Morphological Stabilization of Block Copolymer Worms Using Asymmetric Cross-Linkers during Polymerization-Induced Self-Assembly

Light-Triggered Reversible Swelling of Azobenzene-Containing Block Copolymer Worms via Confined Deformation Prepared by Polymerization-Induced Self-Assembly

Stimuli-responsive block copolymer nanoparticles (NPs) have received close attention in recent years owing to their tremendous application potential in smart materials. Azobenzene-containing NPs are widely studied due to the advantages of light as a stimulus and fast reversible trans-cis isomerization of azobenzene chromophores. However, the inefficient preparation process and difficult reversible transformation of morphologies limit their development. Herein it is demonstrated that the light-triggered reversible swelling behavior of wormlike NPs with high azobenzene content could be realized via confined deformation. These worms are prepared in large quantities via polymerization-induced self-assembly based on the copolymerization of 11-(4-(4-butylphenylazo)phenoxy)undecyl methacrylate (MAAz) and N-(methacryloxy)succinimide (NMAS) monomers. Upon UV/visible light irradiation, the reversible deformation of worms is achieved when the feed molar ratio of NMAS/MAAz is relatively high or via crosslinking using diamines, which leads to the reduction of the photoisomerization efficiency. The diameter variation of the worms is influenced by the amount and types of crosslinkers. Moreover, the scalability of this strategy is further proved by the fabrication of photo- and reductant-responsive crosslinked worms. It is expected that this study not only provides a new route to affording reversible photoresponsive NPs but also offers a unique insight into the reversible photodeformation mechanism of azobenzene-containing NPs.

Exploiting the Monomer-Feeding Mechanism of RAFT Emulsion Polymerization for Polymerization-Induced Self-Assembly of Asymmetric Divinyl Monomers

We exploited the monomer-feeding mechanism of reversible addition-fragmentation chain transfer (RAFT) emulsion polymerization to achieve the successful polymerization-induced self-assembly (PISA) of asymmetric divinyl monomers. Colloidally stable cross-linked block copolymer nanoparticles with various morphologies, such as vesicles, were directly prepared at high solids. Morphologies of the cross-linked block copolymer nanoparticles could be controlled by varying the monomer concentration, degree of polymerization (DP) of the core-forming block, and length of the macro-RAFT agent. X-ray photoelectron spectroscopy (XPS) characterization confirmed the presence of unreacted vinyl groups within the obtained block copolymer nanoparticles, providing a landscape for further functionalization via thiol-ene chemistry. Finally, the obtained block copolymer nanoparticles were employed as additives to tune the mechanical properties of hydrogels. We expect that this study not only offers considerable opportunities for the preparation of well-defined cross-linked block copolymer nanoparticles, but also provides important insights into the controlled polymerization of multivinyl monomers.

Conformationally supramolecular chirality prevails over configurational point chirality in side-chain liquid crystalline polymers

In nature, the communication of primary amino acids in the polypeptides influences molecular-level packing, supramolecular chirality, and the resulting protein structures. In chiral side-chain liquid crystalline polymers (SCLCPs), however, the hierarchical chiral communication between supramolecular mesogens is still determined by the parent chiral source due to the intermolecular interactions. Herein, we present a novel strategy to enable the tunable chiral-to-chiral communication in azobenzene (Azo) SCLCPs, in which the chiroptical properties are not dominated by the configurational point chirality but by the conformationally supramolecular chirality that emerged. The communication of dyads biases supramolecular chirality with multiple packing preference, thereby overruling the configurational chirality of the stereocenter. The chiral communication mechanism between the side-chain mesogens is revealed through the systematic study of the chiral arrangement at the molecular level, including mesomorphic properties, stacking modes, chiroptical dynamics and further morphological dimensions.

NIR-Cleavable and pH-Responsive Polymeric Yolk-Shell Nanoparticles for Controlled Drug Release

Responsive drug release and low toxicity of drug carriers are important for designing controlled release systems. Here, a double functional diffractive o-nitrobenzyl, containing multiple electron-donating groups as a crosslinker and methacrylic acid (MAA) as a monomer, was used to decorate upconversion nanoparticles (UCNPs) to produce robust poly o-nitrobenzyl@UCNP nanocapsules using the distillation-precipitation polymerization and templating method. Poly o-nitrobenzyl@UCNP nanocapsules with a robust yolk-shell structure exhibited near-infrared (NIR) light-/pH-responsive properties. When the nanocapsules were exposed to 980 nm NIR irradiation, the loaded drug was efficiently released by altering the shell of the nanocapsules. The photodegradation kinetics of the poly o-nitrobenzyl@UCNP nanocapsules were studied. The anticancer drug, doxorubicin hydrochloride (DOX), was loaded at pH 8.0 with a loading efficiency of 13.2 wt %. The Baker-Lonsdale model was used to determine the diffusion coefficients under different release conditions to facilitate the design of dual-responsive drug release devices or systems. Additionally, cytotoxicity studies showed that the drug release of DOX could be efficiently triggered by NIR to kill cancer cells in a controlled manner.

Shape-Shifting Thermoresponsive Block Copolymer Nano-Objects

In this Feature Article, we review our recent progress in the design of shape-shifting thermoresponsive diblock copolymer nano-objects, which are prepared using various hydroxyl-functional (meth)acrylic monomers (e.g. 2‑hydroxypropyl methacrylate, 4‑hydroxybutyl acrylate or hydroxybutyl methacrylate) to generate the thermoresponsive block. Unlike traditional thermoresponsive polymers such as poly(N-isopropylacrylamide), there is no transition between soluble and insoluble polymer chains in aqueous solution. Instead, thermally driven transitions between a series of copolymer morphologies (e.g. spheres, worms, vesicles or lamellae) occur on adjusting the aqueous solution temperature owing to a subtle change in the partial degree of hydration of the permanently insoluble thermoresponsive block. Such remarkable self-assembly behavior is unprecedented in colloid science: no other amphiphilic diblock copolymer or surfactant system undergoes such behavior at a fixed chemical composition and concentration. Such shape-shifting nano-objects are characterized by transmission electron microscopy, dynamic light scattering, small-angle X-ray scattering, rheology and variable temperature ¹H NMR spectroscopy. Potential applications for this fascinating new class of amphiphiles are briefly considered.

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.

Mapping the Morphological Landscape of Oligomeric Di-block Peptide-Polymer Amphiphiles

Peptide-polymer amphiphiles (PPAs) are tunable hybrid materials that achieve complex assembly landscapes by combining the sequence-dependent properties of peptides with the structural diversity of polymers. Despite their promise as biomimetic materials, determining how polymer and peptide properties simultaneously affect PPA self-assembly remains challenging. We herein present a systematic study of PPA structure-assembly relationships. PPAs containing oligo(ethyl acrylate) and random-coil peptides were used to determine the role of oligomer molecular weight, dispersity, peptide length, and charge density on self-assembly. We observed that PPAs predominantly formed spheres rather than anisotropic particles. Oligomer molecular weight and peptide hydrophilicity dictated morphology, while dispersity and peptide charge affected particle size. These key benchmarks will facilitate the rational design of PPAs that expand the scope of biomimetic functionality within assembled soft materials.

Block Copolymer Vesicles with Tunable Membrane Thicknesses and Compositions Prepared by Aqueous Seeded Photoinitiated Polymerization-Induced Self-Assembly at Room Temperature

Block copolymer vesicles with diverse functionalities and intrinsic hollow structures have received considerable attention due to their broad applications in biomedical fields, including drug delivery, bioimaging, theranostics, gene therapy, etc. However, efficient preparation of block copolymer vesicles with tunable membrane thicknesses and compositions under mild conditions is still a challenge. Herein, we report an aqueous seeded photoinitiated polymerization-induced self-assembly (photo-PISA) for the precise preparation of block copolymer vesicles at room temperature. By changing the total degree of polymerization (DP) of the hydrophobic block in seeded photo-PISA, one can easily tune the membrane thickness without compromising the morphology of vesicles. Moreover, by adding different comonomers such as hydrophobic monomers, hydrophilic monomers, and cross-linkers into seeded photo-PISA, vesicles with different compositions could be prepared without compromising the morphology and colloidal stability. Polymerization kinetics show that seeded photo-PISA can skip the step of in situ self-assembly with a short homogeneous polymerization stage being observed. To demonstrate potential biological applications, enzymatic nanoreactors were constructed by loading horseradish peroxidase (HRP) inside vesicles via seeded photo-PISA. The enzymatic properties of these nanoreactors could be easily regulated by changing the membrane thickness and hydrophobicity. It is expected that this method can provide a facile platform for the precise preparation of block copolymer vesicles that may find applications in different fields.

Shape-tunable polymeric Janus nanoparticles with hollow cavities derived from polymerization induced self-assembly based crosslinked vesicles

The fabrication of shape-tunable polymeric Janus nanoparticles with hollow cavities derived from polymerization induced self-assembly based crosslinked vesicles is reported for the first time in this work. These novel polymeric JNPs can be applied to an extensive range of applications, wherein nanoparticles with controllable hollow morphologies are needed.

Controlling the Multiple Chiroptical Inversion in Biphasic Liquid-Crystalline Polymers

While controlling the chirality and modulating the helicity is a challenging task, it attracts great research interest for gaining a better understanding of the origin of chirality in nature. Herein, structurally similar azobenzene (Azo) vinyl monomers were designed in which the alkyl chains comprised the chiral stereocenter with different achiral tail lengths. Combining the synchronous polymerization, supramolecular stacking and self-assembly, the multiple chiroptical inversion of the Azo-polymer supramolecular assemblies can be modulated by the tail length and DP of Azo blocks during in situ polymerization. The DP-, UV light-, temperature-, aging time-dependent chiroptical properties and liquid-crystalline (LC) characterization indicated that the amorphous-to-LC phase transition and biphasic LC interconversion allow the transcription of intra-chain π-π stacking, inter-chain H- and J-aggregation, thereby controlling the dynamic multiple reversal of supramolecular chirality.

Pickering Emulsions Stabilized by Diblock Copolymer Worms Prepared via Reversible Addition-Fragmentation Chain Transfer Aqueous Dispersion Polymerization: How Does the Stimulus Sensitivity Affect the Rate of Demulsification?

Responsive Pickering emulsions exhibit promising application in industry owing to the integration of the high storage stability with on-demand demulsification. In this study, stimuli-responsive Pickering emulsions stabilized by poly[oligo(ethylene glycol) methyl ether methacrylate]₁₅-b-poly(diacetone acrylamide)₁₂₀ (E₁₅D₁₂₀) worms were indicated, in which E₁₅D₁₂₀ worms were prepared via reversible addition-fragmentation chain transfer-based aqueous dispersion polymerization using thermo-sensitive POEGMA₁₅ as both the stabilizer block and macro-chain transfer agent. The factors influencing the morphologies of copolymers during polymerization-induced self assembly have been investigated. A series of different morphological polymer nanoparticles including spheres, worms, and vesicles could be produced through rational synthesis. E₁₅D₁₂₀ worms demonstrated excellent emulsifying performances and could be used as emulsifiers to form n-dodecane-in-water Pickering emulsions at a low content. The formed n-dodecane-in-water Pickering emulsions revealed a slow demulsification at pH 10 or 70 °C or pH 10/70 °C combinations, and several hours were needed for the demulsification of Pickering emulsions. However, n-dodecane-in-water Pickering emulsions displayed a rapid demulsification (∼10 min) at an elevated temperature, such as 90 °C. The different demulsification rates were attributed to different sensitivities of E₁₅D₁₂₀ worms to external stimuli. Pickering emulsions integrating a rapid responsive demulsification with a slow one would be well satisfactory on different occasions.

Acrylonitrile-Styrene-Acrylate Particles with Different Microstructure for Improving the Toughness of Poly(styrene-co-acrylonitrile) Resin

Herein, acrylonitrile-styrene-acrylate copolymer (ASA) particles with different microstructure were synthesized by emulsion polymerization and then used for toughening poly(styrene-co-acrylonitrile) (SAN) resin. The structure of ASA particles was confirmed by FTIR. TEM results demonstrated that the particles with different morphologies of multilobe shape, complete core-shell and dumbbell shape were obtained depending on the cross-linker amount. It was found that the toughening efficiency reached the highest when the ASA particles had complete core-shell structure and the shell composition was close to that of the SAN matrix. It was ascribed to the fact that the complete shell layer and similar shell composition provided sufficient interfacial adhesion and transferred stress to induce larger matrix deformation, so that the notched impact strength increased accordingly. Moreover, the notched impact strength of SAN/ASA blend was improved without significantly sacrificing tensile strength when adding 30 wt% ASA particles with the size of around 400 nm. SEM results of the impact-fractured surfaces revealed that irregular fluctuation and numerous microvoids occurred. It was deduced that the toughening mechanism was attributed to the crazings and cavitation of particles. Therefore, this study paved a way of toughening the resin by adjusting the microstructure of the particles including morphology, composition, and size.

Polyether-Based Diblock Terpolymer Micelles with Pendant Anthracene Units-Light-Induced Crosslinking and Limitations Regarding Reversibility

The synthesis of 9-methylanthracenyl glycidyl ether (AnthGE) as a crosslinkable monomer that can be applied in anionic ring opening polymerization is reported. Diblock terpolymers of the composition methoxy-poly(ethylene oxide)-block-poly(2-ethylhexyl glycidyl ether-co-9-methylanthracenyl glycidyl ether) (mPEO-b-P(EHGE-co-AnthGE) with 10 to 24 wt% of AnthGE are synthesized and characterized. Their micellization behavior, as well as their light-induced core-crosslinking via irradiation with UV light (λ = 365 nm) is studied. The results are compared with studies on the dimerization, and the dimer cleavage via irradiation with UV-C light (λ = 254 nm), of the same diblock terpolymer in organic solution, and the small-molecule model compound 9-methoxymethylanthracene. Differences in ¹ H NMR spectra of the crosslinked or dimerized compounds and reaction kinetics of the dimerization reactions under different conditions suggest possible side reactions for the case of the core-crosslinking of micelles in aqueous solution. These side reactions limit the reversibility of the anthracene dimerization reaction in aqueous solutions, even if the anthracene molecule is encapsulated within the hydrophobic core of a polymeric micelle.

One-Step Preparation of Thermo-Responsive Poly(N-isopropylacrylamide)-Based Block Copolymer Nanoparticles by Aqueous Photoinitiated Polymerization-Induced Self-Assembly

Poly(N-isopropylacrylamide) (PNIPAM) is an important thermo-responsive polymer that finds applications in many areas. However, the preparation of PNIPAM-based block copolymer nanoparticles with higher-order morphologies at high solids is challenging. Herein, aqueous photoinitiated polymerization-induced self-assembly (photo-PISA) of N-isopropylacrylamide (NIPAM) using an asymmetrical cross-linker is developed for one-step preparation of PNIPAM-based block copolymer nanoparticles with various morphologies (spheres, worms, and vesicles). It is demonstrated that reaction temperature has a great effect on both polymerization kinetics and morphologies of block copolymer nanoparticles. Reversible addition-fragmentation chain transfer (RAFT) reactive groups embedded inside the PNIPAM core provide a landscape for further functionalization. PNIPAM-based block copolymer nanoparticles with different surface properties are prepared by seeded photo-PISA at room temperature. Finally, these block copolymer nanoparticles are also used as additives to tune mechanical properties of hydrogels via covalent cross-linking.

Directional effect on the fusion of ellipsoidal morphologies into nanorods and nanotubes

Particle fusion is well-recognized as an important spontaneous process to produce higher-order nanostructures during morphology transition in polymerization-induced self-assembly (PISA). However, to our knowledge, the directional contact, adhesion, and fusion of adjacent nanoparticles have been rarely elucidated in PISA. Herein, a directional fusion of ellipsoidal morphologies was demonstrated during PISA of semi-fluorinated liquid-crystalline (SFLC) block copolymers. The ellipsoidal nanostructures, including micelles and vesicles, preferred to undergo a directional fusion in a head-to-head model, leading to the formation of nanorods and nanotubes, respectively. We believe the directional fusion will offer insightful guidance in PISA to the preparation of complicated functional nanostructures.

In situ cross-linking polymerization-induced self-assembly not only generates cross-linked structures but also promotes morphology transition by the cross-linker

Not only cross-linked structures but also a promoting effect on morphology transition has been observed during the in situ cross-linking PISA by RAFT dispersion copolymerization of 2-(diisopropylamino)ethyl methacrylate and cystaminebismethacrylamide.

Pickering Emulsifiers Based on Block Copolymer Nanoparticles Prepared by Polymerization-Induced Self-Assembly

Block copolymer nanoparticles prepared via polymerization-induced self-assembly (PISA) represent an emerging class of organic Pickering emulsifiers. Such nanoparticles are readily prepared by chain-extending a soluble homopolymer precursor using a carefully selected second monomer that forms an insoluble block in the chosen solvent. As the second block grows, it undergoes phase separation that drives in situ self-assembly to form sterically stabilized nanoparticles. Conducting such PISA syntheses in aqueous solution leads to hydrophilic nanoparticles that enable the formation of oil-in-water emulsions. Alternatively, hydrophobic nanoparticles can be prepared in non-polar media (e.g., n-alkanes), which enables water-in-oil emulsions to be produced. In this review, the specific advantages of using PISA to prepare such bespoke Pickering emulsifiers are highlighted, which include fine control over particle size, copolymer morphology, and surface wettability. This has enabled various fundamental scientific questions regarding Pickering emulsions to be addressed. Moreover, block copolymer nanoparticles can be used to prepare Pickering emulsions over various length scales, with mean droplet diameters ranging from millimeters to less than 200 nm.

Enthalpic incompatibility between two steric stabilizer blocks provides control over the vesicle size distribution during polymerization-induced self-assembly in aqueous media

Over the past two decades, block copolymer vesicles have been widely used by many research groups to encapsulate small molecule drugs, genetic material, nanoparticles or enzymes. They have also been used to design examples of autonomous self-propelled nanoparticles. Traditionally, such vesicles are prepared via post-polymerization processing using a water-miscible co-solvent such as DMF or THF. However, such protocols are invariably conducted in dilute solution, which is a significant disadvantage. In addition, the vesicle size distribution is often quite broad, whereas aqueous dispersions of relatively small vesicles with narrow size distributions are highly desirable for potential biomedical applications. Alternatively, concentrated dispersions of block copolymer vesicles can be directly prepared via polymerization-induced self-assembly (PISA). Moreover, using a binary mixture of a relatively long and a relatively short steric stabilizer block enables the convenient PISA synthesis of relatively small vesicles with reasonably narrow size distributions in alcoholic media (C. Gonzato et al., JACS, 2014, 136, 11100-11106). Unfortunately, this approach has not yet been demonstrated for aqueous media, which would be much more attractive for commercial applications. Herein we show that this important technical objective can be achieved by judicious use of two chemically distinct, enthalpically incompatible steric stabilizer blocks, which ensures the desired microphase separation across the vesicle membrane. This leads to the formation of well-defined vesicles of around 200 nm diameter (size polydispersity = 13-16%) in aqueous media at 10% w/w solids as judged by transmission electron microscopy, dynamic light scattering and small-angle X-ray scattering.

Flow-Induced Micellar Morphological Transformation in Microfluidic Chips under Nonequilibrium State: From Aggregates to Spherical Micelles

Self-assembly of block copolymers (BCPs) in microfluidic chips is a versatile yet effective route to produce micellar aggregates with various controllable sizes and morphologies. In this study, the morphological transformation of the BCP of polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) assemblies from irregular aggregates to multicompartment micelles and ultimately to ordered spherical micelles is demonstrated in microfluidic chips. Our experimental and computational simulation results indicate that the transverse diffusion of solvents plays an important role in the morphological transformation of PS-b-P4VP assemblies in the confined flow condition. We find that the mixing time (t_mix) between a BCP/tetrahydrofuran (THF) solution and water affects the morphological transformation. Micellar morphologies are intended to transform from aggregates to ordered spherical structures under a relatively long mixing time (t_mix). In addition, it is observed that the size of the micelles decreases with the increase of the flow velocity ratio by tuning the hydrodynamic conditions of the flows. Moreover, by adjusting the initial polymer solution concentration, temperature, and weight fraction of the introduced homopolystyrene (hPS), which can affect the viscosity of the BCP solution, the flow diffusion in the microfluidic chip and the resulted micellar structures can also be readily adjusted. The current study provides a new flow-driven method to adjust the micellar ordered structural transformation under the nonequilibrium state.

Thermoresponsive Block Copolymer Vesicles by Visible Light-Initiated Seeded Polymerization-Induced Self-Assembly for Temperature-Regulated Enzymatic Nanoreactors

Block copolymer vesicles loaded with active compounds have been employed as decent candidates to mimic complex biological systems that attract considerable interest in different research communities. We herein report a visible light-initiated seeded reversible addition-fragmentation chain transfer (RAFT)-mediated polymerization-induced self-assembly (PISA) for in situ preparation of enzyme-loaded cross-linked block copolymer vesicles without compromising the bioactivity. Permeability of the vesicular membrane can be regulated through changing the solution temperature, allowing further control over the enzymatic reaction rate of enzyme-loaded vesicles. Finally, non-cross-linked thermoresponsive block copolymer vesicles that can transform into worm-like micelles at low temperature are also prepared by this method, allowing the release of bimacromolecules from the vesicles under mild conditions.

In Situ Controlled Construction of a Hierarchical Supramolecular Chiral Liquid-Crystalline Polymer Assembly

Hierarchical supramolecular chiral liquid-crystalline (LC) polymer assemblies are challenging to construct in situ in a controlled manner. Now, polymerization-induced chiral self-assembly (PICSA) is reported. Hierarchical supramolecular chiral azobenzene-containing block copolymer (Azo-BCP) assemblies were constructed with π-π stacking interactions occurring in the layered structure of Azo smectic phases. The evolution of chirality from terminal alkyl chain to Azo mesogen building blocks and further induction of supramolecular chirality in LC BCP assemblies during PICSA is achieved. Morphologies such as spheres, worms, helical fibers, lamellae, and vesicles were observed. The morphological transition had a crucial effect on the chiral expression of Azo-BCP assemblies. The supramolecular chirality of Azo-BCP assemblies destroyed by 365 nm UV irradiation can be recovered by heating-cooling treatment; this dynamic reversible achiral-chiral switching can be repeated at least five times.

One-Pot Synthesis of Cross-linked Block Copolymer Nanowires via Polymerization-Induced Hierarchical Self-Assembly and Photodimerization

Block copolymer (BCP) nanowires are crucially important in diversified fields. However, their applications typically suffer from a tedious fabrication process, heterogeneous morphology, and degradation. Herein, we propose a facile and robust approach to synthesize stilbene-containing BCP nanowires in homogeneous morphology with high stability at high solid content (5%-20% w/w) in one pot. It is realized by the polymerization-induced hierarchical self-assembly and subsequent photodimerization cross-linking under UV irradiation of stilbene mesogens in the core-forming block in the later stage of polymerization. Because of the strong liquid crystalline ordering and photodimerization of stilbene, the cross-linked nanowires can be obtained over a broad BCP composition, which show robust morphological stability when exposed to solvent dissolution tests and water dispersion stability tests. This efficient approach to stabilized nanowires with homogeneous morphology via in situ cross-linking would be useful in various fields, such as nanomedicine and Pickering emulsifiers.

Facile preparation of one-dimensional nanostructures through polymerization-induced self-assembly mediated by host–guest interaction

A RAFT aqueous dispersion polymerization of ferrocenylmethyl acrylate mediated by host–guest interaction was investigated and a series of peculiar one-dimensional morphologies can be readily obtained.

Trending methods employed for polymerization induced self-assembly

Mother Nature produces a perfectly defined architecture that inspires researchers to make polymeric macromolecules for an array of functions. The present article describes recent development in the PISA to synthesize polymeric nano-objects.

Cross-linking polymerization-induced self-assembly to produce branched core cross-linked star block polymer micelles

Copolymerizing a cross-linker in the PISA process spontaneously produces branched core cross-linked block polymer micelles.

Polymerization-induced self-assembly for the fabrication of polymeric nano-objects with enhanced structural stability by cross-linking

This review discusses the strategies of core-cross-linking in most of the PISA literatures (including post-polymerization cross-linking, photo-cross-linking and in situ cross-linking) and the applications of the cross-linked nano-objects.

Cross-linking approaches for block copolymer nano-assemblies via RAFT-mediated polymerization-induced self-assembly

This minireview summarizes the current cross-linking approaches to stabilize block copolymer nano-assemblies obtained via RAFT-mediated PISA process.

Structural Difference in Macro-RAFT Agents Redirects Polymerization-Induced Self-Assembly

Polymerization-induced self-assembly (PISA) has served as a versatile platform for the large-scale preparation of well-defined block copolymer nano-objects. It appears to be "common sense" that block copolymers with narrow molecular weight distributions are inevitable. In this study, we have conducted the direct comparison of reversible addition-fragmentation transfer (RAFT)-mediated PISA of 2-hydroxypropyl methacrylate (HPMA) using polymethacrylate- and polyacrylate-based macro-RAFT agents. Taking advantage of the poor RAFT controllability of polyacrylate-based macro-RAFT agents with respect to HPMA, uniform submicron-sized polymeric microspheres were prepared by photoinitiated RAFT-mediated PISA of HPMA. The diameter of polymeric microspheres can be precisely controlled by further chain-extension of PHPMA. Finally, uniform epoxy-functionalized multicompartment block copolymer particles (MBCPs) were prepared by a two-step photoinitiated RAFT-mediated PISA with poly(glycidyl methacrylate) (PGlyMA) as the third block. The performance of MBCPs as Pickering emulsifiers was evaluated in detail. This study not only expands the scope of RAFT-mediated PISA for preparing well-defined polymer particles but also provides important insights into the mechanism of RAFT-mediated PISA.

Emerging Trends in Polymerization-Induced Self-Assembly

In this Perspective, we summarize recent progress in polymerization-induced self-assembly (PISA) for the rational synthesis of block copolymer nanoparticles with various morphologies. Much of the PISA literature has been based on thermally initiated reversible addition-fragmentation chain transfer (RAFT) polymerization. Herein, we pay particular attention to alternative PISA protocols, which allow the preparation of nanoparticles with improved control over copolymer morphology and functionality. For example, initiation based on visible light, redox chemistry, or enzymes enables the incorporation of sensitive monomers and fragile biomolecules into block copolymer nanoparticles. Furthermore, PISA syntheses and postfunctionalization of the resulting nanoparticles (e.g., cross-linking) can be conducted sequentially without intermediate purification by using various external stimuli. Finally, PISA formulations have been optimized via high-throughput polymerization and recently evaluated within flow reactors for facile scale-up syntheses.

Light-Triggered Reversible Slimming of Azobenzene-Containing Wormlike Nanoparticles Synthesized by Polymerization-Induced Self-Assembly for Nanofiltration Switches

Photoresponsive wormlike block copolymer nanoparticles (NPs) have potential applications in versatile fields, but their preparation suffers from narrow worm phase region and tedious approaches. In this work, azobenzene-containing wormlike NPs based on poly(methylacrylic acid)-b-poly(4-((4-butylphenyl)diazenyl)phenyl methacrylate) are prepared via polymerization-induced self-assembly at high solids concentration in ethanol. The pure wormlike NPs occupy a remarkably broad region in the morphological phase diagram because of the rigid nature of the core-forming block. These wormlike NPs expand resulting from trans-cis transformation upon UV irradiation, and slim near to the original state via visible light irradiation. The diameter and its variation amplitude of worms increase with the chain length of core-forming block. Moreover, a nanofiltration switch for rhodamine B is assembled to illustrate one of its potential applications by remote trigger using light.

Getting into Shape: Reflections on a New Generation of Cylindrical Nanostructures' Self-Assembly Using Polymer Building Blocks

Cylinders are fascinating structures with uniquely high surface area, internal volume, and rigidity. On the nanoscale, a broad range of applications have demonstrated advantageous behavior of cylindrical micelles or bottlebrush polymers over traditional spherical nano-objects. In the past, obtaining pure samples of cylindrical nanostructures using polymer building blocks via conventional self-assembly strategies was challenging. However, in recent years, the development of advanced methods including polymerization-induced self-assembly, crystallization-driven self-assembly, and bottlebrush polymer synthesis has facilitated the easy synthesis of cylindrical nano-objects at industrially relevant scales. In this Perspective, we discuss these techniques in detail, highlighting the advantages and disadvantages of each strategy and considering how the cylindrical nanostructures that are obtained differ in their chemical structure, physical properties, colloidal stability, and reactivity. In addition, we propose future challenges to address in this rapidly expanding field.

Combining the power of heat and light: temperature-programmed photoinitiated RAFT dispersion polymerization to tune polymerization-induced self-assembly

A novel temperature-programmed photo-PISA method which combines the power of heat and light is developed for the preparation of a diverse set of morphologies.

Exploiting Wavelength Orthogonality for Successive Photoinduced Polymerization-Induced Self-Assembly and Photo-Crosslinking

We report a facile benchtop process for the synthesis of cross-linked polymeric nanoparticles by exploiting wavelength-selective photochemistry to perform orthogonal photoinduced polymerization-induced self-assembly (Photo-PISA) and photo-crosslinking processes. We first established that the water-soluble photocatalyst, zinc meso-tetra(N-methyl-4-pyridyl) porphine tetrachloride (ZnTMPyP) could activate the aqueous PET-RAFT dispersion polymerization of hydroxypropyl methacrylate (HPMA). This photo-PISA process could be conducted under low energy red light (λ_max = 595 nm, 10.2 mW/cm²) and without deoxygenation due to the action of the singlet oxygen quencher, biotin (vitamin B₇), which allowed for the synthesis of a range of nanoparticle morphologies (spheres, worms, and vesicles) directly in 96-well plates. To perform wavelength selective nanoparticle cross-linking, we added the photoresponsive monomer, 7-[4-(trifluoromethyl)coumarin] methacrylamide (TCMAm) as a comonomer without inhibiting the evolution of the nanoparticle morphology. Importantly, under red light, exclusive activation of the photo-PISA process occurs, with no evidence of TCMAm dimerization under these conditions. Subsequent switching to a UV source (λ_max = 365 nm, 10.2 mW/cm²) resulted in rapid cross-linking of the polymer chains, allowing for retention of the nanoparticle morphology in organic solvents. This facile synthesis of cross-linked spheres, worms, and vesicles demonstrates the utility of orthogonal light-mediated chemistry for performing decoupled wavelength selective chemical processes.

New Insights into RAFT Dispersion Polymerization-Induced Self-Assembly: From Monomer Library, Morphological Control, and Stability to Driving Forces

Polymerization-induced self-assembly (PISA) has been established as an efficient, robust, and versatile approach to synthesize various block copolymer nano-objects with controlled morphologies, tunable dimensions, and diverse functions. The relatively high concentration and potential scalability makes it a promising technique for industrial production and practical applications of functional polymeric nanoparticles. This feature article outlines recent advances in PISA via reversible addition-fragmentation chain transfer dispersion polymerization. Considerable efforts to understand morphological control, broaden the monomer library, enhance morphological stability, and incorporate multiple driving forces in PISA syntheses are summarized herein. Finally, perspectives on the future of PISA research are discussed.