Search

Vanillyl alcohol has emerged as a widely used building block for the development of biobased monomers. More specifically, the cationic (photo‐)polymerization of the respective diglycidyl ether (DGEVA) is known to produce materials of outstanding thermomechanical performance. Generally, chain transfer agents (CTAs) are of interest in cationic resins not only because they lead to more homogeneous polymer networks but also because they strikingly improve the polymerization speed. Herein, the aim is to compare the cationic chain‐growth photopolymerization with the thermally initiated anionic step‐growth polymerization, with and without the addition of CTAs. Indeed, CTAs lead to faster polymerization reactions as well as the formation of more homogeneous networks, especially in the case of the thermal anionic step‐growth polymerization. Resulting from curing above the TG of the respective anionic step‐growth polymer, materials with outstanding tensile toughness (>5 MJ cm−3) are obtained that result in the manufacture of potential shape‐memory polymers. [ABSTRACT FROM AUTHOR]

Solvent‐free photopolymerization of vinyl monomers to produce high modulus materials with applications in 3D printing and photoswitchable materials is demonstrated. Polymerizable eutectic (PE) mixtures are prepared by simply heating and stirring various molar ratios of N‐isopropylacrylamide (NIPAM), acrylamide (AAm) and 2‐hydroxyethyl methacrylate (HEMA). The structural and thermal properties of the resulting mixtures are evaluated by 1D and 2D NMR spectroscopy as well as differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). UV photocuring kinetics of the PE mixtures is evaluated via in situ photo‐DSC and photorheology measurements. The PE mixtures cure rapidly and display storage moduli that are orders of magnitude greater than equivalent copolymers cured in an aqueous medium. The versatility of these PE systems is demonstrated through the addition of a photoswitchable spiropyran acrylate monomer, as well as applying the PE formulation as a stereolithography (SLA)‐based 3D printing resin. Due to the hydrogen‐bonding network in PE systems, 3D printing of the eutectic resin is possible in the absence of crosslinkers. The addition of a RAFT agent to reduce average polymer chain length enables 3D printing of materials which retain their shape and can be dissolved on demand in appropriate solvents. [ABSTRACT FROM AUTHOR]

The development of visible light‐regulated polymerizations for precision synthesis of polymers has drawn considerable attention in the past years. In this study, an ancient dye, indigo, is successfully identified as a new and efficient photoacid catalyst, which can readily promote the ring‐opening polymerization of lactones under visible light irradiation in a well‐controlled manner, affording the desired polyester products with predictable molecular weights and narrow dispersity. The enhanced acidity of indigos by excitation is crucial to the H‐bonding activation of the lactone monomers. Chain extension and block copolymer synthesis are also demonstrated with this method. [ABSTRACT FROM AUTHOR]

The problem of plastic waste in the environment calls for the development of new polymeric materials designed specifically for easy recycling at the end of their life cycle. Herein, a green polymer system comprising a series of necklace‐shaped polydimethylsiloxanes bearing anthracene dimer units is developed. The polymers have low environmental impact and are easily recycled. Further, their flexibility and glass transition temperatures are easy to control. These necklace‐shaped inorganic polymers are synthesized by photopolymerizing (dimerizing) anthracene‐terminated oligo‐dimethylsiloxane monomers. A key achievement of the present work is the successful chemical recovery of the monomers from the polymers through thermal depolymerization, enabling monomer–polymer recycling. By applying equilibrium polymerization with base catalysts, monomers with a controlled distributed chain length are synthesized from monomers with a constant chain length. The necklace‐shaped polymers synthesized from these randomized monomers have amorphous structures and readily form transparent films. It is possible to modulate the thermal and mechanical properties of the polymers by controlling the average chain length of the polydimethylsiloxane between the anthracene dimers. This investigation presents a method for the synthesis and cyclic utilization of polymer materials with a wide range of applications, including plastics and elastomers. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Photocuring 3D printing of hydrogels, with sophisticated, delicate structures and biocompatibility, attracts significant attention by researchers and possesses promising application in the fields of tissue engineering and flexible devices. After years of development, photocuring 3D printing technologies and hydrogel inks make great progress. Herein, the techniques of photocuring 3D printing of hydrogels, including direct ink writing (DIW), stereolithography (SLA), digital light processing (DLP), continuous liquid interface production (CLIP), volumetric additive manufacturing (VAM), and two photon polymerization (TPP) are reviewed. Further, the raw materials for hydrogel inks (photocurable polymers, monomers, photoinitiators, and additives) and applications in tissue engineering and flexible devices are also reviewed. At last, the current challenges and future perspectives of photocuring 3D printing of hydrogels are discussed. [ABSTRACT FROM AUTHOR]

A novel method based on light‐induced fabrication of a poly (3,4‐ethylenedioxythiophene)‐polycaprolactone (PEDOT‐PCL) scaffold using phenacyl bromide (PAB) as a single‐component photoinitiator is presented. HBr released from the step‐growth polymerization of EDOT is utilized as an in situ catalyst for the chain‐growth polymerization of ε‐caprolactone. Detailed investigations disclose the formation of a self‐assembled nanoporous electroconductive scaffold (1.2 mS cm−1). Fluorescence emission spectra of the fabricated scaffold exhibit a mixed solvatochromic behavior, indicating specific interactions between the self‐assembled scaffold and solvents with varying polarities, as evidenced by transmission electron microscopy (TEM). Moreover, the same light‐induced technique can also be applied for bulk photopolymerization showcasing the versatility and wide‐ranging scope of the originated method. In brief, this study introduces a novel approach for light‐induced polymerization reactions that is merging step‐growth and chain‐growth mechanisms. This innovative approach is promising to facilitate in situ polymerization of monomers possessing diverse functionalities. [ABSTRACT FROM AUTHOR]

Functional inks for light‐based 3D printing are actively being searched for being able to exploit all the potentialities of additive manufacturing. Herein, a fast visible‐light photopolymerization process is showed of conductive PEDOT:PSS hydrogels. For this purpose, a new Type II photoinitiator system (PIS) based on riboflavin (Rf), triethanolamine (TEA), and poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is investigated for the visible light photopolymerization of acrylic monomers. PEDOT:PSS has a dual role by accelerating the photoinitiation process and providing conductivity to the obtained hydrogels. Using this PIS, full monomer conversion is achieved in less than 2 min using visible light. First, the PIS mechanism is studied, proposing that electron transfer between the triplet excited state of the dye (3Rf*) and the amine (TEA) is catalyzed by PEDOT:PSS. Second, a series of poly(2‐hydroxyethyl acrylate)/PEDOT:PSS hydrogels with different compositions are obtained by photopolymerization. The presence of PEDOT:PSS negatively influences the swelling properties of hydrogels, but significantly increases its mechanical modulus and electrical properties. The new PIS is also tested for 3D printing in a commercially available Digital Light Processing (DLP) 3D printer (405 nm wavelength), obtaining high resolution and 500 µm hole size conductive scaffolds. [ABSTRACT FROM AUTHOR]

Herein, the successful development of a metal‐free, solution [2 + 2] photopolymerization of natural cinnamic acid‐derived bisolefinic monomers is reported, which is enabled by a strategy based on direct triplet state access via energy transfer catalysis. 2,2'‐Methoxythioxanthone has been identified as an effective organic photocatalyst for the [2 + 2] photopolymerization in solution, which can be excited by visible light and activate the biscinnamate monomers via triplet energy transfer. This method features its metal‐free conditions, visible light utilization, solution polymerization, and abundant biomass‐based feedstock, as well as processable polymer products, which is different from the rigid, insoluble products obtained from solid‐state photopolymerization. This solution polymerization method also shows a good compatibility to monomer structures; cinnamic acid‐derived bisolefinic monomers with different linkers, including diamine, natural diol, and bisphenol, can all readily undergo [2 + 2] photopolymerization, and be transformed into colorless, sustainable polymers. [ABSTRACT FROM AUTHOR]

3D printing technology offers solutions for numerous needs in industry and the daily life of individuals. In recent years, most research efforts have focused on this technology as the market share has grown and requirements have become specified in their related fields. In this work, a novel visible light induced 3D printing system with high resolution and short printing time using dimanganese decacarbonyl (Mn2(CO)10) in combination with organic halides is reported. The radicals formed through halogen abstraction by photochemically generated manganese pentacarbonyl from organic halides with high quantum efficiency initiate the polymerization of acrylic resins. The kinetics of the process using various halide‐containing molecules in the photoinitiaiting system are investigated with real‐time fourrier transform infrared spectroscopy and photo‐differential scanning calorimetry analyses, and the characteristics of 3D printouts are presented and compared with that of the commercial photoinitiator, 2,4,6‐trimethylbenzoyl)phosphine oxide without Mn2(CO)10. The results obtained confirm that the combination of Mn2(CO)10 and structurally diverse organic halides is a class of promising 3D system for various applications. [ABSTRACT FROM AUTHOR]

Reversible addition‐fragmentation chain transfer (RAFT) polymerization has proven itself as a powerful polymerization technique affording facile control of molecular weight, molecular weight distribution, architecture, and chain end groups ‐ while maintaining a high level of tolerance for solvent and monomer functional groups. RAFT is highly suited to water as a polymerization solvent, with aqueous RAFT now utilized for applications such as controlled synthesis of ultra‐high molecular weight polymers, polymerization induced self‐assembly, and biocompatible polymerizations, among others. Water as a solvent represents a non‐toxic, cheap, and environmentally friendly alternative to organic solvents traditionally utilized for polymerizations. This, coupled with the benefits of RAFT polymerization, makes for a powerful combination in polymer science. This perspective provides a historical account of the initial developments of aqueous RAFT polymerization at the University of Southern Mississippi from the McCormick Research Group, details practical considerations for conducting aqueous RAFT polymerizations, and highlights some of the recent advances aqueous RAFT polymerization can provide. Finally, some of the future opportunities that this versatile polymerization technique in an aqueous environment can offer are discussed, and it is anticipated that the aqueous RAFT polymerization field will continue to realize these, and other exciting opportunities into the future. [ABSTRACT FROM AUTHOR]

Hydrolytically degradable poly(β‐thioether ester ketal) thermosets are synthesized via radical‐mediated thiol‐ene photopolymerization using three novel dialkene acyclic ketal monomers and a mercaptopropionate based tetrafunctional thiol. For all thermoset compositions investigated, degradation behavior is highly tunable based on the structure of the incorporated ketal and pH. Complete degradation of the thermosets is observed upon exposure to acidic and neutral pH, and under high humidity conditions. Polymer networks composed of cross‐link junctions based on acyclic dimethyl ketals degrade the quickest, whereas networks containing acyclic cyclohexyl ketals undergo hydrolytic degradation on a longer timescale. Thermomechanical analysis reveals low glass transition temperatures and moduli typical of thioether‐based thermosets. [ABSTRACT FROM AUTHOR]

Likened to both thermosets and thermoplastics, vitrimers are a unique class of materials that combine remarkable stability, healability, and reprocessability. Herein, this work describes a photopolymerized thiol‐ene‐based vitrimer that undergoes dynamic covalent exchanges through uncatalyzed transamination of enamines derived from cyclic β‐triketones, whereby the low energy barrier for exchange facilitates reprocessing and enables rapid depolymerization. Accordingly, an alkene‐functionalized β‐triketone, 5,5‐dimethyl‐2‐(pent‐4‐enoyl)cyclohexane‐1,3‐dione, is devised which is then reacted with 1,6‐diaminohexane in a stoichiometrically imbalanced fashion (≈1:0.85 primary amine:triketone). The resulting networks exhibit subambient glass transition temperature (Tg = 5.66 °C) by differential scanning calorimetry. Using a Maxwell stress‐relaxation fit, the topology‐freezing temperature (Tv) is calculated to be −32 °C. Small‐amplitude oscillatory shear rheological analysis enables to identify a practical critical temperature above which the vitrimer can be successfully reprocessed (Tv,eff). Via the introduction of excess primary amines, this work can readily degrade the networks into monomeric precursors, which are in turn reacted with diamines to regenerate reprocessable networks. Photopolymerization provides unique spatiotemporal control over the network topology, thereby opening the path for further investigation of vitrimer properties. As such, this work expands the toolbox of chemical upcycling of networks and enables their wider implementation. [ABSTRACT FROM AUTHOR]

In both organic and polymer synthesis, photochemistry of charge transfer complexes (CTCs) is considered as a powerful approach to expand visible‐light‐driven radical chemistry reaction. One reports herein on the development of a class of useful CTCs using pyridinium salts as efficient electron acceptors (combined with N, N, 3,5‐tetramethylaniline, TMA) to achieve a multiwavelength (375–560 nm) metal‐free LED photopolymerization process under mild conditions (open to air, without monomer purification and inhibitor removal). The UV–vis absorption spectra and molecular modeling simultaneously verify its potential blue‐green absorbing wavelength range. Also, their good thermal initiation behavior at relatively low temperatures makes it easier to achieve thick samples and/or polymerization in the shadow region in practice. More importantly, with excellent photoinitiating capability, the formulation is successfully applied to direct laser write (DLW) and high‐resolution 3D printing, yielding a series of objects with well‐defined structures, such as letters, ring, solid squares, and chess pieces. These new pyridinium salt acceptors further extend the applicability to visible photopolymerizable resins and additive‐containing formulations for efficient surface and deep curing. [ABSTRACT FROM AUTHOR]

3D printing has revolutionized the way of manufacturing with a huge impact on various fields, in particular biomedicine. Vat photopolymerization‐based 3D printing techniques such as stereolithography (SLA) and digital light processing (DLP) attract considerable attention owing to their superior print resolution, relatively high speed, low cost, and flexibility in resin material design. As one key element of the SLA/DLP resin, photoinitiators or photoinitiating systems have experienced significant development in recent years, in parallel with the exploration of 3D printing (macro)monomers. The design of new photoinitiating systems cannot only offer faster 3D printing speed and enable low‐energy visible light fabrication, but also can bring new functions to the 3D printed products and even generate new printing methods in combination with advanced optics. This review evaluates recent trends in the development and application of advanced photoinitiators and photoinitiating systems for vat photopolymerization 3D printing, with a wide range of small molecules, polymers, and nanoassemblies involved. Personal perspectives on the current limitations and future directions are eventually provided. [ABSTRACT FROM AUTHOR]

Dye‐sensitized solar cells represent promising alternative photovoltaic (PV) technologies with the advantages of low material cost, ease of production, and high performance for indoor applications. Solid‐state DSCs (ssDSCs) have been developed to greatly diminish the problems of electrolyte leakage and electrode corrosion. However, the power conversion efficiency of ssDSCs generally is much lower than traditional liquid DSCs, resulting in low conductivity and poor pore infiltration of solid HTMs in mesoporous structures. To overcome these problems, in situ photoelectrochemical polymerization (PEP) approach is developed to synthesize polymer HTMs in the porous electrodes, enabling enhancement of pore infiltration fraction and conductivity. The PEP method offers great opportunities for engineering the HTM interfaces, tuning the charge dynamics, and improving the PV performance of ssDSCs. Here the authors aim to present a coherent review of the recent development of material engineering and interfacial optimization for ssDSCs. The recent advances in the PEP are also summarized, with special emphasis on how the influencing factors control the PEP kinetics, the polymer properties as well as the device performance. This review provides a deep understanding of the mechanism of photopolymerization across different conditions, which serves as a guidebook for further optimization of the PEP process for ssDSCs. [ABSTRACT FROM AUTHOR]

A novel visible light induced step‐growth polymerization by electrophilic aromatic substitution between photochemically generated carbocations and dimethoxybenzene nucleophile is described. Conventional step‐growth polymerization and chain‐growth condensation polymerization (CCP) mechanisms are presented. It is found that by changing the molar ratios of the monomers slightly, the CCP mechanism becomes operative and relatively higher molecular weight polymers are obtained because of the higher reactivity of the end groups of the intermediates and oligomers than that of the monomers. The possibility of grafting onto polymers containing epoxide at their side chains by photoinduced chain end activation of poly(dimethoxyphenylene methylene) is demonstrated. This study is expected to promote potential applications of the combination of photoinduced electron transfer reactions and CCP in macromolecular synthesis and material science. [ABSTRACT FROM AUTHOR]

A new visible light induced step‐growth polymerization of dibromoxylene, and diols using dimanganese decacarbonyl and diphenyliodonium salt is described. The polymerization is suggested to proceed by substitution reaction between dixylenium cations formed upon visible light irradiation in the presence of dimanganese decacarbonyl and diphenyl iodonium salt. For the described substitution reaction with diols as nucleophilic component, the scope of the process is studied. Furthermore, the presence of halide groups at chain ends of the resulting polymers provided the possibility of initiating subsequent free radical and free radical promoted cationic resulting in the formation of polyether‐based block copolymers. [ABSTRACT FROM AUTHOR]

The global market for 3D printing materials has grown exponentially in the last decade. Today, photopolymers claim almost half of the material sales worldwide. The lack of sustainable resins, applicable in vat photopolymerization that can compete with commercial materials, however, limits the widespread adoption of this technology. The development of "green" alternatives is of great importance in order to reduce the environmental impact of additive manufacturing. This paper reviews the recent evolutions in the field of sustainable photopolymers for 3D printing. It highlights the synthesis and application of biobased resin components, such as photocurable monomers and oligomers, as well as reinforcing agents derived from natural resources. In addition, the design of biologically degradable and recyclable thermoset products in vat photopolymerization is discussed. Together, those strategies will promote the accurate and waste‐free production of a new generation of 3D materials for a sustainable plastics economy in the near future. [ABSTRACT FROM AUTHOR]

In this study, a new generation of photoinitiator (PI) based on hybrid structures combining benzophenone and triphenylamine is proposed. Remarkably, these photoinitiators (noted monofunctional benzophenone‐triphenylamine (MBP‐TPA) and trifunctional benzophenone‐triphenylamine (TBP‐TPA)) are designed and developed for the photopolymerization under light‐emitting diodes (LEDs). Benzoyl substituents connected with triphenylamine moiety contribute to the excellent absorption properties which results in both high final conversions and polymerization rates in free radical photopolymerization (FRP). Remarkably, TBP‐TPA owning trifunctional benzophenone group exhibits a better Type II PI behavior than well‐known 2‐isopropylthioxanthone for photopolymerization under LED@365 and 405 nm irradiation. FRP and cationic photopolymerization of TBP‐TPA‐based systems are applied on 3D printing experiments, and good profiles of the 3D patterns are observed. The high molecular weight of TBP‐TPA associated with it trifunctional character can also be very interesting for a better migration stability of PIs that is a huge challenge. The development of this new generation of photoinitiators based on benzophenone hybrid structures is a real breakthrough. It reveals that the novel versatile photoinitiators based on benzophenone‐triphenylamine hybrid structures have great potentials for future industrial applications (e.g., 3D printing, composites, etc.). [ABSTRACT FROM AUTHOR]

It is herein reported that a facile application of N‐acyl dibenzazepine (ADBA) photochemistry for preparing photoreversible ADBA based thiol‐ene networks. Crosslinking of the ADBA thiol‐ene networks is successfully achieved by UV induced dimerization of ADBA groups at wavelengths above 300 nm while a subsequent deep UV exposure (λ = 250 nm) results in a well‐defined cleavage of the crosslinks. The photochemical bonding and cleavage of the process has been determined and studied in detail by spectroscopic measurements. [ABSTRACT FROM AUTHOR]

The development of multi‐component orthogonal polymerizations (MOPs) with simple procedure and high efficiency is crucial for rational polymer synthesis. In this work, photo‐triggered Cu(I)‐catalyzed azide‐alkyne cycloaddition (CuAAC) polymerization are first investigated, employing copper(II) thioxanthone carboxylate (Cu(TX)2) as photoredox catalyst and sunlight as stimuli. Then, the novel MOPs using one photoredox catalyst, Cu(TX)2 to simultaneously mediate two different photopolymerizations, are successfully realized in one‐pot, where photo‐induced electron transfer atom transfer radical polymerization and photo‐activated CuAAC polymerization can effectively proceed in a one‐pot and non‐interfering fashion to afford predetermined copolymers with well‐defined structure. [ABSTRACT FROM AUTHOR]

Bioorthogonal chemistry is revolutionizing the fields of biological chemistry and nanomedicine, providing tools to actively probe and perturb native biochemical processes. Photochemistry provides the opportunity to actively and non‐invasively control bioorthogonal reactions, providing sophisticated optochemical tools. Despite the opportunities in bioorthogonal photochemistry, there remain many significant challenges to the clinical translation of current research. This review aims to provide an overview of these challenges and highlight recent examples from the literature that are providing revolutionary solutions to overcoming these barriers. It will highlight new photochemical systems that can be triggered by near infrared light in aqueous solutions and have been demonstrated to function in complex biological systems, including in living animals. It will cover diverse classes of photochemical reactions including photopolymerization, uncaging, conjugation, and photoswitching. The discussion will detail how new approaches are being integrated into polymers or highlight unexploited opportunities. This review intends to showcase how the unique synergy of bioorthogonal photochemistry and polymer science provides vast opportunities in the fields of biomaterials, nanomedicine, and theranostics. This will hopefully provide inspiration to material scientists to integrate bioorthogonal photochemistry into new adaptable materials and ensure translation to solve clinical challenges. [ABSTRACT FROM AUTHOR]

Surface‐tethered macromolecules, or polymer brushes, offer a unique platform for coating surfaces for a wide variety of applications. Surface‐initiated polymerization (SI‐P), through which polymer brushes can be grown directly from an initiator‐functionalized surface, offers a facile, highly customizable approach that is synergistic with photolithography. Using a variety of photolithography devices and SI‐Ps, complex polymer brush architectures can be fabricated with great spatial and temporal control. This article not only addresses techniques, advancements, applications, and possible future directions within the field of polymer brush photolithography, but it also provides resources to assist the reader in selecting the polymerization technique and photolithography device most conducive to a given endeavor. [ABSTRACT FROM AUTHOR]

Three monoamino‐substituted anthraquinone derivatives (AAQs), that is, 1‐aminoanthraquinone (AAQ), 1‐(methylamino)anthraquinone (MAAQ), and 1‐(benzamido)anthraquinone (BAAQ), incorporated with various additives [e.g., triethanolamine (TEAOH) and phenacyl bromide (PhC(═O)CH2Br)] are investigated for their roles as photoinitiating systems of free radical photopolymerization of (meth)acrylate monomers upon the exposure to UV to green LEDs. The AAQs‐based photoinitiating systems, AAQ/TEAOH/PhC(═O)CH2Br and BAAQ/TEAOH/PhC(═O)CH2Br photoinitiators exhibit the highest efficiency for the free radical photopolymerization of DPGDA under the irradiation of blue LED and UV LED, respectively, which is consistent with the extent of overlap between their absorption spectra and the emission spectra of the LEDs. AAQ/TEAOH/PhC(═O)CH2Br photoinitiator can also initiate the free radical photopolymerization of different (meth)acrylate monomers, with an efficiency dependent on the chemical structures of these monomers. [ABSTRACT FROM AUTHOR]

Through thiol‐ene photopolymerization of presynthesized oligomers, advanced clickable nucleic acids (CNA‐2G) are synthesized with sequence‐controlled repeating units. As examples, poly(thymine‐adenine) (polyTA) CNA‐2G and poly(thymine‐thymine‐cytosine) CNA‐2G are synthesized by polymerizing thiol‐ene heterofunctional dimers with pendant thymine‐adenine nucleobases and trimer with pendant thymine‐thymine‐cytosine nucleobases. Based on size exclusion chromatography (SEC) analysis, polyTA and polyTTC have number average molecular weights of 2000 and 1800, respectively, which contain 7–8 pendant nucleobases. Based on the different behavior of the CNA‐2G monomers and CNA‐2G oligomers with two or more pendant nucleobases in photopolymerization, an unusual thiol‐ene chain‐growth propagation mechanism is observed for the former and a common thiol‐ene step‐growth propagation mechanism for the latter. The uncommon thiol‐ene chain‐growth propagation is hypothesized to rely on a six‐membered ring mediated intramolecular hydrogen atom transfer process. [ABSTRACT FROM AUTHOR]

Free radical polymerization upon near‐infrared (NIR) light is still the subject of intense research efforts and remains a huge challenge particularly for long wavelengths (>1000 nm). In this study, a NIR sensitizer operating upon long wavelength (1064 nm) is proposed for an efficient polymerization of acrylate monomers. A new three‐component photoinitiating system is developed comprising the NIR sensitizer in combination with an Iodonium salt (Iod) and an amine. Remarkably, the NIR sensitizer (IR 1064) absorbing strongly in all the near infrared region (700–1200 nm) offers the possibility to use a broad range of irradiation wavelengths, i.e., examples are provided at 785 and 1064 nm. Such long wavelengths are characterized by many advantages such as a deeper penetration of light and therefore a better curing of the monomer but it is also much safer than UV light. Excellent performance is observed for the three‐component IR 1064/Iod/Amine system under air: high conversion of acrylate functions associated with a fast polymerization time. The use of IR 1064 as NIR sensitizer with a broad NIR absorption is—to the best of current knowledge—never proposed in the literature. The photoinitiating performances are studied using real‐time Fourier transform infrared spectroscopy. [ABSTRACT FROM AUTHOR]

A new phosphine is proposed as efficient coinitiator for camphorquinone (CQ)‐based photoinitiating systems for the free radical polymerization of (meth)acrylates. Remarkably, this new co‐initiator can exhibit two functionalities: a phosphine moiety to overcome oxygen inhibition and an iodonium salt moiety as counter cation to initiate the polymerization process. Excellent polymerization performances in the presence of CQ for the free radical polymerization of methacrylates under blue light are observed, and amine‐free systems can be easily developed from the proposed structure. The photopolymerization of composites is also investigated in the presence of the new phosphine (without iodonium counter cation) and very interesting depth of cure can be obtained from the new developed photoinitiating system after only 20 s of irradiation with a blue light‐emitting diode. [ABSTRACT FROM AUTHOR]

In a significant breakthrough from classical molecular (i.e., nonpolymeric) iodonium salts in light‐induced photochemistry, the synthesis and use of new safer polymeric iodonium salts are reported here. They are shown to be involved in charge transfer complexes (CTCs) while in interaction with a safe amino acid derivative (N‐phenylglycine). Also, this study demonstrates i) the formation of CTCs between the iodonium (acceptor) and an aryl/alkyl amine (donor) through UV–vis measurements of the monomer, ii) the formation of radicals in electron spin resonance spin trapping experiments when the CTCs are irradiated by visible light (405 nm), and iii) their efficiency as a photoinitiator to polymerize three different acrylic monomers under LED irradiation at 405 nm under air and their application to 3D resolved laser writing of thick samples (3 mm). High reactivity for polymeric iodonium salts comparable with molecular ones is exhibited with the advantage of potential lower migration. To the best of the authors' knowledge, this is the first reported instance of polymeric iodonium salts acting as polymerization initiators. [ABSTRACT FROM AUTHOR]

Herein, it is reported for the first time that when mixed with choline chloride, itaconic acid (IA), normally a low‐reactive vinyl monomer, undergoes initiator‐free radical polymerization under normal daylight. Furthermore, the process results in the formation of abnormally high‐molecular‐weight poly(itaconic acid) derivatives with Mw greater than ≈800 000 g mol−1. Detailed 1D/2D NMR studies indicate that the polymers have two types of ionizable moieties, that is, anionic carboxylic and cationic choline ester groups in an average molar ratio of 12:1. Potentiometric titration shows polyampholyte behavior of the polymers. Tentative mechanistic studies reveal that the daylight‐induced polymerization is initiated by species generated via interactions of near UV light with IA. However, EPR findings show that choline also participates in secondary radical reactions. The obtained polyampholytes are useful bio‐based materials for fast and straightforward fabrication of polymer–clay nanocomposite hydrogels with excellent mechanical properties. [ABSTRACT FROM AUTHOR]

Abstract: Multihydroxy‐anthraquinone derivatives [i.e., 1,2,4‐trihydroxyanthraquinone (124‐THAQ), 1,2,7‐trihydroxyanthraquinone (127‐THAQ), and 1,2,5,8‐tetrahydroxyanthraquinone (1258‐THAQ)] can interact with various additives [e.g., iodonium salt, tertiary amine, N‐vinylcarbazole, and 2‐(4‐methoxystyryl)‐4,6‐bis(trichloromethyl)‐1,3,5‐triazine] under household green LED irradiation to generate active species (cations and radicals). The relevant photochemical mechanism is investigated using quantum chemistry, fluorescence, cyclic voltammetry, laser flash photolysis, steady state photolysis, and electron spin resonance spin‐trapping techniques. Furthermore, the multihydroxy‐anthraquinone derivative‐based photoinitiating systems are capable of initiating cationic photopolymerization of epoxides or divinyl ethers under green LED, and the relevant photoinitiation ability is consistent with the photochemical reactivity (i.e., 124‐THAQ‐based photoinitiating system exhibits highest reactivity and photoinitiation ability). More interestingly, multihydroxy‐anthraquinone derivative‐based photoinitiating systems can initiate free radical crosslinking or controlled (i.e., reversible addition−fragmentation chain transfer) photopolymerization of methacrylates under green LED. It reveals that multihydroxy‐anthraquinone derivatives can be used as versatile photoinitiators for various types of photopolymerization reactions. [ABSTRACT FROM AUTHOR]

Abstract: Hyperbranched polymers (HBPs), a unique class of dendritic macromolecules, have received continuous interest from macromolecular scientists due to their inherent properties such as high level of functional terminal units, high solubility, and low viscosity. Despite enormous efforts devoted to the synthesis of HBPs by traditional methods such as single and double monomer strategies involving step‐growth polymerization and self‐condensing vinyl polymerization (SCVP) processes, there have been limited attempts to employ light‐induced processes. Photochemical methods, however, exhibit distinct advantages not characteristically disclosed by traditional ones, such as spatial and temporal control, low energy, and site‐specific activation. This review, after a brief summary of the conventional methods, presents the unique features and the key functionalities of the inimers for photoinduced SCVP and strategies for preparing HBPs. [ABSTRACT FROM AUTHOR]

Abstract: Through the construction of an organic photocatalysis system, photoredox catalyst (PC)/additive, where PC stands for photoredox catalyst, an organocatalyzed step transfer‐addition and radical‐termination (O‐START) polymerization irradiated by blue LED light at room temperature is realized. Different types of α,ω‐diiodoperfluoroalkane A and α,ω‐unconjugated diene B are copolymerized through O‐START efficiently, and generate various kinds of functional semifluorinated polymers, including polyolefins and polyesters. The process is affected by several factors; solvents, additives, and feed ratio of A to B. After optimization of all these components, the polymerization efficiency is greatly improved, generating polymers with both relatively high yield and molecular weight. Considering the mild reaction condition, easy operation process, and free‐of‐metal‐catalyst residues in the polymer product, the organocatalytic polymerization strategy provides a simple and efficient approach to functional semifluorinated polymer materials and hopefully opens up their application in high‐tech fields. [ABSTRACT FROM AUTHOR]

Abstract: This review article highlights recent developments in the field of photochemistry and photochemical reversible deactivation radical polymerization applied to aqueous polymerizations. Photochemistry is a topic of significant interest in the fields of organic, polymer, and materials chemistry because it allows challenging reactions to be performed under mild conditions. Aqueous polymerization is of significant interest because water is an environmentally benign solvent, and the use of water enables complex polymer self‐assembly and bioconjugation processes to occur. This review focuses on powerful new developments in photochemical aqueous polymerization reactions and their applications to the synthesis of well‐defined polymer nano‐objects and bioconjugates. It is anticipated that these aqueous photopolymerizations will enable the next generation of self‐assembled structures and biohybrid materials to be developed under mild and environmentally friendly conditions. [ABSTRACT FROM AUTHOR]

Abstract: A versatile platform allowing capture and detection of normal and dysfunctional cells on the same patterned surface is important for accessing the cellular mechanism, developing diagnostic assays, and implementing therapy. Here, an original and effective method for fabricating binary polymer brushes pattern is developed for controlled cell adhesion. The binary polymer brushes pattern, composed of poly(N‐isopropylacrylamide) (PNIPAAm) and poly[poly(ethylene glycol) methyl ether methacrylate] (POEGMA) chains, is simply obtained via a combination of surface‐initiated photopolymerization and surface‐activated free radical polymerization. This method is unique in that it does not utilize any protecting groups or procedures of backfilling with immobilized initiator. It is demonstrated that the precise and well‐defined binary polymer patterns with high resolution are fabricated using this facile method. PNIPAAm chains capture and release cells by thermoresponsiveness, while POEGMA chains possess high capability to capture dysfunctional cells specifically, inducing a switch of normal red blood cells (RBCs) arrays to hemolytic RBCs arrays on the pattern with temperature. This novel platform composed of binary polymer brush pattern is smart and versatile, which opens up pathways to potential applications as microsensors, biochips, and bioassays. [ABSTRACT FROM AUTHOR]

To address the challenge of metal contamination, a 'graft from' approach via organocatalyzed atom transfer radical polymerization (O-ATRP) is developed to synthesize poly(vinylidene fluoride- co-chlorotrifluoroethylene) (P(VDF- co-CTFE)) graft copolymers. N-phenylphenothiazine is utilized as a model organic photoredox catalyst for catalyzing the (co)polymerization of methyl methacrylate (MMA), methacrylate (MA), and n-butyl acrylate (BA). By employing this technique, high temporal control of polymerization and graft content are achieved. A series of P(VDF- co-CTFE)- g-PMMA, P(VDF- co-CTFE)- g-PMA, and P(VDF- co-CTFE)- g-PBA is prepared under mild conditions. The resultant graft copolymer can be used as macroinitiator to re-initiate O-ATRP to synthesize P(VDF- co-CTFE)- g-(PMMA- b-PMA), which might exhibit the potential application as novel dielectric material. [ABSTRACT FROM AUTHOR]

Ene-functionalized ionic liquids with a range of different cationic groups and counteranions react stoichiometrically within a tetrathiol-divinyl ether formulation within 20 minutes to form thiol-ene polymers with measurable ionic conductivities via a photoinitiated polymerization and crosslinking reaction. Dynamic mechanical analysis indicates that these networks are more spatially heterogeneous and possess higher glass transition temperatures ( Tg) compared with thiol-ene formulations without charge. While tuning the molar content of ionic liquid monomer is one method for adjusting the crosslink and charge densities of the thiol-ene polymeric ionic liquid networks, the presence of cation-anion interactions also plays a critical role in dictating the thermomechanical and conductive properties. Particularly, while cationic structure effects are not significant on the polymer properties, the use of a weakly coordinating hydrophobic anion (bistriflimide) instead of bromide-based networks results in an apparent decrease in hydrated ion conductivity (7.4 to 1.5 mS cm−1) and Tg (−9.6 to −17.8 °C). [ABSTRACT FROM AUTHOR]

Well-defined poly(methyl methacrylate) (PMMA) and poly(methyl acrylate) (PMA) are prepared via photochemically induced atom transfer radical polymerization (photoATRP) using ppm amounts of CuBr2/ tris(2-pyridylmethyl)amine and CuBr2/ tris[2-(dimethylamino)ethyl]amine catalyst complexes, respectively, without degassing of polymerization mixture and with no need to introduce an external reducing agent to the system. The effect of ligand to CuBr2 ratio on kinetic and induction period during the polymerization of MMA and MA is investigated. The induction period is influenced also by the amount of oxygen in the polymerization system. Both the kinetics of MA polymerization and the induction period are affected by light intensity. Finally, the high livingness and initiation efficiency of the photoATRP system in the presence of air are proved by chain extension polymerizations. The presented system is valuable from an industrial point of view, since after optimization, well-defined and high-molar-mass poly(meth)acrylates can be prepared without the necessity of degassing the system, while the polymerization can be proceeded quickly and without an induction period. [ABSTRACT FROM AUTHOR]

Self-folding origami is of great interest in current research on functional materials and structures, but there is still a challenge to develop a simple method to create freestanding, reversible, and complex origami structures. This communication provides a feasible solution to this challenge by developing a method based on the digit light processing technique and desolvation-induced self-folding. In this new method, flat polymer sheets can be cured by a light field from a commercial projector with varying intensity, and the self-folding process is triggered by desolvation in water. Folded origami structures can be recovered once immersed in the swelling medium. The self-folding process is investigated both experimentally and theoretically. Diverse 3D origami shapes are demonstrated. This method can be used for responsive actuators and the fabrication of 3D electronic devices. [ABSTRACT FROM AUTHOR]

Vinyl ketone polymers, including phenyl vinyl ketone (PVK), are an important class of polymers due to their ability to degrade upon irradiation with ultraviolet light which makes them useful for a variety of applications. However, traditional radical methods for synthesizing PVK polymers give rise to poor control or are unable to produce block copolymers. This work uses reversible addition-fragmentation chain transfer polymerization (RAFT) and photochemistry to polymerize PVK. When visible blue radiation of 440 ± 10 nm is used as the light source for the photopolymerization, rapid polymerization and well-defined polymers are created. This RAFT method uses PVK as both monomer and radical initiator, exciting the PVK mono­mer by 440 ± 10 nm irradiation to avoid the use of an additional radical initiator. Once the poly­mer is synthesized, it is stable against degradation by blue light (440 ± 10 nm), but upon exposure to ultraviolet (UV) radiation (310 ± 20 nm) significant decrease in molecular weight is observed. The degradation is observed for all poly(PVK) materials synthesized. [ABSTRACT FROM AUTHOR]

A new polymerized ionic liquid has been derived by photopolymerization of a stimuli-responsive ionic liquid surfactant, ILAMPS, which is composed of polymerizable, paired ions. The cation is 1-methyl-3-[11-(acryloyloxy)undecyl] imidazolium (IL), and the anion is 2-acrylamido-2-methyl-1-propanesulfonate (AMPS). This ion combination is a new ionic liquid. The resulting hygroscopic resins are highly polarizable, suitable for sensor design and for ultracapacitor fabrication and proton conducting. Interactions of imidazolium with anions provide basis for stimuli-responsiveness, and are used to promote proton transport. Doping with one equivalent of HPF6 at 0% relative humidity produces a 100-fold increase in proton conductivity at 100-125 °C and activation energies for proton transport lower than those of Nafion at water loadings less than 5 per sulfonate. [ABSTRACT FROM AUTHOR]

The incorporation of ionic liquid (IL) chemistry into functional polymers has extended the properties and applications of polyelectrolytes. However, ILs are expensive due to the presence of fluorinated anions or complicated synthetic steps which limit their technological viability. Here, we show a new family of poly(ionic liquid)s (PILs) which are based in cheap and renewable chemicals and involves facile synthetic approaches. Thus, deep eutectic monomers (DEMs) are prepared for the first time by using quaternary ammonium compounds and various hydrogen bond donors such as citric acid, terephthalic acid or an amidoxime. The deep eutectic formation is made through a simple mixing of the ingredients. Differential scanning calorimetry, nuclear magnetic resonance (NMR) and computational studies reveal the formation of the DEMs due to the ionic interactions. The resulting DEMs are liquid which facilitates their polymerization using mild photopolymerization or polycondensation strategies. Spectroscopic characterizations reveal the successful formation of the polymers. By this way, a new family of PILs can be synthesized which can be used for different applications. As an example, the polymers show promising performance as solid CO2 sorbents. Altogether the deep eutectic monomer route can lead to non-toxic, cheap and easy-to-prepare alternatives to current PILs for different applications. [ABSTRACT FROM AUTHOR]

Self-initiated photografting polymerization is used to couple the polymerizable initiator monomer 2-(2-chloropropanoyloxy)ethyl acrylate to a range of polymeric substrates. The technique requires only UV light to couple the initiator to surfaces. The initiator surface density can be varied by inclusion of a diluent monomer or via selection of initiator and irradiation parameters. The functionality of the initiator surface is demonstrated by subsequent surface-initiated atom transfer radical polymerization. Surfaces are characterized by x-ray photoelectron spectroscopy (XPS), ellipsometry, and atomic force microscopy (AFM), and UV-induced changes to the initiator are assessed by ¹H NMR and gel permeation chromatography (GPC). This is the first time this one-reactant one-step technique has been demonstrated for creating an initiator surface of variable density. [ABSTRACT FROM AUTHOR]

The polymerization of the photocleavable monomer, o-nitrobenzyl methacrylate (NBMA), is investigated using photoinduced electron/energy transfer reversible addition-fragmentation chain transfer polymerization. The polymerizations under visible red ( λmax = 635 nm, 0.7 mW cm−2) and yellow ( λmax = 560 nm, 9.7 mW cm−2) light are performed and demonstrate rational evidence of a controlled/living radical polymerization process. Well-defined poly( o-nitrobenzyl methacrylate) (PNBMA) homopolymers with good control over the molecular weight and polymer dispersity are successfully synthesized by varying the irradiation time and/or targeted degree of polymerization. Chain extension of a poly(oligo(ethylene glycol) methyl ether methacrylate) macro-chain transfer agent with NBMA is carried out to fabricate photocleavable amphiphilic block copolymers (BCP). Finally, these self-assembled BCP rapidly dissemble under UV light suggesting the photoresponsive character of NBMA is not altered during the polymerization under yellow or red light. Such photoresponsive polymers can be potentially used for the remote-controlled delivery of therapeutic compounds. [ABSTRACT FROM AUTHOR]

Facile and scalable fabrication methods are attractive to prepare materials for diverse applications. Herein, a method is presented to prepare cross-linked polymeric nanoparticles with graphene oxide (GO) nanosheets covalently attached to the surface. Alkene-modified GO serves as a surfactant in a miniemulsion polymerization, and the alkene functionalities of GO exposed to the oil-phase are incorporated into the polymer particle through thiol-ene reactions, leaving the unreacted alkene functional groups of the other face of GO available for further functionalization. The surface of GO-armored polymer particles is then modified with a small molecule fluorophore or carboxylic acid functional groups that bind to Fe2O3 and TiO2 nanoparticles. This methodology provides a facile route to preparing complex hybrid composite materials. [ABSTRACT FROM AUTHOR]

The photochemical and electrochemical investigations of commercially available, safe, and cheap fluorescent brighteners, namely, triazinylstilbene (commercial name: fluorescent brightener 28) and 2,5-bis(5-tert-butyl-benzoxazol-2-yl)thiophene, as well as their original use as photoinitiators of polymerization upon light emitting diode (LED) irradiation are reported. Remarkably, their excellent near-UV-visible absorption properties combined with outstanding fluorescent properties allow them to act as high-performance photoinitiators when used in combination with diaryliodonium salt. These two-component photoinitiating systems can be employed for free radical polymerizations of acrylate. In addition, this brightener-initiated photopolymerization is able to overcome oxygen inhibition even upon irradiation with low LED light intensity. The underlying photochemical mechanisms are investigated by electron-spin resonance-spin trapping, fluorescence, cyclic voltammetry, and steady-state photolysis techniques. [ABSTRACT FROM AUTHOR]

A novel procedure has been developed for the Gilch reaction leading to poly( p-phenylene vinylenes) (PPVs). In the first step, selective activation of the starting material is achieved at low temperature. Subsequently, controlled chain growth is induced by lighting the α-halo- p-quinodimethane monomer. In contrast to the thermal Gilch polymerization, the photoinduced process allows adjusting crucial parameters such as intensity and energy of light. The progress of PPV formation can be followed visually or by in situ UV-vis spectroscopy. If the polymers are formed under appropriate conditions, they show very high molar masses, polydispersities in the common range, and higher constitutional homogeneity than thermally grown PPVs. [ABSTRACT FROM AUTHOR]

Type II photoinitiated self-condensing vinyl polymerization for the preparation of hyperbranched polymers is explored using 2-hydroxyethyl methacrylate (HEMA) or 2-(dimethylamino)ethyl methacrylate (DMAEMA), and methyl methacrylate as hydrogen donating inimers and comonomer, respectively, in the presence of benzophenone and camphorquinone under UV and visible light. Upon irradiation at the corresponding wavelength, the excited photoinitiator abstracts hydrogen from HEMA or DMAEMA leading to the formation of initiating radicals. Depending on the concentration of inimers, type of the photoinitiator, and irradiation time, hyperbranched polymers with different branching densities and cross-linked polymers are formed. [ABSTRACT FROM AUTHOR]

Transparent and Self-Healing Elastomers for Reconfigurable 3D Materials B Back Cover b : In article 2200554, Abdon Pena-Francesch, Daniel Crespy and co-worker demonstrate that conversion of a planar polymer sheet into 3D objects is achieved with a reconfigurable transparent self-healing elastomer. The 3D self-healing transparent objects can form containers for storing chemicals, reactors for photopolymerization, which can be reused, reshaped, and recycled. [Extracted from the article]

Initially developed as an elastomer with an excellent record of barrier and chemical resistance properties, poly(disulfide) has experienced a revival linked to the dynamic nature of the S-S covalent bond. A novel photobase-catalyzed oxidative polymerization of multifunctional thiols to poly(disulfide) network is reported. Based solely on air oxidation, the single-step process is triggered by the photodecarboxylation of a xanthone acetic acid liberating a strong bicyclic guanidine base. Starting with a 1 μm thick film based on trithiol poly(ethylene oxide) oligomer, the UV-mediated oxidation of thiols to disulfides occurs in a matter of minutes both selectively, i.e., without overoxidation, and quantitatively as assessed by a range of spectroscopic techniques. Thiolate formation and film thickness determine the reaction rates and yield. Spatial control of the photopolymerization serves to generate robust micropatterns, while the reductive cleavage of S-S bridges allows the recycling of 40% of the initial thiol groups. [ABSTRACT FROM AUTHOR]