Reversible Addition-fragmentation Chain Transfer Emulsion Polymerization Research Articles

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.

Morphology Control via RAFT Emulsion Polymerization-Induced Self-Assembly: Systematic Investigation of Core-Forming Blocks.

Polymerization-induced self-assembly (PISA) is a useful formulation for readily obtaining nanoparticles from block copolymers in situ. Reversible addition–fragmentation chain-transfer (RAFT) emulsion polymerization is utilized as one of the PISA formulations. Various factors have so far been investigated for obtaining nonspherical particles via RAFT emulsion polymerization, such as the steric structure of the shell, the glass-transition temperature (Tg) of the core-forming block, and the water solubility of the core-forming monomer. This study focuses on core-forming blocks without changing the structure of the shell-forming block. In particular, we elucidate the balance between Tg for the core-forming block and the water solubility of the core monomer. A series of alkyl methacrylates, such as methyl methacrylate (MMA), ethyl methacrylate (EMA), and n-propyl methacrylate (PrMA), are emulsion-polymerized in the presence of a poly[poly(ethylene glycol) methyl ether methacrylate] (PPEGMA) macromolecular chain-transfer agent via the RAFT process. The resulting in situ morphology changes to form shapes such as spheres, worms (toroids), and vesicles are systematically investigated. The properties of the core that determine whether a morphological change occurs from spheres are (i) the solubility of the core-forming monomer in water, (ii) the relationship between Tg for the core-forming block and the polymerization temperature, and (iii) the hydrophobic core volume, which changes the packing parameter. These factors allow prediction of the block copolymer morphology produced during RAFT emulsion polymerization of other methacrylates such as n-butyl methacrylate (BuMA), tetrahydrofurfuryl methacrylate (THFMA) with physical properties of the homopolymer (poly(tetrahydrofurfuryl methacrylate) (PTHFMA)) between those for poly(MMA) (PMMA) and PBuMA, and 1-adamantyl methacrylate (ADMA) with low monomer solubility in water and high Tg of the homopolymer (PADMA).

Novel Strategy for the Synthesis of Polymer/Pigment Hybrid Latex via Sulfur-Free RAFT-Mediated Emulsion Polymerization

Reversible addition–fragmentation chain transfer (RAFT) emulsion polymerization is a powerful tool for polymer encapsulation of pigment nanohybrids. Conventional RAFT emulsion polymers, however, contain sulfur residues that contribute to undesired odor and deleterious effects on final materials. Our strategy relies on an amphiphilic macromonomer poly(methacrylic acid-co-methyl methacrylate) P(MAA-co-MMA) with an ω-unsaturated end group synthesized in situ via cobalt(II)-mediated catalytic chain transfer polymerization (CCTP) at the surface of C.I. Pigment Blue 15:3 (PB) particles. Subsequently, these macromonomers are used as the living points to mediate the in situ sulfur-free RAFT (SF-RAFT) emulsion polymerization of monomers (butyl methacrylate (BMA) and butyl acrylate (BA)). It was found that a well-controlled polymerization process was achieved by semibatch SF-RAFT emulsion polymerization on the PB surface, as evidenced by the smooth increase in the molecular weight of polymer chains as the polymerization progressed and by transmission electron microscopy (TEM) results. Due to the sealing effect, these polymer/PB hybrid particles exhibited excellent colloidal stability in the aqueous phase. More importantly, film-forming hybrid particles with a soft P(BMA-co-BA) shell were successfully prepared in this work, which suggested that SF-RAFT-mediated polymerization may offer a useful alternative approach to traditional RAFT emulsion polymers for the preparation of organic/inorganic nanohybrids.

RAFT Emulsion Polymerization of Styrene Using a Poly((N,N-dimethyl acrylamide)-co-(N-isopropyl acrylamide)) mCTA: Synthesis and Thermosensitivity.

Thermoresponsive poly((N,N-dimethyl acrylamide)-co-(N-isopropyl acrylamide)) (P(DMA-co-NIPAM)) copolymers were synthesized via reversible addition−fragmentation chain transfer (RAFT) polymerization. The monomer reactivity ratios were determined by the Kelen–Tüdős method to be rNIPAM = 0.83 and rDMA = 1.10. The thermoresponsive properties of these copo-lymers with varying molecular weights were characterized by visual turbidimetry and dynamic light scattering (DLS). The copolymers showed a lower critical solution temperature (LCST) in water with a dependence on the molar fraction of DMA in the copolymer. Chaotropic and kosmotropic salt anions of the Hofmeister series, known to affect the LCST of thermoresponsive polymers, were used as additives in the aqueous copolymer solutions and their influence on the LCST was demonstrated. Further on, in order to investigate the thermoresponsive behavior of P(DMA-co-NIPAM) in a confined state, P(DMA-co-NIPAM)-b-PS diblock copolymers were prepared via polymerization induced self-assembly (PISA) through surfactant-free RAFT mediated emulsion polymerization of styrene using P(DMA-co-NIPAM) as the macromolecular chain transfer agent (mCTA) of the polymerization. As confirmed by cryogenic transmission electron microscopy (cryoTEM), this approach yielded stabilized spherical micelles in aqueous dispersions where the PS block formed the hydrophobic core and the P(DMA-co-NIPAM) block formed the hydrophilic corona of the spherical micelle. The temperature-dependent behavior of the LCST-type diblock copolymers was further studied by examining the collapse of the P(DMA-co-NIPAM) minor block of the P(DMA-co-NIPAM)-b-PS diblock copolymers as a function of temperature in aqueous solution. The nanospheres were found to be thermosensitive by changing their hydrodynamic radii almost linearly as a function of temperature between 25 °C and 45 °C. The addition of kosmotropic salt anions, as a potentially useful tuning feature of micellar assemblies, was found to increase the hydrodynamic radius of the micelles and resulted in a faster collapse of the micelle corona upon heating.

Synthesis of Poly(methacrylic acid)-block-Polystyrene Diblock Copolymers at High Solid Contents via RAFT Emulsion Polymerization.

The combination of polymerization–induced self-assembly (PISA) and reversible–addition fragmentation chain transfer (RAFT) emulsion polymerization offers a powerful technique to synthesize diblock copolymers and polymeric nanoparticles in a controlled manner. The RAFT emulsion diblock copolymerization of styrene and methacrylic acid (MAA) by using a trithiocarbonate as surfactant and RAFT agent was investigated. The Z-group of the RAFT agent was modified with a propyl-, butyl- and dodecyl- sidechain, increasing the hydrophobicity of the RAFT agent to offer well-controlled polymerization of poly(methacrylic acid)-block-polystyrene (PMAA-b-PS) diblock copolymers at high solid contents between 30–50 wt% in water. The kinetic data of the PMAA homopolymerization with the three different RAFT agents for various solvents was investigated as well as the RAFT emulsion polymerization of the diblock copolymers in pure water. While the polymerization of PMAA-b-PS with a propyl terminus as a Z-group suffered from slow polymerization rates at solid contents above 30 wt%, the polymerization with a dodecyl sidechain as a Z-group led to full conversion within 2 h, narrow molar mass distributions and all that at a remarkable solid content of up to 50 wt%.

RAFT Emulsion Polymerization for (Multi)block Copolymer Synthesis: Overcoming the Constraints of Monomer Order

Synthesis of (multi)block copolymers using reversible addition–fragmentation chain transfer (RAFT) polymerization generally suffers from the limitation that the order of the blocks must be considered. Herein, syntheses of block copolymers by RAFT polymerization using trithiocarbonate RAFT species are conducted as solution, miniemulsion, and emulsion polymerizations to demonstrate that the issue of monomer order for styrene and butyl methacrylate can be largely overcome in emulsion polymerization under carefully chosen conditions. The presence of monomer droplets in emulsion polymerization—in addition to polymer particles that constitute the locus of polymerization—leads to a reduction in the ratio of RAFT end groups to monomer at the locus of polymerization. Consequently, fragmentation of the RAFT adduct radical in the “backward” (“wrong”) direction is associated with fewer monomer additions, thus minimizing the impact of this undesired kinetic event. It is demonstrated that RAFT emulsion polymerization can be exploited to prepare an alternating pentablock copolymer composed of methacrylates (with 10 mol % styrene) and styrene without consideration of monomer order, thereby significantly broadening the scope of RAFT polymerization for multiblock copolymer synthesis.

Synthesis and properties of styrenic triblock copolymers with dual structural asymmetry via RAFT emulsion polymerization

The polystyrene-block-poly(n-butyl acrylate)-block-polystyrene (PSt-b-PBA-b-PSt, SBAS) triblock copolymers (TBCPs) with dual structural asymmetry were synthesized via a reversible addition-fragmentation chain transfer (RAFT) emulsion polymerization. The dual structural asymmetry contained two asymmetric outer PSt blocks and a single short ionic block on one chain end while the SBAS TBCPs had the almost same molecular weight (~100 kDa) and composition (~70 wt% of PSt and ~30 wt% of PBA) excluding the short ionic block. The dual structural asymmetry with a synergistic effect was designed by locating the long PSt block near the short ionic block that was derived from ionic macromolecular RAFT agent. With the SBAS TBCPs having microphase separation structure, the structural asymmetry of two outer PSt blocks tailored the interaction of PSt and PBA blocks, further leading to the change of static tensile and dynamic mechanical properties, and rheology. Structural asymmetry will provide an alternative to tailor-made properties of TBCPs.

Poly[di(ethylene glycol) vinyl ether]-stabilized poly(vinyl acetate) nanoparticles with various morphologies via RAFT aqueous emulsion polymerization of vinyl acetate

Reversible addition fragmentation chain transfer (RAFT) aqueous emulsion polymerization of vinyl acetate (VAc) is performed using poly[di(ethylene glycol) vinyl ether] (PDEGV) macromolecular chain transfer agents (macro-CTAs) including RAFT end-unfunctionalized PDEGV (up to 32%). Emulsion polymerization directly induces PDEGV-b-PVAc diblock copolymer assemblies in water. This facile formulation enables the production of various particle morphologies, such as spheres, rods (ellipsoids), and vesicles, depending on the composition of the block copolymer. Many other examples of RAFT emulsion polymerization syntheses only result in the formation of kinetically trapped spheres, even when targeting highly asymmetric diblock compositions. However, despite being stabilized only by homopolymer PDEGV macro-CTAs, including PDEGV, PVAc-based nanoparticles with various morphologies can be obtained as PDEGV-b-PVAc assemblies. RAFT aqueous emulsion polymerization owes its success to recent RAFT polymerizations of hydroxy-functionalized vinyl ethers. We investigated the RAFT polymerization of DEGV, analyzed the kinetics of PDEGV-b-PVAc nanoparticle formation, and observed the morphology of resultant particles in detail. We also developed a phase diagram for this RAFT aqueous emulsion polymerization formulation that reliably predicts the precise block compositions associated with well-defined particle morphologies. RAFT aqueous emulsion polymerization of vinyl acetate (VAc) was performed using poly[di(ethylene glycol) vinyl ether] (PDEGV) macromolecular chain transfer agents. The emulsion polymerization directly induced PDEGV-b-PVAc diblock copolymer assemblies in water. Owing to the characteristic PDEGV as a highly hydrophilic steric stabilizer, this facile formulation enables the production of various particle morphologies, such as spheres, rods (ellipsoids), and vesicles, depending on the composition of the block copolymer. Each morphology change in the nanoparticles via RAFT aqueous emulsion polymerization owes its success to the recent RAFT polymerizations of vinyl ethers.

Flame Retardant Submicron Particles via Surfactant-Free RAFT Emulsion Polymerization of Styrene Derivatives Containing Phosphorous.

The reversible addition–fragmentation chain transfer (RAFT) emulsion polymerization of diethyl-(4-vinylbenzyl) phosphate (DEVBP) was performed using PEG-TTC as a macro RAFT agent. PEG-TTC (MW 2000, 4000) was synthesized by the esterification of poly (ethylene glycol) methyl ether with a carboxylic-terminated RAFT agent, composed a hydrophilic poly (ethylene glycol) (PEG) block and a hydrophobic dodecyl chain. The RAFT emulsion polymerization of DEVBP was well–controlled with a narrow molecular size distribution. Dynamic light scattering and confocal laser scanning microscopy were used to examine the PEG-b-PDVBP submicron particles, and the length of the PEG chain (hydrophilic block) was found to affect the particle size distribution and molecular weight distribution. The submicron particle size increased with increasing degree of polymerization (35, 65, and 130), and precipitation was observed at a high degree of polymerization (DP) using low molecular weight PEG-TTC (DP 130, A3). The flame retardant properties of the PEG-b-PDVBP were evaluated by thermogravimetric analysis (TGA) and micro cone calorimeter (MCC). In the combustion process, the residue of PEG-b-PDEVBP were above 500 °C was observed (A1 ~ B3, 27 ~ 38%), and flame retardant effect of PEG-b-PDEVBP submicron particles/PVA composite were confirmed by increasing range of temperature and decreasing total heat release with increasing contents of PEG-b-PDEVBP. The PEG-b-PDEVBP submicron particles can provide flame retardant properties to aqueous, dispersion and emulsion formed organic/polymer products.

Synthesis and Characterization of Waterborne Pyrrolidone-Functional Diblock Copolymer Nanoparticles Prepared via Surfactant-free RAFT Emulsion Polymerization

Polymerization-induced self-assembly enables the facile synthesis of a wide range of block copolymer nano-objects in the form of concentrated dispersions. In this context, many surfactant-free reversible addition–fragmentation chain transfer (RAFT) aqueous emulsion polymerization formulations have been reported using various nonionic and polyelectrolytic water-soluble precursors for the steric stabilizer block. In the present study, we examine poly(2-(N-acryloyloxy)ethyl pyrrolidone) (PNAEP) as a new nonionic stabilizer block. A trithiocarbonate-based PNAEP precursor with a mean degree of polymerization of 67 was employed as the steric stabilizer for the RAFT emulsion polymerization of styrene, n-butyl acrylate (nBA), or statistical mixtures thereof. The RAFT emulsion polymerization of styrene using a VA-044 azo initiator at 80 °C and pH 7 led to essentially full conversion within 40 min, with induction times as short as 10 min, whereas gel permeation chromatography analysis confirmed efficient chain exte...

One‐pot synthesis of octablock copolymers of high‐molecular weight via RAFT emulsion polymerization

AbstractMultiblock copolymers (mBCPs) could offer new opportunities to design new nanomaterials with multifunctions or enhanced properties in a cost‐effective way. However, it is still very challenging to obtain high degree of polymerization in each block of mBCPs with large block number using one‐pot synthesis via controlled radical polymerizations. This is due to the accumulation of the dead chains throughout the many step polymerization. In this work, we developed a new highly efficient strategy for preparing mBCPs with large block number using one‐pot reversible addition–fragmentation chain transfer (RAFT) emulsion polymerization, where every polymer block was formed by sequential addition of monomers. We achieved high block degree of polymerizations (~100 per block) for a model system of “octablock” polystyrene (PS) in just 2 hr per block. Experimentally measured molecular weights are in excellent agreement with theoretical predictions. The dead chains generated through the polymerization are negligible due to the low initiator concentration. Yet the polymerization rates are still very fast due to the heterogeneous advantages of emulsion polymerization. We have also applied this strategy to a series of mBCPs from diblock (PS176‐PnBA286)1 to octablock (PS176‐PnBA286)4 (PnBA for poly(n‐butyl acrylate)). The high degree of polymerization in our mBCPs ensures microphase separation even though PS/PnBA system is known for small χ values. We have also found that the tensile properties of our mBCPs increase significantly with increased number of blocks. Our work reveals that the number of blocks is an important molecular variable for tuning the mechanical properties of block copolymers.

In Situ Small-Angle X-ray Scattering Studies During Reversible Addition-Fragmentation Chain Transfer Aqueous Emulsion Polymerization.

Polymerization-induced self-assembly (PISA) is a powerful platform technology for the rational and efficient synthesis of a wide range of block copolymer nano-objects (e.g., spheres, worms or vesicles) in various media. In situ small-angle X-ray scattering (SAXS) studies of reversible addition–fragmentation chain transfer (RAFT) dispersion polymerization have previously provided detailed structural information during self-assembly (see M. J. Derry et al., Chem. Sci.2016, 7, 5078–509030155157). However, conducting the analogous in situ SAXS studies during RAFT aqueous emulsion polymerizations poses a formidable technical challenge because the inherently heterogeneous nature of such PISA formulations requires efficient stirring to generate sufficiently small monomer droplets. In the present study, the RAFT aqueous emulsion polymerization of 2-methoxyethyl methacrylate (MOEMA) has been explored for the first time. Chain extension of a relatively short non-ionic poly(glycerol monomethacrylate) (PGMA) precursor block leads to the formation of sterically-stabilized PGMA-PMOEMA spheres, worms or vesicles, depending on the precise reaction conditions. Construction of a suitable phase diagram enables each of these three morphologies to be reproducibly targeted at copolymer concentrations ranging from 10 to 30% w/w solids. High MOEMA conversions are achieved within 2 h at 70 °C, which makes this new PISA formulation well-suited for in situ SAXS studies using a new reaction cell. This bespoke cell enables efficient stirring and hence allows in situ monitoring during RAFT emulsion polymerization for the first time. For example, the onset of micellization and subsequent evolution in particle size can be studied when preparing PGMA29-PMOEMA30 spheres at 10% w/w solids. When targeting PGMA29-PMOEMA70 vesicles under the same conditions, both the micellar nucleation event and the subsequent evolution in the diblock copolymer morphology from spheres to worms to vesicles are observed. These new insights significantly enhance our understanding of the PISA mechanism during RAFT aqueous emulsion polymerization.

Synthesis of High Molecular Weight Poly(glycerol monomethacrylate) via RAFT Emulsion Polymerization of Isopropylideneglycerol Methacrylate.

High molecular weight water-soluble polymers are widely used as flocculants or thickeners. However, synthesis of such polymers via solution polymerization invariably results in highly viscous fluids, which makes subsequent processing somewhat problematic. Alternatively, such polymers can be prepared as colloidal dispersions; in principle, this is advantageous because the particulate nature of the polymer chains ensures a much lower fluid viscosity. Herein we exemplify the latter approach by reporting the convenient one-pot synthesis of high molecular weight poly(glycerol monomethacrylate) (PGMA) via the reversible addition–fragmentation chain transfer (RAFT) aqueous emulsion polymerization of a water-immiscible protected monomer precursor, isopropylideneglycerol methacrylate (IPGMA) at 70 °C, using a water-soluble poly(glycerol monomethacrylate) (PGMA) chain transfer agent as a steric stabilizer. This formulation produces a low-viscosity aqueous dispersion of PGMA–PIPGMA diblock copolymer nanoparticles at 20% solids. Subsequent acid deprotection of the hydrophobic core-forming PIPGMA block leads to particle dissolution and affords a viscous aqueous solution comprising high molecular weight PGMA homopolymer chains with a relatively narrow molecular weight distribution. Moreover, it is shown that this latex precursor route offers an important advantage compared to the RAFT aqueous solution polymerization of glycerol monomethacrylate since it provides a significantly faster rate of polymerization (and hence higher monomer conversion) under comparable conditions.

Surfactant-Free RAFT Emulsion Polymerization of Styrene Using Thermoresponsive macroRAFT Agents: Towards Smart Well-Defined Block Copolymers with High Molecular Weights.

The combination of reversible addition–fragmentation chain transfer (RAFT) and emulsion polymerization has recently attracted much attention as a synthetic tool for high-molecular-weight block copolymers and their micellar nano-objects. Up to recently, though, the use of thermoresponsive polymers as both macroRAFT agents and latex stabilizers was impossible in aqueous media due to their hydrophobicity at the usually high polymerization temperatures. In this work, we present a straightforward surfactant-free RAFT emulsion polymerization to obtain thermoresponsive styrenic block copolymers with molecular weights of around 100 kDa and their well-defined latexes. The stability of the aqueous latexes is achieved by adding 20 vol % of the cosolvent 1,4-dioxane (DOX), increasing the phase transition temperature (PTT) of the used thermoresponsive poly(N-acryloylpyrrolidine) (PAPy) macroRAFT agents above the polymerization temperature. Furthermore, this cosolvent approach is combined with the use of poly(N,N-dimethylacrylamide)-block-poly(N-acryloylpiperidine-co-N-acryloylpyrrolidine) (PDMA-b-P(APi-co-APy)) as the macroRAFT agent owning a short stabilizing PDMA end block and a widely adjustable PTT of the P(APi-co-APy) block in between 4 and 47 °C. The temperature-induced collapse of the latter under emulsion polymerization conditions leads to the formation of RAFT nanoreactors, which allows for a very fast chain growth of the polystyrene (PS) block. In dynamic light scattering (DLS), as well as cryo-transmission electron microscopy (cryoTEM), moreover, all created latexes indeed reveal a high (temperature) stability and a reversible collapse of the thermoresponsive coronal block upon heating. Hence, this paper pioneers a versatile way towards amphiphilic thermoresponsive high-molecular-weight block copolymers and their nano-objects with tailored corona switchability.

Thermoplastic shape memory polymers with tailor-made trigger temperature

Thermoplastic shape memory polymers (SMPs) as smart materials have a great challenge in adjusting trigger temperature (Tt) for practical device application with high fixity and recovery ratio (>99%). The thermoplastic SMPs based on triblock copolymers have been designed via reversible addition-fragmentation chain transfer (RAFT) emulsion polymerization. The Tt can be manipulated facilely, as designed, with the narrow temperature interval between adjacent Tts (only 10°C), indicating the high resolution of temperature in molecular design of SMPs. The as-designed SMPs have good shape memory ability and the reprogramming ability of shape memory behaviors. This approach can direct the molecular design of thermoplastic SMPs with tailor-made Tt via RAFT emulsion polymerization.

Fluorescent Labeling and Biodistribution of Latex Nanoparticles Formed by Surfactant-Free RAFT Emulsion Polymerization.

The authors report the preparation of a novel range of functional polyacrylamide stabilized polystyrene nanoparticles, obtained by surfactant-free reversible addition-fragmentation chain transfer (RAFT) emulsion polymerization, their fluorescent tagging, cellular uptake, and biodistribution. The authors show the versatility of the RAFT emulsion process for the design of functional nanoparticles of well-defined size that can be used as drug delivery vectors. Functionalization with a fluorescent tag offers a useful visualization tool for tracing, localization, and clearance studies of these carriers in biological models. The studies are carried out by labeling the sterically stabilized latex particles chemically with rhodamine B. The fluorescent particles are incubated in a healthy human renal proximal tubular cell line model, and intravenously injected into a mouse model. Cellular localization and biodistribution of these particles on the biological models are explored.

Molecular design and synthesis of acrylic resin film-forming materials with wide applicable temperature range via RAFT emulsion polymerization

Abstract The symmetric polystyrene- block -poly( n -butyl acrylate)- block -polystyrene (SAS) triblock copolymers with wide applicable temperature range have been designed and synthesized via reversible addition-fragmentation chain transfer (RAFT) emulsion polymerization. The high poly( n -butyl acrylate) (PBA) block content introduced will endow the SAS with the ability of working as film-forming materials. The microphase separation and mechanism of wide applicable temperature range were investigated by differential scanning calorimetry and dynamic mechanical analysis (DMA). The static and dynamic mechanical properties, visible light transmittance, water resistance and thermal stability of SAS were also characterized by tensile test, DMA, spectrophotometer, water absorption and thermogravimetric analysis. The tensile strength decreases and elongation at break increases with the PBA block content of SAS increasing from 50 wt.% to 70 wt.%. The maximum elongation at break reaches 707%. The broad thermoplastic elastic region from −40 °C to 80 °C works well in the surrounding of a big temperature difference due to the PBA block in rubbery state and the PSt block in glassy state. The SAS has high transmittance, low water absorption and favorable thermal stability. This research will provide a reference for film-forming materials with wide applicable temperature range.

RAFT Macro-Surfmers and Their Use in the ab Initio RAFT Emulsion Polymerization To Decouple Nanoparticle Size and Polymer Molecular Weight

Polymeric nanoparticles (NPs) are highly engineered nanoemulsions with applications in several fields. The control over NP surface chemistry, size (Dn), and molecular weight (MW) of the polymer they are made up of plays a paramount role in the optimization of their end-use performance. In this work, the theoretical basis to decouple the dependence between the NP Dn and MW has been presented, and an operative way has been demonstrated via ab initio reversible addition–fragmentation chain transfer (RAFT) emulsion polymerization (AIREP), a “living” heterogeneous process that adopts RAFT macro-surfmers: macromolecular chain transfer agents (CTA) produced via RAFT polymerization of amphiliphic monomers, such as surfmers. The possibility of obtaining the desired length of the lipophilic block or the length of the whole block copolymer and the NP Dn by choosing the correct length of the RAFT macro-surfmer has been assessed. It has been discovered that a wide range of Dn and MW can be achieved, but not very big N...

In situ polarity functionalization and properties of styrenic triblock copolymers synthesized via RAFT emulsion polymerization

ABSTRACTThe in situ polarity functionalization of the styrenic triblock copolymers was accomplished via the block introduction of polar monomer, n‐butyl acrylate, with the help of reversible addition‐fragmentation chain transfer (RAFT) emulsion polymerization. The polarity functionalization, microphase separation, static and dynamic mechanical properties, water resistance, transparency, and thermal stability of the synthesized polarity‐functionalized triblock copolymers, polystyrene‐block‐poly(n‐butyl acrylate)‐block‐polystyrene (SAS), were extensively studied. The poly(n‐butyl acrylate) (PBA) middle block higher than 10 wt % has the favorable toughening effect on polystyrene (PSt) two‐end block due to the microphase separation in SAS. The glass transition of the continuous plastic phase (mainly composed of PSt block) has a much greater influence on the storage modulus than that of the dispersed rubber phase (mainly composed of PBA block). The polarity‐functionalized SAS has good water resistance, high transparency, and robust thermal stability. The polarity‐functionalized SAS will have such a potential application broadening as polar adhesive. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44603.

A Comparative Study of Chemical Routes for Coating Gold Nanoparticles via Controlled RAFT Emulsion Polymerization

The synthesis of core‐shell Au nanoparticles protected by an amphiphilic block copolymer is investigated by distinct reversible addition fragmentation chain transfer (RAFT) emulsion polymerization routes. The controlled polymerization of polymer shells onto Au nanoparticles is attempted by using the macroRAFT (MR) agent based on 2‐(dodecylthiocarbonothioylthio)‐2‐methylpropionic acid synthesized via RAFT polymerization of poly(ethylene glycol) methyl ether acrylate and exploring several approaches, which include (i) post‐modification; (ii) in situ synthesis and (iii) “grafting from” strategies. In the conditions investigated here all these strategies lead to Au polymer nanocomposites but morphological well‐defined core‐shell nanoparticles are only obtained by applying the “grafting from” strategy. In particular, conditions that promote chain extension from the MR agent adsorbed onto the Au nanoparticles are found necessary to obtain nanostructures with such morphological characteristics and that still show the localized surface plasmon resonance typical of colloidal Au nanoparticles.