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The ability to revert polymers to their original monomers represents a crucial chemical recycling technique, promoting sustainability and offering the chance to convert used materials into valuable products. In recent years, numerous studies have explored the use of polymers synthesized via reversible deactivation radical polymerization (RDRP) techniques to facilitate efficient depolymerization reactions. Herein, we report the use of a photocatalyst, zinc tetraphenylporphyrin (ZnTPP), along with light irradiation to accelerate depolymerization of polymers prepared by reversible addition‐fragmentation chain transfer (RAFT) polymerization. We explore various parameters affecting depolymerization efficiency, including solvents, reaction temperature (80, 100, and 120°C), the presence of photocatalysts (ZnTPP and Eosin Y), and the type of RAFT end‐groups, namely trithiocarbonate, dithiobenzoate, and 1H‐pyrazole‐1‐carbodithioate. For instance, when PMMA was diluted to 25 mM in 1,4‐dioxane and heated to 120°C under green light irradiation in the presence of ZnTPP (200 ppm), rapid depolymerization exceeding 70% occurred within 1 h. Without ZnTPP, under similar conditions, the reaction required over 8 h to achieve a slightly lower yield. Furthermore, this method confers moderate oxygen tolerance to the system, enabling depolymerization to proceed without the need of deoxygenation, albeit at a lower rate and consequently lesser monomer recovery (31%). [ABSTRACT FROM AUTHOR]

Antimicrobial polymers (AMPs) have emerged as a promising approach to combat multidrug‐resistant pathogens. Developed from binary polymers, which contain cationic and hydrophobic groups, ternary polymers are enhanced by adding neutral hydrophilic monomers to improve their biocompatibility. Cationic groups have attracted significant attention owing to their pivotal role in AMPs. Although many studies have investigated the effect of cationic groups on antimicrobial activity of binary AMPs, there is a lack of comprehensive and systematic evaluation for ternary AMPs. Therefore, a library of 31 statistical amphiphilic ternary polymers containing different cationic groups, including primary amine, guanidine, and sulfonium groups is prepared to investigate the impact of cationic groups on antimicrobial activity and biocompatibility. It is shown that the cationic balance appears to be a critical factor influencing polymers' antibacterial activity and selectivity. The results reveal that the polymers that have the ratio of the cationic groups ranging between 50% and 60%, coupled with a cationic/hydrophobic ratio in the range of [1.4–2] and an appropriate neutral hydrophilic/hydrophobic balance, exhibited the highest selectivity toward mammalian cells. This study elucidates a structure–property‐performance relationship for ternary AMPs, which contributes to the development of AMPs capable of selectively targeting gram‐negative pathogens. [ABSTRACT FROM AUTHOR]

Membrane emulsification using pore sizes of 100 and 800 nm in conjunction with miniemulsion polymerization has been investigated for monomers with varying water solubilities, namely, styrene, n-butyl methacrylate (nBMA), benzyl methacrylate (BzMA), and n-butyl acrylate (nBA), and compared with previous work on methyl methacrylate (MMA). The O/W interfacial tension is an important parameter for 100 nm pore size (but less so for 800 nm pore size) — increasing O/W interfacial tension leads to an increase in membrane emulsification time as well as increases in the monomer droplet size and particle size. The most nonpolar monomer styrene required impractically long emulsification times. For the other monomers, the miniemulsions were polymerized by radical polymerization, resulting in monomodal particle size distributions. Overall, the results demonstrate that membrane emulsification in tandem with miniemulsion polymerization is a convenient method for synthesis of well-defined polymer nanoparticles of various monomers in the approximate size range 200–3500 nm. [ABSTRACT FROM AUTHOR]

This work presents the synthesis of a novel photosensitive acrylate monomer for use as both a self‐catalyst in the photoinduced electron/energy transfer–reversible addition fragmentation chain transfer (PET‐RAFT) polymerisation process and a photosensitiser (PS) for antibacterial applications. Hydrophilic, cationic, and antimicrobial formulations are explored to compare the antibacterial effects between charged and non‐charged polymers. Covalent attachment of the catalyst to well‐defined linear polymer chains has no effect on polymerisation control or singlet oxygen generation. The addition of the PS to polymers provides activity against S. aureus for all polymer formulations, resulting in up to a 99.99999 % killing efficacy in 30 min. Antimicrobial peptide mimetic polymers previously active against P. aeruginosa, but not S. aureus, gain significant bactericidal activity against S. aureus through the inclusion of PS groups, with 99.998 % killing efficiency after 30 min incubation with light. Thus, a broader spectrum of antimicrobial activity is achieved using two distinct mechanisms of bactericidal activity via the incorporation of a photosensitiser monomer into an antimicrobial polymer. [ABSTRACT FROM AUTHOR]

This contribution details an efficient and controlled photopolymerization regulated by far‐red (λ=680 nm) and NIR (λ=780 and 850 nm) light in the presence of aluminium phthalocyanine and aluminium naphthalocyanine. Initiating radicals are generated by photosensitization of peroxides affording an effective strategy that provides controlled polymerization of a variety of monomers with excellent living characteristics. Critically, long wavelength irradiation provides penetration through thick barriers, affording unprecedented rates of controlled polymerization that can open new and exciting applications. Furthermore, a more optimized approach to performing solar syntheses is presented. By combining the narrow Q‐bands of these photocatalysts with others possessing complementary absorptions, layered, independent polymerizations and organic transformations may be performed in parallel under a single broadband emission source, such as sunlight. [ABSTRACT FROM AUTHOR]

A peculiar radical polymerization reaction is presented in which oxygen serves as a cocatalyst, alongside triethylamine, to provide activation with light in the far‐red (690 nm, 3 mW cm−2) of the PET‐RAFT process in the presence of zinc(II) (2,3,7,8,12,13,17,18‐octaethyl‐5,10,15,20‐tetraphenylporphyrin) as photocatalyst. Apart from the ability to exert temporal control by switching the light on or off, this system possesses the exciting capability of inducing temporal control by removal or reintroduction of oxygen. Furthermore, this multicomponent catalytic system was typified by controlled polymerizations of various acrylate and acrylamide monomers, which all resulted in well‐defined polymers with low dispersity (<1.2). The process displayed excellent living characteristics that were demonstrated through chain extensions and a range of degrees of polymerization (200–1600). [ABSTRACT FROM AUTHOR]

Facing the growing environmental issues provoked by the use of nondegradable polymers in many fields (for example, packing, building, and clothing), tremendous efforts have been made to explore photodegradable materials to alleviate the increase in plastic pollution. Photodegradable materials would exploit significant advantages presented by the use of light, such as abundance, safety and the ability to easily tune intensity and wavelength. In particular, photo‐induced depolymerisation has received increasing attention, which could enable polymers to degrade to their original monomers or small molecules under certain photoirradiation conditions. Most importantly, the obtained molecules or monomers via photo‐induced depolymerisation could be conveniently recycled or further transformed to other high‐value‐added products, which is of great benefit for environmental protection. This Review summarizes recent advances in the growing field of photo‐induced depolymerisation and also considers future challenges that must be addressed. It aims to encourage new researchers to enter this flourishing area and presents a brief guide to the field. [ABSTRACT FROM AUTHOR]

As one of the emerging techniques for preparing discrete oligomers, the photo‐RAFT single unit monomer insertion (SUMI) process has shown its uniqueness and superiority in the control of both monomer sequence and stereochemistry. However, current precision polymer synthesis techniques are still burdened by the scalability challenges, such as low reaction yields, small product quantities, and long production times. Herein, we successfully established a practical protocol to address scalability problems in the photo‐RAFT SUMI processes. A series of discrete oligomers containing up to five monomer units were synthesized in batch and flow reactors by sequential and alternating SUMI of two monomers into a trithiocarbonate RAFT agent under mild reaction conditions and purified by automated flash chromatography. This protocol offers the process with large quantity (grams scale), excellent isolated yields (82%–95% for each step and 59% for five iterations), and short production time (several days for a pentamer). © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1947–1955 [ABSTRACT FROM AUTHOR]

Abstract: Translating controlled/living radical polymerization (CLRP) from batch to the high throughput production of polymer libraries presents several challenges in terms of both polymer synthesis and characterization. Although recently there have been significant advances in the field of low volume, high throughput CLRP, techniques able to simultaneously monitor multiple polymerizations in an “online” manner have not yet been developed. Here, we report our discovery that 5,10,15,20‐tetraphenyl‐21H,23H‐porphine zinc (ZnTPP) is a self‐reporting photocatalyst that can mediate PET‐RAFT polymerization as well as report on monomer conversion via changes in its fluorescence properties. This enables the use of a microplate reader to conduct high throughput “online” monitoring of PET‐RAFT polymerizations performed directly in 384‐well, low volume microtiter plates. [ABSTRACT FROM AUTHOR]

Abstract: Synthetic polymers have shown promise in combating multidrug‐resistant bacteria. However, the biological effects of sequence control in synthetic antimicrobial polymers are currently not well understood. As such, we investigate the antimicrobial effects of monomer distribution within linear high‐order quasi‐block copolymers consisting of aminoethyl, phenylethyl, and hydroxyethyl acrylamides made in a one‐pot synthesis approach via photoinduced electron transfer–reversible addition–fragmentation chain transfer polymerisation (PET‐RAFT). Through different combinations of monomer/polymer block order, antimicrobial and haemolytic activities are tuneable in a manner comparable to antimicrobial peptides. [ABSTRACT FROM AUTHOR]

Uniform synthetic polymers with precisely defined molar mass and monomer sequence (primary structure) have many potential high-value applications. However, a robust and versatile synthetic strategy for these materials remains one of the great challenges in polymer synthesis. Herein we describe proof-of-principle experiments for a modular strategy to produce discrete oligomers by a visible-light-mediated radical chain process. We utilize the high selectivity provided by photo-induced electron/energy transfer (PET) activation to develop efficient single unit monomer insertion (SUMI) into reversible addition-fragmentation chain-transfer (RAFT) agents. A variety of discrete oligomers (single unit species, dimers, and, for the first time, trimers) have been synthesized by sequential SUMI in very high yield under mild reaction conditions. The trimers were used as building blocks for the construction of uniform hexamers and graft copolymers with precisely defined branches. [ABSTRACT FROM AUTHOR]

We survey progress in the development of the processes for radical-promoted single-unit monomer insertion (SUMI) or reversible deactivation radical addition (RDRA), focussing on aminoxyl- [nitroxide-] mediated SUMI (NM-SUMI), reversible-addition-fragmentation chain transfer-SUMI (RAFT-SUMI) and atom-transfer radical addition (ATRA). Radical-promoted thiol-ene processes are also briefly discussed. We detail the strategies for achieving selectivity with respect to single unit insertion vs oligomerization and look critically at progress towards discrete oligomer synthesis by consecutive SUMI reactions. We examine the use of SUMI to install α-, ω- or mid-chain-functionality in RDRP-synthesized polymers. Finally, we examine the prospects for using radical-promoted SUMI in the synthesis of sequence-defined polymers where monomer placement is precisely defined to the level of the individual monomer units in the polymer chain. [Display omitted] [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]

Novel nitric oxide (NO) responsive monomers (NAPMA and APUEMA) containing o-phenylenediamine functional groups have been polymerized to form NO-responsive macromolecular chains as truly biomimetic polymers. Upon exposure to NO-a ubiquitous cellular signaling molecule-the NAPMA- and APUEMA-labeled thermoresponsive copolymers exhibited substantial changes in solubility, clearly characterized by tuneable LCST behavior, thereby inducing self-assembly into nanoparticulate structures. Moreover, the NO-triggered self-assembly process in combination with environmentally sensitive fluorescence dyes could be employed to detect and image endogenous NO. [ABSTRACT FROM AUTHOR]

We report a new approach for the facile synthesis of high-order multiblock copolymers comprising very short blocks. The approach entails sequential addition of different monomers via an iterative single electron transfer-living radical polymerization technique, allowing nearly perfect control of the copolymer microstructure. It is possible to synthesize high-order multiblock copolymers with unprecedented control, i.e., A-B-C-D-E-etc., without any need for purification between iterative 24 h block formation steps. To illustrate this concept, we report the synthesis of model P(MA-b-MA…) homopolymer and P(MA-b-nBuA-b-EA-b-2EHA-b-EA-b-nBuA) copolymer in extremely high yield. Finally, the halide end-group can be modified via "click chemistry", including thiol-bromide click chemistry, sodium methanethiosulfonate nucleophilic substitution, and atom transfer radical nitroxide coupling reaction, to yield functional, structurally complex macromolecules. [ABSTRACT FROM AUTHOR]

The telomerization of dimethylaminoethyl methacrylate (DMAEMA) with mercaptoethanol initiated by 2,2′-azobisisobutyronitrile was first investigated at 70°C and the influence of the type of solvent was studied. The results showed that well-defined telomers of DMAEMA could not be synthetized via telomerization of DMAEMA in water or water/acetonitrile mixture since the telomerization reaction is in competition with the nucleophilic addition of thiol onto the monomer. Transfer constants for mercaptoethanol in benzene and acetonitrile were determined by Mayo''s and O''Brien''s methods. The transfer constant obtained in acetonitrile (0,6) was higher than that obtained in benzene. This difference can be explained by the fact that the thiol was consumed by two reactions: nucleophilic addition and telomerization. The influence of solvents on the polymerization kinetics was enlightened. These results were applied to the synthesis of macromonomers of DMAEMA with isocyanatoethyl methacrylate (IEM). These macromonomers were copolymerized with styrene. [Copyright &y& Elsevier]

This special issue comprises 20 articles dedicated to the synthesis, properties and applications of multi-responsive polymers. Using the most recent macromolecular tools and polymerization techniques, researchers have devised new macromolecules capable to respond to a variety of different external changes, such a variation in temperature, in light intensity and/or in pH. Such macromolecules can be utilized for a variety of applications, including lectin sensing, controlled drug delivery and others. This is a truly stimulating issue, which shows the synthesis of functional monomers until the preparation of smart materials. [ABSTRACT FROM AUTHOR]

In this work, the authors report a novel single‐step, one‐pot process for the synthesis of self‐assembled nanoparticles using a polymerization‐induced self‐assembly (PISA) mechanism. In contrast to conventional approaches employing a pre‐formed macromolecular stabilizer, the disparate reactivities between two monomers, oligo(ethylene glycol) methyl ether methacrylate (OEGMA) and diacetone acrylamide (DAAm), are exploited instead to synthesize a gradient copolymer directly in aqueous solution. Due to the hydrophobicity of poly(DAAm), these gradient copolymers can self‐assemble in situ to form spheres and worms stabilized by the OEGMA residues. A surprisingly broad range of parameters are identified in which the worm morphology can be stabilized, which is highlighted by significant gelation of the reaction mixture in situ. This single‐step gradient copolymerization approach to PISA is more efficient than conventional two‐step syntheses. These results demonstrate improved reproducibility owing to the production of self‐assembled nanoparticles directly in a one‐pot and single‐step synthesis. [ABSTRACT FROM AUTHOR]

The photocatalyst Zn(II) meso‐tetra(4‐sulfonatophenyl)porphyrin (ZnTPPS) is found to substantially accelerate visible‐light‐initiated (red, yellow, green light) single unit monomer insertion (SUMI) of N,N‐dimethylacrylamide into the reversible addition–fragmentation chain transfer (RAFT) agent, 4‐((((2‐carboxyethyl)thio)carbonothioyl)thio)‐4‐cyanopentanoic acid (RAFT1), in aqueous solution. Thus, under irradiation with red (633 nm) or yellow (593 nm) light with 50 mpm (moles per million mole of monomer) ZnTPPS at 30 °C, the rate enhancement provided by photoinduced energy or electron transfer (PET) is ≈sevenfold over the rate of direct photoRAFT‐SUMI (without catalyst), which corresponds to achieving full and selective reaction in hours versus days. Importantly, the selectivity, as judged by the absence of oligomers, is retained. Under green light at similar power, higher rates of SUMI are also observed. However, the degree of enhancement provided by PET‐RAFT‐SUMI over direct photoRAFT‐SUMI as a function of catalyst concentration is less and some oligomers are formed. [ABSTRACT FROM AUTHOR]

PolymerizationIn their Communication on page 8376 ff. J. Xu, C. J. Hawker, G. Moad, C. Boyer et al. show that uniform oligomers can be produced in a modular strategy using photoredox catalysts. [ABSTRACT FROM AUTHOR]

We report for the first time the use of phthalocyanine compounds, in conjunction with the common solvent N-methyl-2-pyrrolidone (NMP), as a photoinitiation system for radical polymerization under various visible and near-infrared wavelengths. A library of redox-inactive metallic phthalocyanine compounds were investigated for their ability to act as photosensitizers in these new two-component photoinitiation systems, for the radical polymerization of (meth)acrylate and (meth)acrylamide monomers. Conventional radical polymerization under these conditions was successful, and moreover, the addition of reversible addition-fragmentation chain transfer (RAFT) agents to these systems led to the production of polymers with molecular weights in agreement with theoretical predictions and molecular weight distributions typically lower than 1.15. In contrast to our previous systems described as photoinduced electron/energy transfer-reversible addition-fragmentation chain transfer (PET-RAFT) where RAFT agent is activated by the photocatalyst, we propose that the phthalocyanine compounds react via a reductive quenching pathway to oxidize NMP to an NMP radical, which can directly initiate the polymerization of monomers. [ABSTRACT FROM AUTHOR]

We report a photoinduced electron/energy transfer-reversible addition-fragmentation chain transfer (PET-RAFT) dispersion polymerization mediated by 5,10,15,20-tetraphenyl-21H,23H-porphine zinc (ZnTPP) under low energy red (λmax = 635 nm) or yellow light (λmax = 560 nm). By varying the degrees of polymerization for the hydrophobic block, nanoparticles of different morphologies (spheres, wormlike micelles, and vesicles) were formed at high monomer conversion (>98%) under visible light irradiation. Interestingly, encapsulation of the ZnTPP catalyst into the nanoparticle core was achieved by direct dialysis against water with no significant change in nanoparticle morphology. These aqueous ZnTPP-loaded nanoparticles were demonstrated to have potential applications in photodynamic therapy owing to their ability to generate singlet oxygen under visible light irradiation. Finally, the ability of ZnTPP to generate singlet oxygen was exploited to perform polymerization without traditional deoxygenation procedures by addition of a singlet oxygen quencher (ascorbic acid). [ABSTRACT FROM AUTHOR]

Controlled/living radical polymerization techniques have transformed polymer chemistry in the last few decades, affording the production of polymers with precise control over both molecular weights and architectures. It is now possible to synthesize almost an infinite variety of macromolecules using nonspecialized equipment, finding applications in high-tech industry. However, they have several shortcomings. Until recently, living radical polymerizations could not be controlled by an external stimulus, such as visible light, pH, mechanical, chemical, etc. Moreover, they are usually sensitive to trace amounts of oxygen in the system. In this Article, we report a photoinduced living polymerization technique, which is able to polymerize a large range of monomers, including conjugated and unconjugated monomers, using ultralow concentrations of an iridium-based photoredox catalyst (typically 1 ppm to monomers) and a low energy visible LED as the light source (1--4.8 W, λmax = 435 nm). The synthesis of homopolymers with molecular weights ranging from 1000 to 2 000 000 g/mol was successfully achieved with narrow molecular weight distributions (Mw/Mn < 1.3). In addition, chain extensions of poly(methacrylate)s, poly(styrene), poly(N-vinyI pyrrolidinone), poly(vinyl ester)s, and poly(acrylate)s were performed to prepare diblock copolymers. The reusability of the catalyst was demonstrated by the synthesis of a decablock polymer by multiple chain extensions. Most importantly, this process was employed to prepare well-defined polymers and multiblock copolymers in the presence of air. [ABSTRACT FROM AUTHOR]