macro-RAFT Agent Research Articles

An Exploration of the Universal and Switchable RAFT-Mediated Synthesis of Poly(styrene-alt-maleic acid)-b-poly(N-vinylpyrrolidone) Block Copolymers.

The synthesis of poly(styrene-alt-maleic anhydride) (SMAnh) and poly(4-tert-butylstyrene-alt-maleic anhydride) (tBuSMAnh) macro-RAFT agents was investigated using universal 3,5-dimethylpyrazole dithiocarbamate and stimuli-responsive N-(4-pyridinyl)-N-methyldithiocarbamate RAFT agents. SMAnh/tBuSMAnh macro-RAFT agents of targeted molecular weight and narrow molecular weight distribution could be synthesized with intentional variation of the terminal monomer unit, allowing for the assessment of two distinctive macro-R-groups. SMAnh macro-RAFT agents were utilized to mediate the thermally initiated polymerization of N-vinylpyrrolidone (NVP), yielding SMAnh-b-PVP, but with significant thermolysis and hydrolysis of dithiocarbamate ω-chain ends. Alternatively, the redox-initiated RAFT-mediated polymerization of NVP at ambient temperatures using hydrolyzed macro-RAFT agents, i.e., poly(styrene-alt-maleic acid) (SMA) and poly(4-tert-butylstyrene-alt-maleic acid) (tBuSMA), was explored. Double hydrophilic SMA-b-PVP and tBuSMA-b-PVP block copolymers could be synthesized but with significant broadening of the molecular weight distribution. This is a result of the formation of dead chains derived from the alkaline hydrolysis of macro-RAFT agents prepolymerization and hydrolysis of dithiocarbamate chain ends throughout the polymerization. The latter is exacerbated by the insertion of NVP at the ω-chain end, which was subsequently investigated via the kinetic analysis of the xanthate- and dithiocarbamate-mediated aqueous homopolymerization of NVP.

How to select macroRAFT agents for efficient synthesis of composite nanoparticles?

The efficient synthesis of polymer/inorganic nanocomposite particles via RAFT-assisted encapsulating emulsion polymerization (REEP) depends on the selection of suitable macroRAFT agents. This work investigates how the structure of macroRAFT agents influences the REEP process, with a particular focus on the solubility differences between oil-soluble and water-soluble initiators and their effects on radical distribution, polymerization rate, and macroRAFT agent optimization. With the water-soluble initiator, the optimal macroRAFT agent structure was PAA12-co-PS6, while with the oil-soluble initiator, the optimal structure was PAA26-co-PS52. The true monomer conversion (Xy) values of the systems were 62 % and 83 %, respectively, with encapsulation efficiency (Y) reaching 100 % in both cases. The shell thicknesses of the polymer/Fe3O4 nanocomposites were 78 % and 84 %, respectively. The average hydrodynamic diameters were 173 nm (PDI = 0.114) and 216 nm (PDI = 0.152), and the saturation magnetizations were 25.65 emu/g and 17.22 emu/g, respectively. We propose a simple screening method for selecting macroRAFT agents based on their ability to solubilize monomers in alkaline aqueous solutions. Emulsion transparency directly correlates with monomer solubilization efficiency and serves as a key indicator of macroRAFT agent suitability. This approach, which aligns with experimental outcomes, demonstrates applicability across a variety of monomers and provides practical guidance for REEP synthesis.

An Investigation on Phase Behavior of ABA-type Block Copolymers Comprising of 2-Hydroxypropyl Acrylate and Poly (Ethylene Glycol)

ABA-type block copolymers consisting of 2-hydroxypropyl acrylate (HPA) and ethylene glycol (EG) segments were prepared by the RAFT polymerization method using two different lengths of macro-RAFT agents based on commercial poly(ethylene glycol)s with average molar masses of 400 and 1450 gmol-1 (PEG400 and PEG1450). By extending the difunctional ends of PEG400 and PEG1450 vertebrate macro-RAFT agents with HPA units, it was aimed to synthesize three ABA type block copolymers of different lengths from each agent. Structural characterization of the copolymers was performed using FTIR and 1H-NMR spectroscopy. In addition to confirming the chemical structures, signal integrations in the 1H-NMR spectrum provided information about the relative proportions of individual repeating units in each copolymer. Six block copolymers were examined for critical dissolution temperatures based on the relative lengths of the blocks and their PEG content. It was determined that all block copolymer systems examined exhibited lower critical solution temperature (LCST) in the range of 17.2-23.9 oC, and as the ratio of EG units in the copolymers increased, the CST of the copolymers increased.

Polymerization-Induced Self-Assembly for the Synthesis of Polyisoprene-Polystyrene Block and Random Copolymers: Towards High Molecular Weight and Conversion.

In this study, reversible addition-fragmentation chain- transfer (RAFT) polymerization combined with the polymerization-induced self-assembly (PISA) technique is used to synthesize polyisoprene (PI)-based block and random copolymers with polystyrene (PS), aiming for high molecular weight and monomer conversion. The focus is to optimize the polymerization conditions to overcome the existing challenge of cross-linking and Diels-Alder reactions during the polymerization of isoprene, which typically constrain the reaction conversion and molecular weight of the final polymers. Using a poly(methacrylic acid) (PMAA) macroRAFT agent synthesized in ethanol at 80°C, random and block copolymers of PS-PI with a target molecular weight of 50000gmole-1 and a high monomer conversion of ≈80% are achieved under optimized conditions in water-emulsion at 35°C. 1H nuclear magnetic resonance (NMR) verified the successful synthesis as well as the high content of 1,4 microstructure in polyisoprene. The thermal analysis via differential scanning calorimetry indicated distinct glass transitions for the microphase-separated PI-PS block copolymer, while a single transition for PI-PS random copolymer, indicating no microphase separation. Furthermore, dynamic light scattering analysis together with transmission electron microscopy provided further insight into the self-assembled emulsion nanoparticles of the polymers indicating a particle size in the range 70 to 130nm.

Efficient Synthesis of μ-A(BC)C Miktoarm Star Polymer Assemblies via Aqueous Photoinitiated Polymerization-Induced Self-Assembly.

In this study, green light-activated photoiniferter reversible addition-fragmentation chain transfer (RAFT) polymerization of glycerol methacrylate was performed using an ω,ω-heterodifunctional macro-RAFT agent. Because of the different RAFT controllability of two RAFT groups toward methacrylic monomers, only one RAFT group was activated under green light irradiation, leading to the formation of a diblock copolymer macro-RAFT agent with one RAFT group located at the chain end and the other RAFT group located between two blocks. The obtained diblock copolymer macro-RAFT agent was then used to mediate aqueous photoinitiated RAFT dispersion polymerization of diacetone acrylamide (DAAM), which formed μ-A(BC)C miktoarm star polymer assemblies with a diverse set of morphologies. Comparing with the ABC triblock copolymer, it was found that the architecture of the μ-A(BC)C miktoarm star polymer facilitated the formation of higher-order morphologies. Kinetic studies indicated that the aqueous photoinitiated RAFT dispersion polymerization exhibited ultrafast polymerization behavior, with quantitative monomer conversion being achieved within 5 min. Size exclusion chromatography analysis confirmed that good RAFT control was maintained during the polymerization. A morphological phase diagram for μ-A(BC)C miktoarm star polymer assemblies was constructed by varying the monomer concentration and the [DAAM]/[Macro-RAFT] ratio. We expect that this study not only develops an approach for the preparation of miktoarm star polymer assemblies but also provides mechanistic insights into the polymerization-induced self-assembly of nonlinear polymers.

Aqueous RAFT Dispersion Polymerization Mediated by an ω,ω-Macromolecular Chain Transfer Monomer: An Efficient Approach for Amphiphilic Branched Block Copolymers and the Assemblies.

Herein, an ω,ω-macromolecular chain transfer monomer (macro-CTM) containing a RAFT (reversible addition-fragmentation chain transfer) group and a methacryloyl group was synthesized and used to mediate photoinitiated RAFT dispersion polymerization of hydroxypropyl methacrylate (HPMA) in water. The macro-CTM undergoes a self-condensing vinyl polymerization (SCVP) mechanism under RAFT dispersion polymerization conditions, leading to the formation of amphiphilic branched block copolymers and the assemblies. Compared with RAFT solution polymerization, it was found that the SCVP process was promoted under RAFT dispersion polymerization conditions. Morphologies of branched block copolymer assemblies could be controlled by varying the monomer concentration and the [HPMA]/[macro-CTM] ratio. The branched block copolymer vesicles could be used as seeds for seeded RAFT emulsion polymerization, and framboidal vesicles were successfully obtained. Finally, degrees of branching of branched block copolymers could be further controlled by using a binary mixture of the macro-CTM and a linear macro-RAFT agent or a small molecule CTM. We believe that this study not only provides a versatile strategy for the preparation of branched block copolymer assemblies but also offers important insights into polymer synthesis via heterogeneous RAFT polymerization.

Synthesis and biological properties of novel glucose-based fluoro segmented macromolecular architectures

The emergence of novel well-defined biological macromolecular architectures containing fluorine moieties displaying superior functionalities can satisfactorily address many biomedical challenges. In this research, ABA- and AB-type glucose-based biological macromolecules were synthesized using acryl-2,3,4,6-tetra-O-acetyl-D-glucopyranoside with pentafluorophenyl (FPM), pentafluorobenzyl (FBM), phenyl (PM) and benzyl (BM) methacrylate-based macro-RAFT agents following RAFT polymerization. The macro-RAFT agents and the corresponding copolymers were characterized by 19F, 1H, and 13C NMR and FTIR spectroscopic techniques to understand the chemical structure, molecular weight by size-exclusion chromatography, thermal analysis by TGA and DSC. Thermal stability (Td5%) of the FPM and FBM fluoro-based polymers was observed in the range of 219–267 °C, while the non-fluoro PM and BM polymers exhibited in the range of 216–264 °C. Among the macro-RAFT agents, PFPM (107 °C, ΔH: 0.613 J/g) and PPM (103 °C, ΔH: 0.455 J/g) showed higher Tm values, while among the block copolymers, PFBM-b-PG (123 °C, ΔH: 0.412 J/g) and PG-b-PFPM-b-PG (126 °C, ΔH: 0.525 J/g) exhibited higher Tm values. PFBMT and PPM macro-RAFT agents, PPM-b-PG and PG-b-PPM-b-PG copolymer spin-coated films showed the highest hydrophobicity (120°) among the synthesized polymers. The block copolymers exhibited self-assembled segregation by using relatively hydrophobic segments as the core and hydrophilic moieties as the corona. Synthesized biological macromolecules exhibit maximum antibacterial activity towards S. aureus than E. coli bacteria. Fluorophenyl (PFPM) and non-fluorobenzyl-based (PBMT) macro-RAFT agents exhibit low IC50 values, suggesting high cytotoxicity. All the triblock copolymers exhibit lesser cytotoxicity than the di-block polymers.

Amphiphilic pH-responsive ABC triblock copolymers via RAFT-mediated aqueous PISA and comparison with their A-b-(B-co-C) diblock copolymer counterparts

The influence of the macroRAFT agent architecture on the morphology of the self-assemblies obtained by aqueous RAFT dispersion polymerization in PISA is studied by comparing amphiphilic AC, A(B-co-C) diblocks and ABC triblock copolymers, constituted of N,N-dimethylacrylamide (DMAm = A), acrylic acid (AA = B) and N-cyanomethylacrylamide (CMAm = C) monomer units. The aim of this study is to better understand the impact of the presence of pH-sensitive acrylic acid units and their spatial distribution in block copolymers. Generally, the presence of a fully protonated intermediate block of PAA between the two blocks (based on PDMAm and PCMAm) favors the formation of higher-order morphologies. These ABC triblock copolymers assemblies are pH-responsive and can undergo morphological transitions through the controlled deprotonation or protonation of the PAA segment, but do not completely dissociate at high pH (i.e. when AA units are fully ionized) unlike their A(B-co-C) diblock counterparts, where the pH-responsive monomer unit is homogeneously distributed within the solvophobic block.

Chloromethylated magnetic polystyrene composite nanoparticles prepared via RAFT-mediated surfactant-free emulsion polymerization

Polystyrene-based magnetic composite nanoparticles with well-defined core-shell morphology, customizable surface functionalization, and adjustable magnetic properties are promising catalyst support materials. In this work, chloromethylated magnetic polystyrene composite nanoparticles are successfully prepared through RAFT-mediated surfactant-free emulsion polymerization. A comprehensive investigation is carried out to explore the influence of copolymer monomer ratios and polymerization degrees on emulsion polymerization conversion and encapsulation efficiency. The results unveil the critical importance of moderately adjusting the hydrophobic/hydrophilic properties of the macroRAFT agents in achieving an effective encapsulation process. Excessive monomer addition is found to disrupt the conditions necessary for emulsion polymerization by causing the detachment of macroRAFT agents from the surface of the modified Fe3O4 nanoclusters. These results are instructive for the future rational design and synthesis of high-performance catalysts.

ABC or ACB triblock copolymers? Changing the RAFT group position in diblock copolymer macro-RAFT agents leads to different PISA behaviors in RAFT dispersion polymerization

ACB and ABC triblock copolymer nanoparticles were prepared by reversible addition–fragmentation chain transfer (RAFT) dispersion polymerization using diblock copolymer macromolecular RAFT (macro-RAFT) agents with different RAFT group positions.

Effects of stirring rate on morphology of aqueous RAFT emulsion PISA-derived block copolymer nanoparticles

The influence of stirring rate on nanoparticle morphology in aqueous RAFT emulsion PISA has been investigated.

Precision synthesis of a biobased myrcene thermoplastic elastomer by using an amphiphilic macro-RAFT agent via emulsion polymerization in aqueous medium

A poly(tert-butyl acrylate)-b-poly(β-myrcene)-b-poly(tert-butyl acrylate) biobased thermoplastic elastomer was prepared by RAFT emulsion polymerization utilizing a precisely devised amphiphilic macro-RAFT agent and can be modified by hydrolysis.

Exploiting the Monomer-Feeding Mechanism of RAFT Emulsion Polymerization for Polymerization-Induced Self-Assembly of Asymmetric Divinyl Monomers.

We exploited the monomer-feeding mechanism of reversible addition-fragmentation chain transfer (RAFT) emulsion polymerization to achieve the successful polymerization-induced self-assembly (PISA) of asymmetric divinyl monomers. Colloidally stable cross-linked block copolymer nanoparticles with various morphologies, such as vesicles, were directly prepared at high solids. Morphologies of the cross-linked block copolymer nanoparticles could be controlled by varying the monomer concentration, degree of polymerization (DP) of the core-forming block, and length of the macro-RAFT agent. X-ray photoelectron spectroscopy (XPS) characterization confirmed the presence of unreacted vinyl groups within the obtained block copolymer nanoparticles, providing a landscape for further functionalization via thiol-ene chemistry. Finally, the obtained block copolymer nanoparticles were employed as additives to tune the mechanical properties of hydrogels. We expect that this study not only offers considerable opportunities for the preparation of well-defined cross-linked block copolymer nanoparticles, but also provides important insights into the controlled polymerization of multivinyl monomers.

Double hydrophilic thermo-sensitive macro-RAFT agents as stabilizers and control agents in styrene emulsion polymerization

Double hydrophilic thermo-sensitive macro-RAFT agents as stabilizers and control agents in styrene emulsion polymerization

Fast Recovery Double-Network Hydrogels Based on Particulate Macro-RAFT Agents.

Synthetic hydrogels struggle to match the high strength, toughness, and recoverability of biological tissues under periodic mechanical loading. Although the hydrophobic polymer chain of polystyrene (PS) may initially collapse into a nanosphere upon contact with water, it has the ability to be elongated when it is subjected to an external force. To address this challenge, we employ the reversible addition-fragmentation chain transfer (RAFT) method to design a carboxyl-substituted polystyrene (CPS) which can form a covalently cross-linked network with four-armed amino-terminated polyethylene glycol (4-armed-PEG-NH2), and a ductile polyacrylamide network is introduced in order to prepare a double-network (DN) hydrogel. Our results demonstrate that the DN hydrogel exhibits exceptional mechanical properties (0.62 kJ m-2 fracture energy, 2510.89 kJ m-3 toughness, 0.43 MPa strength, and 820% elongation) when a sufficient external force is applied to fracture it. Moreover, when the DN hydrogel is subjected to a 200% strain, it displays superior recoverability (94.5%). This holds a significant potential in enhancing the mechanical performance of synthetic hydrogels and can have wide-ranging applications in fields such as tissue engineering for hydrophobic polymers.

Transitioning from Photoinitiation to Thermal Initiation in RAFT Dispersion Polymerization via a Small Modification of the Macro-RAFT Agent: A Scalable Approach for Monodisperse Surface-Functional Polymeric Microspheres

Transitioning from Photoinitiation to Thermal Initiation in RAFT Dispersion Polymerization via a Small Modification of the Macro-RAFT Agent: A Scalable Approach for Monodisperse Surface-Functional Polymeric Microspheres

On-Demand Tunability of Microphase Separation Structure of 3D Printing Material by Reversible Addition/Fragmentation Chain Transfer Polymerization.

Controlling the phase-separated structure of polymer alloys is a promising method for tailoring the properties of polymers. However, controlling the morphology of phase-separated structures is challenging. Recently, phase-separated structures have been fabricated via 3D printing; however, only a few methods that enable on-demand control of phase separation have been reported. In this study, laser-scanning stereolithography, a vat photopolymerization method, is used to form a phase-separated structure via polymerization-induced microphase separation by varying the scanning speed and using macro-reversible addition/fragmentation chain transfer (macro-RAFT) agents with different average molar masses, along with multiarmed macro-RAFT agents; such structures were used to fabricate 3D-printed parts. Various phase-separated morphologies including sea-island and reverse sea-island were achieved by controlling the laser scanning speed and RAFT type. Heterogeneous structures with different material properties were also achieved by simply changing the laser scanning speed. As the deformation due to shrinkage in the process of cleaning 3D-printed parts depends on the laser scanning speed, shape correction was introduced to suppress the effect of shrinkage and obtain the desired shape.

Synthesis of Hydrophobic Block Copolymer Nanoparticles in Alcohol/Water Stabilized by Poly(methyl methacrylate) via RAFT Dispersion Polymerization-Induced Self-Assembly

Poly(methyl methacrylate) (PMMA) is an important common polymer widely used in industry. While PMMA has been used as a core-forming block for polymerization-induced self-assembly (PISA), a powerful approach for the synthesis of block copolymer nanoparticles, it has not been utilized as a corona block due to PMMA being insoluble in common solvents for PISA formulations (e.g., water and alcohols). Exploiting the solubility of PMMA-dithiobenzoate (DTB) in ethanol/water mixtures, such macroRAFT agents have in the present work been successfully employed for reversible addition–fragmentation chain transfer (RAFT) PISA in ethanol/water (80/20 by volume). RAFT dispersion polymerization of benzyl methacrylate mediated by PMMA-DTB macroRAFT agents with various degrees of polymerization has been investigated. Transmission electron microscopy analyses revealed well-defined block copolymer nano-objects, including spheres, worms, as well as vesicles. Nanoparticles comprising a PMMA outer layer would have superior compatibility with various hydrophobic polymer matrices, thereby enabling various new applications such as, e.g., use as nanofillers.

Kinetic Modeling of the Synthesis of Poly(4-vinylpyridine) Macro-Reversible Addition-Fragmentation Chain Transfer Agents for the Preparation of Block Copolymers

Reversible addition-fragmentation chain transfer (RAFT) polymerization is one of the most common controlled polymerization techniques to prepare well-defined, rather narrow dispersed polymers due to reduced demands in reactant preparation. Despite these advantages, RAFT polymerization was so far primarily utilized on small laboratory scales. This study presents a first step to a scaled-up RAFT polymerization by developing and experimentally validating a kinetic model on the example of the polymerization of 4-vinylpyridine (4VP), which to date is not described in the literature. With the implementation of the results from modeling, the synthesis process was extended to a medium scale (from 6 to 36 g), while the same high conversions, molar mass, and low dispersity as in the smaller scale were achieved. The process is also optimized regarding the high degree of livingness necessary for using the 4VP polymers as a macro-RAFT agent in the subsequent reaction step for the synthesis of poly(4-vinylpyridine)-b-polystyrene diblock copolymers by RAFT dispersion polymerization.

Polymer film synthesis from an aqueous latex of polymerization-induced self-assembly (PISA) derived nanofibers

Polymerization-induced self-assembly (PISA) derived spheres and worms (fibers) comprising poly(n-butyl acrylate) as core-forming block (Tg ≈ −49 °C) were synthesized using a poly(acrylic acid-stat-poly(ethylene glycol) methyl ether acrylate) macroRAFT agent. The nanoparticle morphology varied depending on the pH of the system, i.e. spheres at natural pH (≈ 2.5) and worms at pH 5. The core-sections of the particles (both spheres and worms) were crosslinked using ethylene glycol diacrylate. Films were prepared from the synthesized aqueous latexes via simple drop casting in the absence of volatile organic compounds. The influence of the original nanoparticle morphology on the mechanical properties of the films was subsequently explored – “worm film” displayed 1670 % higher tensile strength and 1290 % higher strain at break compared to “sphere film”. These results demonstrate that film properties can be significantly influenced by the original nanoparticle morphology, despite the nanoparticles comprising very similar polymer chains in terms of composition and molecular weight distribution.