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.

Preparation of Polymer-Based Nano-Assembled Particles with Fe3O4 in the Core

Organic-inorganic nanocomposite particles, possessing defined morphologies, represent the next frontier in advanced materials due to their superior collective performance. In this pursuit of efficient preparation of composite nanoparticles, a series of diblock polymers polystyrene-block-poly(tert-butyl acrylate) (PS-b-PtBA) were initially synthesized using the Living Anionic Polymerization-Induced Self-Assembly (LAP PISA) technique. Subsequently, the tert-butyl group on the tert-butyl acrylate (tBA) monomer unit in the diblock copolymer, yielded from the LAP PISA process, was subjected to hydrolysis using trifluoroacetic acid (CF₃COOH), transforming it into carboxyl groups. This resulted in the formation of polystyrene-block-poly(acrylic acid) (PS-b-PAA) nano-self-assembled particles of various morphologies. The pre-hydrolysis diblock copolymer PS-b-PtBA produced nano-self-assembled particles of irregular shapes, whereas post-hydrolysis regular spherical and worm-like nano-self-assembled particles were generated. Utilizing PS-b-PAA nano-self-assembled particles that containing carboxyl groups as polymer templates, Fe₃O₄ was integrated into the core region of the nano-self-assembled particles. This was achieved based on the complexation between the carboxyl groups on the PAA segments and the metal precursors, facilitating the successful synthesis of organic-inorganic composite nanoparticles with Fe₃O₄ as the core and PS as the shell. These magnetic nanoparticles hold potential applications as functional fillers in the plastic and rubber sectors.

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.

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.

Synthesis of Janus Au@BCP nanoparticles via UV light-initiated RAFT polymerization-induced self-assembly

It is a great challenge to fabricate Janus inorganic/polymeric hybrid nanoparticles with both precisely controlled nanostructures and high yields. Herein, we report a new method to synthesize Janus Au@BCPs via UV light-initiated RAFT polymerization-induced self-assembly in situ at a high solid content. This strategy provides a promising alternative for achieving asymmetric hybrid nanoparticles with a controllable size, tunable morphology and convenient operation.

Supramolecular Chirality in Azobenzene-Containing Polymer System: Traditional Postpolymerization Self-Assembly Versus In Situ Supramolecular Self-Assembly Strategy

Recently, the design of novel supramolecular chiral materials has received a great deal of attention due to rapid developments in the fields of supramolecular chemistry and molecular self-assembly. Supramolecular chirality has been widely introduced to polymers containing photoresponsive azobenzene groups. On the one hand, supramolecular chiral structures of azobenzene-containing polymers (Azo-polymers) can be produced by nonsymmetric arrangement of Azo units through noncovalent interactions. On the other hand, the reversibility of the photoisomerization also allows for the control of the supramolecular organization of the Azo moieties within polymer structures. The construction of supramolecular chirality in Azo-polymeric self-assembled system is highly important for further developments in this field from both academic and practical points of view. The postpolymerization self-assembly strategy is one of the traditional strategies for mainly constructing supramolecular chirality in Azo-polymers. The in situ supramolecular self-assembly mediated by polymerization-induced self-assembly (PISA) is a facile one-pot approach for the construction of well-defined supramolecular chirality during polymerization process. In this review, we focus on a discussion of supramolecular chirality of Azo-polymer systems constructed by traditional postpolymerization self-assembly and PISA-mediated in situ supramolecular self-assembly. Furthermore, we will also summarize the basic concepts, seminal studies, recent trends, and perspectives in the constructions and applications of supramolecular chirality based on Azo-polymers with the hope to advance the development of supramolecular chirality in chemistry.

Dual and Multi-Emission Hybrid Micelles Realized through Coordination-Driven Self-Assembly

Building novel functional nanomaterials with a polymer is one of the most dynamic research fields at present. Here, three amphiphilic block copolymers of 8-hydroxyquinoline derivative motifs (MQ) with excellent coordination function were synthesized by Reversible Addition-Fragmentation Chain Transfer Polymerization (RAFT) polymerization. The coordination micelles were prepared through the self-assembly process, which the MQ motifs were dispersed in the hydrophobic polystyrene (PSt) blocks and hydrophilic Poly(N-isopropylacrylamide (PNIPAM)) blocks, respectively. The dual-emission micelles including the intrinsic red light emission of quantum dots (QDs) and the coordination green light emission of Zn2+-MQ complexes were built by introducing the CdSe/ZnS and CdTe/ZnS QDs in the core and shell precisely in the coordination micelles through the coordination-driven self-assembly process. Furthermore, based on the principle of three primary colors that produce white light emission, vinyl carbazole units (Polyvinyl Carbazole, PVK) with blue light emission were introduced into the hydrophilic PNIPAM blocks to construct the white light micelles that possess special multi-emission properties in which the intrinsic red light emission of QDs, the coordination green light of Zn2+-MQ complexes, and the blue light emission of PVK were synergized. The dual and multi-emission hybrid micelles have great application prospects in ratiometric fluorescent probes and biomarkers.

Light and magnetism dual-gated photoinduced electron transfer-reversible addition–fragmentation chain transfer (PET-RAFT) polymerization

PET-RAFT polymerization can be reversibly ceased in the absence of light or under an external magnetic field with a novel raspberry-like γ-Fe₂O₃@CD nanocatalyst.

RAFT dispersion polymerisation of lauryl methacrylate in ethanol–water binary mixtures: synthesis of diblock copolymer vesicles with deformable membranes

Diblock copolymer vesicles with deformable membranes are prepared via RAFT dispersion polymerisation of lauryl methacrylate in an 80 : 20 w/w ethanol–water mixture; visible light irradiation allows facile RAFT chain-end removal from these nano-objects.

Synthesis of lipase–polymer conjugates by Cu(0)-mediated reversible deactivation radical polymerization: polymerization vs. degradation

Cu(0)-RDRP was first used for the polymerization-induced self-assembly of lipase–polymer conjugates, inducing the formation of nanospheres with preserved activity and degradability.

Synthesis and Nano-object Assembly of Biomimetic Block Copolymers for Catalytic Silver Nanoparticles

Biomimetic ABC triblock copolymers of poly[2-(methacryloyloxy)ethyl phosphorylcholine]- b-poly[2-(dimethylamino)ethyl methacrylate]- b-poly(2-hydroxypropyl methacrylate) (PMPC- b-PDMA- b-PHPMA) were synthesized by RAFT aqueous dispersion polymerization of 2-hydroxypropyl methacrylate (HPMA) in the presence of a PMPC- b-PDMA macromolecular chain transfer agent (macro-CTA). This ABC triblock copolymer deploys well-known biocompatible PMPC and PDMA for the coordination of Ag⁺ ions to form silver nanoparticles in situ on reduction, and PHPMA for assembling (core) in water. The synthesis of PMPC- b-PDMA- b-PHPMA starts when both the reactive steric stabilizer of PMPC₂₅- b-PDMA₄ macro-CTA and HPMA monomer are dissolved in water. The growing PHPMA is not soluble in water and begins to assemble based on three-layer onion micelles, in which the outer and inner shells are PMPC and PDMA, respectively. In the synthesis of PMPC₂₅- b-PDMA₄- b-PHPMA _z at a constant 25% (w/w) solids concentration, the resultant assemblies change from spheres to worms to jellyfishes to vesicles when the targeted PHPMA chain length increases from 100mer to 400mer at full monomer conversion. Furthermore, in the synthesis of identical PMPC₂₅- b-PDMA₄- b-PHPMA₄₀₀ copolymers, the assembly morphology can be controlled from vesicles to spheres through worms by varying the solids concentration in the polymerization mixture, decreasing from 25% (w/w) to 15% (w/w) at full monomer conversion. Thus, the final morphology can be tuned by the degree of polymerization of HPMA and the solids concentration in the polymerization mixture. Using the resultant three PMPC₂₅- b-PDMA₄- b-PHPMA₄₀₀ assemblies as scaffolds, Ag(0) nanoparticles (Ag-NPs) are obtained through in situ reduction of AgNO₃ facilitated by electrostatic interactions between the Ag⁺ ions and PDMA moieties. The resultant Ag-NPs loaded in the assemblies exhibit excellent stability, dispersibility, and activity of catalyst for the reduction of p-nitrophenol. The order of rate constants for the reduction using Ag-NPs loaded in the assemblies is worms > vesicles > spheres, which corresponds to the order of the surface areas of the assemblies of PMPC₂₅- b-PDMA₄- b-PHPMA₄₀₀. These results can be achieved thanks to the kinetically frozen PMPC₂₅- b-PDMA₄- b-PHPMA₄₀₀ assemblies with identical compositions.

Synthesis of block copolymer nano-assemblies via ICAR ATRP and RAFT dispersion polymerization: how ATRP and RAFT lead to differences

Block copolymer nano-assemblies were synthesized via ICAR ATRP dispersion polymerization employing the CuBr₂/tris(2-pyridylmethyl)amine catalyst in an alcoholic solvent at a relatively low temperature of 45 °C.

In situ synthesis of PAA-b-PSt nano-assemblies via dispersion RAFT polymerization: effects of PEG in the medium

A facile and efficient approach was proposed to adjust BCP assemblies in PISA by introduction of PEG in the medium. Both PEG amount and molecular weight have significant effects on PAA-b-PSt micelles.