Aqueous dispersion polymerization of diacetone acrylamide (DAAM) by chain extension from a hydrophilic poly(N,N-dimethylacrylamide) (PDMA30) macromolecular chain transfer agent (macro-CTA) to produce PDMA30–PDAAMx block copolymer nano-objects was investigated in detail by systematically varying solids content and degree of polymerization of the core-forming PDAAM, leading to the formation of pure lamellae, mixed lamellae/vesicles, and pure vesicles as revealed by dynamic light scattering (DLS), transmission electron microscopy (TEM), atomic force microscopy (AFM), and scanning electron microscopy (SEM). PDMA30–PDAAMx lamellae were found to span an unprecedented wide space in the morphology phase diagram. Moreover, in situ cross-linking of lamellae via statistical copolymerization of DAAM with an asymmetric cross-linker allyl acrylamide and the effect of cross-linking density on the colloidal and morphological stabilities were studied, representing the first report on in situ cross-linking of lamellae during polymerization-induced self-assembly (PISA). Finally, reversible, temperature-induced morphological transitions from lamellae to worms/spheres on cooling were investigated by DLS, TEM, 1H NMR spectroscopy, and rheology. The kinetics of the temperature-dependent morphological transitions and the rheological properties could be tuned by the cross-linking density.

Polymerization-induced cooperative assembly (PICA) is developed to promote morphological transitions at high solids via RAFT dispersion polymerization, using both a macromolecular chain transfer agent (macro-CTA) and a small molecule chain transfer agent (CTA) to generate nano-objects consisting of well-defined block copolymer and homopolymer. PICA is demonstrated to promote morphological transitions under various conditions. Elemental mapping provides unambiguous evidence for the uniform distribution of the homopolymer within the core of the nano-objects. It is proposed that the growing homopolymer first reaches its solubility limit and forms aggregates, which induce the adsorption of the growing block copolymer. This effective and robust PICA approach significantly expands the capability to promote morphological transitions in RAFT dispersion polymerization and will facilitate the efficient synthesis of various higher-order morphologies at high solids.

Copolymerization has been widely used to tune the thermoresponsive behavior of water-soluble polymers. However, the observation of both upper and lower critical solution temperature (UCST and LCST) from the same type of copolymer comprising only one monomer whose homopolymer is thermosensitive and the other monomer whose homopolymer is nonthermosensitive has not been reported. In this work, well-defined thermoresponsive copolymers with tunable compositions have been synthesized by copolymerization of N-acryloylglycinamide (NAGA) and diacetone acrylamide (DAAM) via reversible addition–fragmentation chain transfer (RAFT) polymerization. The thermal transitions of these copolymers are investigated using a combination of turbidimetry, dynamic light scattering (DLS), proton nuclear magnetic resonance (1H NMR), and Fourier transform infrared (FTIR) spectroscopy. The solubility of these copolymers shows a distinct dependence on the composition. While copolymers with up to 30 mol % NAGA are essentially insoluble, copolymers with 35–55 mol % NAGA or 90–100 mol % NAGA have either LCST- or UCST-type transitions respectively, and soluble copolymers are obtained with 60–85 mol % NAGA. The LCST- and UCST-type transitions are tunable with respect to composition, degree of polymerization, polymer concentration, isotope effect and the presence of electrolyte. Insights from variable-temperature 1H NMR and FTIR spectroscopies reveal the key role of hydrogen-bonding between the NAGA and DAAM units in determining the thermal transitions.

A photocontrolled reversible addition–fragmentation chain transfer (RAFT) polymerization mediated by a supramolecular photoredox catalyst is reported. Cucurbit[7]uril (CB[7]) was used to form a host–guest complex with Zn(II) meso-tetra(4-naphthalylmethylpyridyl) porphyrin (ZnTPOR) to prevent aggregation of ZnTPOR, which in combination with a chain transfer agent (CTA) initiated efficient and controlled RAFT polymerization in water under visible light. RAFT polymerization was significantly affected by the subtle interplay of host–guest, electrostatic, and steric interactions among CB[7], ZnTPOR, and CTA. Polymerization rate was remarkably improved using CB[7]@ZnTPOR in comparison with that using ZnTPOR. The use of supramolecular interactions to modulate photocontrolled RAFT polymerization provides new opportunities to manipulate controlled radical polymerizations.

Polymerization-induced self-assembly (PISA) via reversible addition–fragmentation chain transfer (RAFT) dispersion polymerization is an effective method to produce block copolymer nano-objects of various morphologies at high solids. However, current PISA formulations have been limited to linear block copolymers. We report the synthesis of AB2 star block copolymers via RAFT aqueous dispersion polymerization of diacetone acrylamide using a poly(ethylene glycol) methyl ether bearing two chain transfer agents as the difunctional macromolecular chain transfer agent (macro-CTA), which was efficiently synthesized using 2,4,6-trichloro-1,3,5-triazine and activated esters to afford a high end functionality (97%). The star polymer architecture can significantly promote morphological transitions to obtain higher-order morphologies at both lower solids and lower degrees of polymerization of the core-forming block in comparison with its linear counterpart. This work demonstrates that polymer architecture is another important parameter that should be considered when conducting PISA synthesis to obtain complex morphologies.

AbstractSynthesis of well-defined multiblock and ultrahigh-molecular-weight (UHMW) polymers has been a perceived challenge for reversible-deactivation radical polymerization (RDRP). An even more formidable task is to synthesize these extreme polymers in the presence of oxygen. A novel methodology involving enzymatic cascade catalysis is developed for the unprecedented synthesis of multiblock polymers in open vessels with direct exposure to air and UHMW polymers in closed vessels without prior degassing. The success of this methodology relies on the extraordinary deoxygenation capability of pyranose oxidase (P2Ox) and the mild yet efficient radical generation by horseradish peroxidase (HRP). The facile and green synthesis of multiblock and UHMW polymers using biorenewable enzymes under environmentally benign and scalable conditions provides a new pathway for developing advanced polymer materials.

ABSTRACTA new methodology based on glucose oxidase (GOx) deoxygenation and hydrogen peroxide/vitamin C (H2O2/Vc) redox initiation for conducting RAFT polymerization at low temperature in air is reported. GOx catalyzes reduction of oxygen in the presence of glucose to generate hydrogen peroxide, which is directly used to constitute a redox pair with Vc for the efficient generation of hydroxyl radicals to initiate RAFT polymerization in air. Various experimental parameters including temperature, stirring speed, prepolymerization incubation time, and concentrations of Vc, glucose, and GOx were evaluated with respect to monomer conversion, molecular weight, and dispersity. Efficient removal of oxygen is typically realized within 10 min before polymerization is initiated by addition of Vc, and high conversions are achieved within 5 h. Well-defined homopolymers and block copolymers have been efficiently synthesized with high monomer conversions and low dispersities (< 1.2). Using this new methodology, it is possible to conduct controlled RAFT polymerizations in both open and sealed vessels, though lower conversions but less termination by oxygen are typically observed for the sealed systems. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 164–174

The distinct thermal transition behavior of thermoresponsive block polymers based on poly(ethylene glycol)methyl ether acrylate (PEGA) and their corresponding disulfide-cross-linked nanogels was studied by using FTIR measurements in combination with two-dimensional correlation spectroscopy (2Dcos). Spectral analysis clearly reveals that the sharp thermal transition of the precursor polymer is accompanied by a forced hydration process induced by the formation of hydrogen bonds between the entrapped water molecules and the CO groups, while the nanogel with a relatively continuous thermal transition is related to the existence of various dehydrating states of the CO groups. The C–H groups in the pyridyl disulfide (PDS) units exhibit a distinct change in the thermoresponsive profile of the precursor and the nanogel to show the effect of the polymer architecture on the thermal transition behavior. Additionally, a portion of the poly(N,N-dimethylacrylamide) (PDMA) segments is entrapped in the nanogel core, indicating that the thiol–disulfide exchange reaction occurs rapidly within the nanogels.

A series of well-defined core cross-linked star (CCS) polymeric ionic liquids (PILs) were synthesized via a three-step approach. First, the styrenic imidazole-based CCS polymer (S-PVBnIm) was prepared by the RAFT-mediated heterogeneous polymerization in a water/ethanol solution, followed by the quaternization of S-PVBnIm with bromoalkanes and anion exchange. The CCS polymers were characterized by gel permeation chromatography (GPC), nuclear magnetic resonance (NMR) spectroscopy, Fourier transform infrared spectroscopy (FTIR), thermal gravimetric analysis (TGA), and differential scanning calorimetry (DSC). The obtained CCS polymers were used as the effective emulsifiers for oil-in-water high internal phase emulsions (HIPEs). Multiple oils with different polarity including n-dodecane, undecanol, toluene and octanol were emulsified using 0.5 wt% S-PVBnIm aqueous solution under the acidic condition to form HIPEs with long-term stabilities. The excellent emulsification properties of CCS PILs were demonstrated by HIPE formation for a variety of oils. The properties of HIPEs in terms of emulsion type and oil droplet size were characterized by the confocal laser scanning microscopy (CLSM). The intriguing capability of CCS PILs to stabilize HIPEs of various oils holds great potentials for the practical applications.

In situ cross-linking of nano-objects with controllable morphologies in polymerization-induced self-assembly (PISA) has been a challenge because cross-linking lowers chain mobility and hence inhibits morphology transition. Herein, we propose a novel strategy that allows in situ cross-linking of vesicles in PISA in an aqueous dispersion polymerization formulation. This is realized by utilizing an asymmetric cross-linker bearing two vinyl groups of differing reactivities such that cross-linking is delayed to the late stage of polymerization when morphology transition has completed. Cross-linked vesicles with varying degrees (1–5 mol %) of cross-links were prepared, and their resistance to solvent dissolution and surfactant disruption was investigated. It was found that vesicles with ≥2 mol % cross-links were able to retain their structural integrity and colloidal stability when dispersed in DMF or in the presence of 1% of an anionic surfactant sodium dodecyl sulfate.

Polymerization-induced self-assembly (PISA) is a rapidly evolving method for the efficient preparation of well-defined nano-objects. PISA-generated nano-objects have been explored in this work for the responsive formation of multidomain hydrogels by thermally induced assembly of doubly thermoresponsive triblock terpolymer nanogels. The nanogels consist of a thermoresponsive poly(diethylene glycol ethyl acrylate) (PDEGA) outer block with a lower thermal transition temperature, a hydrophilic poly(N,N-dimethylacrylamide) (PDMA) midblock, and a N,N′-methylenebis(acrylamide) (BIS) cross-linked, thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) core block with a higher thermal transition temperature. The unique location of these two thermoresponsive blocks of differing transition temperatures in the PDEGA–PDMA–P(NIPAM-co-BIS) nanogels is rationally designed to facilitate room-temperature gelation and is synthetically realized via judicious selection of water–ethanol mixtures under dispersion polymerization conditions. The nanogels were characterized by turbidimetry, dynamic light scattering (DLS), and transmission electron microscopy (TEM). Gelation behavior of the nanogels was investigated by the inverted vial method as well as dynamic rheology sweeps. In comparison with PNIPAM–PDMA–P(DEGA-co-BIS) nanogel and a triblock terpolymer of similar composition, the PDEGA–PDMA–P(NIPAM-co-BIS) nanogels exhibit a good combination of gelation sensitivity and gel strength. The gelation ability, sensitivity, and mechanical properties are affected by the block ratios as well as the cross-linking density in the core of the nanogels.

We report emulsion studies using poly(vinylphenyl boronic acid) (PVPBA) linear homopolymer as an effective emulsifier and gelator. Two stabilizing regimes were identified depending on the pH of PVPBA aqueous solutions, i.e., emulsions stabilized by the hompolymer nanoparticles (Pickering emulsions) at pH < pKa and emulsions stabilized by the homopolymer unimers at pH > pKa. In both cases, gelled emulsions were obtained from medium to high internal phase volume fractions with the unimers exhibiting more effective emulsification and gelling properties. Hydrogen bonding between the boronic acid units is proposed to account for the high strength of the emulsions. The emulsions were shown to be pH- and sugar-responsive. Finally, the stable emulsions were used as templates to directly prepare PVPBA macroporous materials and to fabricate multilayered capsules. This remarkable observation that a simple homopolymer can serve as an effective emulsifier and gelator may dramatically extend the scope of potential emulsifiers and inspire further research in the design of new types of efficient emulsifying agents.Keywords: emulsions; gels; H bonding; interfaces; polymers

Efficient synthesis of functionalized, uniform polymer nano-objects in water with controlled morphologies in one step and at high concentrations is extremely attractive, from perspectives of both materials applications and industrial scale-up. Herein, we report a novel formulation for aqueous reversible addition–fragmentation chain transfer (RAFT) dispersion polymerization based on polymerization-induced self-assembly (PISA) to synthesize ketone-functionalized nanospheres and vesicles. Significantly, the core-forming block was composed entirely of a ketone-containing polymer from a commodity monomer diacetone acrylamide (DAAM), resulting in a high density of ketone functionality in the nano-objects. Producing uniform vesicles represents another challenge both in PISA and in the traditional self-assembly process. Aiming at producing uniform nano-objects, especially vesicles, in such a highly efficient aqueous PISA process, we devised strategies to allow sufficient time for the in situ generated polymers to relax and reorganize into vesicles with a remarkably low polydispersity. Specifically, both reducing the radical initiator concentration and lowering the polymerization temperature were shown to be effective for improving the uniformity of vesicles. Such an efficient, aqueous PISA to produce functionalized and uniform nano-objects with controlled morphologies at solid contents up to 20% represents important progress in the field.

Biocatalysis is promising for sustainable production of polymers. Enzyme-initiated reversible addition–fragmentation chain transfer (RAFT) polymerization is reported. Horseradish peroxidase (HRP) catalyzes oxidation of acetylacetone (ACAC) by hydrogen peroxide to generate ACAC radicals, which in the presence of a suitable chain transfer agent initiate efficient and well-controlled RAFT polymerization in aqueous buffer solution at room temperature. The versatility of HRP-initiated RAFT polymerization was demonstrated by controlled polymerization of a wide range of monomers, including both more and less activated monomers, under a variety of conditions, including both homogeneous solution polymerization and heterogeneous dispersion polymerization conditions. In all cases, the polymerization afforded excellent pseudo-first-order kinetics, predictable molecular weights, and narrow molecular weight distributions. Operation via RAFT mechanism of this HRP-initiated polymerization was confirmed by a combination of MALDI-ToF, NMR, and UV–vis as well as by chain extension to make well-defined block copolymers. The mildness, specificity, and biocompatibility of HRP-initiated RAFT polymerization were illustrated by controlled polymerization in undiluted fetal bovine serum (FBS) solution. RAFT polymerization initiated by glucose oxidase (GOx)–HRP enzymatic cascade catalysis was developed, opening up a new avenue to potential green synthesis of precision polymers by controlled radical polymerization in air.

Reversible addition–fragmentation chain transfer (RAFT) dispersion polymerization in cononsolvents of poly(N-isopropylacrylamide) (PNIPAM) was developed as a versatile strategy for the synthesis of thermoresponsive nanogels with controlled composition, functionality and architecture. Cononsolvents composed of mixtures of methanol, ethanol and isopropanol with water were first screened for their suitability as the media for dispersion polymerization of NIPAM, and water–ethanol (75:25, v:v) solution was selected due to good RAFT control, efficient formation of nanogels and low toxicity. RAFT dispersion polymerization of NIPAM in the cononsolvent using poly(N,N-dimethylacrylamide) (PDMA) as the macromolecular chain transfer agent (Macro-CTA) showed good control over the molecular weight, polydispersity and pseudo linear polymerization kinetics, as characterized by gel permeation chromatography (GPC) and 1H NMR. The effect of the molecular weight of Macro-CTA, the degree of polymerization of PNIPAM, the molar ratio of [crosslinker]:[Macro-CTA] and the solid content on the formation and size of nanogels was investigated. The thermal profiles of nanogels were characterized by dynamic light scattering (DLS) both in cononsolvents and water. This cononsolvency strategy for dispersion polymerization was shown to be compatible with the incorporation of hydrophilic comonomers of N-(2-hydroxyethyl)acrylamide (HEAM) and diacetone acrylamide (DAAM). The nanogel containing DAAM was demonstrated for postpolymerization modification using ketone–alkoxyamine chemistry. More importantly, dispersion polymerization in cononsolvents allowed various hydrophobic components, e.g. butyl acrylate (BA), fluorescein O-acrylate (FLA), and 1,6-hexanediol diacrylate (HDDA), to be reliably copolymerized with NIPAM, showing well controlled polymerization, composition, nanogel size and colloidal stability. Finally, an amphiphilic block copolymer PDMA-b-PBA was used as a Macro-CTA to produce the PDMA-b-PBA-b-PNIPAM triblock copolymer and triple-layered nanogel, taking advantage of the solubility of PDMA-b-PBA and the insolubility of PNIPAM in the water–ethanol solution at the polymerization temperature.

We have developed a highly efficient, one-step approach for the synthesis of core cross-linked star (CCS) polymers using commercial macromonomers (polyethylene glycol methyl ether methacrylates) as the arms via RAFT-mediated emulsion polymerization in aqueous media. This approach employs a small molecular chain transfer agent (CTA), commercial macromonomer, hydrophobic cross-linker, and optional hydrophobic spacing monomer as the polymerization recipe to synthesize CCS polymers via direct one-step polymerization in aqueous buffer solution. Various polymerization parameters, including buffer concentration and molar ratio of macromonomer/cross-linker/spacing monomer relative to CTA, were investigated. CCS polymers of high yield and low dispersity were obtained within 4 h under a wide range of conditions. Analysis of polymerization kinetics and macromolecular parameters of the generated polymeric species during the polymerization process led to insights into the mechanistic aspects of the CCS formation process, which was proposed to involve three stages, i.e., polymer chain growth, cross-linking to form CCS, and CCS growth. Finally, synthesis of CCS polymers using macromonomers of different molecular weights pointed to the necessity for optimization of the polymerization conditions for each macromonomer, possibly due to different polymerization rates and steric hindrance.

A series of five core cross-linked star (CCS) polymers has been synthesized by RAFT-mediated heterogeneous polymerization in aqueous media. These CCS polymers consist of poly(MEAx-co-PEGAy) (MEA is 2-methoxyethyl acrylate and PEGA is poly(ethylene glycol) acrylate) of different compositions. They exhibit responsiveness to both temperature and salt. Addition of kosmotropes reduces the cloud point, and addition of chaotropes raises the cloud point. These CCS polymers can stabilize dodecane-in-water high internal phase emulsions (HIPEs) in the absence or presence of salts. Addition of salts has negligible effect on the maximum oil fraction, the size of oil droplets or the stability of the HIPEs. HIPEs with large oil fractions (up to 92 vol%) at low concentrations of CCS polymers (≤1 wt%) can be routinely obtained. When the oil volume fraction is larger than 74 vol%, gelled HIPEs are formed with long-term stabilities (more than three months). The temperature and salt responsiveness of the CCS polymers is transferred to the CCS-stabilized HIPEs. Addition of kosmotropes can enhance demulsification efficiency, while addition of chaotropes can decrease demulsification efficiency or enhance the thermal stability of the CCS-stabilized HIPEs. The emulsification–demulsification cycle can be successfully repeated four times. The facile and aqueous synthesis of CCS polymers and the fast response of the CCS-stabilized HIPEs will open up new opportunities for the preparation and exploitation of a range of smart soft materials.

Efficient preparation of multifunctional nano-objects with controlled morphologies in one step at high concentrations is synthetically challenging, yet is highly desirable, in a broad range of materials applications. Herein, we address this synthetic hurdle by introducing a single commodity monomer 2-(acetoacetoxy)ethyl methacrylate (AEMA) to realize multiple functions. Facile preparation of both nanospheres and vesicles via polymerization induced self-assembly at concentrations of 20–30% provided defined polymeric nanomaterials with reactive handles inherent to the AEMA units. High-yielding keto-alkoxylamine chemistry was utilized to decorate and cross-link the nano-objects. Nanoparticle loading into the designated location within both nano-objects was exemplified with in situ formation of silver nanoparticles. The concept of using a single monomer capable of both morphology control and multifunctionalization is expected to offer significant opportunities in functional nanomaterials.

Nanogels have been well recognized as biocompatible nanomaterials for biomedical applications. Although synthesis of nanogels has been well established, challenges still exist for preparation of advanced nanogels with delicate structures and novel properties to fulfil their role in medical applications. Current research focuses on development of nanogels with multiple responsiveness and novel responsive mechanisms for nanogels to interact with biological microenvironments, development of versatile synthetic strategies for the preparation of multifunctional nanogels that can realize the multifold tasks required for nanogels to function as nanomedicine, and promotion of use of mild/biocompatible enzymatic reactions to potentially impart specificity and selectivity in nanogel synthesis. This mini-review highlights most recent work (mostly over the past two years) in the field of nanogels, and defines the frontiers in the design and synthesis of advanced nanogels for nanomedicine.

The volume phase transition behavior of well-defined thermally responsive poly(2-methoxyethyl acrylate-co-poly(ethylene glycol) methyl ether acrylate)/poly(N,N′-dimethylacrylamide) (P(MEA-co-PEGA)/PDMA) and poly(N-isopropylacrylamide)/poly(N,N′-dimethylacrylamide) (PNIPAM/PDMA) core–shell nanogels, synthesized via reversible addition–fragmentation chain transfer (RAFT) mediated aqueous dispersion polymerization, is studied and compared by applying FTIR measurements in combination with two-dimensional correlation spectroscopy (2Dcos). Analysis through spectral insights clearly illustrates that the continuous dehydration of the C═O groups in the P(MEA-co-PEGA)/PDMA nanogel core predominates the linear volume phase transition while the hydrogen bonding transformation in the PNIPAM/PDMA nanogel core leads to the abrupt decrease in nanogel size on heating. Additionally, considering the core and the shell separately, the data shows that, for both nanogels, the inner core contributes much more to the volume phase transition and the outer shell only undergoes slight dehydration following the core on heating.

Well-defined core cross-linked star (CCS) polymers of poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) were prepared via cross-linking copolymerization in an aqueous-based dispersion polymerization system, mediated by reversible addition–fragmentation chain transfer (RAFT) polymerization. The synthesized CCS polymers were characterized by nuclear magnetic resonance (NMR) spectroscopy, gel permeation chromatography (GPC), dynamic light scattering (DLS), and conductivity and zeta potential measurements. The use of PDMAEMA CCS polymers as effective emulsifiers for oil-in-water emulsions was investigated. Interfacial tension measurements showed that the CCS polymer reduced the interfacial tension between water and oil in a pH-dependent manner. Gelled high internal phase emulsions (HIPEs) were formed at high oil fractions (80–89 vol%) and over a wide range of pH values (2–12). The HIPEs were characterized by conductivity, confocal laser scanning microscopy (CLSM) and rheology. The emulsion properties in terms of oil droplet size, long-term stability and rheology were pH-dependent. Complete demulsification of HIPEs was easily realized 2 min after the addition of base. The CCS-stabilized HIPEs were used as templates to prepare porous hydrophilic polymers by polymerizing the monomers in the continuous aqueous phase. The study presented herein reveals that responsive CCS polymers can be used as effective stabilizers for the formation of responsive HIPEs, which have a wide range of applications.

Homoarm and heteroarm core cross-linked star (CCS) polymers based on poly(N,N-dimethylacrylamide) (PDMA) as the high-polarity arm and poly(2-methoxyethylacrylate) (PMEA) as the low-polarity arm were efficiently prepared via reversible addition-fragmentation chain transfer (RAFT) polymerization in a dispersion polymerization system. PDMA and PMEA arm polymers exhibited similar conversion rates, such that their composition in the heteroarm CCS polymers was easily controlled by the feed ratio in the synthesis. The ability to control the arm composition allowed facile tuning of the polarity of the CCS polymers. Heteroarm CCS polymers self-assembled in water to form aggregates and their size was related to the composition and polarity of the CCS polymers. The composition and polarity of the CCS polymers significantly affected the emulsifying behaviour of the CCS polymers as emulsifiers. Oil-in-water (o/w) emulsions were favoured for CCS polymers with relatively high polarity and lowering the polarity of CCS polymers to a certain degree enhanced the stability of the emulsions. Multiple emulsions, both o/w and water-in-oil (w/o), were gradually produced when the polarity of CCS polymers was gradually lowered and the oil fraction in the emulsion samples was gradually increased, and at the same time the emulsions also became increasingly less stable.

Core cross-linked star (CCS) polymers of poly(N,N-dimethylacrylamide) (PDMA) were prepared and explored as macromolecular chain transfer agents (Macro-CTAs) in the emulsion polymerization of styrene. The mass ratio of styrene:CCS and the solid content were systematically varied to elucidate their effect on the size and morphology of the particles. Control experiments using linear PDMA as a Macro-CTA were also performed in order to understand the mechanistic difference in CCS-mediated emulsion polymerization. While a two-phase process was typical of emulsion polymerization using linear Macro-CTAs, the CCS polymers functioned as “seeds” for the emulsion polymerization of styrene and exhibited a much higher polymerization rate. Significant clustering of spherical particles was observed when the mass ratio of styrene:CCS was increased while maintaining the solid content. On the other hand, linear and branched fibers were observed when the solid content was increased while maintaining the mass ratio of styrene:CCS. This morphology transformation is unique to CCS-mediated emulsion polymerization, and a protrusion mechanism caused by the cross-links in the core of the CCS was proposed to account for the aggregation of spherical particles into clusters or fibers.

Well-defined amphiphilic heteroarm core cross-linked star (CCS) polymer was efficiently synthesized by RAFT-mediated arm-first strategy in dispersion polymerization, and its direct self-assembly in water was demonstrated.

Thermosensitive polymeric materials based on copolymers of oligo(ethylene glycol) methacrylates are attracting significant attention in various materials sectors. The preparation of their thermosensitive microgels/nanogels via the aqueous dispersion polymerization process is, however, limited by low monomer loading and thus low solid content of the final colloids. Moreover, the preparation of nanogels by reversible addition-fragmentation chain transfer (RAFT) mediated dispersion polymerization has been further hampered by the poor RAFT control of the polymerization process. In this article, we report the development of thermosensitive copolymers based on poly(2-methoxyethyl acrylate-co-poly(ethylene glycol) methyl ether acrylate) (P(MEA-co-PEGA)) and their use for nanogel synthesis by RAFT dispersion polymerization in water. The thermosensitive copolymers exhibited sharp thermal transitions upon increasing thee temperature above their lower critical solution temperature. The use of MEA as the majority comonomer and poly(N,N′-dimethylacrylamide) as the RAFT agent and stabilizer for the synthesis of nanogels allowed monomer loadings of up to 20%, which significantly improved the solid content of the dispersion polymerization system. Moreover, the dispersion copolymerization of MEA with PEGA was under excellent RAFT control up to complete monomer conversion. The synthesized nanogels showed an unprecedented linear relationship between nanogel size and temperature, suggesting expanded applications of such responsive polymeric materials.

Nanogel synthesis by RAFT polymerization is an emerging field for the control of architectures and functions of polymeric nanomaterials for bioapplications. In this Feature Article, we review the recent development in nanogel synthesis using preformed RAFT polymers and by direct RAFT polymerizations.

Core cross-linked star polymers of low polydispersity were efficiently prepared in high yield by RAFT-mediated emulsion and dispersion polymerizations in water at high solid content. These star polymers were demonstrated to be effective emulsifiers, and the emulsion was successfully used as template to fabricate polymer particles.

Reversible addition−fragmentation chain transfer (RAFT) aqueous dispersion polymerization was used to synthesize a novel type of core−shell nanogel containing linear poly(ethylene glycol) (PEG) and/or nonlinear polymers with oligo(ethylene glycol) side chains. These nanogels with low polydispersities were synthesized efficiently with tunable sizes and thermosensitivities. The nanogels containing nonlinear polymers with oligo(ethylene glycol) side chains as the shell had enhanced stability during freeze−thawing process and in biologically relevant solutions including 1.5 M NaCl, 1% bovine serum albumin (BSA) and 100% fetal bovine serum (FBS) solutions. Aminolysis and hydrolysis of the chain transfer agents (CTAs) in the nanogels were studied and the nanogels exhibited enhanced stability in comparison with molecularly dissolved polymers. The chemical stability of the CTAs in the nanogels was well-correlated with the in vitro cell viability studies of the nanogels using lung cancer cells.

Aqueous dispersion polymerization systems mediated by reversible addition–fragmentation chain transfer (RAFT) process have been less studied in comparison with other heterogeneous polymerization systems due to limited number of monomer/polymer pairs that are suitable for such a condition. We report a novel dispersion polymerization system based on 2-methoxyethyl acrylate (MEA) which is highly water-soluble, but its polymer is not. Using a hydrophilic polymer, poly(poly(ethylene glycol) methyl ether methacrylate) (PPEGMA), as the macromolecular chain transfer agent (Macro-CTA), both solution and dispersion polymerization of MEA were studied. Chain extension by MEA from PPEGMA was successfully realized in DMF solution polymerization. In dispersion polymerization of MEA in water, PPEGMA was used as both a RAFT mediating species and a steric stabilizer for the formed nanoparticles. The dispersion polymerization of MEA in water was highly efficient using a redox initiator, potassium persulfate/sodium ascorbate, at low temperatures. Simultaneous control of both colloidal stability and RAFT process was realized. Block copolymers with small polydispersity indices were efficiently produced up to complete monomer conversion at solids content up to 32% w/v, in the form of nanoparticles of 40–60 nm diameter.

A convenient methodology involving cascade aminolysis/Michael addition and alkyne–azide click reaction was developed for polymers and polymeric core–shell nanoparticles, synthesized via RAFT-mediated homogeneous and heterogeneous polymerisation processes, respectively, to provide well-defined heterofunctional polymeric materials.

A convenient methodology involving cascade aminolysis/Michael addition and alkyne–azide click reaction was developed for polymers and polymeric core–shell nanoparticles, synthesized via RAFT-mediated homogeneous and heterogeneous polymerisation processes, respectively, to provide well-defined heterofunctional polymeric materials.

Well-defined amphiphilic heteroarm core cross-linked star (CCS) polymer was efficiently synthesized by RAFT-mediated arm-first strategy in dispersion polymerization, and its direct self-assembly in water was demonstrated.

Core cross-linked star polymers of low polydispersity were efficiently prepared in high yield by RAFT-mediated emulsion and dispersion polymerizations in water at high solid content. These star polymers were demonstrated to be effective emulsifiers, and the emulsion was successfully used as template to fabricate polymer particles.

Nanogel synthesis by RAFT polymerization is an emerging field for the control of architectures and functions of polymeric nanomaterials for bioapplications. In this Feature Article, we review the recent development in nanogel synthesis using preformed RAFT polymers and by direct RAFT polymerizations.