to produce. They can be switched from an active "on" state to an inert "off" state in response to external stimuli, allowing the production of photocatalyst with adaptability, recyclability, and orthogonal control on different chemical reactions. Despite this versatility, the application of artificial smart material in the field of heterogeneous photocatalysis has not yet been maximized. In this Minireview, we will examine the recent developments of this emerging class of stimuli-responsive heterogeneous photocatalytic systems. We will discuss the synthesis route of appending photoactive components into different triggerable systems and, in particular, the controlled activation and recovery of the materials.

Recent advances utilized in artificial switchable catalysis

Developing "green" catalytic systems with desirable performance such as solubility, recyclability, and switchability is a great challenge. However, inspired by nature, the studies on synthesis and activity of artificial switchable metal catalysts and organocatalysts have become an intense, fervid, and challenging field of research. The peculiarity of these catalysts is that they can be generally triggered in the "on" or "off" states by several external stimuli such as light, heat, solvents, pH change, coordination events or ion influxes, redox processes, mechanical forces, or other changes in reaction conditions. A large number of review articles are available in these areas. However, most efforts are currently focused on the invention of new types of switchable catalysts with different forms of stimuli-response units incorporated within their architectures in order to achieve control over the catalytic activity and regio-, chemo- and stereocontrol of various chemical reactions. Thus, in this review, we begin with a brief introduction to switchable catalysts, followed by discussion of types of stimuli and the influence factors on their activities in the field of biomedical engineering, and catalysis as well as related catalytic mechanisms summarized and discussed. The emphasis is on the recent advances utilized in artificial switchable catalysis.

Atom Transfer Radical Polymerization: A Mechanistic Perspective

Since its inception, atom transfer radical polymerization (ATRP) has seen continuous evolution in terms of the design of the catalyst and reaction conditions; today, it is one of the most useful techniques to prepare well-defined polymers as well as one of the most notable examples of catalysis in polymer chemistry. This Perspective highlights fundamental advances in the design of ATRP reactions and catalysts, focusing on the crucial role that mechanistic studies play in understanding, rationalizing, and predicting polymerization outcomes. A critical summary of traditional ATRP systems is provided first; we then focus on the most recent developments to improve catalyst selectivity, control polymerizations via external stimuli, and employ new photochemical or dual catalytic systems with an outlook to future research directions and open challenges.

Photoredox Catalysis in Photocontrolled Cationic Polymerizations of Vinyl Ethers

ConspectusAdvances in photocontrolled polymerizations have expanded the scope of polymer architectures and structures that can be synthesized for various applications. The majority of these polymerizations have been developed for radical processes, which limits the diversity of monomers that can be used in macromolecular design. More recent developments of photocontrolled cationic polymerizations have taken a step toward addressing this limitation and have expanded the palette of monomers that can be used in stimuli-regulated polymerizations, enabling the synthesis of previously inaccessible polymeric structures. This Account will detail our group's studies on cationic polymerization processes where chain growth is regulated by light and highlight how these methods can be combined with other stimuli-controlled polymerizations to precisely dictate macromolecular structure.Photoinitiated cationic polymerizations are well-studied and important processes that have control over initiation. However, we wanted to develop systems where we had spatiotemporal control over both polymer initiation and chain growth. This additional command over the reaction provides the ability to manipulate the growing polymer with an external stimulus during a polymerization, which can be used to control structure. To achieve this goal, we set out to develop a method to photoreversibly generate a cation at a growing chain end that could participate in a controlled polymerization process. We took inspiration from previous work on cationic degenerate chain transfer polymerizations of vinyl ethers that used thiocarbonylthio chain transfer agents. These polymerizations were initiated by a strong acid and gave well-defined poly(vinyl ether)s. We posited that we could remove the acid initiator in these systems and reversibly oxidize the thiocarbonylthio chain ends in these reactions with a photocatalyst to give a photocontrolled cationic polymerization of vinyl ethers. This Account will focus on our journey to discover cationic photocontrolled polymerizations. We will summarize our initial developments and detail our mechanistic understanding of these reactions using both organic and inorganic based photocatalysts, and we will outline more recent efforts to expand cationic degenerate chain transfer polymerizations to other thioacetal initiators. Finally, we will detail how these photocontrolled cationic polymerizations can be used to switch monomer selectivity in situ using light to control polymer structure. At the end of the Account, we will discuss our vision for future potential applications of these photocontrolled cationic polymerizations in the synthesis of novel block copolymers and next generation cross-linked networks.

Iron-Catalyzed Oxidative C-O and C-N Coupling Reactions Using Air as Sole Oxidant

We describe the oxygenation of tertiary arylamines, and the amination of tertiary arylamines and phenols. The key step of these coupling reactions is an iron-catalyzed oxidative C-O or C-N bond formation which generally provides the corresponding products in high yields and with excellent regioselectivity. The transformations are accomplished using hexadecafluorophthalocyanine-iron(II) (FePcF16 ) as catalyst in the presence of an acid or a base additive and require only ambient air as sole oxidant.

Triarylamine Enriched Organostannoxane Drums: Synthesis, Optoelectrochemical Properties, Association Studies, and Gelation Behavior

The straightforward synthesis of three organotin clusters endowed with six triarylamine-based moieties is reported herein. The optoelectronic properties of the molecules, as well as their ability to form gels, were investigated. The association ability of the compounds was studied as well by means of variable temperature nuclear magnetic resonance (NMR) and ultraviolet-visible (UV-vis) spectroscopy. The optimization of the geometry of the compounds has been performed and compared to the X-ray diffraction of the crystals. The results obtained through this comparison are useful for the explanation of their different gelation behaviors. In fact, organostannoxane drum 1 exhibits a strong ability to form organized supramolecular structures by means of a number of noncovalent short contacts that finally yield luminescent organogels in aromatic solvents.

Development of High Throughput Photopolymerizations Using Micron-Sized Ultrathin Metal-Organic Framework Nanosheets

Polymer syntheses in a high throughput format are still challenging due to the tedious procedures for prior deoxygenation and catalyst removal. Two-dimensional (2D) metal-organic framework (MOF) nanosheets are advantageous for elevating the catalytic efficiency and catalyst recyclability. Polymerization of a wide variety of monomers, including hydrophilic acrylamides and hydrophobic acrylates, was attempted directly in a multi-well plate by employing Zn-ZnPPF-2D nanosheets (PPF = porphyrin paddlewheel framework) as a heterogeneous photocatalyst. Various parameters such as monomer concentration, catalyst concentration and light wavelength were investigated with respect to their effects on polymerization rate and the degree of control over the molecular weight and molecular weight distribution. Due to the larger surface area and more accessible catalytic sites, the top-performing Zn-ZnPPF-2D exhibited fast polymerization kinetics over the Zn-ZnPPF-3D bulk crystals. In addition, the synthesis of triblock copolymers with a single loading of catalysts confirmed the outstanding catalytic performance of these 2D MOF catalysts. Finally, PET-RAFT polymerization was demonstrated to be achievable entirely in a microliter-scale human cell culture medium. As such, this strategy provides high levels of control and precision over macromolecular synthesis outcomes that best align with the requirements of high throughput approaches towards biological applications. This article is protected by copyright. All rights reserved.

Expanding monomer scope and enabling post-modification in photocontrolled radical ring-opening polymerization of vinylcyclopropanes by an iodine transfer strategy

Visible light-driven iodine transfer polymerization provides efficient and unique access to novel poly(vinylcyclopropanes) with enhanced material properties.

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.

Controlled Cationic Polymerization Using RAFT Agents with Selenonium Cations as Metal-Free Lewis Acids: From Homogeneous to Heterogeneous Catalysis

Living cationic polymerization is a well-known technique, but it is generally limited by strict operating conditions. Here, a series of selenonium cations was used as a new class of catalysts...

Aqueous Protein-Polymer Bioconjugation via Photoinduced RAFT Polymerization Using High Loading Heterogeneous Catalyst

Light-driven polymerization, such as photoinduced electron/energy transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization, enables biological benign conditions and versatile functional polymer structure design, which is readily used in protein-polymer bioconjugates. However, conventional metalloporphyrinic homogeneous catalysts for PET-RAFT polymerization suffer from limited aqueous solubility and tedious purification. Here we demonstrate the design of PET-RAFT photocatalyst from the reticular assembled Zr-porphyrinic metal-organic frameworks (MOFs), along with a biomacromolecule-based chain transfer agent, as efficient bioconjugation tools in water. Our methodology offers manufacturing advantages on bioconjugates under mild conditions such that MTT (3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide) and cytotoxicity assays have shown the preservation of the protein integrity, bioactivity, and high cell viability after PET-RAFT polymerization. We find that the fast kinetics are benefiting from the ultrahigh loading of metalloporphyrins in MOF-525-Zn. This heterogeneous catalyst also allows us to maintain living characteristics to incorporate myriads of monomers into block copolymers. Other advantages like easy postreaction purification, reusability, and high oxygen tolerance even in an open system are demonstrated. This study provides a tool of highly efficient heterogeneous photocatalysts for polymer-protein bioconjugation in aqueous media and paves the road for biological applications.

Conjugated Cross-linked Phenothiazines as Green or Red Light Heterogeneous Photocatalysts for Copper-Catalyzed Atom Transfer Radical Polymerization

Using the power of light to drive controlled radical polymerizations has provided significant advances in synthesis of well-defined polymers. Photoinduced atom transfer radical polymerization (ATRP) systems often employ UV light to regenerate copper activator species to mediate the polymerization. Taking full advantage of long-wavelength visible light for ATRP would require developing appropriate photocatalytic systems that engage in photoinduced electron transfer processes with the ATRP components to generate activating species. Herein, we developed conjugated microporous polymers (CMP) as heterogeneous photocatalysts to exploit the power of visible light in promoting copper-catalyzed ATRP. The photocatalyst was designed by cross-linking phenothiazine (PTZ) as a photoactive core in the presence of dimethoxybenzene as a cross-linker via the Friedel-Crafts reaction. The resulting PTZ-CMP network showed photoactivity in the visible region due to the extended conjugation throughout the network because of the aromatic groups connecting the PTZ units. Therefore, photoinduced copper-catalyzed ATRP was performed with CMPs that regenerated activator species under green or red light irradiation to start the ATRP process. This resulted in efficient polymerization of acrylate and methacrylate monomers with high conversion and well-controlled molecular weight. The heterogeneous nature of the photocatalyst enabled easy separation and efficient reusability in subsequent polymerizations.

Influence of Molecular Weight Distribution on the Thermoresponsive Transition of Poly(N-isopropylacrylamide)

A series of poly(N-isopropylacrylamide) (PNIPAm) homopolymers with narrow molecular weight distributions (MWDs) is prepared via photoinduced electron/energy transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization. The thermal transition temperature of these polymer samples is analyzed via turbidity measurements in water/N,N'-dimethylformamide mixtures, which show that the cloud point temperatures are inversely proportional to the weight average molecular weight (M_w ). Binary mixtures of the narrowly distributed PNIPAm samples are also prepared and the statistical parameters for the MWDs of these blends are determined. Very interestingly, for binary blends of the PNIPAm samples, the thermoresponsive transition is not only dependent on the M_w , which has been shown previously, but also on higher order statistical parameters of the MWDs. Specifically, at very high values of skewness and kurtosis, the polymer blends deviate from a single sharp thermoresponsive transition toward a broader thermal response, and eventually to a regime of two more distinct transitions. This work highlights the importance of in-depth characterization of polymer MWDs for thermoresponsive polymers.

Metal-Free Cationic Polymerization of Vinyl Ethers with Strict Temporal Control by Employing an Organophotocatalyst

By virtue of spatiotemporal control over the chain propagating, visible-light-regulated organocatalytic photoredox cationic polymerization provides an appealing approach for the construction of metal-free, well-defined polymers and materials. However, so far, organic photocatalysts capable of mediated cationic polymerization of vinyl ethers are quite limited, and the photocontrol or efficiency is often eroded due to the difficulty in achieving a good activation-deactivation balance, which is greatly dependent on the redox property of the catalyst. Here, we introduce a new type of organic photocatalysts, bisphosphonium salts, which show high performance in the photoregulated reversible addition-fragmentation chain transfer cationic polymerization of vinyl ethers and allow the synthesis of poly(vinyl ethers) with predictable molecular weights and narrow dispersities at low ppm catalyst loadings under visible light. In particular, the tunable redox potential and excellent stability endow the bisphosphonium salts strict temporal control, thus enabling the metal-free polymerization with a halt in a long dark period.

New Light in Polymer Science: Photoinduced Reversible Addition-Fragmentation Chain Transfer Polymerization (PET-RAFT) as Innovative Strategy for the Synthesis of Advanced Materials

Photochemistry has attracted great interest in the last decades in the field of polymer and material science for the synthesis of innovative materials. The merging of photochemistry and reversible-deactivation radical polymerizations (RDRP) provides good reaction control and can simplify elaborate reaction protocols. These advantages open the doors to multidisciplinary fields going from composite materials to bio-applications. Photoinduced Electron/Energy Transfer Reversible Addition-Fragmentation Chain-Transfer (PET-RAFT) polymerization, proposed for the first time in 2014, presents significant advantages compared to other photochemical techniques in terms of applicability, cost, and sustainability. This review has the aim of providing to the readers the basic knowledge of PET-RAFT polymerization and explores the new possibilities that this innovative technique offers in terms of industrial applications, new materials production, and green conditions.

Aerobic Visible-Light-Driven Borylation of Heteroarenes in a Gel Nanoreactor

Heteroarene boronate esters constitute valuable intermediates in modern organic synthesis. As building blocks, they can be further applied to the synthesis of new materials, since they can be easily transformed into any other functional group. Efforts toward novel and efficient strategies for their preparation are clearly desirable. Here, we have achieved the borylation of commercially available heteroarene halides under very mild conditions in an easy-to-use gel nanoreactor. Its use of visible light as the energy source at room temperature in photocatalyst-free and aerobic conditions makes this protocol very attractive. The gel network provides an adequate stabilizing microenvironment to support wide substrate scope, including furan, thiophene, selenophene, and pyrrole boronate esters.

Unravelling an oxygen-mediated reductive quenching pathway for photopolymerisation under long wavelengths

Photomediated-reversible-deactivation radical polymerisation (photo-RDRP) has a limited scope of available photocatalysts (PCs) due to multiple stringent requirements for PC properties, limiting options for performing efficient polymerisations under long wavelengths. Here we report an oxygen-mediated reductive quenching pathway (O-RQP) for photoinduced electron transfer reversible addition-fragmentation chain transfer (PET-RAFT) polymerisation. The highly efficient polymerisations that are performed in the presence of ambient air enable an expanded scope of available PCs covering a much-broadened absorption spectrum, where the oxygen tolerance of PET-RAFT allows high-quality polymerisation by preventing the existence of O2 in large amounts and efficient O-RQP is permitted due to its requirement for only catalytic amounts of O2. Initially, four different porphyrin dyes are investigated for their ability to catalyse PET-RAFT polymerisation via an oxidative quenching pathway (OQP), reductive quenching pathway (RQP) and O-RQP. Thermodynamic studies with the aid of (time-dependent) density functional theory calculations in combination with experimental studies, enable the identification of the thermodynamic constraints within the OQP, RQP and O-RQP frameworks. This knowledge enables the identification of four phthalocyanine photocatalysts, that were previously thought to be inert for PET-RAFT, to be successfully used for photopolymerisations via O-RQP. Well-controlled polymerisations displaying excellent livingness are performed at wavelengths in the red to near-infrared regions. The existence of this third pathway O-RQP provides an attractive pathway to further expand the scope of photocatalysts compatible with the PET-RAFT process and facile access to photopolymerisations under long wavelengths.

Blue light driven free-radical polymerization using arylazo sulfones as initiators

The polymerization of a broad range of electron-poor olefins has been achieved under free-radical conditions by using arylazo sulfones as visible light photoinitiators.

Self-catalyzing photoredox polymerization for recyclable polymer catalysts

A photoactive eosin Y-derived monomer was developed that can induce photoelectron/energy transfer, while simultaneously partaking in the polymerization as a monomer, affording polymer catalysts with tunable eosin Y incorporations.

Research Progress Review of Preparation and Applications of Fluorescent Hydrogels

The fluorescent gel with good flexibility and biocompatibility has attracted more and more attention due to its excellent optical properties. In this paper, the research progresses in preparation methods and applications of fluorescent gels are reviewed. In addition, the preparation methods of self-assembly and polymerization of fluorescent gel are also introduced. In this paper, it should be noted that some outstanding research about the fluorescent gels used in sensors, bio-imaging probes, drug delivery, and other application fields is summarized. This work provides useful reference information for further exploration and study of fluorescent hydrogels.

Magnetic Janus nanocomposites with iridium(iii) complexes for heterogeneous catalysis of logic controlled RAFT polymerization using multiplexed external switching

Photoinduced electron/energy transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization has emerged as a versatile and highly-efficient method for the polymerization of more activated monomers including N,N-dimethylacrylamide and methyl acrylate, and less activated monomers including N-vinylpyrrolidone and vinyl acetate, whilst imposing composition, sequence and spatiotemporal regulation. Although significant progress has been achieved in terms of ability to regulate PET-RAFT polymerization through the implementation of myriad environmental cues, it is still a great challenge to introduce multiple external switches within a single catalyst to accomplish logic toggling of controlled radical polymerization (CRP). Herein, we report the synthesis and characterization of Fe₃O₄@aSiO₂@PNMIr Janus nanocomposites coupled with immobilized heteroleptic iridium(iii) complexes for heterogeneous catalysis of PET-RAFT polymerization. With this catalytic nanoarchitecture, we demonstrate multi-stimuli switching of CRPs using three different external physical manipulations: light "ON"/"OFF", magnet "OUT"/"IN" and temperature "LOW"/"HIGH". In addition, these magnetic Janus nanocomposites endowed radical polymerization with various attractive characteristics such as compatibility of myriad monomer formulations including "more activated" and "less activated" monomers, unique oxygen tolerance and ppm-level catalyst dosage. Logic-controlled polymerization with Fe₃O₄@aSiO₂@PNMIr nanocomposites provides a straightforward, robust and user-friendly strategy for realizing multiplexed external switching of polymer propagation using a single nanocatalyst without the involvement of exogenous reagents.

Cu(II)-Catalyzed Ortho C(sp2)-H Diarylamination of Arylamines To Synthesize Triarylamines

A copper-catalyzed, directed ortho C-H diarylamination of indoles, indolines, anilines, and N-aryl-7-azaindoles has been established. Only copper salt as the catalyst and oxygen as the terminal oxidant are used to synthesize triarylamines using various diarylamines including carbazole and phenothiazine. Mechanistic interrogation reveals that copper plays a dual role.

Polymer Nanofibers Exhibiting Remarkable Activity in Driving the Living Polymerization under Visible Light and Reusability

Visible light-driving syntheses have emerged as a powerful tool for organic synthesis and for the preparation of macromolecules under mild and environmentally benign conditions. However, precious but nonreusable photosensitizers or photocatalysts are often required to activate the reaction, limiting its practicality. Here, it is reported that poly(1,4-diphenylbutadiyne) (PDPB) nanofibers exhibit remarkable activity in driving the living free radical polymerization under visible light. Moreover, PDPB nanofibers are very stable under irradiation of visible light and can be reused without appreciable loss of activity even after repeated cycling. The nanofiber will be a promising photocatalyst with excellent reusability and stability for the reactions driven by visible light.

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.