Reversible-Addition Fragmentation Chain Transfer Step-Growth Polymerization

Synthesis of Degradable Mainchain Semifluorinated Polyester by CuAAC with Reaction-Enhanced Reactivity of Intermediate (RERI) Mechanism

Quantitative insertion of functionality into polymer chains via step-growth polymerization is challenging due to the random bimolecular reaction and relatively low extent of reaction. Herein, a copper-catalyzed azide-alkyne cycloaddition (CuAAC) step-growth polymerization with reaction-enhanced reactivity of intermediates (RERI) mechanism is applied for the precise insertion of degradable functions into the mainchain semifluorinated polymer and endowed it with controlled degradability. In this CuAAC polymerization, bis-alkynyl-terminated (A2) monomer can be quantitatively consumed when the slightly excess of 2,2-bis(azidomethyl)propane-1,3-diyl bis(2-methylpropanoate) (BiAz, B2) monomer with RERI effect is employed. The CuAAC copolymerization of o-nitrobenzyl ester-derived A2 (A2-ONB), fluorinated A2 (A2-F), and B2 monomers produced the mainchain semifluorinated copolymers with tunable chemical composition and high molecular weight, along with the random and quantitative insertion of [A2-ONB] units. These mainchain semifluorinated copolymers are capable of controlled degradation profile under ultraviolet radiation and can undergo complete degradation under basic condition. This work provided a simple approach for preparing mainchain semifluorinated polymers with controlled degradability.

Diverse reactivity of maleimides in polymer science and beyond

Maleimides are remarkably versatile functional groups, capable of participating in homo- and copolymerizations, Diels-Alder and (photo)cycloadditions, Michael additions, and other reactions. Their reactivity has afforded materials ranging from polyimides with high upper service temperatures to hydrogels for regenerative medicine applications. Moreover, maleimides have proven to be an enabling chemistry for pharmaceutical development and bioconjugation via straightforward modification of cysteine residues. To exert spatiotemporal control over reactions with maleimides, multiple approaches have been developed to photocage nucleophiles, dienes, and dipoles. Additionally, further substitution of the maleimide alkene (e.g., mono- and di-halo-, thio-, amino-, and methyl-maleimides, among other substituents) confers tunable reactivity and dynamicity, as well as responsive mechanical and optical properties. In this mini-review, we highlight the diverse functionality of maleimides, underscoring their notable impact in polymer science. This moiety and related heterocycles will play an important role in future innovations in chemistry, biomedical, and materials research.

A novel label-free impedance biosensor for KRAS G12C mutations detection based on PET-RAFT and ROP synergistic signal amplification

The KRAS G12C mutations, as crucial biomarkers, are closely associated with non-small cell lung cancer. Here, a novel label-free electrochemical biosensor with synergistic signal amplification of photocell energy transfer-reversible addition fragmentation chain transfer (PET-RAFT) and ring-opening polymerization (ROP) was developed for the first time for sensitive detection of KRAS G12C mutations. Specifically, hairpin DNA (hDNA), which act as biomolecular probe, was self-assembled on Au electrode surface by Au-S bond. 4-cyano-4-[(dodecylsulfanylthiocarbonyl) sulfanyl] pentanoic acid (CDTPA), the chain transfer agent of PET-RAFT reaction, was then attached to hDNA via amide bond. After that, the target DNA (tDNA) was captured on the electrode surface by complementary base pairing with hDNA. Subsequently, large numbers of electro-active monomers N-acryloxysuccinimide (NAS) were successfully grafted to the electrode surface via PET-RAFT reaction, which provided plenty of junction sites for doxorubicin-polycaprolactone (Dox-PCL) synthesized by ROP. Finally, the Dox-PCL was connected to the electrode surface by ester bond, significantly amplifying the electrochemical signal. Under optimized conditions, the biosensor has a wide linear detection range of 0.1 pM to 1 μM, with a detection limit of 86.9 fM. Attribute to its high sensitivity, specificity, reproducibility and stability, this biosensor possesses considerable potential in early diagnosis of disease and biomedical research.

RAFT Polymerization for Advanced Morphological Control: From Individual Polymer Chains to Bulk Materials

Control of the morphology of polymer systems is achieved through reversible-deactivation radical polymerization techniques such as Reversible Addition-Fragmentation chain Transfer (RAFT). Advanced RAFT techniques offer much more than just "living" polymerization - the RAFT toolkit now enables morphological control of polymer systems across many decades of length-scale. Morphological control is explored at the molecular-level in the context of syntheses where individual monomer unit insertion provides sequence-defined polymers (single unit monomer insertion, SUMI). By being able to define polymer architectures, the synthesis of bespoke shapes and sizes of nanostructures becomes possible by leveraging self-assembly (polymerization induced self-assembly, PISA). Finally, it is seen that macroscopic materials can be produced with nanoscale detail, based on phase-separated nanostructures (polymerization induced microphase separation, PIMS) and microscale detail based on 3D-printing technologies. RAFT control of morphology is seen to cross from molecular level to additive manufacturing length-scales, with complete morphological control over all length-scales.

Photo-Mediated RAFT Step-Growth Polymerization With Diacrylate Monomers: Investigating Versatility and Oxygen Tolerance

Photomediated reversible addition fragmentation chain transfer (RAFT) step-growth polymerization is performed using a trithiocarbonate-based chain transfer agent (CTA) and acrylate-based monomers both with and without a photocatalyst. The versatility of photo-mediated RAFT step-growth is demonstrated by one-pot synthesis of a graft copolymer via sequential monomer addition. Furthermore, oxygen-tolerant photo-mediated RAFT step-growth is demonstrated, facilitated by the appropriate selection of photocatalyst and solvent pair (zinc tetraphenyl porphyrin [ZnTPP] and dimethyl sulfoxide [DMSO]), enabling ultralow volume polymerization under open-air conditions.

Strategies for preparation of chitosan based water-soluble fluorescent probes to detect Cr3+ and Cu2+ ions

The low solubility of chitosan (CS) imposes adverse effects on its application. In this work, one of the aims is to improve the water solubility of CS. By introducing water-soluble side chains to CS, this aim was achieved. Besides, fluorescent moieties were incorporated into the side chains, the fluorescent copolymers were endowed with Cr3+ and Cu2+ ions recognition ability. Firstly, a reversible addition-fragmentation chain transfer polymerization (RAFT) reagent with naphthalimide units and CC groups was prepared. Water-soluble monomer methyl acrylic acid (MAA) was employed in the RAFT polymerization. Thus, water-soluble polymer with fluorescent unit and -C ≡ C on both ends of the polymer was obtained. They were introduced into CS, and the CS-based fluorescent copolymers were obtained eventually. The amount of MAA introduced could be tuned to obtain three side chains of different lengths. It was found that the more MAA was introduced, the better the solubility of CS-TP was. The detection limits (LOD) of Cr3+ and Cu2+ were 44.6 nM and 54.5 nM, respectively. The detection of Cr3+ and Cu2+ ions is further combined with a mobile APP to realize real-time, portable, and visual detection. And the application in the logic gate, a new detection platform, is prepared.

Glycopolymeric Micellar Nanoparticles for Platelet-Mediated Tumor-Targeted Delivery of Docetaxel for Cancer Therapy

The high level of accumulation of therapeutic agents in tumors is crucial for cancer treatment. Compared to the passive tumor-targeting effect, active tumor-targeting delivery systems, primarily mediated by peptides with high production costs and reduced circulation time, are highly desired. Platelet-driven technologies have opened new avenues for targeted drug delivery prevalently through a membrane coating strategy that involves intricate manufacturing procedures or the fucoidan-mediated hitchhiking method with limited platelet affinity. Here, a novel type of amphiphilic glycopolymer self-assembled micellar nanoparticle has been developed to adhere to naturally activated platelets in the blood. The simultaneous integration of fucose and sialic acid segments into glycopolymers enables closer mimicry of the structure of P-selectin glycoprotein ligand-1 (PSGL-1), thereby increasing the affinity for activated platelets. It results in the formation of glycopolymeric micelle-platelet hybrids, facilitating targeted drug delivery to tumors. The selective platelet-assisted cellular uptake of docetaxel (DTX)-loaded glycopolymeric micelles leads to lower IC50 values against 4T1 cells than that of free DTX. The directed tumor-targeting effect of activated platelets has significantly improved the tumor accumulation capacity of the glycopolymeric nanoparticles, with up to 21.0% found in tumors within the initial 0.2 h. Additionally, with acid-responsive drug release and inherent antimetastasis properties, the glycopolymeric nanoparticles ensured potent therapeutic efficacy, prolonged survival time, and reduced cardiotoxicity, presenting a new and unexplored strategy for platelet-directed drug delivery to tumors, showing promising prospects in treating localized tumors and preventing tumor metastasis.

Synthesis of Dendrimer-Like Molecules with Partial Carbon Chain via Iterative Single Unit Monomer Insertions

Carbon-chain dendritic polymers hold unique properties and promising applications. However, synthesizing carbon-chain dendrimers, beyond conjugated ones, remains a challenge. Here, the use of the iterative single unit monomer insertion technique for synthesizing 2.5 generation partial-carbon-chain dendrimers (G2.5) is described, utilizing bismaleimide as the core, a maleimide-trithiocarbonate conjugate as the branching unit, and indene as the spacer unit, following a divergent growth strategy. The optimized conditions for synthesizing the maleimide-trithiocarbonate branching unit are a bismaleimide to trithiocarbonate ratio of 5:1 and a reaction time of 30 min. The structures are verified using 1H nuclear magnetic resonance, gel permeation chromatography, and matrix-assisted laser desorption/ionization-time of flight mass spectra. A four-arm star polymer is then synthesized using the G2.5 as the core. This synthesis of a partial-carbon-chain dendrimer establishes a foundational step toward creating all-carbon-chain ones and may open new application avenues in material science.

Orthogonal Radical and Cationic Single-Unit Monomer Insertions for Engineering Polymer Architectures

The single-unit monomer insertion (SUMI), derived from living/controlled polymerization, can be directly functionalized at the end or within the chain of polymers prepared by living/controlled polymerization, offering potential applications in the preparation of polymers with complex architectures. Many scenarios demand the simultaneous incorporation of monomers suitable for different polymerization methods into complex polymers. Therefore, it becomes imperative to utilize SUMI technologies with diverse mechanisms, especially those that are compatible with each other. Here, we reported the orthogonal SUMI technique, seamlessly combining radical and cationic SUMI approaches. Through the careful optimization of monomer and chain transfer agent pairs and adjustments to reaction conditions, we can efficiently execute both radical and cationic SUMI processes in one pot without mutual interference. The utilization of orthogonal SUMI pairs facilitates the integration of radical and cationic reversible addition-fragmentation chain transfer (RAFT) polymerization in various configurations. This flexibility enables the synthesis of diblock, triblock, and star polymers that incorporate both cationically and radically polymerizable monomers. Moreover, we have successfully implemented a mixing mechanism of free radicals and cations in RAFT step-growth polymerization, resulting in the creation of a side-chain sequence-controlled polymer brushes.

Synthesis and Thermo-Selective Recycling of Diels-Alder Cyclopentadiene Thermoplastics

Catalyst-free and reversible step-growth Diels-Alder (DA) polymerization has a wide range of applications in polymer synthesis and is a promising method for fabricating recyclable thermoplastics. The effectiveness of polymerization and depolymerization relies on the chemical building blocks, often utilizing furan as the diene and maleimide as the dienophile. Compared to the traditional diene-dienophile or two-component approach that requires precise stoichiometry, cyclopentadiene (Cp) can serve dual roles via self-dimerization. This internally balanced platform offers a route to access high-molecular-weight polymers and a dynamic handle for polymer recycling, which has yet to be explored. Herein, through a reactivity investigation of different telechelic Cp derivatives, the uncontrolled cross-linking of Cp was addressed, revealing the first successful DA homopolymerization. To demonstrate the generality of our methodology, we synthesized and characterized six Cp homopolymers with backbones derived from common thermoplastics, such as poly(dimethylsiloxane), hydrogenated polybutadiene, and ethylene phthalate. Among these materials, the hydrogenated polybutadiene-Cp analog can be thermally depolymerized (Mn = 68 to 23 kDa) and repolymerized to the parent polymer (Mn = 68 kDa) under solvent- and catalyst-free conditions. This process was repeated over three cycles without intermediate purification, confirming the efficient thermo-selective recyclability. The varied degradable properties of the other four Cp-incorporated thermoplastics were also examined. Overall, this work provides a general methodology for accessing a new class of reversible homopolymers, potentially expanding the design and construction of sustainable thermoplastics.

Pyrazole carbodithiolate-driven iterative RAFT single-additions

In this Communication, we comprehensively investigated substituent effects relevant to iterative reversible activation fragmentation chain transfer (RAFT) single unit monomer insertion (SUMI) reactions. Through the use of the pyrazole carbodithiolate (PCDT) "Z-group" as the chain transfer component in RAFT SUMI, we show the importance of "Z-group" effects and its interplay with "R-group" (the carbon-centred radical precursor) effects. We also expanded the scope of RAFT SUMI to new monomer types and sequences thereof. As such, the C-S bond dissocation/reformation steps were found to be crucial factors in SUMI, and it was found that general substituent effects must be wholistically examined for every step of this reaction. This stands in contrast with conventional knowledge of RAFT polymerisation, where the main consideration is often centred around the propagation stage, i.e., the key C-C bond formation step. Indeed, contrary to SUMI, the latter characteristic was observed in the analogous alternating copolymerisation.

Controlled switching thiocarbonylthio end-groups enables interconvertible radical and cationic single-unit monomer insertions and RAFT polymerizations

To emulate the ordered arrangement of monomer units found in natural macromolecules, single-unit monomer insertion (SUMI) have emerged as a potent technique for synthesizing sequence-controlled vinyl polymers. Specifically, numerous applications necessitate vinyl polymers encompassing both radically and cationically polymerizable monomers, posing a formidable challenge due to the distinct thiocarbonylthio end-groups required for efficient control over radical and cationic SUMIs. Herein, we present a breakthrough in the form of interconvertible radical and cationic SUMIs achieved through the manipulation of thiocarbonylthio end-groups. The transition from a trithiocarbonate (for radical SUMI) to a dithiocarbamate (for cationic SUMI) is successfully accomplished via a radical-promoted reaction with bis(thiocarbonyl) disulfide. Conversely, the reverse transformation utilizes the reaction between dithiocarbamate and bistrithiocarbonate disulfide under a cationic mechanism. Employing this strategy, we demonstrate a series of synthetic examples featuring discrete oligomers containing acrylate, maleimide, vinyl ether, and styrene, compositions unattainable through the SUMI of a single mechanism alone.

Tuning the Mechanical Properties of 3D-printed Objects by the RAFT Process: From Chain-Growth to Step-Growth

Photoinduced 3D printing based on the reversible addition-fragmentation chain transfer (RAFT) process has emerged as a robust method for creating diverse functional materials. However, achieving precise control over the mechanical properties of these printed objects remains a critical challenge for practical application. Here, we demonstrated a RAFT step-growth polymerization of a bifunctional xanthate and bifunctional vinyl acetate. Additionally, we demonstrated photoinduced 3D printing through RAFT step-growth polymerization with a tetrafunctional xanthate and a bifunctional vinyl acetate. By adjusting the molar ratio of the components in the printing resins, we finely tuned the polymerization mechanism from step-growth to chain-growth. This adjustment resulted in a remarkable range of tunable Young's moduli, ranging from 7.6 MPa to 997.1 MPa. Moreover, post-functionalization and polymer welding of the printed objects with varying mechanical properties opens up a promising way to produce tailor-made materials with specific and tunable properties.

Polymer Functionalization by RAFT Interchange

Here, we report a simple approach for end group functionalization of linear polymers and graft copolymers via an interchange process of reversible addition-fragmentation chain transfer (RAFT) polymerization chain transfer agents (CTAs). The high functional group tolerance of the RAFT process allows a library of functionalities to be introduced. Moreover, this approach allows multiple functional groups to be installed simultaneously. Furthermore, as an alternative to end group analysis, we report the utility of the supernatant of the reaction mixture to determine the degree of functionalization.

ENGINEERED INTRAVENOUS THERAPIES FOR TRAUMA

Trauma leading to severe hemorrhage and shock on average kills patients within 3 to 6 hours after injury. With average prehospital transport times reaching 1-6 hours in low- to middle-income countries, stopping the bleeding and reversing hemorrhagic shock is vital. First-generation intravenous hemostats rely on traditional drug delivery platforms, such as self-assembling systems, fabricated nanoparticles, and soluble polymers due to their active targeting, biodistribution, and safety. We discuss some challenges translating these therapies to patients, as very few have successfully made it through preclinical evaluation in large-animals, and none have translated to the clinic. Finally, we discuss the physiology of hemorrhagic shock, highlight a new low volume resuscitant (LVR) PEG-20k, and end with considerations for the rational design of LVRs.

Step-growth polymerization by the RAFT process

Reversible Addition-Fragmentation Chain Transfer (RAFT) step-growth polymerization is an emerging method that synergistically combines the benefits of RAFT polymerization (functional group and user-friendly nature) and step-growth polymerization (versatility of the polymer backbone). This new polymerization method is generally achieved by using bifunctional reagents of monomer and Chain Transfer Agent (CTA), that efficiently yield Single Monomer Unit Insertion (SUMI) adducts under stoichiometrically balanced conditions. This review covers a brief history of the RAFT-SUMI process and its transformation into RAFT step-growth polymerization, followed by a comprehensive discussion of various RAFT step-growth systems. Furthermore, characterizing the molecular weight evolution of step-growth polymerization is elaborated based on the Flory model. Finally, a formula is introduced to describe the efficiency of the RAFT-SUMI process, assuming rapid chain transfer equilibrium. Examples of reported RAFT step-growth and SUMI systems are then categorized based on the driving force.

Rapid RAFT Polymerization of Acrylamide with High Conversion

Rapid RAFT polymerization can significantly improve production efficiency of PAM with designed molecular structure. This study shows that ideal Reversible Addition–Fragmentation Chain Transfer (RAFT) polymerization of acrylamide is achieved in dimethyl sulfoxide (DMSO) solution at 70 °C. The key to success is the appropriate choice of both a suitable RAFT chain transfer agent (CTA) and initiating species. It is illustrated that dodecyl trithiodimethyl propionic acid (DMPA) is a suitable trithiocarbonate RAFT CTA and is synthesized more easily than other CTAs. Compared to other RAFT processes of polymers, the reaction system shortens reaction time, enhances conversion, and bears all the characteristics of a controlled radical polymerization. The calculation result shows that high concentrations can reduce high conversions, accelerate the reaction rate, and widen molecular weight distributions slightly. This work proposes an excellent approach for rapid synthesis of PAMs with a restricted molecular weight distribution.

Cationic Single-Unit Monomer Insertion (cSUMI): From Discrete Oligomers to the α-/ω-End and In-Chain Sequence-Regulated Polymers

Single-unit monomer insertion (SUMI) has become an important strategy for the synthesis of sequence-controlled vinyl polymers due to its strong versatility and high efficiency. However, all reported SUMI processes are based on a free-radical mechanism, resulting in a limited number of monomer types being applicable to SUMI or a limited number of sequences of structural units that SUMI can synthesize. Herein, we developed a novel SUMI based on a cationic mechanism (cSUMI), which operates through a degenerative (similar to radical SUMI) but cationic chain transfer process. By optimizing the chain transfer agent (CTA) and monomer pairs, a high-efficiency cSUMI was achieved for vinyl ether and styrene monomers. Based on this reaction, a range of discrete oligomers containing vinyl ether and styrene moieties, and even α-/ω-end and in-chain sequence-regulated polymers were synthesized, most of which cannot be achieved by radical SUMI. In addition, we explored the application of these sequence-regulated polymers in the preparation of miktoarm star polymers, delivery of photosensitizers, and solubilization of fluorescence probes. The development of SUMI with a new mechanism will certainly broaden the scope of structures and sequences in precise vinyl-based polymers.

RAFT Step-Growth Polymerization of Diacrylates

RAFT step-growth polymerization was previously demonstrated with monomers that bear low rate of homopropagation to favor the chain transfer process; by contrast, acrylates are known to be fast homopropagating monomers, thereby posing serious challenges for RAFT step-growth. Here, we identified a chain transfer agent (CTA) that rapidly yields single unit monomer inserted (SUMI) CTA adducts with a model acrylate monomer. Using a bifunctional reagent of this CTA, we successfully demonstrated RAFT step-growth polymerization with diacrylates, yielding linear polymer backbones. Furthermore, we achieved inclusion of functionality (i.e., disulfide) into RAFT step-growth polymer via a disulfide incorporated bifunctional CTA. Grafting from this backbone resulted in molecular brush polymers with cleavable functionality in each repeat unit of the backbone, allowing selective degradation to afford well-defined unimolecular species of two polymeric side chains. Given the wide selection of commercially available diacrylates, RAFT step-growth polymerization of diacrylates will further enable facile synthesis of complex architectures with modular backbones.

Catalyst-Free, Visible-Light-Induced Step-Growth Polymerization by a Photo-RAFT Single-Unit Monomer Insertion Reaction

Photoinduced polymerization is an attractive technique with the advantages of easy operation, mild conditions, and excellent temporospatial controllability. However, the application of this technique in step-growth polymerization is highly challenging. Here, we present a catalyst-free, visible-light-induced step-growth polymerization method utilizing a photo-RAFT single-unit monomer insertion reaction between the xanthate and vinyl ether groups. Benefitting from this reaction, a pendant cationic RAFT agent can be generated in each repeating unit of the polymer backbone. Both cationic and radical side chain extensions were successfully realized, providing a facile approach for the postpolymerization of step-growth polymers for the development of various functional polymeric materials.

Reversible Addition-Fragmentation Chain Transfer Step-Growth Polymerization with Commercially Available Inexpensive Bis-Maleimides

Here, commercially available N-aromatic substituted bismaleimides were used in RAFT step-growth polymerization for the first time. In our initial report (J. Am. Chem. Soc. 2021, 143 (39), 15918-15923), maleimide precursors...

Photomediated RAFT step-growth polymerization with maleimide monomers

Photomediated RAFT step-growth polymerization was performed with and without the presence of a photocatalyst using a trithiocarbonate-based CTA and a maleimide monomer.