Novel Amphiphilic Multiarm, Starlike Coil–Rod Diblock Copolymers via a Combination of Click Chemistry with Living Polymerization

Fast and Scalable Synthetic Route to Densely Grafted, Branched Polystyrenes and Polydienes via Anionic Polymerization Utilizing P2VP as Branching Point

Defined, branched polymer architectures with low dispersity and architectural purity are of great interest to polymer science but are challenging to synthesize. Besides star and comb, especially the pom-pom topology is of interest as it is the simplest topology with exactly two branching points. Most synthetic approaches to a pom-pom topology reported a lack of full control and variability over one of the three topological parameters, the backbone or arm molecular weight and arm number. A new, elegant, fast, and scalable synthetic route without the need for post-polymerization modification (PPM) or purification steps during the synthesis to a pom-pom and a broad variety of topologies made from styrene and dienes is reported, with potential application to barbwire, bottlebrush, miktoarm star, Janus type polymers, or multi-graft copolymers. The key is to inset short poly(2-vinyl-pyridine) blocks (<2 mol% in the branched product) into the backbone as branching points. Carb anions can react at the C6 carbon of the pyridine ring, grafting the arms onto the backbone. Since the synthetic route to polystyrene pom-poms has only two steps and is free of PPM or purification, large amounts of up to 300 g of defined pom-pom structures can be synthesized in one batch.

Polymer-Ligated Nanocrystals Enabled by Nonlinear Block Copolymer Nanoreactors: Synthesis, Properties, and Applications

The past several decades have witnessed substantial advances in synthesis and self-assembly of inorganic nanocrystals (NCs) due largely to their size- and shape-dependent properties for use in optics, optoelectronics, catalysis, energy conversion and storage, nanotechnology, and biomedical applications. Among various routes to NCs, the nonlinear block copolymer (BCP) nanoreactor technique has recently emerged as a general yet robust strategy for crafting a rich diversity of NCs of interest with precisely controlled dimensions, compositions, architectures, and surface chemistry. It is notable that nonlinear BCPs are unimolecular micelles, where each block copolymer arm of nonlinear BCP is covalently connected to a central core or polymer backbone. As such, their structures are static and stable, representing a class of functional polymers with complex architecture for directing the synthesis of NCs. In this review, recent progress in synthesizing NCs by capitalizing on two sets of nonlinear BCPs as nanoreactors are discussed. They are star-shaped BCPs for producing 0D spherical nanoparticles, including plain, hollow, and core-shell nanoparticles, and bottlebrush-like BCPs for creating 1D plain and core/shell nanorods (and nanowires) as well as nanotubes. As the surface of these NCs is intimately tethered with the outer blocks of nonlinear BCPs used, they can thus be regarded as polymer-ligated NCs (i.e., hairy NCs). First, the rational design and synthesis of nonlinear BCPs via controlled/living radical polymerizations is introduced. Subsequently, their use as the NC-directing nanoreactors to yield monodisperse nanoparticles and nanorods with judiciously engineered dimensions, compositions, and surface chemistry is examined. Afterward, the intriguing properties of such polymer-ligated NCs, which are found to depend sensitively on their sizes, architectures, and functionalities of surface polymer hairs, are highlighted. Some practical applications of these polymer-ligated NCs for energy conversion and storage and drug delivery are then discussed. Finally, challenges and opportunities in this rapidly evolving field are presented.

A Versatile Strategy for Unimolecular Micelle-Derived Hollow Polymer Nanoparticles as General Nanoreactors

We reported the synthesis of a well-defined hollow polymer nanoparticle derived from star-shaped unimolecular micelles. β-Cyclodextrin was first applied as an efficient macroinitiator to prepare a star-shaped PCL via ring-opening polymerization (ROP). Then, the star-shaped PCL was modified to be a macro-RAFT agent for photoinduced electron/energy transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization of S-Cl monomers. The prepared unimolecular micelles can be photocross-linked under UV irradiation after a simple nucleophilic substitution reaction, which made -Cl groups to be -N₃ groups. After the selective removal of the PCL core, hollow polymer nanoparticles were achieved and exhibited to be a general nanoreactor strategy for the fabrication of nanocrystals with well-controlled architectures. Compared with unimolecular micelle templates, the nanocrystals prepared by hollow templates are absolutely pure as no polymer chains are embedded in the inorganic nanocrystals. In addition, by changing the concentration of the precursor, the structure of the nanocrystal can be changed from a normal spherical structure to a hollow structure.

Multiarm star polymers based on thiol–ene photoclick cyclodextrin cores

Highly efficient synthesis of multifunctional initiators based on cyclodextrin (CD) cores was achieved by a thiol–ene photoclick strategy. They were successfully employed in a “core-first” approach to prepare multiarm star polymers via ATRP.

Influence of Branches on the Phase Behavior of (AB)f Starlike Block Copolymer under Cylindrical Confinement

Experimentally, self-assembled morphologies of the (AB)_f starlike block copolymer are strongly dependent on the number of arms, f. For example, the 2- and 4-arm starlike block copolymers exhibited the morphologies of hexagonally arrayed polystyrene cylinder in the polyisoprene matrix while order-bicontinuous nanostructures were observed in 8-, 12-, and 18-arm stars. Theoretically, we found that the transition sequence for (AB)₃ is C₁^B → Dk^B → P₂^B → L₂^B, which becomes C₁^B → L₁^B when f > 6. To explore the influence of f on the phase behavior of (AB)_f under cylindrical confinement, we calculated the two-dimensional phase diagram with respect to the volume fraction and the pore diameter. Our conclusions show that the topologies of the phase diagram are independent of the number of arms; however, the number of arms does affect the phase boundary, which inevitably leads to the different phase transition sequences at fixed volume fraction. Therefore, from the calculated phase diagram, the influence of f on the phase behavior of the starlike copolymer is fully understood.

Enabling Tailorable Optical Properties and Markedly Enhanced Stability of Perovskite Quantum Dots by Permanently Ligating with Polymer Hairs

Instability of perovskite quantum dots (QDs) toward humidity remains one of the major obstacles for their long-term use in optoelectronic devices. Herein, a general amphiphilic star-like block copolymer nanoreactor strategy for in situ crafting a set of hairy perovskite QDs with precisely tunable size and exceptionally high water and colloidal stabilities is presented. The selective partition of precursors within the compartment occupied by inner hydrophilic blocks of star-like diblock copolymers imparts in situ formation of robust hairy perovskite QDs permanently ligated by outer hydrophobic blocks via coprecipitation in nonpolar solvent. These size- and composition-tunable perovskite QDs reveal impressive water and colloidal stabilities as the surface of QDs is intimately and permanently ligated by a layer of outer hydrophobic polymer hairs. More intriguingly, the readily alterable length of outer hydrophobic polymers renders the remarkable control over the stability enhancement of hairy perovskite QDs.

Theoretical insight on hybrid nanocomposites of graphene quantum dot and carbazole-carbazole dyes as an efficient sensitizer of DSSC

The feasibility of the hybrid nanocomposites of the graphene quantum dot (GQD) and carbazole-carbazole dyes as the efficient sensitizer of dye-sensitized solar cells (DSSC) is investigated. By using the first principles density functional theory (DFT), we fully optimize the geometrical structures of GQD, the carbazole-carbazole dyes, and their hybrid nanocomposites. The harmonic frequency analysis is used to confirm the energy stability of the optimized structures. The optical absorptions of the structures are calculated with the time-dependent DFT (TDDFT). Using the I^-/I₃^- electrolyte and the conduction band minimum of TiO₂ electrode as a sample, we examine the feasibility of the nanocomposites as the sensitizer of DSSC with the charge spatial separation and the molecular orbital energy levels of the nanocomposites. The results demonstrate all the considered nanocomposites have suitable energy levels of the frontier orbitals and significantly charge spatial separation. TDDFT results show the oscillator strengths of all nanocomposites demonstrate the obvious enhancement in the visible light region. Moreover, the appropriate open-circuit voltage value, the larger light-harvesting efficiency, and larger driving force are also identified for these nanocomposites. Therefore, the nanocomposites could be the more promising candidates of sensitizer for DSSC in comparison with the separate carbazole-carbazole dyes.

Star-Shaped Block Copolymers: Effective Polymer Gelators of High-Performance Gel Electrolytes for Electrochemical Devices

Ion gels composed of copolymers and ionic liquids (ILs) have attracted great interest as polymer gel electrolytes for various electrochemical applications. Here, we present highly robust ion gels based on a six-arm star-shaped block copolymer of (poly(methyl methacrylate)- b-polystyrene)₆ ((MS)₆) and an ionic liquid of 1-ethyl-3-methylimidazolium bis(trifluoromethyl sulfonyl)imide ([EMI][TFSI]). Compared to typical ion gels based on linear polystyrene- b-poly(methyl methacrylate)- b-polystyrene (SMS), the (MS)₆-based gels show mechanical moduli of more than twice under various strains (e.g., stretching, compression, and shear). In addition, the outstanding mechanical property is maintained even up to 180 °C without a gel-sol transition. To demonstrate that (MS)₆-based ion gels can serve as effective gel electrolytes for electrochemical applications, tris(2,2'-bipyridyl)ruthenium(II) (Ru(bpy)₃²⁺), a representative electrochemiluminescent (ECL) luminophore, is incorporated into the gels. In particular, flexible ECL devices based on (MS)₆ gels exhibit high durability against bending deformation compared to devices with gels based on linear SMS having a similar molecular weight and a composition. This result implies that star-shaped block copolymers are effective gelators for achieving flexible/wearable electrochemical electronics.

Functional materials generated by allying cyclodextrin-based supramolecular chemistry with living polymerization

Cyclodextrin molecules are cyclic oligosaccharides that display a unique structure including an inner side and two faces on their outer sides.

Complexes of magnetic nanospheres with amphiprotic polymer-Zn systems for the selective isolation of lactoferrin

Amphiprotic polymer-Zn complex magnetic nanospheres, termed Fe₃O₄@PCL-CMC-Zn, are designed and prepared via a step-wise synthetic strategy. Hydrophobic polycaprolactone (PCL) is firstly coated onto the magnetic Fe₃O₄ nanospheres, and then hydrophilic carboxymethylcellulose (CMC) is grafted onto the hydrophobic PCL blocks via an esterification reaction, followed by finally chelating with Zn²⁺ ions. The homogeneous core-shell structure and fastened amphiprotic polymer layer provide the as-prepared Fe₃O₄@PCL-CMC-Zn magnetic nanospheres with improved protein binding behavior, and the chelated Zn²⁺ offers the nanospheres favorable adsorption selectivity towards apo-lactoferrin. The adsorption capacity of apo-lactoferrin is high, up to 615.3 mg g^-1. The exploitation of FeCl₃ as a stripping reagent not only provides efficient recovery of the adsorbed apo-lactoferrin, i.e. a recovery of 83.2%, but also achieves the restoration of the lactoferrin structure. The Fe₃O₄@PCL-CMC-Zn magnetic nanospheres are then employed as a sorbent for the selective isolation of lactoferrin from human colostrum samples, obtaining high-purity lactoferrin as demonstrated by SDS-PAGE and Q-TOF LC-MS assays.

Light-enabled reversible self-assembly and tunable optical properties of stable hairy nanoparticles

The ability to dynamically organize functional nanoparticles (NPs) via the use of environmental triggers (temperature, pH, light, or solvent polarity) opens up important perspectives for rapid and convenient construction of a rich variety of complex assemblies and materials with new structures and functionalities. Here, we report an unconventional strategy for crafting stable hairy NPs with light-enabled reversible and reliable self-assembly and tunable optical properties. Central to our strategy is to judiciously design amphiphilic star-like diblock copolymers comprising inner hydrophilic blocks and outer hydrophobic photoresponsive blocks as nanoreactors to direct the synthesis of monodisperse plasmonic NPs intimately and permanently capped with photoresponsive polymers. The size and shape of hairy NPs can be precisely tailored by modulating the length of inner hydrophilic block of star-like diblock copolymers. The perpetual anchoring of photoresponsive polymers on the NP surface renders the attractive feature of self-assembly and disassembly of NPs on demand using light of different wavelengths, as revealed by tunable surface plasmon resonance absorption of NPs and the reversible transformation of NPs between their dispersed and aggregated states. The dye encapsulation/release studies manifested that such photoresponsive NPs may be exploited as smart guest molecule nanocarriers. By extension, the star-like block copolymer strategy enables the crafting of a family of stable stimuli-responsive NPs (e.g., temperature- or pH-sensitive polymer-capped magnetic, ferroelectric, upconversion, or semiconducting NPs) and their assemblies for fundamental research in self-assembly and crystallization kinetics of NPs as well as potential applications in optics, optoelectronics, magnetic technologies, sensory materials and devices, catalysis, nanotechnology, and biotechnology.

Water-soluble fluorescent unimolecular micelles: ultra-small size, tunable fluorescence emission from the visible to NIR region and enhanced biocompatibility for in vitro and in vivo bioimaging

Water-soluble fluorescent unimolecular micelles with ultra-small size and various fluorescence emission for multicolor imaging.

Acid-Activatable Theranostic Unimolecular Micelles Composed of Amphiphilic Star-like Polymeric Prodrug with High Drug Loading for Enhanced Cancer Therapy

Stimuli-responsive nanomedicine with theranostic functionalities with reduced side-effects has attracted growing attention, although there are some major obstacles to overcome before clinical applications. Herein, we present an acid-activatable theranostic unimolecular micelles based on amphiphilic star-like polymeric prodrug to systematically address typical existing issues. This smart polymeric prodrug has a preferable size of about 35 nm and strong micellar stability in aqueous solution, which is beneficial to long-term blood circulation and efficient extravasation from tumoral vessels. Remarkably, the polymeric prodrug has a high drug loading rate up to 53.1 wt%, which induces considerably higher cytotoxicity against tumor cells (HeLa cells and MCF-7 cells) than normal cells (HUVEC cells) suggesting a spontaneous tumor-specific targeting capability. Moreover, the polymeric prodrug can serve as a fluorescent nanoprobe activated by the acidic microenvironment in tumor cells, which can be used as a promising platform for tumor diagnosis. The superior antitumor effect in this in vitro study demonstrates the potential of this prodrug as a promising platform for drug delivery and cancer therapy.

Facile synthesis and chiral recognition of block and star copolymers containing stereoregular helical poly(phenyl isocyanide) and polyethylene glycol blocks

A new Pd(ii) initiator bearing an alkyne headgroup was designed and synthesized.

pH-Responsive unimolecular micelles based on amphiphilic star-like copolymers with high drug loading for effective drug delivery and cellular imaging

A theranostic nanoplatform based on pH-responsive amphiphilic star-like copolymers for theranostic and NIR imaging applications.

Synthesis of platinum(ii) complex end functionalized star polymers: luminescence enhancements and unimolecular micelles in solvents of weakened quality

Platinum(ii) complex end functionalized star polymers have been synthesized by reacting K₂PtCl₄ with star ligands ended with 2,6-bis(benzimidazol-2′-yl)pyridine. They show luminescence enhancements and form unimolecular micelles in solvents of weakened quality.

Precisely Size-Tunable Monodisperse Hairy Plasmonic Nanoparticles via Amphiphilic Star-Like Block Copolymers

In situ precision synthesis of monodisperse hairy plasmonic nanoparticles with tailored dimensions and compositions by capitalizing on amphiphilic star-like diblock copolymers as nanoreactors are reported. Such hairy plasmonic nanoparticles comprise uniform noble metal nanoparticles intimately and perpetually capped by hydrophobic polymer chains (i.e., "hairs") with even length. Interestingly, amphiphilic star-like diblock copolymer nanoreactors retain the spherical shape under reaction conditions, and the diameter of the resulting plasmonic nanoparticles and the thickness of polymer chains situated on the surface of the nanoparticle can be readily and precisely tailored. These hairy nanoparticles can be regarded as hard/soft core/shell nanoparticles. Notably, the polymer "hairs" are directly and permanently tethered to the noble metal nanoparticle surface, thereby preventing the aggregation of nanoparticles and rendering their dissolution in nonpolar solvents and the homogeneous distribution in polymer matrices with long-term stability. This amphiphilic star-like block copolymer nanoreactor-based strategy is viable and robust and conceptually enables the design and synthesis of a rich variety of hairy functional nanoparticles with new horizons for fundamental research on self-assembly and technological applications in plasmonics, catalysis, energy conversion and storage, bioimaging, and biosensors.

Unimolecular Micelles from Layered Amphiphilic Dendrimer-Like Block Copolymers

In this report, we synthesized layered amphiphilic dendrimer-like block copolymers containing a polystyrene core and poly(p-tert-butoxystyrene)/poly(p-hydroxylstyrene) shell (coded G4-PtBOS/G4-PHOS). The synthetic method is easy involving anionic polymerization, epoxidation, ring-opening reaction and hydrolysis reaction. The hydrolyzed G4-PtBOS was soluble in alkaline water and behaved as unimolecular micelle, as demonstrated by the results of DLS, cryo- and normal TEM, and pyrene entrapping experiment. The stability of the unimolecular micelles was investigated via ζ-potential measurements.

Organic-Inorganic Nanocomposites via Placing Monodisperse Ferroelectric Nanocrystals in Direct and Permanent Contact with Ferroelectric Polymers

Organic-inorganic nanocomposites composed of polymers and nanoparticles offer a vast design space of potential material properties, depending heavily on the properties of these two constituents and their spatial arrangement. The ability to place polymers in direct contact with functional nanoparticles via strong bonding, that is, stable chemical interaction without the dissociation of surface capping polymers, provides a means of preventing nanoparticles from aggregation and increasing their dispersibility in nanocomposites, and promises opportunities to explore new properties and construction of miniaturized devices. However, this is still a challenging issue and has not yet been largely explored. Here, we report an unconventional strategy to create in situ organic-inorganic nanocomposites comprising monodisperse ferroelectric nanoparticles directly and permanently tethered with ferroelectric polymers by capitalizing on rationally designed amphiphilic star-like diblock copolymer as nanoreactors. The diameter of ferroelectric nanoparticles and the chain length of ferroelectric polymers can be precisely tuned. The dielectric and ferroelectric properties of nanocomposites containing different sizes of ferroelectric nanoparticles were scrutinized. Such bottom-up crafting of intimate organic-inorganic nanocomposites offers new levels of tailorability to nanostructured materials and promises new opportunities for achieving exquisite control over the surface chemistry and properties of nanocomposites with engineered functionality for diverse applications in energy conversion and storage, catalysis, electronics, nanotechnology, and biotechnology.

Continuous crafting of uniform colloidal nanocrystals using an inert-gas-driven microflow reactor

Recent research has witnessed rapid advances in synthesis of nanocrystals, which has led to the development of a large variety of approaches for producing nanocrystals with controlled dimensions. However, most of these techniques lack the high-throughput production. Herein, we report on a viable and robust strategy based on an inert-gas-driven microflow reactor for continuous crafting of high-quality colloidal nanocrystals. With the judicious introduction of the inert-gas driven capability, the microflow reactor provides an attractive platform for continuous production of colloidal nanocrystals in large quantities, including easily-oxidized nanocrystals. The as-synthesized nanocrystals possessed a uniform size and shape. Intriguingly, the size of nanocrystals can be effectively tailored by varying the flow rate and the precursor concentration. We envision that the microflow reactor strategy is general and offers easy access to a wide range of scalable nanocrystals for potential applications in sensors, optics, optoelectronics, solar energy conversion, batteries, photocatalysis, and electronic devices.

Self-assembly of miktoarm star-like ABn block copolymers: from wet to dry brushes

Self-assembly of miktoarm star-like ABn block copolymer in both selective solvent (A- or B-selective) and miscible homopolymer matrix (A or B homopolymer), that is, formation of micelles, was for the first time investigated by theoretical calculations based on self-consistent mean field theory. Interestingly, the calculation revealed that the size of micelles in solvent was smaller than that in homopolymer under the same conditions. In B-selective solvent, with increasing number of B blocks n in miktoarm star-like ABn block copolymer at a fixed volume fraction of A block, the micellar size decreased gradually. In stark contrast, when miktoarm star-like ABn block copolymer dissolved in B homopolymer matrix at molecular weight ratio of B homopolymer to ABn block copolymer fH = 0.30, the overall micellar size decreased nonmonotonically as the number of B blocks n in ABn block copolymer increased. The largest micelle was formed in AB2 (i.e., n = 2). This intriguing finding can be attributed to a wet-to-dry brush transition that occurred from n = 1 to n = 2 in the micellization of miktoarm star-like ABn block copolymer. Moreover, the micellization behaviors of miktoarm star-like ABn block copolymer in A-selective solvent and A homopolymer matrix were also explored, where the overall micellar size in both scenarios was found to decrease monotonically as n in ABn block copolymer increased. These self-assembled nanostructures composed of miktoarm star-like ABn block copolymers may promise a wide range of applications in size-dependent drug delivery and bionanotechnology.

Synthesis and properties of clickable A(B-b-C)20 miktoarm star-shaped block copolymers with a terminal alkyne group

A novel and reactive A(B-b-C)₂₀ miktoarm star-shaped block copolymer has been successfully synthesized through ATRP reaction combined with click reactions.

A versatile strategy for uniform hybrid nanoparticles and nanocapsules

A novel and versatile strategy for uniform organo-silica hybrid nanoparticles and nanocapsules was developed. The key to our strategy is the implementation of spherical star-like homopolymers and diblock copolymers with well-controlled molecular weights that form unimolecular micelles in solution as nanoreactors.

Unimolecular micelles of amphiphilic cyclodextrin-core star-like block copolymers for anticancer drug delivery

Amphiphilic star-like block copolymers form robust biocompatible unimolecular micelles that are efficient in the delivery of anticancer drugs such as doxorubicin.

Water-soluble star-shaped brush-like block copolymers: synthesis and application as multicompartment nanoreactors for fabrication of quantum dot colloidal nanocrystal clusters

Water-soluble multi-arm star-shaped brush-like block copolymers of (PEO-g-PAA)-b-PEO were synthesized and exploited as polymeric nanoreactors to structure-direct in situ fabrication of CdSe QD colloidal nanocrystal clusters.

Self-assembly of 21-arm star-like diblock copolymer in bulk and under cylindrical confinement

Phase behaviors of a 21-arm star-like diblock copolymer in bulk and under confinement were explored by using the pseudo-spectral method of a self-consistent mean field theory. An asymmetrical phase diagram in bulk was constructed by comparing the free energy of different structures. The gyroid phase was found to possess a large phase region when the inner block in the star-like diblock copolymer has a small volume fraction, suggesting the propensity to form the gyroid phase under this condition. Combined with the early experimental work, a scaling law correlating the period of lamellae D(multiarms) formed from multi-arm star-like block copolymers with the number of arms f was identified, that is, D(multiarms) = D/f(1/2), where D is the period of a linear diblock copolymer with the same degree of polymerization N as a star-like diblock copolymer. The scaling law was also substantiated by the scaling theory. The bridging fraction of the lamellae formed in a star-like diblock copolymer was nearly 100%, which is advantageous for improving its mechanical properties. Some interesting two-dimensional and three-dimensional morphologies were yielded under the cylindrical confinement, where a 3D double helix was found to be the most stable structure.