Hydrolytic Susceptibility of Dithioester Chain Transfer Agents and Implications in Aqueous RAFT Polymerizations

Synthesis and Characterization of All-Acrylic Tetrablock Copolymer Nanoparticles: Waterborne Thermoplastic Elastomers via One-Pot RAFT Aqueous Emulsion Polymerization

Reversible addition-fragmentation chain transfer (RAFT) aqueous emulsion polymerization is used to prepare well-defined ABCB tetrablock copolymer nanoparticles via sequential monomer addition at 30 °C. The A block comprises water-soluble poly(2-(N-acryloyloxy)ethyl pyrrolidone) (PNAEP), while the B and C blocks comprise poly(t-butyl acrylate) (PtBA) and poly(n-butyl acrylate) (PnBA), respectively. High conversions are achieved at each stage, and the final sterically stabilized spherical nanoparticles can be obtained at 20% w/w solids at pH 3 and at up to 40% w/w solids at pH 7. A relatively long PnBA block is targeted to ensure that the final tetrablock copolymer nanoparticles form highly transparent films on drying such aqueous dispersions at ambient temperature. The kinetics of polymerization and particle growth are studied using 1H nuclear magnetic resonance spectroscopy, dynamic light scattering, and transmission electron microscopy, while gel permeation chromatography analysis confirmed a high blocking efficiency for each stage of the polymerization. Differential scanning calorimetry and small-angle X-ray scattering studies confirm microphase separation between the hard PtBA and soft PnBA blocks, and preliminary mechanical property measurements indicate that such tetrablock copolymer films exhibit promising thermoplastic elastomeric behavior. Finally, it is emphasized that targeting an overall degree of polymerization of more than 1000 for such tetrablock copolymers mitigates the cost, color, and malodor conferred by the RAFT agent.

Synthesis and Characterization of Charge-Stabilized Poly(4-hydroxybutyl acrylate) Latex by RAFT Aqueous Dispersion Polymerization: A New Precursor for Reverse Sequence Polymerization-Induced Self-Assembly

The reversible addition-fragmentation chain transfer (RAFT) aqueous dispersion polymerization of 4-hydroxybutyl acrylate (HBA) is conducted using a water-soluble RAFT agent bearing a carboxylic acid group. This confers charge stabilization when such syntheses are conducted at pH 8, which leads to the formation of polydisperse anionic PHBA latex particles of approximately 200 nm diameter. The weakly hydrophobic nature of the PHBA chains confers stimulus-responsive behavior on such latexes, which are characterized by transmission electron microscopy, dynamic light scattering, aqueous electrophoresis, and ¹H NMR spectroscopy. Addition of a suitable water-miscible hydrophilic monomer such as 2-(N-(acryloyloxy)ethyl pyrrolidone) (NAEP) leads to in situ molecular dissolution of the PHBA latex, with subsequent RAFT polymerization leading to the formation of sterically stabilized PHBA-PNAEP diblock copolymer nanoparticles of approximately 57 nm diameter. Such formulations constitute a new approach to reverse sequence polymerization-induced self-assembly, whereby the hydrophobic block is prepared first in aqueous media.

TEMPO-Modified Polymethacrylates as Mediators in Electrosynthesis: Influence of the Molecular Weight on Redox Properties and Electrocatalytic Activity

Homogeneous catalysts ("mediators") are frequently employed in organic electrosynthesis to control selectivity. Despite their advantages, they can have a negative influence on the overall energy and mass balance if used only once or recycled inefficiently. Polymediators are soluble redox-active polymers applicable as electrocatalysts, enabling recovery by dialysis or membrane filtration. Using anodic alcohol oxidation as an example, we have demonstrated that TEMPO-modified polymethacrylates (TPMA) can act as efficient and recyclable catalysts. In the present work, the influence of the molecular size on the redox properties and the catalytic activity was carefully elaborated using a series of TPMAs with well-defined molecular weight distributions. Cyclic voltammetry studies show that the polymer chain length has a pronounced impact on the key-properties. Together with preparative-scale electrolysis experiments, an optimum size range was identified for polymediator-guided sustainable reaction control.

A Perspective on the History and Current Opportunities of Aqueous RAFT Polymerization

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

Investigating the Effect of End-Group, Molecular Weight, and Solvents on the Catalyst-Free Depolymerization of RAFT Polymers: Possibility to Reverse the Polymerization of Heat-Sensitive Polymers

Reversing reversible deactivation radical polymerization (RDRP) to regenerate the original monomer is an attractive prospect for both fundamental research and industry. However, current depolymerization strategies are often applied to highly heat-tolerant polymers with a specific end-group and can only be performed in a specific solvent. Herein, we depolymerize a variety of poly(methyl methacrylate) materials made by reversible addition–fragmentation chain-transfer (RAFT) polymerization and terminated by various end groups (dithiobenzoate, trithiocarbonate, and pyrazole carbodithioate). The effect of the nature of the solvent on the depolymerization conversion was also investigated, and key solvents such as dioxane, xylene, toluene, and dimethylformamide were shown to facilitate efficient depolymerization reactions. Notably, our approach could selectively regenerate pure heat-sensitive monomers (e.g., tert-butyl methacrylate and glycidyl methacrylate) in the absence of previously reported side reactions. This work pushes the boundaries of reversing RAFT polymerization and considerably expands the chemical toolbox for recovering starting materials under relatively mild conditions.

End-functionalized polymers by controlled/living radical polymerizations: synthesis and applications

This review focuses on end-functionalized polymers synthesized by controlled/living radical polymerizations and the applications in fields including bioconjugate formation, surface modification, topology construction, and self-assembly.

Controlled (Co)Polymerization of Methacrylates Using a Novel Symmetrical Trithiocarbonate RAFT Agent Bearing Diphenylmethyl Groups

Herein, we report a novel type of symmetrical trithiocarbonate chain transfer agent (CTA) based diphenylmethyl as R groups. The utilization of this CTA in the Reversible Addition-Fragmentation chain Transfer (RAFT) process reveals an efficient control in the polymerization of methacrylic monomers and the preparation of block copolymers. The latter are obtained by the (co)polymerization of styrene or butyl acrylate using a functionalized macro-CTA polymethyl methacrylate (PMMA) previously synthesized. Data show low molecular weight dispersity values (Đ < 1.5) particularly in the polymerization of methacrylic monomers. Considering a typical RAFT mechanism, the leaving groups (R) from the fragmentation of CTA should be able to re-initiate the polymerization (formation of growth chains) allowing an efficient control of the process. Nevertheless, in the case of the polymerization of MMA in the presence of this symmetrical CTA, the polymerization process displays an atypical behavior that requires high [initiator]/[CTA] molar ratios for accessing predictable molecular weights without affecting the Đ. Some evidence suggests that this does not completely behave as a common RAFT agent as it is not completely consumed during the polymerization reaction, and it needs atypical high molar ratios [initiator]/[CTA] to be closer to the predicted molecular weight without affecting the Đ. This work demonstrates that MMA and other methacrylic monomers can be polymerized in a controlled way, and with "living" characteristics, using certain symmetrical trithiocarbonates.

Organo-Cobalt Complexes in Reversible-Deactivation Radical Polymerization

Cobalt complexes have played an essential role in different chemical reactions. One of them that has attracted substantial attention in polymer science is cobalt mediated radical polymerization (CMRP), which is famous for its remarkable efficiency in controlling the radical polymerization of vinyl acetate (VAc) and other less active monomers (LAMs). Two pathways, reversible termination (RT) and degenerative transfer (DT), were recognized to control the polymerization in CMRP and could be further used to rationalize the mechanism of other RDRP methods. These control mechanisms were then found to be correlated to the redox potential of cobalt complexes and thus could be judged more quantitatively. The control of polymer composition and tacticity could also be achieved by using CMRP. The hybridization of CMRP and atom transfer radical polymerization (ATRP) could directly synthesize the vinyl acetate/methyl methacrylate and vinyl acetate/styrene block copolymers in one pot. The copolymer of acrylates and 1-octene could be obtained by visible-light-induced CMRP. With the addition of bulky Lewis acid, CMRP of N,N-dimethylacrylamide (DMA) showed high isotacticities with the contents of meso dyads (m) and meso triads (mm) up to 94 % and 87 %, respectively, and generated the crystalline PDMA with T_m as high as 276 °C. This personal account reviewed the development of CMRP with the mechanistic understanding, the control of composition and stereoselectivity of the polymeric products, and its perspective.

Bromoform-assisted aqueous free radical polymerisation: a simple, inexpensive route for the preparation of block copolymers

Synthesis of ‘uncontrolled’ commercially-relevant block copolymers by metal- and sulfur-free, bromoform-assisted polymerisation.

Synthesis of polyampholytic diblock copolymers via RAFT aqueous solution polymerization

Two new classes of polyampholytic diblock copolymers are prepared via RAFT aqueous solution polymerization and their aqueous solution behaviour is assessed using 1H NMR spectroscopy, dynamic light scattering and aqueous electrophoresis measurements.

Proapoptotic Peptide Brush Polymer Nanoparticles via Photoinitiated Polymerization-Induced Self-Assembly

Herein, we report the photoinitiated polymerization-induced self-assembly (photo-PISA) of spherical micelles consisting of proapoptotic peptide-polymer amphiphiles. The one-pot synthetic approach yielded micellar nanoparticles at high concentrations and at scale (150 mg mL-1 ) with tunable peptide loadings up to 48 wt. %. The size of the micellar nanoparticles was tuned by varying the lengths of hydrophobic and hydrophilic building blocks. Critically, the peptide-functionalized nanoparticles imbued the proapoptotic "KLA" peptides (amino acid sequence: KLAKLAKKLAKLAK) with two key properties otherwise not inherent to the sequence: 1) proteolytic resistance compared to the oligopeptide alone; 2) significantly enhanced cell uptake by multivalent display of KLA peptide brushes. The result was demonstrated improved apoptosis efficiency in HeLa cells. These results highlight the potential of photo-PISA in the large-scale synthesis of functional, proteolytically resistant peptide-polymer conjugates for intracellular delivery.

In situ SAXS studies of a prototypical RAFT aqueous dispersion polymerization formulation: monitoring the evolution in copolymer morphology during polymerization-induced self-assembly

Small-angle X-ray scattering (SAXS) is used to characterize the in situ formation of diblock copolymer spheres, worms and vesicles during reversible addition-fragmentation chain transfer (RAFT) aqueous dispersion polymerization of 2-hydroxypropyl methacrylate at 70 °C using a poly(glycerol monomethacrylate) steric stabilizer. 1H NMR spectroscopy indicates more than 99% HPMA conversion within 80 min, while transmission electron microscopy and dynamic light scattering studies are consistent with the final morphology being pure vesicles. Analysis of time-resolved SAXS patterns for this prototypical polymerization-induced self-assembly (PISA) formulation enables the evolution in copolymer morphology, particle diameter, mean aggregation number, solvent volume fraction, surface density of copolymer chains and their mean inter-chain separation distance at the nanoparticle surface to be monitored. Furthermore, the change in vesicle diameter and membrane thickness during the final stages of polymerization supports an 'inward growth' mechanism.

Fabrication of low-fouling, high-loading polymeric surfaces through pH-controlled RAFT

Low-fouling and high-loading surfaces are increasingly important for biosensing and blood purification technologies. Selective and efficient target binding from complex media can be achieved with poly(carboxybetaine) (pCB) surfaces that consist of a dense brush layer to resist non-specific protein adsorption and a sparse “mushroom” upper layer for high-density capture agent immobilization (i.e. high-loading). We developed pH-controlled surface-reversible addition–fragmentation chain-transfer (S-RAFT) polymerization to simplify fabrication of multi-modal, low-fouling and high-loading pCB surfaces without the need for quenching or re-initiation steps, toxic transition metals or light irradiation. Multi-modal polymer layers were produced through partial polymer termination by temporarily raising the pH to aminolyse a fraction of dormant chain transfer agents (CTAs); remaining polymer chains with intact CTAs continued uninterrupted extension to create the “mushroom” upper layer. The multi-modal pCB surfaces were low-fouling towards proteins (<6.7 ng cm⁻²), and macrophages. Compared to mono-modal brush surfaces, multi-modal pCB surfaces were high-loading with 5-fold greater capture agent immobilization (e.g. antibody) and 4-fold greater target binding (e.g. biotin-fluorescein).

pH-Controlled surface-reversible addition–fragmentation chain-transfer (S-RAFT) polymerization yields a one-pot synthesis for bimodal polymeric surfaces for improved capture agent immobilization.

Enlightening advances in polymer bioconjugate chemistry: light-based techniques for grafting to and from biomacromolecules

Photochemistry has revolutionized the field of polymer-biomacromolecule conjugation. Ligation reactions necessitate biologically benign conditions, and photons have a significant energy advantage over what is available thermally at ambient temperature, allowing for rapid and unique reactivity. Photochemical reactions also afford many degrees of control, specifically, spatio-temporal control, light source tunability, and increased oxygen tolerance. Light-initiated polymerizations, in particular photo-atom-transfer radical polymerization (photo-ATRP) and photoinduced electron/energy transfer reversible addition-fragmentation chain transfer polymerization (PET-RAFT), have been used for grafting from proteins, DNA, and cells. Additionally, the spatio-temporal control inherent to light-mediated chemistry has been utilized for grafting biomolecules to hydrogel networks for many applications, such as 3-D cell culture. While photopolymerization has clear advantages, there are factors that require careful consideration in order to obtain optimal control. These factors include the photocatalyst system, light intensity, and wavelength. This Perspective aims to discuss recent advances of photochemistry for polymer biomacromolecule conjugation and potential considerations while tailoring these systems.

Synthesis of block cationic polyacrylamide precursors using an aqueous RAFT dispersion polymerization

Synthesis of cationic polyacrylamides (CPAMs) by introducing cationic polymer precursors followed by chain extension of acrylamide (AM) homopolymer blocks via RAFT polymerization is a promising approach for engineering high-performance CPAMs. However, the aqueous solution polymerization of AM usually leads to high viscosity, thus limiting the solid content in the polymerization system. Herein a novel approach is introduced that uses a random copolymer of AM and methacryloxyethyltrimethyl ammonium chloride (DMC) as a macro RAFT chain transfer agent (mCTA) and stabilizer for aqueous RAFT dispersion polymerization of AM. The AM/DMC random copolymers synthesized by RAFT solution polymerization, having narrow dispersities (Đ _s) at different molecular weights and cationic degrees (C _s), could serve as the mCTA, which was confirmed by mCTA chain extension in aqueous solution polymerization of AM under different C _s, solid contents, AM addition contents, extended PAM block lengths, and mCTA chain lengths. The block CPAMs had a Đ value of less than 1.2. A model was developed using the method of moments with consideration of the diffusion control effect, for further understanding the chain extension kinetics. Predicted polymerization kinetics provided an accurate fit of the experimental data. The AM/DMC random copolymers were further used for aqueous RAFT dispersion polymerization of AM under different polymerization temperatures, C _s, and mCTA chain lengths. The resulting products had a milky appearance, and the block copolymers had Đ _s of less than 1.3. Higher C _s and longer chain lengths on mCTAs were beneficial for stabilizing the polymerization systems and produced smaller particle sizes and less particle aggregation. The products remained stable at room temperature storage for more than a month. The results indicate that aqueous RAFT dispersion polymerization using random copolymers of AM and DMC at moderate cationic degrees as a stabilizer and mCTA is a suitable approach for synthesizing CPAM block precursors at an elevated solid content.

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.

Dithioesters: simple, tunable, cysteine-selective H2S donors

Dithioesters have a rich history in polymer chemistry for RAFT polymerizations and are readily accessible through different synthetic methods. Here we demonstrate that the dithioester functional group is a tunable motif that releases H2S upon reaction with cysteine and that structural and electronic modifications enable the rate of cysteine-mediated H2S release to be modified. In addition, we use (bis)phenyl dithioester to carry out kinetic and mechanistic investigations, which demonstrate that the initial attack by cysteine is the rate-limiting step of the reaction. These insights are further supported by complementary DFT calculations. We anticipate that the results from these investigations will allow for the further development of dithioesters as important chemical motifs for studying H2S chemical biology.

A mild and quantitative route towards well-defined strong anionic/hydrophobic diblock copolymers: synthesis and aqueous self-assembly

Well-defined hydrophobic/strong anionic diblock copolymers were synthesized through a protected hydrophobic intermediate. Their self-assembly in aqueous solution was subsequently studied.

RAFT-mediated polymerisation of dialkylaminoethyl methacrylates in tert-butanol

Dialkylaminoethyl methacrylates were polymerised by RAFT in tert-butanol to make macro-chain transfer agents for subsequent grafting onto various substrates.

The influence of gradient and statistical arrangements of guanidinium or primary amine groups in poly(methacrylate) copolymers on their DNA binding affinity

Herein, we report the first gradient guanidinium containing cationic copolymers and investigate their binding ability to plasmid DNA (pDNA).

Temperature-responsive copolymers without compositional drift by RAFT copolymerization of 2-(acryloyloxy)ethyl trimethylammonium chloride and 2-(diethylamino)ethyl acrylate

Thermoresponsive copolymers based on AEtMACl and protonated DEAEA feature RAFT copolymerization kinetics with both apparent reactivity ratios of about 1.

In Situ Spectroscopic Studies of Highly Transparent Nanoparticle Dispersions Enable Assessment of Trithiocarbonate Chain-End Fidelity during RAFT Dispersion Polymerization in Nonpolar Media

We report the synthesis of highly transparent poly(stearyl methacrylate)-poly(2,2,2-trifluoroethyl methacrylate) (PSMA-PTFEMA) diblock copolymer nanoparticles via polymerization-induced self-assembly (PISA) in nonpolar media at 70 °C. This was achieved by chain-extending a PSMA precursor block via reversible addition-fragmentation chain transfer (RAFT) dispersion polymerization of TFEMA in n-tetradecane. This n-alkane has the same refractive index as the PTFEMA core-forming block at 70 °C, which ensures high light transmittance when targeting 33 nm spherical nanoparticles. Such isorefractivity enables visible absorption spectra to be recorded with minimal light scattering even at 30% w/w solids. However, in situ monitoring of the trithiocarbonate RAFT end-groups during PISA requires selection of a weak n → π* band at 446 nm. Conversion of TFEMA into PTFEMA causes a contraction in the reaction solution volume, leading to an initial increase in absorbance that enables the kinetics of polymerization to be monitored via dilatometry. At ∼98% TFEMA conversion, this 446 nm band remains constant for 2 h at 70 °C, indicating surprisingly high RAFT chain-end fidelity (and hence pseudoliving character) under monomer-starved conditions. In situ 19F NMR spectroscopy studies provide evidence for (i) the onset of micellar nucleation, (ii) solvation of the nanoparticle cores by TFEMA monomer, and (iii) surface plasticization of the nanoparticle cores by n-tetradecane at 70 °C. Finally, the kinetics of RAFT chain-end removal can be conveniently monitored by in situ visible absorption spectroscopy: addition of excess initiator at 70 °C causes complete discoloration of the dispersion, with small-angle X-ray scattering studies confirming no change in nanoparticle morphology under these conditions.

Synthesis and Assembly of Designer Styrenic Diblock Polyelectrolytes

Harnessing molecular design principles toward functional applications of ion-containing macromolecules relies on diversifying experimental data sets of well-understood materials. Here, we report a simple, tunable framework for preparing styrenic polyelectrolytes, using aqueous reversible addition-fragmentation chain transfer (RAFT) polymerization in a parallel synthesis approach. A series of diblock polycations and polyanions were RAFT chain-extended from poly(ethylene oxide) (PEO) using (vinylbenzyl)trimethylammonium chloride (PEO-b-PVBTMA) and sodium 4-styrenesulfonate (PEO-b-PSS), with varying neutral PEO block lengths, charged styrenic block lengths, and RAFT end-group identity. The materials characterization and kinetics study of chain growth exhibited control of the molar mass distribution for both systems. These block polyelectrolytes were also demonstrated to form polyelectrolyte complex (PEC) driven self-assemblies. We present two simple outcomes of micellization to show the importance of polymer selection from a broadened pool of polyelectrolyte candidates: (i) uniform PEC-core micelles comprising PEO-b-PVBTMA and poly(acrylic acid) and (ii) PEC nanoaggregates comprising PEO-b-PVBTMA and PEO-b-PSS. The materials characteristics of these charged assemblies were investigated with dynamic light scattering, small-angle X-ray scattering, and cryogenic-transmission electron microscopy imaging. This model synthetic platform offers a straightforward path to expand the design space of conventional polyelectrolytes into gram-scale block polymer structures, which can ultimately enable the development of more sophisticated ionic materials into technology.

Beyond Gene Transfection with Methacrylate-Based Polyplexes-The Influence of the Amino Substitution Pattern

Methacrylate-based polymers represent promising nonviral gene delivery vectors, since they offer a large variety of polymer architectures and functionalities, which are beneficial for specific demands in gene delivery. In combination with controlled radical polymerization techniques, such as the reversible addition-fragmentation chain transfer polymerization, the synthesis of well-defined polymers is possible. In this study we prepared a library of defined linear polymers based on (2-aminoethyl)-methacrylate (AEMA), N-methyl-(2-aminoethyl)-methacrylate (MAEMA), and N,N-dimethyl-(2-aminoethyl)-methacrylate (DMAEMA) monomers, bearing pendant primary, secondary, and tertiary amino groups, and investigated the influence of the substitution pattern on their gene delivery capability. The polymers and the corresponding plasmid DNA complexes were investigated regarding their physicochemical characteristics, cytocompatibility, and transfection performance. The nonviral transfection by methacrylate-based polyplexes differs significantly from poly(ethylene imine)-based polyplexes, as a successful transfection is not affected by the buffer capacity. We observed that polyplexes containing a high content of primary amino groups (AEMA) offered the highest transfection efficiency, whereas polyplexes bearing tertiary amino groups (DMAEMA) exhibited the lowest transfection efficiency. Further insights into the uptake and release mechanisms could be identified by fluorescence and transmission electron microscopy, emphasizing the theory of membrane-pore formation for the time-efficient endosomal release of methacrylate-based vectors.

Photochemistry for Well-Defined Polymers in Aqueous Media: From Fundamentals to Polymer Nanoparticles to Bioconjugates

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

Stability of Trithiocarbonate RAFT Agents Containing Both a Cyano and a Carboxylic Acid Functional Group

The hydrolytic degradation of widely used cyano-containing, acid-bearing trithiocarbonate reversible addition-fragmentation chain-transfer (RAFT) agents has been identified and shown to effect the RAFT polymerization and end-group fidelity of PMMA polymers. The hydrolysis occurred when the RAFT agents were stored under the recommended conditions. Degradation was identified in both commercially available and popular synthetic RAFT agents. ¹H and ¹³C NMR as well as mass spectroscopy show that the cyano functionality hydrolyzes to the amide adduct. Doping of this amide degradation product into RAFT polymerizations of MMA results in increased dispersities and changes in expected end-group fidelities. The ability to identify this degradation product and remove it from the RAFT agent before use will allow better control over polymer properties and postmodification processes commonly used in complex polymer systems, nanomedicines, and bioconjugates.

Design of Dithiobenzoate RAFT Agent Bearing Hydroxyl Groups and Its Application in RAFT Polymerization for Telechelic Diol Polymers

RAFT polymerization is attractive for its reliability, facile operation, and high tolerance to a wide variety of monomers, functional groups, solvents, and temperatures. Herein, we report the RAFT-based synthesis of well-defined polymers bearing hydroxyl groups at two terminals by using various monomers. We found that the molecular weight of obtained polymers was half that of a target value when a trithiocarbonate-type chain transfer agent (CTA) was used, suggesting that the polymers unexpectedly cleaved at the middle of the polymer chain as the reaction was proceeding. To address the problem, we synthesized a novel “dithiobenzoate”-type CTA, 2-[N-(2-hydroxyethyl)carbamoyl]prop-2-yl 4-hydroxydithiobenzoate (HECPHD), which bears hydroxyl groups at both terminals, and we succeeded in RAFT polymerization with various monomers without a cleavage of the polymers.

H2O2 Enables Convenient Removal of RAFT End-Groups from Block Copolymer Nano-Objects Prepared via Polymerization-Induced Self-Assembly in Water

RAFT-synthesized polymers are typically colored and malodorous due to the presence of the sulfur-based RAFT end-group(s). In principle, RAFT end-groups can be removed by treating molecularly dissolved copolymer chains with excess free radical initiators, amines, or oxidants. Herein we report a convenient method for the removal of RAFT end-groups from aqueous dispersions of diblock copolymer nano-objects using H2O2. This oxidant is relatively cheap, has minimal impact on the copolymer morphology, and produces benign side products that can be readily removed via dialysis. We investigate the efficiency of end-group removal for various diblock copolymer nano-objects prepared with either dithiobenzoate- or trithiocarbonate-based RAFT chain transfer agents. The advantage of using UV GPC rather than UV spectroscopy is demonstrated for assessing both the kinetics and extent of end-group removal.

Aqueous RAFT at pH zero: enabling controlled polymerization of unprotected acyl hydrazide methacrylamides

A first example of controlled radical polymerization of monomers containing unprotected acyl hydrazide pendent groups was demonstrated using aqueous RAFT polymerization at pH = 0.

Study of the RAFT homopolymerization and copolymerization of N-[3-(dimethylamino)propyl]methacrylamide hydrochloride and evaluation of the cytotoxicity of the resulting homo- and copolymers

Well-defined p(DMAPMA·HCl) homopolymers with good chain extension ability were obtained by the RAFT in acidic conditions and precipitation in acetone.

Synthesis of ultra-high molecular weight ABA triblock copolymers via aqueous RAFT-mediated gel polymerisation, end group modification and chain coupling

Novel ultra-high molecular weight ABA triblock copolymers were synthesised using aqueous RAFT polymerisation, end-group modification and chain coupling.