Reversible Addition-fragmentation Chain-transfer Radical Polymerization Research Articles

Synthesis of Ethylene–Vinyl Acetate Copolymers by Reversible Addition–Fragmentation Chain-Transfer Radical Polymerization

Reversible addition–fragmentation chain-transfer radical copolymerization of ethylene with vinyl acetate in the presence of azobis(isobutyronitrile) and xanthate as a chain-transfer agent was studied. Products containing 12–42 mol % vinyl acetate units were prepared under varied reaction conditions. The glass transition points and degradation temperatures of the polymers were determined. The rheological properties of ethylene–vinyl acetate copolymers were studied in detail. The effect of additions of the copolymers synthesized on the rheological characteristics of diesel fuel was evaluated. The ethylene–vinyl acetate copolymers synthesized reduce the limiting filterability temperature of the diesel fuel.

Statistical Copolymers of N-Vinylpyrrolidone and 2-Chloroethyl Vinyl Ether via Radical RAFT Polymerization: Monomer Reactivity Ratios, Thermal Properties, and Kinetics of Thermal Decomposition of the Statistical Copolymers.

The radical statistical copolymerization of N-vinyl pyrrolidone (NVP) and 2-chloroethyl vinyl ether (CEVE) was conducted using the Reversible Addition-Fragmentation chain Transfer (RAFT) polymerization technique, employing [(O-ethylxanthyl)methyl]benzene (CTA-1) and O-ethyl S-(phthalimidylmethyl) xanthate (CTA-2) as the Chain Transfer Agents (CTAs), leading to P(NVP-stat-CEVE) products. After optimizing copolymerization conditions, monomer reactivity ratios were estimated using various linear graphical methods, as well as the COPOINT program, which was applied in the framework of the terminal model. Structural parameters of the copolymers were obtained by calculating the dyad sequence fractions and the monomers' mean sequence lengths. Thermal properties of the copolymers were studied by Differential Scanning Calorimetry (DSC) and kinetics of their thermal degradation by Thermogravimetric Analysis (TGA) and Differential Thermogravimetry (DTG), applying the isoconversional methodologies of Ozawa-Flynn-Wall (OFW) and Kissinger-Akahira-Sunose (KAS).

Synthesis of Ethylene–Vinyl Acetate Copolymers by Reversible Addition–Fragmentation Chain-Transfer Radical Polymerization

Synthesis of Ethylene–Vinyl Acetate Copolymers by Reversible Addition–Fragmentation Chain-Transfer Radical Polymerization

Photoinduced 3D Printing through a Combination of Cationic and Radical RAFT Polymerization

Photopolymerization-based three-dimensional (3D) printing techniques have been widely utilized to fabricate polymeric materials with complex architectures. The application of reversible deactivation radical polymerization (RDRP) in 3D printing is emerging as a powerful tool to introduce various postprinting abilities but is still at an early stage. Here, a photoinduced free radical-promoted cationic reversible addition–fragmentation chain transfer (RAFT) polymerization method was developed, utilizing the direct photolysis of the RAFT agent as a radical source, which was further combined with photo-iniferter RAFT polymerization to prepare polymer networks. The polymerization mechanism was studied by model polymerization using monofunctional monomers. The effects of each component on the properties of the final materials and polymerization behavior of the cross-linking systems were studied in detail. This method was successfully applied in a digital light processing (DLP) technique-based commercial 3D printer. Finally, polymer welding of the printed objects through both cationic and radical RAFT chain extension was realized, expanding avenues of postprinting and future applications in various fields.

Organocatalytic, Stereoselective, Cationic Reversible Addition-Fragmentation Chain-Transfer Polymerization of Vinyl Ethers.

Tacticity is a crucial factor affecting the properties of synthetic polymer materials. Here, we introduce a type of chiral organic Brønsted acid catalyst, 1,1'-bi-2-naphthol-derived N,N'-bis(triflyl)phosphoramidimidates (PADIs), for the cationic polymerization of vinyl ethers, which enables the development of the first organocatalytic, highly stereoselective, cationic reversible addition-fragmentation chain-transfer (RAFT) polymerization of vinyl ethers with a trithiocarbonate chain-transfer agent. This metal-free RAFT process could afford isotactic poly(vinyl ethers) with high stereoselectivity, controllable molecular mass, and narrow dispersity at low catalyst loadings (as low as 200 ppm). Moreover, the trithiocarbonate chain-end allows for chain extension to synthesize diblock copolymers comprising an isotactic poly(vinyl ether) block, by a mechanistic switching from stereoselective cationic RAFT polymerization to visible-light-regulated cationic and radical RAFT polymerization.

Free- and reversible deactivation radical (co)polymerization of isobutylene in water under environmentally benign conditions

The synthesis of a linear polyisobutylene is achieved for the first time by free radical polymerization. The reaction was performed in environmentally friendly conditions, i.e., in an aqueous medium using cyclodextrin solubilizer, around room temperature. This mild and straightforward radical polymerization resulted in a predominantly linear polymer with low dispersity. Isobutylene was also copolymerized with acrylamide via this cyclodextrin assisted aqueous free-radical polymerization, leading to new poly(isobutylene-co-acrylamide) amphiphilic copolymers. The feed composition of copolymerization had a huge effect on the composition and, therefore, the resulting copolymer's solubility. Reversible addition-fragmentation chain transfer radical polymerization (RAFT) of isobutylene was also carried out using a PEG-based symmetrical macro chain transfer agent. Poly(PEG-b-isobutylene-b-PEG) block-copolymer was formed in this one-pot reaction. This novel polymerization method for isobutylene opens new, environmentally benign routes to produce novel copolymers for various applications.

Stereospecific cationic RAFT polymerization of bulky vinyl ethers and stereoblock poly(vinyl alcohol) via mechanistic transformation to radical RAFT polymerization of vinyl acetate

The simultaneous control of molecular weight and tacticity in cationic polymerization remains challenging. Here, we propose a new approach for stereospecific living cationic polymerization by combining cationic reversible addition-fragmentation chain transfer (RAFT) polymerization with thiocarbonylthio compounds and stereospecific cationic polymerization of bulky vinyl ethers with Lewis acid catalysts. In this combined system, the molecular weight was controlled by the RAFT process between the growing cationic and dormant dithiocarbamate chain ends, whereas the tacticity was controlled by stereospecific propagation based on the steric hindrance of bulky side groups and counteranions derived from the Lewis acid catalysts. Herein, we demonstrate the availability of this approach in the cationic polymerization of various bulky vinyl ethers, such as tert‑butyl, benzyl, trimethylsilyl, and tert‑butyldimethylsilyl vinyl ether, using dithiocarbamates and BF3•OEt2 or EtAlCl2 in toluene at –78 °C. Isotactic-rich poly(vinyl ether)s with controlled molecular weights and dithiocarbamate chain-end groups were obtained from a series of bulky vinyl ethers and were converted into molecular-weight-controlled isotactic poly(vinyl alcohol) (mm ≥ 70%) with a high melting temperature (Tm ~ 230 °C). Furthermore, isotactic-b-atactic stereoblock PVA (mm/mr/rr = 75/25/5 and 23/48/29, Tm ~ 210 °C) was synthesized by mechanistic transformation from the stereospecific cationic RAFT polymerization of trimethylsilyl vinyl ether into the radical RAFT polymerization of vinyl acetate using diphenyl dithiocarbamate as the common RAFT agent followed by simultaneous deprotection of the silyl and acetyl groups.

Near-Infrared, Light-Induced Cationic and Radical RAFT Polymerization Catalyzed by Iron Complex.

A near-infrared (NIR) light induced controlled cationic polymerization is presented here. The halide abstraction reaction between the cyclopentadienyl iron dicarbonyl dimer (Fe2(Cp)2(CO)4) and an organic halide is utilized to generate initial radicals or cations under mild conditions, which can be further combined with both radical and cationic reversible addition-fragmentation chain transfer (RAFT) polymerization. Well-defined poly(vinyl ether)s and polyacrylates are prepared successfully under NIR light by this method. The excellent penetration ability of NIR light through thick barriers has been verified by polymerization in the presence of an A4 paper. In addition, iron-based radical polymerization has been used for three-dimensional (3D) printing to fabricate materials with different thicknesses.

Micellar Organocatalysis Using Smart Polymer Supports: Influence of Thermoresponsive Self-Assembly on Catalytic Activity.

Micellar catalysts with a switchable core are attractive materials in organic synthesis. However, little is known about the role of the shell forming block on the performance of the catalyst. Thermoresponsive block copolymers based on poly(N-isopropylacrylamide-co-vinyl-4,4-dimethylazlactone) attached to different permanently hydrophilic blocks, namely poly(ethylene glycol), poly(N,N-dimethylacrylamide), and poly(2,3-dihydroxypropyl acrylate), were successfully synthesized via reversible addition/fragmentation chain transfer radical polymerization (RAFT). Post-polymerization attachment of an amino-functionalized L-prolineamide using the azlactone ring-opening reaction afforded functionalized thermoresponsive block copolymers. Temperature-induced aggregation of the functionalized block copolymers was studied using dynamic light scattering. It was shown that the chemical structure of the permanently hydrophilic block significantly affected the size of the polymer self-assemblies. The functionalized block copolymers were subjected to an aldol reaction between p-nitrobenzaldehyde and cyclohexanone in water. Upon temperature-induced aggregation, an increase in conversion was observed. The enantioselectivity of the polymer-bound organocatalyst improved with an increasing hydrophilic/hydrophobic interface as a result of the different stability of the polymer aggregates.

Controllable length adjustment of polyaniline particle with temperature sensitive block copolymer as template

Although the diameter of conductive polymer nanoparticles can be controlled effectively, the uniformity of particle length is still very challenging. In this study, with the temperature‐sensitive block copolymer PS111‐b‐PNIPAM114 as the template, the morphology and size of polyaniline (PANI) particles had been controllably adjusted through the change of temperature. Additionally, the electrochemical performance of each sample was investigated. After PS111‐b‐PNIPAM114 was synthesized through the reversible addition‐fragmentation chain transfer radical polymerization (RAFT), with its vesicular micelle as the “template”, the PANI particles with uniform length distribution were prepared successfully at 40°C. The average length of PANI particles after template removal was 254.07 nm with a short tail distribution, which was closer to the average than the standard normal distribution. Electrochemical results of PANI showed that it had good electrochemical activity with fast charge and discharge ability. And, with the current density of 1 A·g−1, its discharge‐specific capacitance could reach up to 805.61 F·g−1.

Weak bases, an efficient accelerator for the RAFT of isoprene

The use of weak bases as accelerators for reversible addition-fragmentation chain transfer radical polymerization (RAFT) of isoprene is demonstrated. Adding weak bases to RAFT polymerization, the conversion of isoprene could be greatly improved and reach about 50%. The effects of weak base on the polymerization were investigated. The living and controlled character of the RAFT polymerization of isoprene was confirmed by the linear increase in molecular weight with monomer conversion, the narrow molecular weight distribution and synthesis of polyisoprene-block-polystyrene (PIP-b-PS) block copolymer. The results of 1HNMR spectroscopy show that the structure of polyisoprene (PIP) with weak bases as accelerators was the same to the structure of PIP without any accelerator. The data presented here prove that weak bases are an efficient accelerator to inhibit Diels-Alder reaction of isoprene in the RAFT polymerization.

Fully Degradable Thioester-Functional Homo- and Alternating Copolymers Prepared through Thiocarbonyl Addition–Ring-Opening RAFT Radical Polymerization

The radical ring-opening polymerization (RROP) of thionolactones provides access to thioester backbone-functional copolymers but has, to date, only been demonstrated on acrylic copolymers. Herein, the thionolactone dibenzo[c,e]oxepane-5-thione (DOT) was subjected to azobisisobutyronitrile (AIBN)-initiated free-radical homopolymerization, which produced a thioester-functional homopolymer with a glass-transition temperature of 95 °C and the ability to degrade exclusively into predetermined small molecules. However, the homopolymerization was impractically slow and precluded the introduction of functionality. Conversely, the reversible addition–fragmentation chain-transfer (RAFT)-mediated copolymerization of DOT with N-methylmaleimide (MeMI), N-phenylmaleimide (PhMI), and N-2,3,4,5,6-pentafluorophenylmaleimide (PFPMI) rapidly produced well-defined copolymers with the tendency to form alternating sequences increasing in the order MeMI ≪ PhMI < PFPMI, with estimated reactivity ratios of rDOT = 0.198 and rPFPMI = 0.0078 for the latter system. Interestingly, defects in the alternating structure were more likely caused by (degradable) DOT–DOT sequences rather than (nondegradable) MI–MI sequences, which was confirmed through the paper spray mass spectrometric analysis of the products from aminolytic degradation. Upon the aminolysis of backbone thioesters, maleimide repeating units were ring-opened, forming bisamide structures. Conversely, copolymer degradation through a thiolate did not result in imide substitution but nucleophilic para-fluoro substitution on PFPMI comonomer units, indicating the ability of DOT–MI copolymers to degrade under different conditions and to form differently functional products. The RROP of thionolactones has distinct advantages over the RROP of cyclic ketene acetals and is anticipated to find use in the development of well-defined degradable polymer materials.

Controlled Synthesis of Methacrylic Acid-Methyl Acrylate Copolymers and Their Properties at Various Interfaces

Conditions were found for controlled reversible addition-fragmentation chain-transfer radical polymerization to obtain narrow-dispersity gradient methacrylic acid-methyl acrylate copolymer (Mn = 1.59 × 104). A copolymer of similar composition and molecular mass (Mn = 1.81 × 104) with random distribution of units was obtained by radical copolymerization in the presence of dodecyl mercaptan. The behavior of the gradient and random copolymers, each containing ∼14 mol % methacrylic acid units, was studied in solutions, Langmuir monolayers, and Langmuir-Blodgett films. Several ranges of the existence of associates and micelles, preserved upon transfer in a Langmuir-Blodgett film, were revealed for the narrow-dispersity copolymer at the water-air interface depending on pH of the subphase. Associates in the form of ribbon structures and molecular ensembles of nanometric size (network structure with loop-like fragments) are observed in the AFM images of Langmuir-Blodgett films of the gradient and random copolymers, respectively.

Synthesis and Properties of Upper Critical Solution Temperature Responsive Nanogels.

A random copolymer ((U/A10)165) bearing pendent ureido groups and a small amount (10 mol %) of primary amino groups exhibits an upper critical solution temperature (UCST). We prepared a diblock copolymer (PMPC20P(U/A10)165) composed of water-soluble poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) and (U/A10)165 blocks via reversible addition-fragmentation chain-transfer radical polymerization with postmodification reaction. The subnumbers are the degrees of polymerization of each block. Although in water PMPC20P(U/A10)165 dissolves as a unimer above the UCST phase transition temperature ( Tp), it forms polymer micelles composed of dehydrated (U/A10)165 cores and hydrophilic PMPC shells. A nanogel was prepared by cross-linking the pendent primary amines in the micelle core using (hydroxymethyl)phosphonium chloride below Tp. NMR and light-scattering data indicated that the nanogel core shrinks upon dehydration below Tp and swells upon hydration above Tp. The nanogel can encapsulate guest molecules such as hydrophobic fluorescence probes and bovine serum albumin (BSA) below Tp mainly owing to hydrophobic interactions in the core. Encapsulated BSA can be held in the nanogel core below Tp and subsequently released above Tp.

Highly selective and sensitive ratiometric fluorescent polymer dots for detecting hypochlorite in 100% aqueous media

Hypochlorite (ClO-), as a momentous reactive oxygen species (ROS), is highly desirable due to it associated with a number of human diseases. Therefore, the development of simple and convenient water-soluble ratiometric fluorescent probes is of great significance. In this work, water-soluble ratiometric fluorescent polymer dots (FPDs) for detecting ClO- were prepared via incorporation of reversible addition-fragmentation chain transfer radical polymerization (RAFT), grafting technique and coprecipitation strategy. Upon the addition of ClO-, due to the intramolecular heavy atom effect (HAE) by chlorine (Cl), the fluorescence of fluorescein units in FPDs was significantly quenched, while another reference fluorophore (P2) in FPDs keeps constant. Furthermore, the FPDs exhibited excellent sensitivity (detection limit: 2.2 nM) and selectivity, good water-solubility. In addition, FPDs was successfully utilized to detect ClO- in tap water and drink water. It implies that the nanoprobes have the great potential applications in biological sensing and imaging.

Synthesis of Amphiphilic Block Copolymers Based on SKA by RAFT Polymerization

AbstractTemperature‐sensitive amphiphilic block copolymers of 2,2‐dimethyl‐1,3‐dioxolan‐4‐yl‐methyl acrylate (solketal acrylate, SKA) and N‐isopropyl acrylamide (NIPAAm) have been prepared via reversible addition‐fragmentation chain transfer radical polymerization (RAFT). A kinetics study of SKA polymerization is performed in order to find a compatible RAFT chain transfer agents (CTA) and versatile polymerization conditions for the synthesis of well‐defined poly(2,2‐dimethyl‐1,3‐dioxolan‐4‐yl‐methyl acrylate) (PSKA). Depending on the RAFT‐CTA and the reaction time, PSKA with molar masses up to 5700 g mol−1 and dispersity values as low as 1.1 could be prepared. Additionally, the end group distribution of PSKA is investigated via electrospray ionization‐ion mobility separation–mass spectrometry. The chain extensions of the homopolymers for the second block of NIPAAm are analyzed with size‐exclusion chromatography. Amphiphilic block copolymers are obtained after hydrolysis of hydrophobic PSKA block to target hydrophilic poly(2,3‐dihydroxypropyl acrylate) block.

Poly(Ionic Liquid) Based Chemosensors for Detection of Basic Amino Acids in Aqueous Medium

Naked-eye detection of amino acids (AA) in water is of great significance in the field of bioanalytical applications. Herein, polymerized ionic liquids (PILs) with controlled chain length structures were synthesized via reversible addition–fragmentation chain-transfer (RAFT) polymerization and post-quaternization approach. The AA recognition performance of PILs with different alkyl chain lengths and molecular weights was evaluated by naked-eye color change and ultraviolet-visible (UV–vis) spectral studies. These PILs were successfully used for highly sensitive and selective detection of Arg, Lys, and His in water. The recognition performance was improved effectively with increased molecular weight of PILs. The biosensitivity of the PILs in water was strongly dependent on their aggregation effect and polarization effect. Highly sensitive and selective detection of AA was successfully accomplished by introducing positively charged pyridinium moieties and controlled RAFT radical polymerization.

Effects of RAFT Agent on the Chloromethylstyrene Polymerizations in a Simultaneous Radiation Grafting System.

Reversible addition-fragmentation chain transfer (RAFT) agent was added into a simultaneous radiation grafting system and its effects on graft polymerization and homopolymerization were investigated. Chloromethylstyrene (CMS) was graft polymerized onto ethylene-tetrafluoroethylene copolymer (ETFE) films under γ-ray sources via simultaneous irradiation. The non-grafted poly(CMS) in the grafted films were extracted by xylene at 120 °C. The poly(CMS) was characterized by NMR and GPC instruments. Addition of the RAFT agent suppressed both graft polymerization and homopolymerization. However, under a high concentration of RAFT agent, the homopolymerization in the monomer solution could occur through a typical RAFT polymerization while polymerization in the ETFE films proceeded via RAFT and conventional radical polymerization, resulting in poly(CMS) in the ETFE films with molecular weight dispersity higher than 1.0 but lower than that without RAFT agent. Furthermore, it was found that the molecular weight of the poly(CMS) in the ETFE films was several times higher than that of the poly(CMS) in the monomer solution.

Fabrication of Water-soluble Fluorescent Polymeric Micelles for Selective Detection of Hg&lt;sup&gt;2+&lt;/sup&gt; in Blood Serum

In this study, amphiphilic diblock copolymers were designed and synthesized via the incorporation of reversible addition-fragmentation chain transfer radical polymerization (RAFT) and a subsequent grafting technique. Subsequently, Hg2+-sensitive water-soluble fluorescent polymeric micelles (FNs) were prepared by a reprecipitation strategy. The spectroscopic characteristics demonstrate that the fluorescein isothiocyanate (FITC) was successfully linked into the polymer. Due to the promoted reaction of desulfurization cyclization by Hg2+, the fluorescence of fluorescein in FNs was obviously quenched. The as-prepared FNs showed admirable Hg2+-sensitivity (detection limit: 54 nM), excellent water-solubility and high selectivity. In addition, FNs were successfully used to determine Hg2+ in blood serum. We expected that the as-prepared FNs could perform potential applications in imaging, sensing, and bioanalytic chemistry.

Light-responsive terpolymers based on polymerizable photoacids

We present the synthesis and characterization of amphiphilic terpolymers containing photoacids based on 1-naphthol using reversible addition fragmentation chain transfer radical polymerization (RAFT).