Visible-Light-Induced Passerini Multicomponent Polymerization

Plenty of Space in the Backbone: Radical Ring-Opening Polymerization

Radical polymerization is the most widely applied technique in both industry and fundamental science. However, its major drawback is that it typically yields polymers with non-functional, non-degradable all-carbon backbones-a limitation that radical ring-opening polymerization (rROP) allows to overcome. The last decade has seen a surge in rROP, primarily focused on creating degradable polymers. This pursuit has resulted in the creation of the first readily degradable materials through radical polymerization. Recent years have witnessed innovations in new monomers that address previous design limitations, such as ring strain and reactivity ratios. Furthermore, advances in integrating rROP with reversible deactivation radical polymerization (RDRP) have facilitated the incorporation of complex, customizable chemical payloads into the main polymer chain. This short review discusses the latest developments in monomer design with a focused analysis of their limitations in a broader historical context. Recently evolving strategies for compatibility of rROP monomers with RDRP are discussed, which are key to precision polymer synthesis. The latest chemistry surveyed expands the horizon beyond mere hydrolytic degradation. Now is the time to explore the chemical potential residing in the previously inaccessible polymer backbone.

Recent Developments in Functional Polymers via the Kabachnik-Fields Reaction: The State of the Art

Recently, multicomponent reactions (MCRs) have attracted much attention in polymer synthesis. As one of the most well-known MCRs, the Kabachnik-Fields (KF) reaction has been widely used in the development of new functional polymers. The KF reaction can efficiently introduce functional groups into polymer structures; thus, polymers prepared via the KF reaction have unique α-aminophosphonates and show important bioactivity, metal chelating abilities, and flame-retardant properties. In this mini-review, we mainly summarize the latest advances in the KF reaction to synthesize functional polymers for the preparation of heavy metal adsorbents, multifunctional hydrogels, flame retardants, and bioimaging probes. We also discuss some emerging applications of functional polymers prepared by means of the KF reaction. Finally, we put forward our perspectives on the further development of the KF reaction in polymer chemistry.

Isocyanide-Based Multicomponent Reactions Promoted by Visible Light Photoredox Catalysis

Isocyanide-based multicomponent reactions claim a one century-old history of flourishing developments. On the other hand, the enormous impact of recent progresses in visible light photocatalysis has boosted the identification of new straightforward and green approaches to both new and known chemical entities. In this context, the application of visible light photocatalytic conditions to multicomponent processes has been promoting key stimulating advancements. Spanning from radical-polar crossover pathways, to photoinduced and self-catalyzed transformations, to reactions involving the generation of imidoyl radical species, the present literature analysis would provide a general and critical overview about the potentialities and challenges of exploiting isocyanides in visible light photocatalytic multicomponent reactions.

Linear Cyclobutane-Containing Polymer Synthesis via [2 + 2] Photopolymerization in an Unconfined Environment under Visible Light

The [2 + 2] photopolymerization of diolefinic monomers is an appealing approach for the construction of polymeric materials. Herein, we demonstrate that the establishment of an effective donor-acceptor conjugation by introducing electron-donating alkoxy groups at appropriate positions of the benzene ring could activate p-phenylenediacrylate (PDA), thus enabling the development of the first solution [2 + 2] photopolymerization of such monomers under the irradiation of visible light. Variation on the alkoxy groups and the ester parts could allow access to a series of linear cyclobutane-containing polymer products with high molecular weight (up to 140 kDa) and good solubility in common solvents. Further, temporal control and postpolymerization modification with preinstalled pendant C═C bonds via thiol-ene click reaction are also demonstrated with this [2 + 2] photopolymerization system.

Solution [2 + 2] photopolymerization of biomass-derived nonrigid biscinnamate monomers enabled by energy transfer catalysis

Visible light-mediated [2 + 2] photopolymerization of nonrigid biscinnamate monomers has been realized in solution via energy transfer catalysis, featuring its operation simplicity, controllability, and a general monomer scope.

Passerini chemistries for synthesis of polymer pro-drug and polymersome drug delivery nanoparticles

New materials chemistries are urgently needed to overcome the limitations of existing biomedical materials in terms of preparation, functionality and versatility, and also in regards to their compatibility with biological...

One-pot cascade polycondensation and Passerini three-component reactions for the synthesis of functional polyesters

A one-pot cascade four-component polymerization and post-polymerization modification reaction is introduced to synthetic polymer chemistry.

Three-Component Dynamic Covalent Chemistry: From Janus Small Molecules to Functional Polymers

A new multicomponent reaction involving 2-hydroxybenzaldehyde, amine, and 2-mercaptobenzaldehyde (HAM reaction) has been developed and applied to multicomponent polymerization and controlled radical polymerization for the construction of random and block copolymers. This chemistry features mild reaction conditions, high yield, simple isolation, and water as the only byproduct. With the advantages of the distinct nucleophilicity of thiol and hydroxyl groups, the chemistry could be used for stepwise labeling and modifications on primary amines. The Janus chemical joint formed from this reaction exhibits degradability in buffers and generates the corresponding starting reagents, allowing amine release. Interestingly, the chemical joint exhibits thermally activated reversibility with water as the catalyst. This multicomponent dynamic covalent feature has been applied to the metamorphosis of random and block copolymers, generating polymers with diverse architectures. This chemistry is expected to be broadly applicable to synthetic polymer chemistry and materials science.

Four component Passerini polymerization of bulky monomers under high shear flow

We introduce a four component Passerini polymerization utilizing sterically bulky isocyanide monomers. Under typical Passerini conditions, bulky isocyanides do not react within standard Passerini reaction timescales (hours). We overcome this challenge via the unique physiochemical conditions present in a vortex fluidic device, reducing the reaction time to 2 h on average. Under these high-shear thin-film conditions, bulky isocyanides are readily incorporated into the multicomponent polymerization without the need of high-pressure or temperature. Finally, we demonstrate that the four component approach using functional cyclic anhydrides allows for post-polymerization modification.

Going Beyond the Carothers, Flory and Stockmayer Equation by Including Cyclization Reactions and Mobility Constraints

A challenge in the field of polymer network synthesis by a step-growth mechanism is the quantification of the relative importance of inter- vs. intramolecular reactions. Here we use a matrix-based kinetic Monte Carlo (kMC) framework to demonstrate that the variation of the chain length distribution and its averages (e.g., number average chain length x_n), are largely affected by intramolecular reactions, as mostly ignored in theoretical studies. We showcase that a conventional approach based on equations derived by Carothers, Flory and Stockmayer, assuming constant reactivities and ignoring intramolecular reactions, is very approximate, and the use of asymptotic limits is biased. Intramolecular reactions stretch the functional group (FG) conversion range and reduce the average chain lengths. In the likely case of restricted mobilities due to diffusional limitations because of a viscosity increase during polymerization, a complex x_n profile with possible plateau formation may arise. The joint consideration of stoichiometric and non-stoichiometric conditions allows the validation of hypotheses for both the intrinsic and apparent reactivities of inter- and intramolecular reactions. The kMC framework is also utilized for reverse engineering purposes, aiming at the identification of advanced (pseudo-)analytical equations, dimensionless numbers and mechanistic insights. We highlight that assuming average molecules by equally distributing A and B FGs is unsuited, and the number of AB intramolecular combinations is affected by the number of monomer units in the molecules, specifically at high FG conversions. In the absence of mobility constraints, dimensionless numbers can be considered to map the time variation of the fraction of intramolecular reactions, but still, a complex solution results, making a kMC approach overall most elegant.

Visible Light Induced Step-Growth Polymerization by Substitution Reactions

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.

Facile Multicomponent Polymerization and Postpolymerization Modification via an Effective Meldrum's Acid-Based Three-Component Reaction

Providing access to highly diverse polymer structures by multicomponent reactions is highly desirable; efficient Meldrum's acid-based multicomponent reactions, however, have been rarely highlighted in polymer chemistry. Here, the three-component reaction of Meldrum's acid, indole, and aldehyde is introduced into polymer synthesis. Direct multicomponent polymerization of Meldrum's acid, dialdehyde, and diindole can perform under mild conditions, resulting in complex Meldrum's acid-containing polymers with well-defined structures, and high molecular weights. Additionally, nearly quantitative postpolymerization modification can also perform via this Meldrum's acid-based multicomponent reaction. These results indicate that Meldrum's acid-based multicomponent reaction will be a potential tool to prepare novel polymers.

Catalyst-Free Four-Component Polymerization of Propiolic Acids, Benzylamines, Organoboronic Acids, and Formaldehyde toward Functional Poly(propargylamine)s

Multicomponent polymerizations (MCPs) are a group of fascinating polymer synthesis approaches that are developed rapidly in the recent decade. As a popular alkyne-based MCP, the A³ -polycouplings of alkynes, aldehydes, and amines are developed for the synthesis of poly(propargylamine)s under the catalysis of metal catalysts. In this work, through the design of carboxylic acid group-activated alkyne monomers, a catalyst-free, four-component polymerization of propiolic acids, benzylamines, organoboronic acids, and formaldehyde is reported under mild condition at 45 °C in dichloroethane. This four-component polymerization is applicable to different monomer structures, which can afford seven poly(propargylamine)s with up to 94% yields and molecular weights of up to 13 900 g mol^-1 . Moreover, the poly(propargylamine)s demonstrate good solubility and processibility, high thermal stability and light refractivity, unique photophysical property, and so on. The simple monomers, mild condition, low cost, high efficiency, and procedure simplicity of this catalyst-free four-component polymerization demonstrates an elegant example of functional polymer synthesis.

100th Anniversary of Macromolecular Science Viewpoint: Re-examining Single-Chain Nanoparticles

Single-chain nanoparticles (SCNP) are a class of polymeric nanoparticles obtained from the intramolecular cross-linking of polymers bearing reactive pendant groups. The development of SCNP has drawn tremendous attention since the fabrication of SCNP mimics the self-folding behavior in natural biomacromolecules and is highly desirable for a variety of applications ranging from catalysis, nanomedicine, nanoreactors, and sensors. The versatility of novel chemistries available for SCNP synthesis has greatly expanded over the past decade. Significant progress was also made in the understanding of a structure-property relationship in the single-chain folding process. In this Viewpoint, we discuss the effect of precursor polymer topology on single polymer folding. We summarize the progress in SCNP of complex architectures and highlight unresolved issues in the field, such as scalability and topological purity of SCNP.

Multicomponent Reactions in Polymer Chemistry Utilizing Heavier Main Group Elements

Herein, a concise overview of the use of heavier main group elements in multicomponent reactions and their use in polymer chemistry is provided. Incorporating heavier elements into macromolecular structures via multicomponent reactions allows for the rapid development of materials with unique properties that are not readily achieved using carbon, nitrogen, and/or oxygen. Elements in Group 13, Group 14, Group 15, and Group 16 are specifically covered examining both the familiar and unfamiliar properties of these elements and how they are used in multicomponent chemistry. Furthermore, elements that both take part in the reaction mechanism and remain in the macromolecular structure upon completion are only briefly explored. Some of the state-of-the-art work going into developing these heavier element multicomponent reactions are highlighted and it is hoped to inspire other polymer chemists to explore other parts of the periodic table.

Catalyst-Free Multicomponent Cyclopolymerizations of Diisocyanides, Activated Alkynes, and 1,4-Dibromo-2,3-Butanedione: a Facile Strategy toward Functional Polyiminofurans Containing Bromomethyl Groups

Polymers containing iminofuran (PIFs) are rarely reported due to the lack of simple and effective synthesis methods. In this work, a novel multicomponent cyclopolymerization (MCCP) of diisocyanides, activated alkynes, and 1,4-dibromo-2,3-butanedione using catalyst-free one-pot reactions under mild conditions to prepare PIFs containing bromomethyl groups is reported. PIFs with good solubility and thermal stability are obtained with high M_w s (up to 19 600) and good yields (up to 89.5%) under optimized polymerization conditions. The structure of the PIFs is characterized by nuclear magnetic resonance, Fourier transform infrared spectroscopy, and gel permeation chromatography. The photophysical properties indicate that polymers P1a2b3 and P1c2b3 have cluster-triggered emission characteristics. Thin films made from PIFs quickly degrade under UV irradiation. Moreover, the obtained polymers are decorated with bromomethyl and carboxylate groups in the side chain, which can be postfunctionalized to prepare multifunctional materials, such as star branched polymers and biomedical carrier materials. Thus, this work not only enriches the field of polymerization based on isocyanates and activated alkynes but also provides a facile strategy toward functional iminofuran polymers.

A new soft-matter material with old chemistry: Passerini multicomponent polymerization-induced assembly of AIE-active double-helical polymers with rapid visible-light degradability

Mimicking the superstructures and functions of natural chiral materials is beneficial to understand specific biological activities in living organisms and broaden applications in the fields of chemistry and materials sciences. However, it is still a great challenge to construct water-soluble, double-helical polymers with multiple responsiveness. Herein, we report for the first time a straightforward, general strategy to address this issue by taking advantage of Passerini multicomponent polymerization-induced assembly (PMPIA). The polymerization-induced generation of supramolecular interactions in chiral α-acyloxy amides drives the assembly of polymers and improves their stability in various solvents. This double-helical polymer is sensitive to metal ions, temperature, pH, and solvents, making both the superstructure and the AIE effect reversibly adjustable. Meanwhile, the hydrogen-bonding-assisted cyclization of photolabile α-acyloxy amides accelerates the degradation of helical polymers under visible-light irradiation. It is anticipated that this novel PMPIA strategy opens new horizons to inspire the design of advanced chiral/helical polymers with multiple functions.

Role of External Field in Polymerization: Mechanism and Kinetics

The past decades have witnessed an increasing interest in developing advanced polymerization techniques subjected to external fields. Various physical modulations, such as temperature, light, electricity, magnetic field, ultrasound, and microwave irradiation, are noninvasive means, having superb but distinct abilities to regulate polymerizations in terms of process intensification and spatial and temporal controls. Gas as an emerging regulator plays a distinctive role in controlling polymerization and resembles a physical regulator in some cases. This review provides a systematic overview of seven types of external-field-regulated polymerizations, ranging from chain-growth to step-growth polymerization. A detailed account of the relevant mechanism and kinetics is provided to better understand the role of each external field in polymerization. In addition, given the crucial role of modeling and simulation in mechanisms and kinetics investigation, an overview of model construction and typical numerical methods used in this field as well as highlights of the interaction between experiment and simulation toward kinetics in the existing systems are given. At the end, limitations and future perspectives for this field are critically discussed. This state-of-the-art research progress not only provides the fundamental principles underlying external-field-regulated polymerizations but also stimulates new development of advanced polymerization methods.

Recent advances in light-regulated non-radical polymerisations

This review summarises recent advances in light-regulated non-radical polymerisations as well as the applications in materials science.

Multicomponent polymerization toward biodegradable polymers with diverse responsiveness in tumor microenvironments

Multicomponent polymerization (MCP), as a powerful synthetic tool, has been widely utilized to prepare diverse functional polymers for optical, electronic, and biomedical applications.

Ag2O-catalysed nucleophilic isocyanation: selective formation of less-stable benzylic isonitriles

Both primary and secondary benzylic isonitriles were exclusively produced by the Ag₂O-catalysed reaction of benzylic phosphates and trimethylsilyl cyanide without formation of the thermodynamically favoured regioisomers, benzylic nitriles.