Pyrene-Based Organic Photoredox Catalysts for Carbon-Carbon Bond-Forming Reactions: Reductive Coupling of Aromatic Carbonyl and Imine Compounds

Metal-free photoredox catalysts built upon a pyrene core were developed for carbon-carbon bond-forming reactions. Among these catalysts, a pyrene derivative containing a urea moiety effectively facilitated the reductive coupling of aromatic carbonyl and imine compounds under blue LED irradiation. This process provided the corresponding vicinal diols and diamines in good yields.

Microporous Block Copolymers Modified with Cu(II)-Coordinated Polyethylene Oxide-Substituted Silicas for Analytical Sensors

The influence of stable-to-self-condensation Cu(II)-coordinated polyoxyethylene-substituted silicas (ASiP-Cu-0.5) on the synthesis of microporous block copolymers (OBCs) whose structural feature is the existence of coplanar polyisocyanate blocks of acetal nature (O-polyisocyanates) and a flexible-chain component of amphiphilic nature was studied. The use of ASiP-Cu-0.5 increased the yield of O-polyisocyanate blocks and the microphase separation of OBC. The resulting OBCs turned out to be effective sorbents for the analytical reagents PAN and PHENAZO, which, being in the micropore cavity, interacted with copper(II) and magnesium ions. To reduce the thickness of the selective OBC layer ten-fold and simplify the technology for obtaining analytical test systems, polyethylene terephthalate was used as a substrate for applying OBC. It was found that the increased sensitivity of the resulting test systems was due to the fact that in thin reaction layers, the efficiency of the formation of O-polyisocyanate blocks noticeably increased.

Synthesis of Block Copolymers by Mechanistic Transformation from Reversible Complexation Mediated Living Radical Polymerization to the Photoinduced Radical Oxidation/Addition/Deactivation Process

A versatile strategy for the fabrication of block copolymers by the combination of two discrete living polymerization techniques─reversible complexation mediated living radical polymerization (RCMP) and photoinduced radical oxidation addition deactivation (PROAD) processes─is reported. First, RCMP is conducted to yield poly(methyl methacrylate) with iodide end groups (PMMA-I). In the following step, PMMA-I is used as macroinitiator for living PROAD cationic polymerization of isobutyl vinyl ether. Successful formation of the block copolymers is confirmed by 1H NMR, FT-IR, GPC, and DSC investigations.

Photoinduced Organocatalyzed Atom Transfer Radical Polymerization (O-ATRP): Precision Polymer Synthesis Using Organic Photoredox Catalysis

The development of photoinduced organocatalyzed atom transfer radical polymerization (O-ATRP) has received considerable attention since its introduction in 2014. Expanding on many of the advantages of traditional ATRP, O-ATRP allows well-defined polymers to be produced under mild reaction conditions using organic photoredox catalysts. As a result, O-ATRP has opened access to a range of sensitive applications where the use of a metal catalyst could be of concern, such as electronics, certain biological applications, and the polymerization of coordinating monomers. However, key limitations of this method remain and necessitate further investigation to continue the development of this field. As such, this review details the achievements made to-date as well as future research directions that will continue to expand the capabilities and application landscape of O-ATRP.

Organocatalytic PET-RAFT polymerization with a low ppm of organic photocatalyst under visible light

The development of light-mediated controlled radical polymerization has benefited from the discovery of novel photocatalysts, which could allow precise light control over the polymerization process and the production of well-defined polymers.

Organocatalytic orthogonal ATRP and ring-opening polymerization using a single dual-function photocatalyst

Organocatalytic orthogonal atom transfer radical polymerization and ring-opening polymerization have been achieved using a single designer dual-function photocatalyst.

Metal-Free Organocatalyzed Atom Transfer Radical Polymerization: Synthesis, Applications, and Future Perspectives

Reversible deactivation radical polymerization (RDRP) is a class of powerful techniques capable of synthesizing polymers with a well-defined structure, properties, and functionalities. Among the available RDRPs, ATRP is the most investigated. However, the necessity of a metal catalyst represents a drawback and limits its use for some applications. O-ATRP emerged as an alternative to traditional ATRP that uses organic compounds that catalyze polymerization under light irradiation instead of metal. The friendly nature and the robustness of O-ATRP allow its use in the synthesis of tailorable advanced materials with unique properties. In this review, the fundamental aspects of the reductive and oxidative quenching mechanism of O-ATRP are provided, as well as insights into each component and its role in the reaction. Besides, the breakthrough recent studies that applied O-ATRP for the synthesis of functional materials are presented, which illustrate the significant potential and impact of this technique across diverse fields.

Preparation of IgG imprinted polymers by metal-free visible-light-induced ATRP and its application in biosensor

Immunoglobulin G (IgG) is related to the occurrence of many diseases, such as measles and inflammatory. In this paper, IgG imprinted polymers (IgGIPs) were fabricated on the surface of nano Au/nano Ni modified Au electrode (IgGIPs/AuNCs/NiNCs/Au) via metal-free visible-light-induced atom transfer radical polymerization (MVL ATRP). The IgGIPs were prepared by IgG conjugated with fluorescein isothiocyanate (FITC-IgG) as both a template and a photocatalyst. After the templates were removed, the photocatalysts (FITC) would not remain in the polymer and avoided all the effect of catalysts on the electrode. The fabricated electrodes were examined by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). Under the optimized conditions, IgGIPs/AuNCs/NiNCs/Au was prepared and used as an electrochemical biosensor. The biosensor could be successfully applied for the determination of IgG by differential pulse voltammetry (DPV) measurement. The results showed that the proposed biosensor displayed a broader linear range and a lower detection limit for IgG determination when it was compared to those similar IgG sensors. The linear range from 1.0 × 10-6 mg L-1 to 1.0 × 101 mg L-1 was obtained with a low detection limit (LOD) of 2.0 × 10-8 mg L-1 (S/N = 3). Briefly, the biosensor in this study introduced an easy and non-toxic method for IgG determination and also provided a progressive approach for designing protein imprinted polymers.

Amphiphilic copolymers in biomedical applications: Synthesis routes and property control

The request of new materials, matching strict requirements to be applied in precision and patient-specific medicine, is pushing for the synthesis of more and more complex block copolymers. Amphiphilic block copolymers are emerging in the biomedical field due to their great potential in terms of stimuli responsiveness, drug loading capabilities and reversible thermal gelation. Amphiphilicity guarantees self-assembly and thermoreversibility, while grafting polymers offers the possibility of combining blocks with various properties in one single material. These features make amphiphilic block copolymers excellent candidates for fine tuning drug delivery, gene therapy and for designing injectable hydrogels for tissue engineering. This manuscript revises the main techniques developed in the last decade for the synthesis of amphiphilic block copolymers for biomedical application. Strategies for fine tuning the properties of these novel materials during synthesis are discussed. A deep knowledge of the synthesis techniques and their effect on the performance and the biocompatibility of these polymers is the first step to move them from the lab to the bench. Current results predict a bright future for these materials in paving the way towards a smarter, less invasive, while more effective, medicine.

One-step synthesis of poly(methacrylate)-b-polyester via “one organocatalyst, two polymerizations”

In a “one organocatalyst, two polymerizations” system, triarylsulfonium hexafluorophosphate salt could spontaneously catalyze photo-ATRP and ROP. A well-defined PTMC-b-PMMA block copolymer was successfully synthesized in one-step.

Using One Photoredox Catalyst to Simultaneously Mediate Two Different Polymerizations for Photo-Triggered Multi-Component Orthogonal Polymerizations

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.

In-situ syntheses of graft copolymers by metal-free strategies: combination of photoATRP and ROP

A completely metal-free and environmentally friendly strategy is demonstrated for the preparation of graft copolymers by combining photoinduced Atom Transfer Radical Polymerization (ATRP) and Ring Opening Polymerization (ROP). Polymerizations are simultaneously realized in a one-pot manner. For this purpose, bare vinyl monomers, vinyl monomers with hydroxyl functional groups, and lactone monomers were simultaneously polymerized under visible light using specific catalysts. While vinyl monomers construct the main chain, the lactone monomers were polymerized from the hydroxyl functions present at the side chain. Spectral and chromatographic analyses prove that the utilized strategy is successful in the preparation of graft copolymers controlled molecular weights and narrow distributions.

Macromolecular Engineering by Applying Concurrent Reactions with ATRP

Modern polymeric material design often involves precise tailoring of molecular/supramolecular structures which is also called macromolecular engineering. The available tools for molecular structure tailoring are controlled/living polymerization methods, click chemistry, supramolecular polymerization, self-assembly, among others. When polymeric materials with complex molecular architectures are targeted, it usually takes several steps of reactions to obtain the aimed product. Concurrent polymerization methods, i.e., two or more reaction mechanisms, steps, or procedures take place simultaneously instead of sequentially, can significantly reduce the complexity of the reaction procedure or provide special molecular architectures that would be otherwise very difficult to synthesize. Atom transfer radical polymerization, ATRP, has been widely applied in concurrent polymerization reactions and resulted in improved efficiency in macromolecular engineering. This perspective summarizes reported studies employing concurrent polymerization methods with ATRP as one of the reaction components and highlights future research directions in this area.

Organocatalytic sequential ring-opening polymerization of a cyclic ester and anionic polymerization of a vinyl monomer

Organocatalysis has provided new tools for making block copolymers, in particular active species able to polymerize monomers of different chemical nature such as cyclic esters, cyclic carbonates and epoxides. We report herein the first example of an organocatalytic active species able to polymerize sequentially a cyclic ester, ε-decalactone, and a vinyl monomer, methyl methacrylate. The resulting block copolymer shows the properties of thermoplastic elastomers.

Photophysics and photochemistry of NIR absorbers derived from cyanines: key to new technologies based on chemistry 4.0

Cyanines derived from heptamethines were mainly discussed regarding their functionalization to broaden the solubility in different surroundings exhibiting either hydrophilic or hydrophobic properties and to tailor made the ΔG et photopysical properties with respect to absorption and fluorescence. Electrochemical properties were additionally considered for some selected examples. The cyanines chosen comprised as end groups either indolenine, benzo[e]- or benzo[cd]indolium pattern, which facilitated to shift the absorption between 750-1000 nm. This enabled their use in applications with light sources emitting in the near-infrared (NIR) region selected from high power LEDs or lasers with line-shaped focus. The absorbers considered were discussed regarding their function as sensitizer for applications related to Chemistry 4.0 standards. These were mainly photopolymer coatings, which can be found for applications in the graphic industry or to protect selected substrates. The huge release of heat on demand upon turning ON or OFF the NIR light source enables them for photothermal treatment in processes requesting heat to initiate either chemical (activated reactions) or physical (melting, evaporation) events.

One-Step and Metal-Free Synthesis of Triblock Quaterpolymers by Concurrent and Switchable Polymerization

A one-step and metal-free route to triblock quaterpolymers from mixtures of vinyl monomers, epoxides, anhydrides, and racemic lactide (rac-LA) has been described, which bridges three polymerization cycles involving ring-opening copolymerization (ROCOP) of epoxides/anhydrides, ring-opening polymerization (ROP) of rac-LA, and RAFT polymerization of vinyl monomers. Taking advantage of the switchable polymerization between ROCOP and ROP, concurrent chain propagation of ROCOP/RAFT and ROP/RAFT sequentially occurs by using a trithiocarbonate compound with carboxylic group (TTC-COOH) as a versatile chain transfer agent. The multiple-chain transfer effect enables independent and precise control over the molecular weights of the three blocks and ensures narrow distribution of the resultant triblock quaterpolymers (Đ < 1.20). This work demonstrates the possibility to acquire block copolymers with high degree of structural complexities in a single efficient process by combining different block polymerization strategies.

Iodine-mediated photo-controlled atom transfer radical polymerization (photo-ATRP) and block polymerization combined with ring-opening polymerization (ROP) via a superbase

Most organocatalysts for photo-controlled atom transfer radical polymerization (photo-ATRP) are metal complexes or synthetically elaborate organic dyes, which are toxic and expensive.

One-Pot Synthesis of Star Copolymers by the Combination of Metal-Free ATRP and ROP Processes

A completely metal-free strategy is demonstrated for the preparation of star copolymers by combining atom transfer radical polymerization (ATRP) and ring-opening polymerization (ROP) for the syntheses of block copolymers. These two different metal-free controlled/living polymerizations are simultaneously realized in one reaction medium in an orthogonal manner. For this purpose, a specific core with functional groups capable of initiating both polymerization types is synthesized. Next, vinyl and lactone monomers are simultaneously polymerized under visible light irradiation using specific catalysts. Spectral and chromatographic evidence demonstrates the success of the strategy as star copolymers are synthesized with controlled molecular weights and narrow distributions.

Controlled Synthesis of Block Copolymers by Mechanistic Transformation from Atom Transfer Radical Polymerization to Iniferter Process

A straightforward transformation protocol combining two distinct living polymerization methods for the controlled synthesis of block copolymers is described. In the first step, bromo-terminated poly(methyl methacrylate) is prepared by atom transfer radical polymerization (ATRP). Then, a bromide end group is substituted with a triphenylmethyl (trityl) functionality under visible light irradiation using dimanganese decacarbonyl (Mn₂ (CO)₁₀ ) photochemistry. The resulting polymers with trityl end groups are used as macroiniferter for the polymerization of styrene and tert-butyl acrylate (tBA) to yield desired block copolymers with narrow molecular weight distribution. Moreover, the amphiphilic copolymers with acrylic acid functionalities are obtained by the hydrolyzation of poly(tert-butyl acrylate) containing block copolymers with trifluoroacetic acid.

Dual Polymerizations: Untapped Potential for Biomaterials

Block copolymers with unique architectures and those that can self-assemble into supramolecular structures are used in medicine as biomaterial scaffolds and delivery vehicles for cells, therapeutics, and imaging agents. To date, much of the work relies on controlling polymer behavior by varying the monomer side chains to add functionality and tune hydrophobicity. Although varying the side chains is an efficient strategy to control polymer behavior, changing the polymer backbone can also be a powerful approach to modulate polymer self-assembly, rigidity, reactivity, and biodegradability for biomedical applications. There are many developments in the syntheses of polymers with segmented backbones, but these developments are not widely adopted as strategies to address the unique constraints and requirements of polymers for biomedical applications. This review highlights dual polymerization strategies for the synthesis of backbone-segmented block copolymers to facilitate their adoption for biomedical applications.

Integration of metal-free ring-opening metathesis polymerization and organocatalyzed ring-opening polymerization through a bifunctional initiator

We demonstrate the first integration of metal-free ROMP and organocatalyzed ROP to provide entirely metal-free syntheses of block copolymers.

Sequence-Selective Terpolymerization from Monomer Mixtures Using a Simple Organocatalyst

One-step synthesis of block copolymer from mixed monomers is of great interest and challenge. Using a simple non-nucleophilic organobase as the catalyst, we have achieved sequence-selective terpolymerization from a mixture of phthalic anhydride (PA), an epoxide, and rac-lactide (LA). Alcohol-initiated alternating copolymerization of PA and epoxide occurs first and exclusively because PA is substantially more active than LA for reacting with base-activated hydroxyl. When PA is fully consumed, LA polymerizes from the termini of the first block while excess epoxide stays intact because of the mild basicity of the catalyst. The two polymerizations thus occur tandemly, both in chemoselective manners, so that an aromatic-aliphatic block copolyester is generated in this one-step synthesis. The effectiveness and versatility of this approach is demonstrated by the use of ethylene oxide and several monosubstituted epoxides as well as mono-, di-, or tetrahydroxy initiators.

Synthesis of polymers with on-demand sequence structures via dually switchable and interconvertible polymerizations

The synthesis of polymers with on-demand sequence structures is very important not only for academic researchers but also for industry. However, despite the existing polymerization techniques, it is still difficult to achieve copolymer chains with on-demand sequence structures. Here we report a dually switchable and controlled interconvertible polymerization system; in this system, two distinct orthogonal polymerizations can be selectively switched ON/OFF independent of each other and they can be interconverted promptly and quantitatively according to external stimuli. Thus, the external stimuli can manipulate the insertion of distinct monomers into the resulting copolymer chains temporally, spatially, and orthogonally, allowing the on-demand precise arrangement of sequence structures in the resulting polymers. This dually switchable and interconvertible polymerization system provides a powerful tool for synthesizing materials that are not accessible by other polymerization methods.

Photoinduced metal-free atom transfer radical polymerizations: state-of-the-art, mechanistic aspects and applications

Photoinduced atom transfer radical polymerization has recently been the center of intensive research in synthetic polymer chemistry because of the unique possibility of topological and temporal control in addition to precise control of macromolecular structure offered by conventional ATRP.

Hybrid block copolymers of polyesters/polycarbonates and polypeptides synthesized via one-pot sequential ring-opening polymerization

Polyester/polycarbonate-b-polypeptide hybrid block copolymers were synthesized by a sequential ring-opening polymerization in a one-pot manner.

Block Copolymers: Synthesis, Self-Assembly, and Applications

Research on block copolymers (BCPs) has played a critical role in the development of polymer chemistry, with numerous pivotal contributions that have advanced our ability to prepare, characterize, theoretically model, and technologically exploit this class of materials in a myriad of ways in the fields of chemistry, physics, material sciences, and biological and medical sciences. The breathtaking progress has been driven by the advancement in experimental techniques enabling the synthesis and characterization of a wide range of block copolymers with tailored composition, architectures, and properties. In this review, we briefly discussed the recent progress in BCP synthesis, followed by a discussion of the fundamentals of self-assembly of BCPs along with their applications.

A Metal-Free Approach to 1,2-Diamines via Visible Light-Driven Reductive Coupling of Imines with Perylene as a Photoredox Catalyst

A simple, metal-free, and versatile approach to 1,2-diamines has been developed based on reductive coupling reactions of various imines, where perylene, an aromatic hydrocarbon, was used as a photoredox catalyst under visible light irradiation using a white light-emitting diode. The use of 1 mol % perylene enabled almost complete conversion of the imines, leading to the formation of their corresponding 1,2-diamines, which were isolated in good yields. The ratios between dl and meso diamines ranged from 31:69 to 82:18 depending on the substituents of the imines.

Synthesis of block copolymers by mechanistic transformation from photoinitiated cationic polymerization to a RAFT process

A novel synthetic strategy for the synthesis of block copolymers based on mechanistic transformation from photoinitiated cationic polymerization to radical addition fragmentation transfer polymerization is presented.