RAFT-mediated Emulsion Polymerization Research Articles

Multifunctional Layer-by-Layer Coating Based on a New Amphiphilic Block Copolymer via RAFT-Mediated Polymerization-Induced Self-Assembly Process.

In this hi-tech world, the "smart coatings" have sparked significant attention among materials scientists because of their versatile applications. Various strategies have been developed to generate smart coatings in the past 2 decades. The layer-by-layer (LbL) technique is the most commonly employed strategy to produce a smart coating for suitable applications. Here, we present a smart coating with healing, antifogging, and fluorescence properties fabricated by the LbL assembly of an anionic amphiphilic block copolymer latex and cationic inorganic POSS (polyhedral-oligomeric-silsesquioxane) nanoparticles. In this case, a new anionic block copolymer (BCP), {poly(sodium styrene sulfonate)-block-poly[2-(acetoacetoxy)ethyl methacrylate]}, (PSS-b-PAAEMA) was synthesized via surfactant-free RAFT-mediated emulsion polymerization using the PISA technique. The PSS-b-PAAEMA was characterized by 1H NMR, dynamic light scattering, scanning electron microscopy, and transmission electron microscopy analyses as well as by UV-vis and photoluminescence spectroscopy. For LbL coating fabrication, an amine-modified glass was successively dipped in the anionic latex and cationic POSS solution. The transparent coating exhibited good fluorescence properties under UV light (blue color). The antifogging performance of the coating was also investigated using both cold-warm and hot-vapor techniques. Additionally, the coating surface showed a significant healing activity with a healing efficiency of >75% through ionic interaction. Thus, this finding provides a simple low volatile organic compound (VOC) water-based LbL coating with multifunctional properties that can be a potential material for versatile applications.

Synthesis of Star-Shaped Nanocrystalline Cellulose/Fluorinated Polyacrylate via RAFT-Mediated Emulsion Polymerization and Its Application on Fabric Finishing

Synthesis of Star-Shaped Nanocrystalline Cellulose/Fluorinated Polyacrylate via RAFT-Mediated Emulsion Polymerization and Its Application on Fabric Finishing

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.

Strong and UV-Responsive Plant Oil-Based Ethanol Aqueous Adhesives Fabricated Via Surfactant-free RAFT-Mediated Emulsion Polymerization

Strong and UV-Responsive Plant Oil-Based Ethanol Aqueous Adhesives Fabricated Via Surfactant-free RAFT-Mediated Emulsion Polymerization

In situ cross-linking in RAFT-mediated emulsion polymerization: Reshaping the preparation of cross-linked block copolymer nano-objects by polymerization-induced self-assembly

Large-scale preparation of cross-linked block copolymer nano-objects using polymerization-induced self-assembly (PISA) generally suffers from the limitation that high degrees of cross-linking in the early stage must be avoided. Herein, we demonstrate that the intrinsic monomer-feeding mechanism of reversible addition-fragmentation chain transfer (RAFT)-mediated emulsion polymerization can be used to delay in situ cross-linking during PISA, allowing the preparation of cross-linked block copolymer nano-objects with high cross-linker contents. When using hydrophobic cross-linkers, the cross-linker along with monomer diffuses from monomer droplets to micelles gradually. When using hydrophilic cross-linkers, the cross-linker is prone to stay in water rather than diffuse into hydrophobic micellar cores. 1H NMR analysis confirmed the consumption behavior of cross-linkers during RAFT-mediated emulsion polymerization regardless of cross-linkers used. A variety of cross-linkers with different aqueous solubilities, symmetries, and functional groups were employed to prepare cross-linked block copolymer nano-objects. It is demonstrated that increasing the content of cross-linker promoted the formation of higher-order morphologies. We expect this study will not only expand the scope of RAFT-mediated PISA for in situ preparation of cross-linked block copolymer nano-objects, but also inspires researchers in this field to prepare novel polymer nanoparticles based on the unique mechanism of RAFT-mediated emulsion polymerization.

Tuning the Cloud-Point and Flocculation Temperature of Poly(2-(diethylamino)ethyl methacrylate)-Based Nanoparticles via a Postpolymerization Betainization Approach.

The ability to tune the behavior of temperature-responsive polymers and self-assembled nanostructures has attracted significant interest in recent years, particularly in regard to their use in biotechnological applications. Herein, well-defined poly(2-(diethylamino)ethyl methacrylate) (PDEAEMA)-based core–shell particles were prepared by RAFT-mediated emulsion polymerization, which displayed a lower-critical solution temperature (LCST) phase transition in aqueous media. The tertiary amine groups of PDEAEMA units were then utilized as functional handles to modify the core-forming block chemistry via a postpolymerization betainization approach for tuning both the cloud-point temperature (TCP) and flocculation temperature (TCFT) of these particles. In particular, four different sulfonate salts were explored aiming to investigate the effect of the carbon chain length and the presence of hydroxyl functionalities alongside the carbon spacer on the particle’s thermoresponsiveness. In all cases, it was possible to regulate both TCP and TCFT of these nanoparticles upon varying the degree of betainization. Although TCP was found to be dependent on the type of betainization reagent utilized, it only significantly increased for particles betainized using sodium 3-chloro-2-hydroxy-1-propanesulfonate, while varying the aliphatic chain length of the sulfobetaine only provided limited temperature variation. In comparison, the onset of flocculation for betainized particles varied over a much broader temperature range when varying the degree of betainization with no real correlation identified between TCFT and the sulfobetaine structure. Moreover, experimental results were shown to partially correlate to computational oligomer hydrophobicity calculations. Overall, the innovative postpolymerization betainization approach utilizing various sulfonate salts reported herein provides a straightforward methodology for modifying the thermoresponsive behavior of soft polymeric particles with potential applications in drug delivery, sensing, and oil/lubricant viscosity modification.

How the Reactive End Group of Macro-RAFT Agent Affects RAFT-Mediated Emulsion Polymerization-Induced Self-Assembly.

Polymerization-induced self-assembly via reversible addition-fragmentation chain transfer (RAFT)-mediated emulsion polymerization is an emerging method in which macro-RAFT agents are chain extended with hydrophobic monomers in water to form block copolymer nano-objects. However, almost all RAFT-mediated emulsion polymerizations are limited to AB diblock copolymers by using monofunctional macro-RAFT agents with non-reactive end groups. In this study, the first investigation on how the reactive end group of macro-RAFT agent affects RAFT-mediated emulsion polymerization is reported. Three macro-RAFT agents with different end groups are synthesized and employed in RAFT-mediated emulsion polymerization. Effects of end groups on morphologies of block copolymer nano-objects and polymerization process are studied. Block copolymer nano-objects prepared by using an asymmetric difunctional macro-RAFT agent can be functionalized by further chain extension on the surface. It is expected that the current study will not only expand the scope of RAFT-mediated emulsion polymerization, but also provide a novel strategy to prepare functional polymer nanoparticles.

Polymerization-Induced Self-Assembly via RAFT-Mediated Emulsion Polymerization of Methacrylic Monomers

Polymerization-induced self-assembly via reversible addition–fragmentation transfer (RAFT)-mediated emulsion polymerization has served as a versatile platform for scalable preparation of well-defin...

Interaction of Cationic, Anionic, and Nonionic Macroraft Homo- and Copolymers with Laponite Clay.

The functionalization of Laponite RD platelets with different cationic, anionic, and nonionic homo- and copolymers synthesized by reversible addition-fragmentation chain transfer (RAFT) has been investigated. The effective interaction of the macromolecular RAFT agents (macroRAFTs) with the inorganic particles is known to be of crucial importance for the successful coating of minerals with polymers via RAFT-mediated emulsion polymerization to produce polymer-encapsulated inorganic particles. The macroRAFT agents synthesized in the present work contain carefully selected reinitiating R groups, which bear either ionizable tertiary amine or quaternary ammonium moieties (from 2-(dimethylamino)ethyl methacrylate, DMAEMA), negatively charged acrylic acid (AA) repeat units, or neutral polyethylene glycol (PEG) side chains, and are capable of interacting with Laponite via different adsorption mechanisms. The equilibrium adsorption of these RAFT (co)polymers was investigated by the plotting of adsorption isotherms, and either L-type or H-type curves were obtained. The hydrophobicity of the macroRAFT was shown to promote adsorption, as did the pending configuration of the PEG block. Charge repulsion between AA and the negatively charged surface of Laponite at pH 7.5, on the other hand, was prejudicial for adsorption, while the strong electrostatic interaction between the cationic DMAEMA molecules and the Laponite surface led to high-affinity-type curves.

Photoinitiated Polymerization-Induced Self-Assembly via Visible Light-Induced RAFT-Mediated Emulsion Polymerization.

Aqueous emulsion polymerization is one of the most commonly used techniques in industry for the production of polymer latexes. In this contribution, we present photoinitiated polymerization-induced self-assembly (photo-PISA) based on aqueous visible light-induced reversible addition-fragmentation chain transfer (RAFT)-mediated emulsion polymerization at room temperature. A wide range of morphologies including spheres, worms, and vesicles have been achieved at room temperature by modulating reaction parameters. Additionally, this method enables access to inorganic nanoparticles-loaded vesicles by adding inorganic nanoparticles at the beginning of the polymerization. Finally, an oxygen-tolerant RAFT-mediated emulsion polymerization has been developed, allowing the synthesis of polymer nano-objects at low volumes (e.g., in a 96-well plate). This study is expected to expand the scope of photo-PISA for the preparation of various block copolymer nano-objects in water at room temperature.

Controlling the Morphology of Film-Forming, Nanocomposite Latexes Containing Layered Double Hydroxide by RAFT-Mediated Emulsion Polymerization

Stable nanocomposite latexes with sandwich, encapsulated, or armored morphology were produced by starved-feed emulsion polymerization in the presence of layered double hydroxide (LDH) nanoparticles. Four statistical copolymers of acrylic acid (AA) and n-butyl acrylate (BA) were adsorbed on the LDH surface, and a film-forming methyl acrylate (MA)/BA (8:2 mass/mass) monomer feed was chosen to facilitate subsequent film formation under ambient conditions. P(AA17.5-co-BA17.5)-R (R = RAFT function) produced the sandwich morphology, while P(AA7.5-co-BA7.5)-R gave the encapsulated morphology, which is remarkable given that nonencapsulated morphologies are normally considered to be the preferred equilibrium structures for nanocomposite particles. Adsorption behavior and monomer conversion profiles were very similar for the two systems, and we tentatively ascribe the morphological difference to the higher density of RAFT functions in the P(AA7.5-co-BA7.5)-R system. A RAFT-free analogue produced armored latexes, highlighting the importance of the RAFT function for promoting growth of the polymer shell from the nanoparticle surface.

Synthesis of poly(chloroprene)-based block copolymers by RAFT-mediated emulsion polymerization

Chloroprene (CP)-based block copolymers were synthesized via the RAFT-mediated emulsion polymerization of CP using polyacrylate macro-chain transfer agents (CTAs) via a one-pot (in-situ), two-step process. The quantitative formation of hydrophobic macro-CTA in the latex in the first step and subsequent incorporation of CP monomer into the latex using a high internal phase emulsion (HIPE) in the second step were observed to be crucial for producing poly(CP)-based block copolymers. The formation of poly(CP)-b-poly(n-butyl acrylate)s were confirmed by an evident shift in the SEC traces and the 1H and DOSY NMR measurements. The block copolymers exhibited microphased structures composed of the poly(CP) matrix with low Tg (−30 °C) and the poly(nBA) spherical phase with lower Tg (−50 to −60 °C), as revealed by dynamic mechanical analysis (DMA) and transmission electron microscopy (TEM). This study represents the first report of the controlled synthesis of poly(CP)-based block copolymers by RAFT-mediated emulsion polymerization using HIPE.

Tailored microstructure and mechanical properties of nanocomposite films made from polyacrylic/LDH hybrid latexes synthesized by RAFT-mediated emulsion polymerization

New layered double hydroxide (LDH)-filled nanocomposites with tunable microstructures and mechanical properties obtained from film-forming latexes.

RAFT‐mediated emulsion polymerization of chloroprene and impact of chain‐end structure on chloroprene rubbers

ABSTRACTThe reversible addition‐fragmentation chain transfer (RAFT) polymerization of chloroprene (CP) in an emulsion system using a dithiocarbamate‐type RAFT agent was studied. The controlled RAFT‐mediated emulsion polymerization was achieved by the appropriate combination of a RAFT agent and nonionic surfactant (polyoxyethylene phenyl ether) using a water‐soluble initiator (VA‐044) at 35 °C. An almost linear first‐order kinetic plot was observed until relatively high conversion (>80%) with molecular weights between 22,300 and 33,100 and relatively narrow molecular weight distributions (Mw/Mn ≦ 1.5) were achieved. The amount of the emulsifier used and the pH of the system were found to affect the controlled character, polymerization rate, and induction period, which are related to the size of the emulsion particles. Large‐scale RAFT‐mediated emulsion polymerization was also employed to afford industrially applicable poly(CP) (Mw > 25 × 104, resulting product > 2300 g). The vulcanized CP rubber obtained from the RAFT‐synthesized poly(CP) exhibited better physical properties, particularly tensile modulus and compression set, which may be due to the presence of the reactive end groups and the absence of low‐molecular‐weight products. We also evaluated the impact of the chain‐end structure on the mechanical and physical properties of these industrially important CP rubbers with carbon black. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46008.

RAFT-mediated emulsion polymerization of styrene with a thermoresponsive MacroCTA

Heterogeneous RAFT polymerization is an attractive ‘living’ radical polymerization technique to control not only the molecular weight distribution but also the particles size distribution. Here, we demonstrate the use of a thermoresponsive RAFT macro chain transfer agent (MacroCTA) to form seed particles for the chain extension of styrene to form block copolymer latex particles. By incorporating a few styrene units into the MacroCTA, the polymerizations become faster, producing both narrow particle size and molecular weight distributions. This is due to the ‘superswelling effect’, in which all the seed particles swell with monomer and nucleated at the same time. The resulting latex particles could then be transformed into a variety of nanostructures by cooling below the lower critical solution temperature of the thermoresponsive block in the presence of a plasticizer for polystyrene. The dominant structure was cylindrical worms with the observation of other structures including jelly fish and the rare disc. Cooling under ultrasound produced either vesicles or cauliflower structures. The work demonstrated that utilizing the ‘superswelling effect’, control over the rate, and molecular weight and particle size distributions could be obtained, providing design parameters to construct new nanostructures.

Polymer-encapsulated γ-Fe2O3 nanoparticles prepared via RAFT-mediated emulsion polymerization

Composite organic/inorganic latexes encapsulating iron oxide (IO) nanoparticles of maghemite (γ-Fe2O3) were successfully synthesized by surfactant-free reversible addition-fragmentation chain transfer (RAFT)-mediated emulsion polymerization. γ-Fe2O3 was first dispersed in an aqueous solution containing a statistical copolymer constituted of acrylic acid (AA) and n-butyl acrylate (BA) units, prepared by RAFT polymerization (so-called macroRAFT agent). Taking benefit from the affinity of carboxylic acid groups for iron oxide, the P(AA10-co-BA10) macroRAFT agent was adsorbed onto the surface of IO nanoparticles leading to the formation of macroRAFT/IO clusters. The interaction between the macroRAFT agent and the IO surface was investigated by the study of the adsorption isotherms, indicating that the amount of adsorbed macroRAFT agent increased with increasing macroRAFT concentration. However, a high fraction of the macroRAFT chains (up to 47%) remained in the aqueous phase. The clusters were then engaged in batch emulsion polymerization of styrene or of methyl methacrylate (MMA)/BA mixtures. IO encapsulation was however unsuccessful, and a phase separation between the polymer and the IO clusters was observed. In contrast, semi-batch emulsion polymerization of MMA/BA (90/10 wt ratio) led to effective encapsulation. Morphology studies suggest that the formation of stable latexes containing large IO clusters mainly depends on the concentration of the macroRAFT agent and the pH. Under optimized conditions, a latex with superparamagnetic properties (Ms = 16.2 emu g−1) encapsulating almost all the initial IO nanoparticles was successfully produced.

Synthesis of Polymer/Silica Hybrid Latexes by Surfactant-Free RAFT-Mediated Emulsion Polymerization

The reversible addition–fragmentation chain transfer (RAFT) polymerization technique was used to synthesize random copolymers of poly(ethylene glycol) methyl ether acrylate) (PEGA) and n-butyl acrylate (BA) and terpolymers of acrylic acid (AA), PEGA and BA with a trithiocarbonate reactive end-group. These macromolecular RAFT agents (macro-RAFTs) were subsequently adsorbed at the surface of size-monodisperse colloidal silica particles with diameters varying between 40 and 450 nm. Adsorption isotherms for both macro-RAFTs could be well fitted to the Langmuir adsorption model, the AA-based macro-RAFT agent showing however a lower maximum adsorption. The adsorbed macro-RAFT agents were subsequently chain extended with a mixture of methyl methacrylate (MMA) and BA by starved feed emulsion polymerization. Cryo-TEM analysis of the resulting hybrid latexes synthesized in the presence of the P(AA-co-PEGA-co-BA) terpolymers resulted in multipod-like particles while the P(PEGA-co-BA) copolymers showed the formation ...

Xyloglucan-Functional Latex Particles via RAFT-Mediated Emulsion Polymerization for the Biomimetic Modification of Cellulose.

Herein, we report a novel class of latex particles composed of a hemicellulose, xyloglucan (XG), and poly(methyl methacrylate) (PMMA), specially designed to enable a biomimetic modification of cellulose. The formation of the latex particles was achieved utilizing reversible addition-fragmentation chain transfer (RAFT) mediated surfactant-free emulsion polymerization employing XG as a hydrophilic macromolecular RAFT agent (macroRAFT). In an initial step, XG was functionalized at the reducing chain end to bear a dithioester. This XG macroRAFT was subsequently utilized in water and chain extended with methyl methacrylate (MMA) as hydrophobic monomer, inspired by a polymerization-induced self-assembly (PISA) process. This yielded latex nanoparticles with a hydrophobic PMMA core stabilized by the hydrophilic XG chains at the corona. The molar mass of PMMA targeted was varied, resulting in a series of stable latex particles with hydrophobic PMMA content between 22 and 68 wt % of the total solids content (5-10%). The XG-PMMA nanoparticles were subsequently adsorbed to a neutral cellulose substrate (filter paper), and the modified surfaces were analyzed by FT-IR and SEM analyses. The adsorption of the latex particles was also investigated by quartz crystal microbalance with dissipation monitoring (QCM-D), where the nanoparticles were adsorbed to negatively charged model cellulose surfaces. The surfaces were analyzed by atomic force microscopy (AFM) and contact angle (CA) measurements. QCM-D experiments showed that more mass was adsorbed to the surfaces with increasing molar mass of the PMMA present. AFM of the surfaces after adsorption showed discrete particles, which were no longer present after annealing (160 °C, 1 h) and the roughness (Rq) of the surfaces had also decreased by at least half. Interestingly, after annealing, the surfaces did not all become more hydrophobic, as monitored by CA measurements, indicating that the surface roughness was an important factor to consider when evaluating the surface properties following particle adsorption. This novel class of latex nanoparticles provides an excellent platform for cellulose modification via physical adsorption. The utilization of XG as the anchoring molecule to cellulose provides a versatile methodology, as it does not rely on electrostatic interactions for the physical adsorption, enabling a wide range of cellulose substrates to be modified, including neutral sources such as cotton and bacterial nanocellulose, leading to new and advanced materials.

Facile production of nanoaggregates with tuneable morphologies from thermoresponsive P(DEGMA-co-HPMA)

RAFT-mediated emulsion polymerization of styrene and subsequent morphological transition produces nanoaggregates with tuneable morphologies.

Rapid synthesis of ultrahigh molecular weight and low polydispersity polystyrene diblock copolymers by RAFT-mediated emulsion polymerization

An environmentally friendly emulsion technique produces uniform nanoparticles with precise control over molecular weight and particle size.