Inverse Miniemulsion Periphery RAFT Polymerization: A Convenient Route to Hollow Polymeric Nanoparticles with an Aqueous Core

Carboxy-Functionalized pH Responsive Capsule Polymer Particles Fabricated by Particulate Interfacial Photocrosslinking

pH-responsive capsule particles show promise for various applications, such as self-healing materials, micro/nanoreactors, and drug delivery systems. Herein, carboxy-functionalized capsule polymer particles possessing neutral-alkali pH responsive controlled release capability were...

Core–shell Microgels Having Zwitterionic Hydrogel Core and Temperature-responsive Shell Prepared via Inverse Miniemulsion RAFT Polymerization

Stimuli-responsive core–shell microgels are of significant interest because of their fascinating applications due to the different swelling/shrinkage properties of their core and shell networks. Because such stimuli-responsive core–shell microgels are...

Interfacial Photo-Cross-Linking: Simple but Powerful Approach for Fabricating Capsule Polymer Particles with Tunable pH-Responsive Controlled Release Capability

Herein, we describe capsule polymer particles with precisely controlled pH-responsive release properties prepared directly via the interfacial photo-cross-linking of spherical poly(2-diethylaminoethyl methacrylate-co-2-cinnamoylethyl methacrylate) (P(DEAEMA-CEMA)) particles. In the interfacial photo-cross-linking, photoreactive cinnamoyl groups in the polymer particles were cross-linked via [2π + 2π] cycloaddition reactions at the polymer/water interface, showing that the shell-cross-linked hollow polymer particles can be directly prepared from spherical polymer particles. The approach has fascinating advantages such as using minimal components, simplicity, and not requiring sacrificial template particles and toxic solvents. The following important observations are made: (I) encapsulated materials were stably retained in the capsule particles under neutral pH conditions; (II) encapsulated materials were released from the capsule particles under acidic pH conditions; (III) the release kinetics of encapsulated materials were controlled by the pH conditions; i.e., immediate and sustained release was achieved by varying the acidity of the aqueous media; (IV) the photoirradiation time did not significantly affect the release kinetics under different pH conditions; and (V) the pH-responsive release properties were regulated by changing the polymer composition in P(DEAEMA-CEMA). Furthermore, by exploiting the pH-responsiveness, capsule particles are successfully obtained via an all-aqueous process from spherical polymer particles. The advantages of the all-aqueous encapsulation process allowed the water-soluble biomacromolecules such as DNA and saccharides to be successfully encapsulated in the P(DEAEMA-CEMA) hollow particles. With this simple interfacial photo-cross-linking strategy, we envision the ready synthesis of sophisticated particulate materials for broad application in advanced research fields.

Facile synthesis of micron-size Janus particles by one-pot suspension polymerization and their functional modification

A novel strategy for preparing micron-size Janus particles with easily-functionalized surfaces was established by one-pot W/O/W-type suspension polymerization for the first time.

Cross-Linker-Controlled Ostwald Ripening in Emulsion Polymerization of Hollow Copolymer Nanoparticles

We propose a synthesis method for hollow copolymer nanoparticles, in which the size is controllable by the wettability of the materials designed by relative energy difference (RED). We investigated the influence of cross-linkers in RED and the hollow polymer nanoparticle synthesis. The size of the nanoparticles was characterized by scanning electron microscopy and transmission electron microscopy images. The diameter size of the hollow copolymer (styrene-co-methyl methacrylate) changes from 400 to 141 nm and the average core-vacancy sizes changes from 330 to 71 nm as increasing the feed ratio of the cross-linker, divinyl benzene, from 0.07 to 0.43. Cross-linkers in polymerization precipitates a polymerization reaction to produce seed copolymer particles quickly. The seed copolymer is a more transferrable medium through the surfactants across emulsion droplets and inhibits emulsion growth by unstable concentration variations of seed copolymers in emulsions. Therefore, Ostwald ripening was reduced by a higher feeding ratio of the cross-linker in the copolymer, which tends to produce smaller sized hollow nanoparticles.

Size-Controllable, Single-Step, and Scalable Synthesis of Hollow Polymer Nanoparticles

Hollow polymer nanoparticles are of great importance in various industrial fields such as drug delivery vehicles in pharmaceutics, high thermal insulation materials for heat flow blocking and energy savings, and materials with unique optical properties. While the fabrication methods for hollow polymer nanoparticles have been studied and developed by numerous researchers, most synthesis methods require a rather complicated process, including a thorough core-washing step to formulate pores inside the particles. Single-step synthesis methods were developed to overcome this practical issue by utilizing the sacrificial solvent filling the pores temporarily and having it naturally evaporate without further process; however, such processes could not produce sub-200 nm diameter particles, which limit the application for high surface area applications. Herein, we have developed an innovative synthesis method that can overcome the particle size limitation by utilizing a sacrificial solvent for pore formation and a recondensation inhibitor. Pseudo-state Ostwald ripening was realized by selecting the sacrificial solvent with less affinity to the copolymer of hollow polymer particles, thus inhibiting the particle growth during polymerization. We have successfully obtained 120 nm diameter hollow PS-PMMA copolymer particles in large quantity via the single-step preparation of emulsion polymerization.

Facile fabrication of shell crosslinked microcapsule by visible light induced graft polymerization for enzyme encapsulation

A strategy to encapsulate enzymes into microcapsule fabricated by visible light-induced graft polymerization using CaCO₃microparticles as template was developed.

Miniemulsion polymerization using carboxylated graphene quantum dots as surfactants: effects of monomer and initiator type

The effectiveness of carboxylated graphene quantum dots (cGQDs) as sole surfactants have been investigated in miniemulsion polymerization of 8 different vinyl monomers, initiated by oil-soluble initiator AIBN and water-soluble initiator VA-044.

Magnetic Polyurea Nano-Capsules Synthesized via Interfacial Polymerization in Inverse Nano-Emulsion

Polyurea (PU) nano-capsules have received voluminous interest in various fields due to their biocompatibility, high mechanical properties, and surface functionality. By incorporating magnetic nanoparticle (MNPs) into the polyurea system, the attributes of both PU and MNPs can be combined. In this work, we describe a facile and quick method for preparing magnetic polyurea nano-capsules. Encapsulation of ionic liquid-modified magnetite nanoparticles (MNPs), with polyurea nano-capsules (PU NCs) having an average size of 5–20 nm was carried out through interfacial polycondensation between amine and isocyanate monomers in inverse nano-emulsion (water-in-oil). The desired magnetic PU NCs were obtained utilizing toluene and triple-distilled water as continuous and dispersed phases respectively, polymeric non-ionic surfactant cetyl polyethyleneglycol/polypropyleneglycol-10/1 dimethicone (ABIL EM 90), diethylenetriamine, ethylenediamine diphenylmethane-4,4′-diisocyanate, and various percentages of the ionic liquid-modified MNPs. High loading of the ionic liquid-modified MNPs up to 11 wt% with respect to the dispersed aqueous phase was encapsulated. The magnetic PU NCs were probed using various analytical instruments including electron microscopy, infrared spectroscopy, X-ray diffraction, and nuclear magnetic spectroscopy. This unequivocally manifested the successful synthesis of core-shell polyurea nano-capsules even without utilizing osmotic pressure agents, and confirmed the presence of high loading of MNPs in the core.

Emulsion and miniemulsion techniques in preparation of polymer nanoparticles with versatile characteristics

In recent years, polymer nanoparticles (PNPs) have found their ways into numerous applications extending from electronics to photonics, conducting materials to sensors and medicine to biotechnology. Physical properties and surface morphology of PNPs are the most important parameters that significantly affect on their exploitations and can be controlled through the synthesis process. Emulsion and miniemulsion techniques are among the most efficient and wide-spread methods for preparation of PNPs. The objective of this review is to present and highlight the recent developments in the advanced PNPs with specific properties that are produced through emulsion and miniemulsion processes.

Nanovoid Membranes Embedded with Hollow Zwitterionic Nanocapsules for a Superior Desalination Performance

In order to lower the capital and operational cost of desalination and wastewater treatment processes, nanofiltration (NF) membranes need to have a high water permeation and ionic rejection, while also maintaining a stable performance through antifouling resistance. Recently, Turing-type reaction conditions [ Science 2018, 360, 518-521] and sacrificed metal organic frame (MOF) nanoparticles [ Nat. Commun. 2018, 9, 2004] have been reported to introduce nanovoids into thin-film composite (TFC) polyamide (PA) NF membranes for an improved performance. Herein, we report a one-step fabrication of thin-film nanocomposite membranes (TFNM) with controllable nanovoids in the polyamide layer by introducing hollow zwitterionic nanocapsules (HZN_Cs) during interfacial polymerization. It was found that embedding HZN_Cs increases the membrane internal free volume, external surface area, and hydrophilicity, thus enhancing the water permeation and antifouling resistance without trading off the rejection of multivalent ions. For example, water permeation of the NF membranes embedded with about 19.0 wt % of HZN_Cs (73 L m^-2 h^-1) increased by 70% relative to the value of the control TFC NF membrane without HZN_Cs (43 L m^-2 h^-1). This increase comes while also maintaining 95% rejection of Na₂SO₄. Further, we also determined the effect of the mass loading of HZN_Cs on the top surface of the TFC NF membranes on the membrane performance. This work provided a direct and simple route to fabricate advanced desalination membranes with a superior separation performance.

Reductively Responsive Gel Capsules Prepared Using a Water-Soluble Zwitterionic Block Copolymer Emulsifier

Utilizing the unique solubility of poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC), which is soluble in only water and alcohol, we synthesized a water-soluble block copolymer emulsifier composed of a hydrophilic PMPC block and an amphiphilic poly[oligo(ethylene glycol) methacrylate] (POEGMA) block via reversible addition-fragmentation chain transfer (RAFT) polymerization. Water-in-oil (W/O) emulsions were successfully formed in the presence of the resulting PMPC- b-POEGMA, which acted as a stabilizer of water droplets in a chloroform continuous phase because the PMPC and POEGMA blocks were distributed to the water and chloroform phases, respectively. Next, the amphiphilic poly[poly(ethylene glycol) methacrylate] (PPEGMA) gel layer, which contained bis(2-methacryloyl)oxyethyl disulfide as a reductively responsive cross-linker, was prepared by inverse miniemulsion periphery RAFT polymerization from the PMPC- b-POEGMA that stabilized the W/O emulsions. The resulting PPEGMA gel capsules were colloidally stable in not only chloroform but also water without additional hydrophilic surface modification. The drug-release behavior from the PPEGMA gel capsules in response to dithiothreitol (DTT), which is a reducing agent, was investigated using fluorescein-conjugated dextran (FITC-Dex) as a model drug. The FITC-Dex release rate from the gel capsules in a phosphate buffer solution (pH 7.4, 20 mM) with DTT was fast compared to that without DTT. The reductively responsive FITC-Dex release is attributed to the cleavage of disulfide bonds that act as cross-links in the PPEGMA gel layer. The fascinating properties of the PPEGMA gel capsules suggest that they can provide a useful platform for designing drug carriers for protein and gene delivery and nanobioreactors.

Nanoencapsulation of phase change materials for advanced thermal energy storage systems

Phase change materials (PCMs) allow the storage of large amounts of latent heat during phase transition. They have the potential to both increase the efficiency of renewable energies such as solar power through storage of excess energy, which can be used at times of peak demand; and to reduce overall energy demand through passive thermal regulation. 198.3 million tons of oil equivalent were used in the EU in 2013 for heating. However, bulk PCMs are not suitable for use without prior encapsulation. Encapsulation in a shell material provides benefits such as protection of the PCM from the external environment and increased specific surface area to improve heat transfer. This review highlights techniques for the encapsulation of both organic and inorganic PCMs, paying particular attention to nanoencapsulation (capsules with sizes <1 μm). We also provide insight on future research, which should focus on (i) the development of multifunctional shell materials to improve lifespan and thermal properties and (ii) advanced mass manufacturing techniques for the economically viable production of PCM capsules, making it possible to utilize waste heat in intelligent passive thermal regulation systems, employing controlled, "on demand" energy release/uptake.

CO2 switchable hollow nanospheres

HYPOTHESIS

Hollow nanospheres, characterized by a cavity inside a solid shell, have potential applications due to their unique structure, but the unchangeable morphology and permeability of the shell restrain their further practical utilization. While several smart hollow nanospheres that can respond to pH, ion strength, and temperature have been developed, they are inclined to suffer from problems associated with high energy consumption or the difficult removal of residual stimulants. Thus, it is desirable to develop a novel and free-of-residual trigger stimulating mode.

EXPERIMENTS

In this work, CO₂ is used to fabricate smart hollow nanospheres composed of crosslinked poly(diethylamino-ethyl methacrylate) (PDEAEMA) network from polystyrene (PS)/PDEAEMA core-shell nanospheres by a template-removal technique. The morphology evolution of the resultant nanospheres during the fabrication process was characterized by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), thermogravimetry analysis (TGA) and dynamic light scattering (DLS) and was visualized by transmission electron microscopy (TEM) and scanning electron microscopy (SEM).

FINDINGS

Hollow nanospheres can be generated by experiencing a morphology change from a core nanosphere, core-shell, yolk-shell to a final hollow structure. The increase in shell-stiffness can restrain the collapse of hollow spheres. It is demonstrated that CO₂ is easy to introduce and remove (via N₂ input) without stimulation residues in this system. In addition, mild CO₂/N₂ purging can only reversibly change the swelling/collapse of hollow particles; violent CO₂/N₂ bubbling can reversibly regulate both the size and aggregation/re-dispersion state of the hollow nanospheres, which can be intuitively observed by atomic force microscopy (AFM).

Fabrication of polymer capsules by an original multifunctional, active, amphiphilic macromolecule, and its application in preparing PCM microcapsules

Based on our recent discovery that D-PGMA solution showed excellent amphiphilic and reinitiation properties, an eco-friendly, facile and scalable method to prepare polymeric capsules was proposed.

A facile route to segmented copolymers by fusing ambient temperature step-growth and RAFT polymerization

We introduce the facile synthesis of segmented copolymers by a catalyst-free Diels-Alder (DA) reaction at ambient temperature via step-growth and subsequent reversible addition fragmentation chain transfer (RAFT) polymerization. High molecular weight step-growth polymers are readily obtained (M_w = 40 000 g mol^-1), featuring trithiocarbonate moieties in their chain, which allow monomer insertion via RAFT polymerization yielding high molecular weight species.

PEO-based brush-type amphiphilic macro-RAFT agents and their assembled polyHIPE monolithic structures for applications in separation science

Polymerized High Internal Phase Emulsions (PolyHIPEs) were prepared using emulsion-templating, stabilized by an amphiphilic diblock copolymer prepared by reversible addition fragmentation chain transfer (RAFT) polymerization. The diblock copolymer consisted of a hydrophilic poly(ethylene glycol) methyl ether acrylate (PEO MA, average Mn 480) segment and a hydrophobic styrene segment, with a trithiocarbonate end-group. These diblock copolymers were the sole emulsifiers used in stabilizing "inverse" (oil-in-water) high internal phase emulsion templates, which upon polymerization resulted in a polyHIPE exhibiting a highly interconnected monolithic structure. The polyHIPEs were characterized by FTIR spectroscopy, BET surface area measurements, SEM, SEM-EDX, and TGA. These materials were subsequently investigated as stationary phase for high-performance liquid chromatography (HPLC) via in situ polymerization in a capillary format as a 'column housing'. Initial separation assessments in reversed-phase (RP) and hydrophilic interaction liquid chromatographic (HILIC) modes have shown that these polyHIPEs are decorated with different microenvironments amongst the voids or domains of the monolithic structure. Chromatographic results suggested the existence of RP/HILIC mixed mode with promising performance for the separation of small molecules.

Hollow polymer particles: a review

Herein, the basic principles, such as the definitions, classifications, and properties, of hollow polymer particles (HPPs) are critically investigated.

Hollow Casein-Based Polymeric Nanospheres for Opaque Coatings

Casein-based hollow polymeric sphere were fabricated through emulsifier-free polymerization coupled with alkali swelling approach. Hollow structure and nanoscale size of casein-based polymeric spheres were verified by TEM, AFM, SEM, and UV-vis spectra. The as-obtained hollow spheres were proved exhibiting superior opaque characteristic. Through adjusting the structural parameters, for example, MAA usages and MAA content in seed to core, sphere film showed tunable visible-light transmittance and antiultraviolet property. The formation mechanism of casein-based hollow sphere has been discussed in depth. Worth mentioning, the resultant hollow polymeric sphere can easily form films itself at room temperature, which would open a new possibility of designing opaque coatings in several fields, such as leather, packaging, paper making, biomedical, and special indoor coating applications.

Preparation of inverse polymerized high internal phase emulsions using an amphiphilic macro-RAFT agent as sole stabilizer

Oil-in-water (‘inverse’) High Internal Phase Emulsions (HIPEs) have been prepared using an amphiphilic macro-RAFT agent with toluene as the internal dispersed phase (∼80 vol%) and an aqueous monomer solution as the continuous phase.

Synthesis of microcapsules using inverse emulsion periphery RAFT polymerization via SPG membrane emulsification

Synthesis of polymeric capsules with good control over the particle size and size distribution is demonstratedviaa novel approach involving SPG membrane emulsification.

Synthesis of crosslinked polymeric nanocapsules using catanionic vesicle templates stabilized by compressed CO2

The synthesis of polymeric nanocapsules in the approximate diameter range 40-100 nm (TEM/SEM) using catanionic surfactant vesicle templates stabilized by subcritical CO2 is demonstrated. Near equimolar aqueous solutions of the surfactants sodium dodecyl sulfate (SDS) and dodecyltrimethylammonium bromide (DTAB) experienced immediate vesicle destabilization and precipitation in the absence of CO2. However, pressurization with CO2 (5 MPa) dramatically enhanced the stability of the initial vesicles, and enabled swelling of the bilayers with hydrophobic monomers via diffusion loading (loading of monomers into preformed bilayers). Subsequent radical crosslinking polymerization of the monomers n-butyl methacrylate/tert-butyl methacrylate/ethylene glycol dimethacrylate contained within the bilayers was conducted at room temperature using UV-initiation under CO2 pressure. The hollow structure of the resultant nano-objects was confirmed by successful encapsulation and retention of the dye Nile Blue. It is demonstrated that using this method, polymeric nanocapsules can be successfully prepared using diffusion loading of up to 94 wt% monomer (rel. to surfactant) stabilized by CO2.

Biocompatible Glycopolymer Nanocapsules via Inverse Miniemulsion Periphery RAFT Polymerization for the Delivery of Gemcitabine

Encapsulation of hydrophilic cancer drugs in polymeric nanocapsules was achieved in a one-pot process via the inverse miniemulsion periphery RAFT polymerization (IMEPP) approach. The chosen guest molecule was gemcitabine hydrochloride, which is used as the first-line treatment of pancreatic cancer. The resulting nanocapsules were confirmed to be ∼200 nm, with excellent encapsulation (∼96%) and loading (∼12%) efficiency. Postpolymerization reaction was successfully conducted to create glyocopolymer nanocapsules without any impact on the loads as well as the nanocapsules size or morphology. The loaded nanocapsules were specifically designed to be responsive in a reductive environment. This was confirmed by the successful disintegration of the nanocapsules in the presence of glutathione. The gemcitabine-loaded nanocapsules were tested in vitro against pancreatic cancer cells (AsPC-1), with the results showing an enhancement in the cytotoxicity by two fold due to selective accumulation and release of the nanocapsules within the cells. The results demonstrated the versatility of IMEPP as a tool to synthesize functionalized, loaded-polymeric nanocapsules suitable for drug-delivery application.

Synthesis of pH-Responsive Nanocapsules via Inverse Miniemulsion Periphery RAFT Polymerization and Post-Polymerization Reaction

We report herein the versatility of inverse miniemulsion periphery RAFT polymerization (IMEPP) and postpolymerization reaction in producing pH-responsive nanocapsules with different functionalities. The robustness of the polymeric nanocapsules was confirmed by their ability to undergo reactions, be dried, and be redispersed in various solvents without any changes in size and core-shell morphology. Nanocapsules bearing carboxylic acid (COOH) functionalities were produced via hydrolysis, while nanocapsules bearing tertiary-amine (N-X₃) functionalities were synthesized via aminolysis. The responsive behavior of the nanocapsules was tested in aqueous solution with pHs ranging from 3 to 12. Nanocapsules with COOH functionalities were found to swell under basic conditions due to the deprotonated carboxylate ions. In contrast, nanocapsule with tertiary amine functionalities underwent swelling in acidic conditions.

Emerging methods for the fabrication of polymer capsules

Hollow polymer capsules are attracting increasing research interest due to their potential application as drug delivery vectors, sensors, biomimetic nano- or multi-compartment reactors and catalysts. Thus, significant effort has been directed toward tuning their size, composition, morphology, and functionality to further their application. In this review, we provide an overview of emerging techniques for the fabrication of polymer capsules, encompassing: self-assembly, layer-by-layer assembly, single-step polymer adsorption, bio-inspired assembly, surface polymerization, and ultrasound assembly. These techniques can be applied to prepare polymer capsules with diverse functionality and physicochemical properties, which may fulfill specific requirements in various areas. In addition, we critically evaluate the challenges associated with the application of polymer capsules in drug delivery systems.