Versatile PISA templates for tailored synthesis of nanoparticles

Versatile morphology transition of nano-assemblies via ultrasonics/microwave assisted aqueous polymerization-induced self-assembly based on host-guest interaction

Nano-assemblies have wide applications in biomedicine, functional coatings, Pickering emulsifiers, hydrogels, and so forth. The preparation of assemblies mainly utilizes the polymerization-induced self-assembly (PISA) method, which can produce high-concentration nanoscale assemblies in one step. However, the initiation processes of most reported PISA are limited to thermal initiation. Here, we reported two green and efficient methods for synthesizing nano-assemblies with various morphologies using ultrasound (20 kHz)/ microwave (500 W) assisted aqueous-phase RAFT-PISA in 3 h and 1 h. Cyclodextrin (CD) and styrene (St) nucleating monomer were complexed in a 1:1 ratio. Then, using Poly (ethylene glycol) methyl ether as the macromolecular reversible addition-fragmentation chain transfer (RAFT) agent (PEG-CTA) to control the CD/St complexes, the conversion rate of St monomer was respectively 27 %-60 %, 20 %-30 % within 3 h and 1 h under ultrasonics/microwave assisted PISA. Results showed that the morphologies of the assemblies are not only related to the length of PS block, but also to the assistance types and the remaining monomer concentration. The results showed that only PEG45-b-PS90 and PEG45-b-PS241 assemblies prepared by ultrasonics assisted PISA form evolved lamellaes and vesicles (100 nm), which break through the limitation of kinetic freezing. But the ultrasonic reaction on morphology of assemblies is not all favourable. For one thing, it can promote the movement of particles; for another, it makes reverse morphology transformation and sphere is preferred morphology. Therefore, the main reason of morphology evolution is the remaining monomer concentration of PEG45-b-PS90 and PEG45-b-PS241 assemblies reaches to 55 %-65 %, which promoting the segment movement. The results showed that the morphology of the assemblies prepared by microwave assisted PISA changed from spherical micelles to short rods, and finally to vesicles (120-140 nm) as the length of hydrophobic PS block increases. The kinetic freezing problem was solved in microwave-assisted PISA due to the action of microwaves and more remaining monomer concentration. Both them can boost particles movement.

Preparation of diblock copolymer nano-assemblies by ultrasonics assisted ethanol-phase polymerization-induced self-assembly

Assemblies are widely used in biomedicine, batteries, functional coatings, Pickering emulsifiers, hydrogels, and luminescent materials. Polymerization-induced self-assembly (PISA) is a method for efficiently preparing particles, mainly initiated thermally. However, thermally initiated PISA usually requires a significant amount of time and energy. Here, we demonstrate the preparation of nano-assemblies with controllable morphologies and size using ultrasound (20 kHz) assisted ethanol-phase RAFT-PISA in three hours. Using poly (N, N-dimethylaminoethyl methacrylate) as the macromolecular reversible addition-fragmentation chain transfer agent (PDMA-CTA) to control the nucleating monomer benzyl methacrylate (BzMA), we obtained nano-assemblies with different morphologies. With the length of hydrophobic PBzMA block growth, the morphologies of the assemblies at 15 wt% solid content changed from spheres to vesicles, and finally to lamellae; the morphologies of the assemblies at 30 wt% changed from spheres micelles to short worms, then vesicles, and finally to large compound vesicles. With the same targeted degree of polymerization, nano-assemblies having a 30 wt% solid content display a more evolved morphology. The input of ultrasonic energy makes the system have higher surface free energy, results the mass fraction interval of solventphilic blocks (fhydrophilic) corresponding to the formation of spherical micelles is expanded from fhydrophilic > 45 % to fhydrophilic > 31 % under ultrasound and the fhydrophilic required to form worms, vesicles, and large composite vesicles decreases in turn. It is worth noting that the fhydrophilic interval of worms prepared by ultrasonics assisted PISA gets larger. Overall, the highly green, externally-regulatable and fast method of ultrasonics assisted PISA can be extended to vastly different diblock copolymers, for a wide range of applications.

Tunable Polymer Nanoreactors from RAFT Polymerization-Induced Self-Assembly: Fabrication of Nanostructured Carbon-Coated Anatase as Battery Anode Materials with Variable Morphology and Porosity

We demonstrate a modular synthesis approach to yield mesoporous carbon-coated anatase (denoted as TiO₂/C) nanostructures. Combining polymerization-induced self-assembly (PISA) and reversible addition-fragmentation chain-transfer (RAFT) dispersion polymerization enabled the fabrication of uniform core-shell polymeric nanoreactors with tunable morphologies. The nanoreactors comprised of a poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) shell and a poly(benzyl methacrylate) (PBzMA) core. We selected worm-like and vesicular morphologies to guide the nanostructuring of a TiO₂ precursor, namely, titanium(IV) bis(ammonium lactato)dihydroxide (TALH). Subsequent carbonization yielded nanocrystalline anatase and simultaneously introduced a porous carbon framework, which also suppressed the crystal growth (∼5 nm crystallites). The as-prepared TiO₂/C materials comprised of a porous structure, with large specific surface areas (>85 m²/g) and various carbon contents (20-30 wt %). As anode components in lithium-ion batteries, our TiO₂/C nanomaterials improved the cycling stability, facilitated high overall capacities, and minimized the capacity loss compared to both their sans carbon and commercial anatase analogues.

RAFT-mediated polymerization-induced self-assembly (RAFT-PISA): current status and future directions

Polymerization-induced self-assembly (PISA) combines polymerization and self-assembly in a single step with distinct efficiency that has set it apart from the conventional solution self-assembly processes. PISA holds great promise for large-scale production, not only because of its efficient process for producing nano/micro-particles with high solid content, but also thanks to the facile control over the particle size and morphology. Since its invention, many research groups around the world have developed new and creative approaches to broaden the scope of PISA initiations, morphologies and applications, etc. The growing interest in PISA is certainly reflected in the increasing number of publications over the past few years, and in this review, we aim to summarize these recent advances in the emerging aspects of RAFT-mediated PISA. These include (1) non-thermal initiation processes, such as photo-, enzyme-, redox- and ultrasound-initiation; the achievements of (2) high-order structures, (3) hybrid materials and (4) stimuli-responsive nano-objects by design and adopting new monomers and new processes; (5) the efforts in the realization of upscale production by utilization of high throughput technologies, and finally the (6) applications of current PISA nano-objects in different fields and (7) its future directions.

Kinetically stable sub-50 nm fluorescent block copolymer nanoparticles via photomediated RAFT dispersion polymerization for cellular imaging

Self-assembled block copolymer nanoparticles (NPs) have emerged as major potential nanoscale vehicles for fluorescence bioimaging. The preparation of NPs with high yields possessing high kinetic stability to prevent the leakage of fluorophore molecules is crucial to their practical implementation. Here, we report a photomediated RAFT polymerization-induced self-assembly (PISA) yielding uniform and nanosized poly((oligo(ethylene glycol) acrylate)-block-poly(benzyl acrylate) particles (POEGA-b-PBzA) with a concentration of 22 wt%, over 20 times more than with micellization and nanoprecipitation. The spherical diblock copolymer nanoparticles have an average size of 10-50 nm controllable through the degree of polymerization of the stabilizing POEGA block. Subsequent dialysis against water and swelling with Nile red solution led to highly stable fluorescent NPs able to withstand the changes in concentration, ionic strength, pH or temperature. A PBzA/water interfacial tension of 48.6 mN m^-1 hinders the exchange between copolymer chains, resulting in the trapping of NPs in a "kinetically frozen" state responsible for high stability. A spectroscopic study combining fluorescence and UV-vis absorption agrees with a preferential distribution of fluorophores in the outer POEGEA shell despite its hydrophobic nature. Nile red-doped POEGA-b-PBzA micelles without initiator residues and unimers but with high structural stability turn out to be noncytotoxic, and can be used for the optical imaging of cells. Real-time confocal fluorescence microscopy shows a fast cellular uptake using C2C12 cell lines in minutes, and a preferential localization in the perinuclear region, in particular in the vesicles.

Organic–inorganic hybrid nanomaterials prepared via polymerization-induced self-assembly: recent developments and future opportunities

This review highlights recent developments in the preparation of organic–inorganic hybrid nanomaterials via polymerization-induced self-assembly.

Sonochemical preparation of polymer-metal nanocomposites with catalytic and plasmonic properties

Polymer-metal nanocomposites are of increasing interest for a wide range of applications; however, the preparation of these nanocomposites often requires the addition of external initiation and reducing agents for the synthesis of polymer and metal nanoparticles, respectively. Herein, we demonstrate the preparation of polymer-metal nanocomposites for improved catalytic performance by utilizing ultrasound as both the initiation and reducing source. Specifically, synthesis of the macro-RAFT agent containing poly[2-(dimethylamino)ethyl methacrylate], followed by ultrasound-initiated polymerization-induced self-assembly (sono-PISA), provides triblock copolymer nanoparticles containing tertiary amine groups. These polymer nanoparticles were further used as the scaffold for the in situ reduction of metal ions (Au and Pd ions) by radicals generated via sonolysis of water without additional reducing agents. The immobilization of metal nanoparticles has been confirmed by TEM and electron diffraction patterns. Polymer-Au nanocomposites with stepwise-grown AuNPs can be applied as surface-enhanced Raman scattering (SERS) substrates for 4-aminothiophenol (4-ATP) detection. Furthermore, the catalytic performances of these prepared polymer-Au and polymer-Pd nanocomposites were examined for aerobic alcohol oxidation and the Suzuki-Miyaura cross-coupling reaction, respectively. Overall, this strategy is expected to greatly expand the utility of ultrasound in the preparation of polymer-metal nanocomposites and promote the catalytic applications of these nanocomposites.

Non-thermally initiated RAFT polymerization-induced self-assembly

This review summarizes the recent non-thermal initiation methods in RAFT mediated polymerization-induced self-assembly (PISA), including photo-, redox/oscillatory reaction-, enzyme- and ultrasound wave-initiation.

Characterizing the Core-Shell Architecture of Block Copolymer Nanoparticles with Electron Microscopy: A Multi-Technique Approach

Electron microscopy has proved to be a major tool to study the structure of self-assembled amphiphilic block copolymer particles. These specimens, like supramolecular biological structures, are problematic for electron microscopy because of their poor capacity to scatter electrons and their susceptibility to radiation damage and dehydration. Sub-50 nm core-shell spherical particles made up of poly(hydroxyethyl acrylate)–b–poly(styrene) are prepared via polymerization-induced self-assembly (PISA). For their morphological characterization, we discuss the advantages, limitations, and artefacts of TEM with or without staining, cryo-TEM, and SEM. A number of technical points are addressed such as precisely shaping of particle boundaries, resolving the particle shell, differentiating particle core and shell, and the effect of sample drying and staining. TEM without staining and cryo-TEM largely evaluate the core diameter. Negative staining TEM is more efficient than positive staining TEM to preserve native structure and to visualize the entire particle volume. However, no technique allows for a satisfactory imaging of both core and shell regions. The presence of long protruding chains is manifested by patched structure in cryo-TEM and a significant edge effect in SEM. This manuscript provides a basis for polymer chemists to develop their own specimen preparations and to tackle the interpretation of challenging systems.

Diblock Copolymer Core-Shell Nanoparticles as Template for Mesoporous Carbons: Independent Tuning of Pore Size and Pore Wall Thickness

Latex templating using core-shell particles represents a unique opportunity to design mesoporous carbons with a high level of control on textural properties. This new class of organic colloid templates is synthesized by polymerization-induced self-assembly (PISA) in which a solvophilic poly(hydroxyethyl acrylate) (PHEA) homopolymer is chain extended with a solvophobic polystyrene (PS) via a photomediated reversible-addition-fragmentation-transfer (RAFT) polymerization. The resultant PHEA-b-PS diblock copolymer nanoparticles exhibit a PS core stabilized by a PHEA shell, with two blocks characterized by a low molecular weight dispersity (1.1-1.3) and an adjustable degree of polymerization (DP). The core-shell structured nanoparticles are used as soft template for the formation of mesostructured carbons from phloroglucinol and glyoxylic acid in methanol solution. A micro- and mesostructured cellular foam is obtained having uniform, interconnected, and narrowly distributed mesopores ranging between 15 and 30 nm in diameter, a specific surface area up to 719 m² g^-1, and a total pore volume of (0.4-1.3) cm³ g^-1. The mesopore size can be controlled by adjusting the diameter of the PS core (16-29 nm), while the wall thickness can be tailored independently by varying the size of the solvated PHEA shell (5-25 nm). An increase of PHEA block's DP from 25 to 85 gradually extends the stabilizing shell dimension, thus increasing the wall thickness up to 10 nm, and causing the shift from interconnected to isolated mesopores. By comparison, much thinner walls (2-3 nm) are obtained with conventional latex templates such as polystyrene nanoparticles or colloidal silica. Decreasing PHEA DP to 17 induces the formation of copolymer vesicles that can be used as template to create mesoporous carbons with nonspherical mesopores.