Ultra‐Fast Synthesis of Multivalent Radical Nanoparticles by Ring‐Opening Metathesis Polymerization‐Induced Self‐Assembly

Kinetically Controlled Preparation of Worm-like Micelles with Tunable Diameter/Length and Structural Stability

Anisotropic nanoparticles such as worm-like micelles have aroused much attention due to their promising applications from templates to drug delivery. The fabrication of worm-like micelles with tunable structural stability and control over their diameter and length is of great importance but still challenging. Herein, we report a kinetically controlled ring-opening metathesis polymerization-induced self-assembly (ROMPISA) for the robust preparation of kinetically trapped worm-like micelles with tunable diameter/length at enlarged experimental windows by the rational manipulation of kinetic factors, including solvent property, temperature, and π-π stacking effects. The resultant worm structures were thermodynamically metastable and capable of excellent structural stability at room temperature due to the kinetic trapping effect. At elevated temperatures, these thermodynamically metastable worms could undergo morphology evolution into vesicular structures in a controlled manner. Moreover, the structural stability of worms could also be significantly enhanced by in situ cross-linking. Overall, this kinetically controlled ROMPISA opens a new avenue for PISA chemistry that is expected to prepare "smart" polymer materials by manipulating kinetic factors.

Degradable Block Copolymer Nanoparticles Synthesized by Polymerization-Induced Self-Assembly

Polymerization-induced self-assembly (PISA) combines polymerization and in situ self-assembly of block copolymers in one system and has become a widely used method to prepare block copolymer nanoparticles at high concentrations. The persistence of polymers in the environment poses a huge threat to the ecosystem and represents a significant waste of resources. There is an urgent need to develop novel chemical approaches to synthesize degradable polymers. To meet with this demand, it is crucial to install degradability into PISA nanoparticles. Most recently, degradable PISA nanoparticles have been synthesized by introducing degradation mechanisms into either shell-forming or core-forming blocks. This Minireview summarizes the development in degradable block copolymer nanoparticles synthesized by PISA, including shell-degradable, core-degradable, and all-degradable nanoparticles. Future development will benefit from expansion of polymerization techniques with new degradation mechanisms and adaptation of high-throughput approaches for both PISA syntheses and degradation studies.

Group-Transfer Polymerization-Induced Self-Assembly (GTPISA) in Non-polar Media: An Organocatalyzed Route to Block Copolymer Nanoparticles at Room Temperature

Polymerization-induced self-assembly (PISA) enables the synthesis at large scale of a wide variety of functional nanoparticles. However, a large number of works are related to controlled radical polymerization (CRP) methods and are generally undertaken at elevated temperatures (>50 °C). Here is the first report on methacrylate-based nanoparticles fabricated by group transfer polymerization-induced self-assembly (GTPISA) in non-polar media (n-heptane). This GTPISA process is achieved at room temperature (RT) using 1-methoxy-1-(trimethylsiloxy)-2-methylprop-1-ene (MTS) and tetrabutylammonium bis-benzoate (TBABB) as initiator and organic catalyst, respectively. Under these conditions, well-defined metal-free and colorless diblock copolymers are produced with efficient crossover from the non-polar stabilizing poly(lauryl methacrylate) (PLMA) block to the non-soluble poly(benzyl methacrylate) (PBzMA) segment. The resulting PLMA-b-PBzMA block copolymers simultaneously self-assemble into nanostructures of various sizes and morphologies. GTPISA in non-polar solvent proceeds rapidly at RT and avoids the use of sulfur or halogenated compounds or metallic catalysts associated with the implementation of CRP methods, thus expanding the potential of PISA formulations for applications in non-polar environments.

(Bio)degradable and Biocompatible Nano-Objects from Polymerization-Induced and Crystallization-Driven Self-Assembly

Polymerization-induced self-assembly (PISA) and crystallization-driven self-assembly (CDSA) techniques have emerged as powerful approaches to produce a broad range of advanced synthetic nano-objects with high potential in biomedical applications. PISA produces nano-objects of different morphologies (e.g., spheres, vesicles and worms), with high solids content (∼10-50 wt %) and without additional surfactant. CDSA can finely control the self-assembly of block copolymers and readily forms nonspherical crystalline nano-objects and more complex, hierarchical assemblies, with spatial and dimensional control over particle length or surface area, which is typically difficult to achieve by PISA. Considering the importance of these two assembly techniques in the current scientific landscape of block copolymer self-assembly and the craze for their use in the biomedical field, this review will focus on the advances in PISA and CDSA to produce nano-objects suitable for biomedical applications in terms of (bio)degradability and biocompatibility. This review will therefore discuss these two aspects in order to guide the future design of block copolymer nanoparticles for future translation toward clinical applications.

Influence of Solvent on RAFT-mediated Polymerization of Benzyl Methacrylate (BzMA) and How to Overcome the Thermodynamic/Kinetic Limitation of Morphology Evolution during Polymerization-Induced Self-Assembly

Polymerization-induced self-assembly (PISA) has been demonstrated to be a powerful strategy to produce polymeric nano-objects of various morphologies. Dependent on the solubility of monomers, PISA is usually classified into two...

Brush-like polymers: design, synthesis and applications

With the development of controlled polymerisation, almost all polymerisation strategies have been successfully transplanted to surface-initiated polymerisation. The resulting polymer brushes have emerged as an effective tool for surface functionalization and modulation of the surface properties of materials. To meet various demands it is possible to tailor a material surface with polymer brushes that have diverse dimensionalities, morphologies and compositions. The crowded environment within polymer brushes as well as the stretched conformation of polymer chains sometimes provide unique physicochemical properties, which lead to the delicate creation of inorganic-organic hybridised nanostructures, anti-fouling coatings, biomedical carriers, and materials for use in lubrication, photonics and energy storage. So far, challenges remain in the high-precision synthesis and topological control needed to realize extended applications of polymer brushes. In this Feature Article, we highlight the topology, potential application prospects and various synthetic protocols, particularly for recently established methods, for the efficient synthesis of polymer brushes, as well as their benefits and limitations.

Methods to Determine Chain-Breaking Antioxidant Activity of Nanomaterials beyond DPPH•. A Review

This review highlights the progress made in recent years in understanding the mechanism of action of nanomaterials with antioxidant activity and in the chemical methods used to evaluate their activity. Nanomaterials represent one of the most recent frontiers in the research for improved antioxidants, but further development is hampered by a poor characterization of the ''antioxidant activity'' property and by using oversimplified chemical methods. Inhibited autoxidation experiments provide valuable information about the interaction with the most important radicals involved in the lipid oxidation, namely alkylperoxyl and hydroperoxyl radicals, and demonstrate unambiguously the ability to stop the oxidation of organic materials. It is proposed that autoxidation methods should always complement (and possibly replace) the use of assays based on the quenching of stable radicals (such as DPPH• and ABTS•+). The mechanisms leading to the inhibition of the autoxidation (sacrificial and catalytic radical trapping antioxidant activity) are described in the context of nanoantioxidants. Guidelines for the selection of the appropriate testing conditions and of meaningful kinetic analysis are also given.

Nitroxides as Building Blocks for Nanoantioxidants

Nitroxides are an important class of radical trapping antioxidants whose promising biological activities are connected to their ability to scavenge peroxyl (ROO^•) radicals. We have measured the rate constants of the reaction with ROO^• (k_inh) for a series of 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) derivatives as 5.1 × 10⁶, 1.1 × 10⁶, 5.4 × 10⁵, 3.7 × 10⁵, 1.1 × 10⁵, 1.9 × 10⁵, and 5.6 × 10⁴ M^-1 s^-1 for -H, -OH, -NH₂, -COOH, -NHCOCH₃, -CONH(CH₂)₃CH₃, and ═O substituents in the 4 position, with a good Marcus relationship between log (k_inh) and E° for the R₂NO^•/R₂NO⁺ couple. Newly synthesized Pluronic-silica nanoparticles (PluS) having nitroxide moieties covalently bound to the silica surface (PluS-NO) through a TEMPO-CONH-R link and coumarin dyes embedded in the silica core, has k_inh = 1.5 × 10⁵ M^-1 s^-1. Each PluS-bound nitroxide displays an inhibition duration nearly double that of a structurally related "free" nitroxide. As each PluS-NO particle bears an average of 30 nitroxide units, this yields an overall ≈60-fold larger inhibition of the PluS-NO nanoantioxidant compared to the molecular analogue. The implications of these results for the development of novel nanoantioxidants based on nitroxide derivatives are discussed, such as the choice of the best linkage group and the importance of the regeneration cycle in determining the duration of inhibition.

TEMPO-Functionalized Nanoreactors from Bottlebrush Copolymers for the Selective Oxidation of Alcohols in Water

Polymeric nanoreactors in water fabricated by the self-assembly of amphiphilic copolymers have attracted much attention due to their good catalytic performance without using organic solvents. However, the disassembly and instability of relevant nanostructures often compromise their potential applicability. Herein, the preparation of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-containing nanoreactors by the self-assembly of amphiphilic bottlebrush copolymers has been demonstrated. First, a macromonomer having a norbornenyl polymerizable group was prepared by RAFT polymerization of hydrophobic and hydrophilic monomers. The macromonomer was further subjected to ring-opening metathesis polymerization to produce an amphiphilic bottlebrush copolymer. Further, TEMPO, as a catalyst, was introduced into the hydrophobic block through the activated ester strategy. Finally, TEMPO-functionalized polymeric nanoreactors were successfully obtained by self-assembly in water. The nanoreactors exhibited excellent catalytic activities in selective oxidation of alcohols in water. More importantly, the reaction kinetics showed that the turnover frequency is greatly increased compared to that of the similar nanoreactor prepared from liner copolymers under the same conditions. The outstanding catalytic activities of the nanoreactors from bottlebrush copolymers could be attributed to the more stable micellar structure using the substrate concentration effect. This work presents a new strategy to fabricate stable nanoreactors, paving the way for highly efficient organic reactions in aqueous solutions.

Crosslinked Polydicyclopentadiene Nanoparticles via Ring-Opening Metathesis Polymerization-Induced Self-Assembly Approach

In this communication, the preparation of crosslinked polydicyclopentadiene (PDCPD) nanoparticles via ring-opening metathesis polymerization (ROMP)-induced self-assembly approach is reported. For the ROMPs, the macromolecular chain transfer agents (Macro-CTAs) are synthesized via the ring-opening polymerization (ROP) of ε-caprolactone (CL) with cis-2-butene-1,4-diol as the initiator. The ROMPs are performed with chloroform, tetrahydrofuran, toluene, 1,4-dioxane, and N,N-dimethylacetamide as the solvents, respectively, which are catalyzed with Grubbs second generation catalyst. It is found that the crosslinked PDCPD nanoparticles are obtained with spherical, cylindrical to planar morphologies, depending on the molecular weights of Macro-CTAs, the concentrations of DCPD and the natures of solvents. The polymerization induced self-assembly (ROMPISA) by the use of a non-norbornene-based macromolecular chain transfer agent provides a new and efficient approach to prepare crosslinked polymer nanoparticles.

Flash Technology-Based Self-Assembly in Nanoformulation: From Fabrication to Biomedical Applications

Advances in nanoformulation have driven progress in biomedicine by producing nanoscale tools for biosensing, imaging, and drug delivery. Flash-based technology, the combination of rapid mixing technique with the self-assembly of macromolecules, is a new engine for the translational nanomedicine. Here, we review the state-of-the-art in flash-based self-assembly including theoretical and experimental principles, mixing device design, and applications. We highlight the fields of flash nanocomplexation (FNC) and flash nanoprecipitation (FNP), with an emphasis on biomedical applications of FNC, and discuss challenges and future directions for flash-based nanoformulation in biomedicine.

Boron-rich, cytocompatible block copolymer nanoparticles by polymerization-induced self-assembly

A new methacrylic boronate ester is synthesized and exploited to produce biocompatible nanoparticles with a boron-rich core by PISA.

Towards nanoparticles with site-specific degradability by ring-opening copolymerization induced self-assembly in organic medium

Radical ring-opening copolymerization-induced self-assembly (rROPISA) was successfully applied to the synthesis of core-, surface- or surface plus core-degradable nanoparticles in heptane, leading to site-specific degradability by rROPISA.

Proapoptotic Peptide Brush Polymer Nanoparticles via Photoinitiated Polymerization-Induced Self-Assembly

Herein, we report the photoinitiated polymerization-induced self-assembly (photo-PISA) of spherical micelles consisting of proapoptotic peptide-polymer amphiphiles. The one-pot synthetic approach yielded micellar nanoparticles at high concentrations and at scale (150 mg mL-1 ) with tunable peptide loadings up to 48 wt. %. The size of the micellar nanoparticles was tuned by varying the lengths of hydrophobic and hydrophilic building blocks. Critically, the peptide-functionalized nanoparticles imbued the proapoptotic "KLA" peptides (amino acid sequence: KLAKLAKKLAKLAK) with two key properties otherwise not inherent to the sequence: 1) proteolytic resistance compared to the oligopeptide alone; 2) significantly enhanced cell uptake by multivalent display of KLA peptide brushes. The result was demonstrated improved apoptosis efficiency in HeLa cells. These results highlight the potential of photo-PISA in the large-scale synthesis of functional, proteolytically resistant peptide-polymer conjugates for intracellular delivery.

Recent Advances in the Synthesis and Application of Polymer Compartments for Catalysis

Catalysis is one of the most important processes in nature, science, and technology, that enables the energy efficient synthesis of essential organic compounds, pharmaceutically active substances, and molecular energy sources. In nature, catalytic reactions typically occur in aqueous environments involving multiple catalytic sites. To prevent the deactivation of catalysts in water or avoid unwanted cross-reactions, catalysts are often site-isolated in nanopockets or separately stored in compartments. These concepts have inspired the design of a range of synthetic nanoreactors that allow otherwise unfeasible catalytic reactions in aqueous environments. Since the field of nanoreactors is evolving rapidly, we here summarize-from a personal perspective-prominent and recent examples for polymer nanoreactors with emphasis on their synthesis and their ability to catalyze reactions in dispersion. Examples comprise the incorporation of catalytic sites into hydrophobic nanodomains of single chain polymer nanoparticles, molecular polymer nanoparticles, and block copolymer micelles and vesicles. We focus on catalytic reactions mediated by transition metal and organocatalysts, and the separate storage of multiple catalysts for one-pot cascade reactions. Efforts devoted to the field of nanoreactors are relevant for catalytic chemistry and nanotechnology, as well as the synthesis of pharmaceutical and natural compounds. Optimized nanoreactors will aid in the development of more potent catalytic systems for green and fast reaction sequences contributing to sustainable chemistry by reducing waste of solvents, reagents, and energy.

Enhancing the Efficacy of Metal-Free MRI Contrast Agents via Conjugating Nitroxides onto PEGylated Cross-Linked Poly(Carboxylate Ester)

Herein, two water-soluble PROXYL-based magnetic resonance imaging (MRI) macromolecular organic contrast agents (mORCAs) are designed and synthesized: linear and cross-linked PCE-mPEG-Ppa-PROXYL. They are prepared by conjugating linear and cross-linked poly(carboxylate ester) (PCE) with poly(ethylene glycol) (mPEG2000)-modified nitroxides (PROXYL), respectively. Both mORCAs form self-assembled aggregates in an aqueous phase and PROXYL is protected inside a hydrophobic core to achieve great resistance to reduction in the physiological environment, and they have low toxicity. Since cross-linked PCE-mPEG-Ppa-PROXYL possess a branched architecture, its self-assembled aggregate is more stable and compact with a greater particle size. Cross-linked PCE-mPEG-Ppa-PROXYL outperform the linear one in the following aspects: 1) its longitudinal relaxivity (r 1 = 0.79 mm -1 s-1) is higher than that of the linear one (r 1 = 0.64 mm -1 s-1) and both excel the best mORCA reported so far (r 1 = 0.42 mm -1 s-1); 2) its blood retention time (≈48 h) is longer than that of its linear counterpart (≈10 h); 3) cross-linked PCE-mPEG-Ppa-PROXYL provided better MR imaging contrast resolution in normal organs (liver and kidney) and tumor of mice than the linear one. Overall, cross-linked PCE-mPEG-Ppa-PROXYL may have great potential to be a novel metal-free macromolecular contrast agent for MR imaging.

A Methoxyamine-Protecting Group for Organic Radical Battery Materials-An Alternative Approach

An alternative synthetic route towards the widely employed electroactive poly(TEMPO methacrylate) (PTMA) via a thermally robust methoxyamine-protecting group is demonstrated herein. Protection of the radical moiety of hydroxy-TEMPO with a methyl functionality and subsequent esterification with methacrylic anhydride allows the high-yielding formation of the novel monomer methyl-TEMPO methacrylate (MTMA). The polymerization of MTMA to poly(MTMA) (PMTMA) is investigated via free radical polymerization and reversible addition-fragmentation chain-transfer polymerization (RAFT), a reversible-deactivation radical polymerization technique. Cleavage of the temperature-stable methoxyamine functionality by oxidative treatment of PMTMA with meta-chloroperbenzoic acid (mCPBA) releases the electroactive PTMA. The redox activity of PTMA was confirmed by cyclic voltammetry in lithium-ion coin cells.

CO2-Responsive Nano-Objects with Assembly-Related Aggregation-Induced Emission and Tunable Morphologies

CO₂-responsive polymeric nano-objects with assembly-related aggregation-induced emission (AIE) are obtained via polymerization-induced self-assembly (PISA) of 2-(dimethylamino)ethyl methacrylate (DMAEMA), 2-(4-formylphenoxy)ethyl methacrylate (MAEBA), and 4-(1,2,2-triphenylvinyl)phenyl methacrylate (TPEMA). These nano-objects exhibit, depending on the feed of MAEBA, a morphology evolution process from spherical micelles to vesicles. Due to the presence of DMAEMA units, CO₂ promotes morphology transformation of the nano-objects from spheres to a mixture of "jellyfish" and vesicles and vesicles to complex vesicles. Moreover, TPEMA endows the AIE feature to these nano-objects, offering a strategy to monitor the morphology evolution process in real time. Thus, this approach is significant for exploring the assembly mechanism of copolymer in polymerization-induced self-assembly and designing multistimuli-responsive polymeric nanomaterials with tunable morphologies and sizes.

Polymerization techniques in polymerization-induced self-assembly (PISA)

The development of controlled/“living” polymerization greatly stimulated the prosperity of the fabrication and application of block copolymer nano-objects.

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.

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.

Self-assembly of amphiphilic copolymers containing polysaccharide: PISA versus nanoprecipitation, and the temperature effect

The self-assembly methods and the temperature have a considerable impact on the morphology of the resulting nanoobjects in the case of amphiphilic glycopolymers.

Ring-Opening Polymerization of N-Carboxyanhydride-Induced Self-Assembly for Fabricating Biodegradable Polymer Vesicles

Polymerization-induced self-assembly (PISA) is regarded as one of the most important strategies in macromolecular nanotechnology, as it can create a wide range of nanoparticles at high concentrations and on a large scale. However, open-to-air PISA with biodegradable product is still a complicated challenge, as traditional PISA is usually carried out under oxygen-free conditions to afford nonbiodegradable polymers. To meet the above challenges, we propose a convenient one-pot open-to-air ring-opening polymerization (ROP) of N-carboxyanhydride (NCA)-induced self-assembly (NCA-PISA) at 10 °C, without the need for degassing, heating, catalysts, or chain transfer agents. The morphologies of nanoparticles depend on the ratio of the initiator to the monomer and the solid content. Polymer vesicles can be fabricated when the ratio and the solid content are 1:20 and 20%, respectively. Overall, this versatile one-pot NCA-PISA provides an insight into facilely fabricating biodegradable nanoparticles in air.

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.

Ring-opening metathesis polymerization-induced self-assembly (ROMPISA)

Ring-opening metathesis polymerization-induced self-assembly (ROMPISA) has expanded the preparation of PISA nano-objects beyond radical polymerization approaches. In this highlight article, we summarize current advances and existing challenges in ROMPISA methodologies.

Nitroxide radical-containing polynorbornenes by ring-opening metathesis polymerization as stabilizing agents for polyolefins

A series of original 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-containing dicarboximide norbornene monomers have been synthesized and polymerized via ring-opening metathesis polymerization using the Grubbs 3^rd generation catalyst.

Straightforward access to biocompatible poly(2-oxazoline)-coated nanomaterials by polymerization-induced self-assembly

Poly(2-ethyl-2-oxazoline) chain transfer agents are employed in photoinitiated RAFT PISA, providing access to biocompatible core–shell polymeric nanostructures with various morphologies.