Macromolecular Reversible Addition-fragmentation Chain Transfer Agent Research Articles

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.

Polymer/C.I. Pigment Red 170 hybrid latexes prepared by RAFT-mediated surfactant-free emulsion polymerization

By using organic pigment-based ink-jet inks, the digital ink-jet printing of textiles is one kind of environmentally friendly technology for cleaner dyeing. Due to the shortcomings of easy agglomeration and poor water dispersion stability of organic nanoparticles, however, the encapsulation and dispersion of organic pigment nanoparticles are also hot and difficult research problems. In this work, we report the reversible addition-fragmentation chain transfer (RAFT) polymerization technology was used to synthesize random copolymer of 2-(dimethylamino) ethyl methacrylate (DMAEMA), poly(ethylene glycol) methyl ether methacrylate (PEGA), and methyl methacrylate (MMA) or butyl acrylate (BA) with a trithiocarbonate reactive end-group. These cationic macromolecular RAFT agents (macro-RAFT) with a pH of 5 were subsequently adsorbed at the surface of size-monodisperse colloidal Pigment Red 170 particles. The absorbed macro-RAFT agents were considered to be the living points to mediate the RAFT polymerization of monomers (MMA and BA) by starved feed emulsion polymerization. TEM results shown that the resulting hybrid latexes synthesized in presence of the tri-copolymer macro-RAFT agents resulted in the formation of individually encapsulated pigment particles. In addition, the dynamic light scattering (DLS), zeta potential and stability tests found that the macro-RAFT agent participated in the growing latex stabilization which is the key to obtaining the stable and uniform core-shell hybrid latex. More importantly, the preparation of film-forming copolymer/pigment hybrid latex in this study shown that the high potential of the P(DMAEMA- co -PEGA- co -MMA or BA) macro-RAFT agent for the development of polymer-pigment hybrid latexes which has good application properties. • Cationic and brush-type macro-RAFT agents were synthesized through RAFT polymerization. • Amphiphilic macro-RAFT agent has good adsorption and dispersion properties for the C.I. Pigment Red 170. • The film-forming polymers with lower T g are successfully encapsulated on the surface of pigment. • The encapsulated polymer/pigment hybrid latexes exhibit excellent dispersion stability with freeze-thaw, storage and pH.

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.

Preparation of ABA triblock copolymer assemblies through “one-pot” RAFT PISA

Poly(N,N-dimethyl acrylamide)-block-poly(styrene)-block-poly(N,N-dimethyl acrylamide) (PDMAc-b-PSt-b-PDMAc) amphiphilic triblock copolymer micro/nano-objects were synthesized through reversible addition-fragmentation chain transfer (RAFT) dispersion polymerization of St mediated with poly(N,N-dimethyl acrylamide) trithiocarbonate (PDMAc-TTC-PDMAc) bi-functional macromolecular RAFT agent. It is found that the morphology of the PDMAc-b-PSt-b-PDMAc copolymer micro/nano-objects like spheres, vesicles and vesicle with hexagonally packed hollow hoops (HHHs) wall can be tuned by changing the solvent composition. In addition, vesicles with two sizes (600 nm, 264 nm) and vesicles with HHHs features were also synthesized in high solid content systems (30 wt% and 40 wt%, respectively). Besides, as compared with typical AB diblock copolymers (A is the solvophilic, stabilizer block, and B is the solvophobic block), ABA triblock copolymers tend to form higher order morphologies, such as vesicles, under similar conditions. The finding of this study provides a new and robust approach to prepare block copolymer vesicles and other higher order micelles with special structure via PISA.

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.

Thermal stability of RAFT-based poly(methyl methacrylate): A kinetic study of the dithiobenzoate and trithiocarbonate end-group effect

Thermal stability of dithiobenzoate- (DB) and trithiocarbonate- (TC) terminated poly(methyl methacrylate) (PMMA) synthesized via reversible addition–fragmentation chain transfer (RAFT) polymerization is systematically studied under dynamic heating and prolonged isothermal treatment at 100–180 °C. It is demonstrated that in the presence of functional end-groups the onset of mass loss can be shifted relative to conventional PMMA, either toward higher (PMMA-DB) or lower (PMMA-TC) temperatures. Irrespective of the polymer molar mass, a loss of PMMA chain-end functionality clearly manifests itself upon 24 h of isothermal treatment at 120 °C for DB end-groups and already at 100 °C for TC ones. At 120 °C (for PMMA-TC) and 140 °C (for PMMA-DB) the ability of both polymers to serve as macromolecular RAFT agents in the chain extension processes ceases almost completely. The kinetics of functional end-groups elimination depends on their chemical nature. In the case of DB-groups, the reaction is of the first order, whereas TC-groups containing two CS bonds demonstrate more complex degradation kinetics. We propose a two-step mechanism of TC-group elimination, which enables interpretation of the observed experimental data.

Ketone-Functionalized Polymer Nano-Objects Prepared via Photoinitiated Polymerization-Induced Self-Assembly (Photo-PISA) Using a Poly(diacetone acrylamide)-Based Macro-RAFT Agent.

Herein, ketone-functionalized diblock copolymer nano-objects are prepared by photoinitiated reversible addition-fragmentation chain transfer (RAFT) dispersion polymerization of tert-butyl acrylate (tBA) using a poly(diacetone acrylamide) (PDAAM)-based macromolecular RAFT (macro-RAFT) agent in ethanol/water (60/40, w/w) at room temperature. A high polymerization rate is observed via the exposure of visible light (λmax = 405 nm, 0.45 mW cm-2 ) with near quantitative monomer conversion being achieved within 60 min. A morphological phase diagram is constructed by changing the degree of polymerization (DP) of PtBA and the monomer concentration. The morphologies of polymer nano-objects are further tuned by incorporating isobornyl acrylate (IBOA) into the core-forming block. The ketone-functionalized diblock copolymer nano-objects can be shell-cross-linked by reacting with a diamine. Finally, the shell-cross-linked polymer nano-objects are further hydrolyzed and employed as a template for the synthesis of silver composites.

Layer-By-Layer Self-Assembly of Polyelectrolytic Block Copolymer Worms on a Planar Substrate.

Cationic and anionic block copolymer worms are prepared by polymerization-induced self-assembly via reversible addition–fragmentation chain transfer (RAFT) aqueous dispersion copolymerization of 2-hydroxypropyl methacrylate and glycidyl methacrylate (GlyMA), using a binary mixture of a nonionic poly(ethylene oxide) macromolecular RAFT agent and either a cationic poly([2-(methacryloyloxy)ethyl]trimethylammonium chloride) or an anionic poly(potassium 3-sulfopropyl methacrylate) macromolecular RAFT agent. In each case, covalent stabilization of the worm cores was achieved via reaction of the epoxide groups on the GlyMA repeat units with 3-mercaptopropyltriethoxysilane. Aqueous electrophoresis studies indicated a pH-independent mean zeta potential of +40 mV and −39 mV for the cationic and anionic copolymer worms, respectively. These worms are expected to mimic the rigid rod behavior of water-soluble polyelectrolyte chains in the absence of added salt. The kinetics of adsorption of the cationic worms onto a planar anionic silicon wafer was examined at pH 5 and was found to be extremely fast at 1.0 w/w % copolymer concentration in the absence of added salt. Scanning electron microscopy (SEM) analysis indicated that a relatively constant worm surface coverage of 16% was achieved at 20 °C for adsorption times ranging from just 2 s up to 2 min. Furthermore, the successive layer-by-layer deposition of cationic and anionic copolymer worms onto planar surfaces was investigated using SEM, ellipsometry, and surface zeta potential measurements. These techniques confirmed that the deposition of oppositely charged worms resulted in a monotonic increase in the mean layer thickness, with a concomitant surface charge reversal occurring on addition of each new worm layer. Unexpectedly, two distinct linear regimes were observed when plotting the mean layer thickness against the total number of adsorbed worm layers, with a steeper gradient (corresponding to thicker layers) being observed after the deposition of six worm layers.

Investigation of the Adsorption of Amphipathic macroRAFT Agents onto Montmorillonite Clay.

Recently, there has been significant interest in the use of the reversible addition-fragmentation chain-transfer (RAFT) technique to generate a variety of organic/inorganic colloidal composite particles in aqueous dispersed media using the so-called macroRAFT-assisted encapsulating emulsion polymerization (REEP) strategy. In this process, special attention should be paid to the adsorption of the macromolecular RAFT (macroRAFT) agent onto the inorganic particles, as it determines the final particle morphology and can also influence latex stability. In this work, different amphipathic macroRAFT agents were synthesized by RAFT, and their adsorption onto commercial Montmorillonite clay Cloisite Na+ (MMT) was studied by means of adsorption isotherms. Three types of macroRAFT agents were considered: a nonionic one based on poly(ethylene glycol) methyl ether acrylate (PEGA) and n-butyl acrylate (BA), anionic ones, including a block copolymer and random copolymers, based on acrylic acid (AA), BA and PEGA, and cationic ones based on 2-(dimethylamino)ethyl methacrylate (DMAEMA), BA and PEGA. Six adsorption isotherm models (Langmuir, Freundlich, Tempkin, Redlich-Peterson, Sips, and Brunauer-Emmett-Teller) were adjusted to the experimental isotherms. The nonionic macroRAFT agent formed a monolayer on the clay surface with a maximum adsorption capacity of 400 mg g-1 at pH 8, as determined from the Sips adsorption model. Adsorption of the AA-based macroRAFT agents onto MMT was moderate at alkaline pH due to electrostatic repulsions, but increased with decreasing pH. The DMAEMA-based macroRAFT agents displayed a much stronger interaction with the oppositely charged MMT surface at acidic pH due to electrostatic interactions, and the concentration of adsorbed macroRAFT agent reached values as high as 800 mg g-1. The BET model fitted the experimental data relatively well indicating multilayer adsorption promoted by the presence of the hydrophobic BA units. In addition, the cationic macroRAFT agents afforded stable MMT/macroRAFT agent complexes as evaluated by dynamic light scattering and zeta potential analyses.

Surfactant-free poly(vinylidene chloride) latexes via one-pot RAFT-mediated aqueous polymerization

Water-soluble polymers obtained by reversible addition-fragmentation chain transfer (RAFT) polymerization were used for the production of surfactant-free poly(vinylidene chloride) (PVDC)-based latexes in a one-pot/two-step process that was exclusively conducted in water. In the first step, the hydrophilic macromolecular RAFT (macroRAFT) agent (i.e. poly(acrylic acid) (PAA), poly(methacrylic acid) (PMAA) or poly(sodium 4-styrenesulfonate) (PSSNa)) was synthesized in water using a trithiocarbonate RAFT agent, 4-cyano-4-thiothiopropylsulfanyl pentanoic acid (CTPPA). The macroRAFT agent was then directly utilized as reactive stabilizer for the aqueous emulsion copolymerization of vinylidene chloride (VDC) and methyl acrylate (MA) inspired by a polymerization-induced self-assembly (PISA) process. The developed recipes employed a very low amount of macroRAFT agent compared to the hydrophobic monomers (typically less than 2 wt%) and amphiphilic block copolymers of PAA-b-P(VDC-co-MA), PMAA-b-P(VDC-co-MA) or PSSNa-b-P(VDC-co-MA) were thus produced in situ, providing stabilization to the P(VDC-co-MA) particles. Stable, surfactant-free latexes were successfully obtained in each case with solids content up to 40 wt%. Surface tension measurements performed on the final dispersions showed that the amount of residual macroRAFT agent in water was negligible demonstrating that this strategy indeed gave rise to particles stabilized by covalently-anchored hydrophilic polymers. The PSSNa macroRAFT agents proved to be particularly interesting candidates achieving stable latexes of less than 100 nm leading to the formation of transparent films which did not whiten after being immersed in water.

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.

A feasible method of preparation of block copolymer latex films with stable microphase separation structures

RAFT (reversible addition–fragmentation chain transfer) miniemulsion polymerization was engaged to engineer latex particle morphology. With this approach, a macromolecular amphiphilic RAFT agent with epoxy groups was synthesized that assembled onto the surface of monomer mini-droplets. It caused the polymer chains to grow inwards gradually in particles as polymerization proceeded. The batch polymerization of n-butyl acrylate (BA) followed by addition of styrene (St) led to the formation of PBA-b-PSt diblock copolymer shell–core latex, where epoxy groups were enriched on the particle surface. The shell–core ratio was varied feasibly by changing the mass of St. When the structured latexes were dried, epoxy groups underwent efficient curing reactions triggered by a thermal-latent curing agent (dicyandiamide) in a controlled manner, leading to the formation of bonded PBA blocks connecting the PSt blocks in adjacent particles. Mechanical tests show that the films behaved like ductile materials, whose modulus and elongation at break were functions of copolymer compositions. Furthermore, curing reaction was a very robust method of preserving film morphology which correlated well with that observed for the latex particles. The results demonstrated a feasible method of preparation of latex films with stable microphase separation structures and thus improved mechanical properties.

Study of the solution and aqueous emulsion copolymerization of vinylidene chloride with methyl acrylate in the presence a poly(ethylene oxide) macromolecular RAFT agent

The reversible addition-fragmentation chain transfer (RAFT) copolymerization of vinylidene chloride (VDC) with methyl acrylate (MeA) was studied in the presence of poly(ethylene oxide)-based macromolecular RAFT (macroRAFT) agents of the trithiocarbonate type (PEO-TTC) in solution and in aqueous emulsion. Firstly the formation of PEO-b-P(VDC-co-MeA) diblock copolymers was performed in toluene solution at 30 °C and a good control over the polymerization with high chain-end functionality was shown. A first aqueous emulsion copolymerization of VDC with MeA was performed using one of the amphiphilic PEO-b-P(VDC-co-MeA) diblock copolymers as macromolecular stabilizer. Then, in a series of experiments the PEO-TTC macroRAFT agents were directly tested as both chain transfer agents and stabilizing agents in similar conditions (aqueous batch emulsion copolymerization of VDC with MeA at 70 °C). The influence of the nature and concentration of the initiating system and the presence or not of a buffer were studied. We demonstrated that in simple conditions, nanometric latex particles composed of amphiphilic PEO-b-P(VDC-co-MeA) diblock copolymers formed by polymerization-induced self-assembly (PISA). It can thus be concluded that PEO-TTC macroRAFT agents are valuable non-ionic macromolecular stabilizers in the emulsion copolymerization of VDC and MeA and allow the formation of core–shell diblock copolymer particles in the absence of free surfactant. However, when rather high molar masses of the hydrophobic PVDC-based block were targeted, the determined molar masses deviated from the theoretical values.

Effect of the pH on the RAFT Polymerization of Acrylic Acid in Water. Application to the Synthesis of Poly(acrylic acid)-Stabilized Polystyrene Particles by RAFT Emulsion Polymerization

The reversible addition–fragmentation chain transfer (RAFT) polymerization of acrylic acid (AA) in water was studied in detail at different pHs using 4-cyano-4-thiothiopropylsulfanyl pentanoic acid (CTPPA) as a control agent and 4,4′-azobis(4-cyanopentanoic acid) (ACPA) as an initiator. Well-defined hydrophilic macromolecular RAFT agents (PAA-CTPPA) were obtained and further used directly in water for the polymerization of styrene. The corresponding polymerization-induced self-assembly (PISA) process was evaluated at different pHs and it was shown that working in acidic conditions (pH = 2.5) led to well-defined amphiphilic block copolymer particles (Đ < 1.4) of small size (below 50 nm). When the pH increased, the control over the growth of the polystyrene (PS) block was gradually lost. Chain extension experiments of PAA-CTPPA with N-acryloylmorpholine (NAM), a hydrosoluble and non-pH sensitive monomer, performed at different pHs showed that the very first addition–fragmentation steps that occurred in water were impeded when PAA was ionized leading to partial consumption of PAA-CTPPA and thus to PS molar masses higher than expected. Varying the PAA-CTPPA concentration at pH = 2.5 led in all cases to stable particles composed of well-defined block copolymers with PS segments of different molar masses.

Poly(vinylidene chloride)-Based Amphiphilic Block Copolymers

The controlled/living free-radical copolymerization of vinylidene chloride (VDC) with methyl acrylate (MeA) or acrylic acid (AA) was studied by the reversible addition–fragmentation chain transfer (RAFT) technique using a trithiocarbonate RAFT agent. The reactions were performed in 1,4-dioxane solution at 30 °C and led to good control and high chain-end functionality. P(VDC-co-MeA)-b-PAA, PAA-b-P(VDC-co-MeA), and PAA-b-P(VDC-co-AA) amphiphilic block copolymers were then prepared in the same conditions, starting either from a hydrophobic P(VDC-co-MeA) macromolecular RAFT (macro-RAFT) agent or from a hydrophilic PAA one. The advantage of the first synthesis pathway relies on the very good transfer efficiency to trithiocarbonate-ended P(VDC-co-MeA) and on the rapid consumption of the latter even when low percentages (10 mol %) of MeA comonomer are incorporated in the macro-RAFT agent. In contrast, for the second approach a rapid consumption of the macro-RAFT agent is only reached with 30 mol % of MeA in the ...

Toward a Better Understanding of the Parameters that Lead to the Formation of Nonspherical Polystyrene Particles via RAFT-Mediated One-Pot Aqueous Emulsion Polymerization

The emulsion polymerization of styrene in the presence of hydrophilic poly(methacrylic acid-co-poly(ethylene oxide) methyl ether methacrylate), P(MAA-co-PEOMA), macromolecular RAFT (reversible addition–fragmentation chain transfer) agents possessing a trithiocarbonate reactive group and 19 ethylene oxide subunits in the grafts was performed to create in situ P(MAA-co-PEOMA)-b-polystyrene amphiphilic block copolymer self-assemblies. The system was studied using the following conditions: a pH of 5, two different compositions of the MAA/PEOMA units (50/50 and 67/33, mol/mol), different molar masses of the macroRAFT agents, and various concentrations of the latter targeting different molar masses for the polystyrene block. This work completes a previous one performed at pH 3.5, under otherwise similar experimental conditions, for which only spherical particles were obtained [Zhang et al. Macromolecules2011, 44, 7584]. For both MAA/PEOMA compositions, the system led to different nano-object morphologies such a...

Effect of the solvent composition on the morphology of nano-objects synthesized via RAFT polymerization of benzyl methacrylate in dispersed systems

A hydrophilic macromolecular RAFT (reversible addition–fragmentation chain transfer) agent (macroRAFT agent) composed of 50 mol% methacrylic acid and 50 mol% poly(ethylene oxide) monomethyl ether methacrylate end-capped by a reactive trithiocarbonate group (P(MAA-co-PEOMA)) was used in the polymerization of benzyl methacrylate (BzMA) in different media, ethanol–water and 1,4-dioxane–water mixtures. Depending on the solvent composition, the polymerization showed features of either a dispersion polymerization (monomer soluble in the initial medium) or an emulsion polymerization (monomer insoluble in the initial medium). In all cases, the RAFT mechanism led to the in situ formation of well-defined amphiphilic P(MAA-co-PEOMA)-b-PBzMA block copolymers that self-assembled during the growth step into self-stabilized nano-objects, according to a polymerization-induced micellization process. For a given composition of the block copolymer, the final morphology depended strongly on the solvent composition. The presence of the organic co-solvent was favorable to the formation of fibers while an increased amount of water favored the formation of spherical particles. Compared to the ethanol–water system, in which the non-spherical objects existed only above 77–80 vol% of ethanol, in 1,4-dioxane–water mixtures the morphological transition was observed at a lower proportion of organic co-solvent (close to 20 vol%). For a given molar mass of the macroRAFT agent and an increased molar mass of the PBzMA block in a given solvent composition (ethanol–water, 95/5, v/v), the morphology changed from spheres to fibers and then to large spheres or vesicles. The molar mass window in which fibers were obtained was wider than that observed in pure water at pH 5 using the same macroRAFT agent [X. Zhang et al., Macromolecules, 2011, 44, 4149].

Preparation of well‐defined block copolymer having one polystyrene segment and another poly(styrene‐alt‐maleic anhydride) segment with RAFT polymerization

AbstractBlock copolymers, polystyrene‐b‐poly(styrene‐co‐maleic anhydride), have been prepared by reversible addition‐fragmentation chain transfer (RAFT) polymerization technique using three different approaches: 1‐phenylethyl phenyldithioacetate (PEPDTA) directly as RAFT agent, mediated polystyrene (PS) block as the macromolecular PS‐RAFT agent and mediated poly(styrene‐maleic anhydride) (SMA) block with alternating sequence as the macromolecular SMA‐RAFT agent. Copolymers synthesized in the one‐step method using PEPDTA as RAFT agent possess one PS block and one SMA block with gradient structure. When the macromolecular RAFT agents are employed, copolymers with one PS block and one alternating SMA block can be produced. However, block copolymers with narrow molecular weight distribution (MWD) can only be obtained using the PS‐RAFT agent. The MWD deviates considerably from the typical RAFT polymerization system when the SMA is used as the RAFT agent. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Stable azlactone-functionalized nanoparticles prepared from thermoresponsive copolymers synthesized by RAFT polymerization

A new class of stable azlactone-functionalized thermoresponsive nanoparticles have been synthesized and characterized. Such particles are based on well-defined copolymers of poly(N-isopropylacrylamide) (PNIPAM), poly(N,N-dimethylacrylamide) (PDMA) and poly(2-vinyl-4,4-dimethylazlactone) (PVDM) copolymers synthesized using reversible addition–fragmentation chain transfer (RAFT) polymerization. A well-defined PNIPAM macromolecular RAFT agent and a PDMA macromolecular RAFT agent of low polydispersities (PDIs = 1.04–1.12) were used to mediate the copolymerizations of DMA/VDM and of NIPAM/VDM, respectively, resulting in copolymers of Mn ranging from 19 500 g mol−1 to 64 600 g mol−1 and PDIs ranging from 1.04 to 1.20. Depending on the number-average polymerization degrees of NIPAM, DMA and VDM, lower critical solution temperatures (LCSTs) ranging from 36 °C to 44 °C were measured. Two block copolymers PNIPAM46-b-P(VDM6-co-DMA65) and PDMA23-b-P(VDM10-co-NIPAM46) have a LCST that occurs at the physiological temperature. Above the LCST, the resulting nanoparticles were covalently stabilized by reacting a diamine with azlactone rings. The size exclusion chromatography (SEC) analyses revealed that all unimers are incorporated into the core-crosslinked structures and into the shell-crosslinked structures. This new strategy of crosslinking nanoparticles based on thermoresponsive copolymers is of particular interest as it is highly efficient. The azlactone groups remaining in core-crosslinked nanoparticles are suitable to react with dansylhydrazine as shown by SEC analysis using UV detection.