Water-soluble organo-silica hybrid nanotubes templated by cylindrical polymer brushes

Self-Assembled Crystalline Bundles in Soluble Metal-Organic Nanotubes

The use of nanotubes in the solution state is crucial not only for the exploration of physical and chemical behaviors at the molecular level but also for application such as thin-film fabrication. Surface modification is generally used to solubilize carbon nanotubes (CNTs) and various synthetic nanotubes; however, this method may affect the surface properties of the original nanotubes, and the detailed crystal structure obtained after modification is unclear. Here, we report the synthesis of a crystalline and soluble metal-organic nanotube consisting of a cationic tubular framework and an anion with a long alkyl chain. The nanotubular structures are formed not only in the solid state but also in the solution state, as confirmed by an X-ray structural analysis, optical measurements, and electron microscopy studies. This nanotube system is realized in different states without any surface modification, which is quite different from typical CNTs and synthetic nanotubes. In addition, self-assembled crystalline bundles are directly observed using transmission electron microscopy (TEM) for the first time in a metal-organic nanotube system. The bundle structures are also confirmed by atomic force microscopy (AFM) observations of thin nanotube films. We envisage a systematic design of such soluble metal-organic nanotubes that will enable direct observation of mass transport behavior in channels of bundles or a single nanotube, as well as a wide range of thin-film applications.

Synthesis and Visualization of bottlebrush-shaped segmented hyperbranched polymers

Visualization of single molecular morphology provides an intuitive evidence to understand the relationships of molecular structure-synthetic method. Herein, by combining the architectural features of molecular bottlebrush (MBB) and segmented hyperbranched...

Conformation, Self-Organization and Thermoresponsibility of Polymethacrylate Molecular Brushes with Oligo(ethylene glycol)-block-oligo(propylene glycol) Side Chains

Polymethacrylic molecular brushes with oligo(ethylene glycol)-block-oligo(propylene glycol) side chains were investigated by static and dynamic light scattering and viscometry. The solvents used were acetonitrile, tetrahydrofuran, chloroform, and water. The grafted copolymers were molecularly dispersed and dissolved in tetrahydrofuran and acetonitrile. In these solvents, the molar masses of copolymers were determined. In thermodynamically good solvents, namely tetrahydrofuran and acetonitrile, investigated copolymers have a high intramolecular density and the shape of their molecules resembles a star-shaped macromolecule. In chloroform and water, the micelle-like aggregates were formed. Critical micelle concentrations decreased with the lengthening of the hydrophobic block. Molecular brushes demonstrated thermosensitive behavior in aqueous solutions. The phase separation temperatures reduced with an increase in the content of the oligo(propylene glycol) block.

Polymer-Grafted Porous Silica Nanoparticles with Enhanced CO2 Permeability and Mechanical Performance

Three different types of polymer ligands, poly(methyl methacrylate) (PMMA), poly(methyl methacrylate-random-poly(ethylene glycol)methyl ether methacrylate) (PMMA-r-PEGMEMA), and poly(ionic liquid)s (PIL), were grafted onto the surface of 15 nm solid and large hollow porous silica nanoparticles (average particle size ∼60 nm) by surface-initiated atom transfer radical polymerization (SI-ATRP) to demonstrate the enhanced carbon dioxide (CO₂) permeability as well as mechanical properties. After characterizing the purified products, free-standing bulk films were fabricated by the solvent-casting method. The poly(ionic liquid) nanocomposite films exhibited a much higher carbon dioxide permeance than PMMA and PMMA-r-PEGMEMA systems with a similar silica content. Also, the hollow silica-mixed matrix membranes showed a significant enhancement in CO₂ permeability compared to the 15 nm solid silica films because of the pore structure. Despite the transparency loss due to the scattering of larger particle sizes, the hollow silica particle brush films exhibited the same mechanical properties as the 15 nm solid silica-derived ones.

Recent Advances in the Synthesis of Polymer-Grafted Low-K and High-K Nanoparticles for Dielectric and Electronic Applications

The synthesis of polymer-grafted nanoparticles (PGNPs) or hairy nanoparticles (HNPs) by tethering of polymer chains to the surface of nanoparticles is an important technique to obtain nanostructured hybrid materials that have been widely used in the formulation of advanced polymer nanocomposites. Ceramic-based polymer nanocomposites integrate key attributes of polymer and ceramic nanomaterial to improve the dielectric properties such as breakdown strength, energy density and dielectric loss. This review describes the "grafting from" and "grafting to" approaches commonly adopted to graft polymer chains on NPs pertaining to nano-dielectrics. The article also covers various surface initiated controlled radical polymerization techniques, along with templated approaches for grafting of polymer chains onto SiO2, TiO2, BaTiO3, and Al2O3 nanomaterials. As a look towards applications, an outlook on high-performance polymer nanocomposite capacitors for the design of high energy density pulsed power thin-film capacitors is also presented.

Cylindrical polymer brushes-anisotropic unimolecular micelle drug delivery system for enhancing the effectiveness of chemotherapy

Polymer systems can be designed into different structures and morphologies according to their physical and chemical performance requirements, and are considered as one of the most promising controlled delivery systems that can effectively improve the cancer therapeutic index. However, the majority of the polymer delivery systems are designed to be simple spherical nanostructures. To explore morphology/size-oriented delivery performance optimization, here, we synthesized three novel cylindrical polymer brushes (CPBs) by atom transfer radical polymerization (ATRP), which were cellulose-g-(CPT-b-OEGMA) (CCO) with different lengths (~86, ~40, and ~21 nm). The CPBs are composed of bio-degradable cellulose as the carrier, poly(ethylene glycol) methyl ether methacrylate (OEGMA) as hydrophily block, and glutathione (GSH)-responsive hydrophobic camptothecin (CPT) monomer as loaded anticancer drug. By controlling the chain length of the initiator, three kinds of polymeric prodrugs with different lengths (CCO-1, CCO-2, and CCO-3) could be self-organized into unimolecular micelles in water. We carried out comparative studies of three polymers, whose results verified that the shorter CPBs exhibited higher drug release efficiency, more cellular uptake, and enhanced tumor permeability, accompanied by shortened blood circulation time and lower tumor accumulation. As evidenced by in vivo experiments, the shorter CPBs exhibited higher anti-tumor efficiency, revealing that the size advantage has a higher priority than the anisotropic structure advantage. This provided vital information as to design an anisotropic polymer-based drug delivery system for cancer therapy.

Two-Step Divergent Synthesis of Monodisperse and Ultra-Long Bottlebrush Polymers from an Easily Purifiable ROMP Monomer

The longest bottlebrush polymers reported so far (up to 7 μm in length) were synthesized in two steps from a norbornene derivative bearing two 2-bromoisobutylate moieties (NB). The key to this achievement is the excellent reactivity of NB in ring opening metathesis polymerization, which proceeded in a well-controlled manner with quantitative conversion of NB for monomer-initiator ratios ranging up to 10,000. The resultant polymer derived from NB was readily converted to various bottlebrush polymers in a divergent synthetic route by grafting vinyl monomers from the 2-bromoisobutylate units in NB via atom transfer radical polymerization. The structure of the ultra-long bottlebrush polymer was directly observed using atomic force microscopy.

Silica Nanoparticles

Silica consists of one silicon atom and two oxygen atoms (SiO₂) and is commonly used in various aspects of daily life. For example, it has been used as glass, insulator, and so on. Nowadays, silica is used as core reagents for fabricating and encapsulating nanoparticles (NPs). In this chapter, the usage of silica in nanotechnology is described. Synthesis and surface modification of silica nanoparticles (SiNPs), including via the Stöber method, reverse microemulsion method, and modified sol-gel method, are illustrated. Then, various NPs with silica encapsulation are explained. At last, the biological applications of those mentioned NPs are described.

Self-Assembly of Molecular Brushes with Polyimide Backbone and Amphiphilic Block Copolymer Side Chains in Selective Solvents

Three-component molecular brushes with a polyimide backbone and amphiphilic block copolymer side chains with different contents of the “inner” hydrophilic (poly(methacrylic acid)) and “outer” hydrophobic (poly(methyl methacrylate)) blocks were synthesized and characterized by molecular hydrodynamics and optics methods in solutions of chloroform, dimethylformamide, tetrahydrofuran and ethanol. The peculiarity of the studied polymers is the amphiphilic structure of the grafted chains. The molar masses of the molecular brushes were determined by static and dynamic light scattering in chloroform in which polymers form molecularly disperse solutions. Spontaneous self-assembly of macromolecules was detected in dimethylformamide, tetrahydrofuran and ethanol. The aggregates size depended on the thermodynamic quality of the solvent as well as on the macromolecular architectural parameters. In dimethylformamide and tetrahydrofuran, the distribution of hydrodynamic radii of aggregates was bimodal, while in ethanol, it was unimodal. Moreover, in ethanol, an increase in the poly(methyl methacrylate) content caused a decrease in the hydrodynamic radius of aggregates. A significant difference in the nature of the blocks included in the brushes determines the selectivity of the used solvents, since their thermodynamic quality with respect to the blocks is different. The macromolecules of the studied graft copolymers tend to self-organization in selective solvents with formation of a core–shell structure with an insoluble solvophobic core surrounded by the solvophilic shell of side chains.

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.

Nanofabrication within unimolecular nanoreactors

Nanoparticles (NPs) have been a research focus over the last three decades owing to their unique properties and extensive applications. It is crucial to precisely control the features of NPs including topology, architecture, composition, size, surface and assembly because these features will affect their properties and then applications. Ingenious nanofabrication strategies have been developed to precisely control these features of NPs, especially for templated nanofabrication within predesigned nanoreactors. Compared with conventional nanoreactors (hard templates and supramolecular nanoreactors), unimolecular nanoreactors exhibit (1) covalently stable nanostructures uninfluenced by environmental variations, (2) extensively regulated features of the structure including topology, composition, size, surface and valence due to the rapid development of polymer chemistry, and (3) effective encapsulation of abundant guests with or without strong interaction to achieve the function of loading, delivery and conversion of guests. Thus, unimolecular nanoreactors have shown fascinating prospects as templates for nanofabrication. Various NPs with expected topologies (sphere, rod, tube, branch, and ring), architectures (compact, hollow, core-shell, and necklace-like), compositions (metal, metal oxide, semiconductor, doping, alloy, silica, and composite), sizes (generally 1-100 nm), surface properties (hydrophilic, hydrophobic, reactivity, valence and responsivity) and assemblies (oligomer, chain, and aggregate) can be fabricated easily within reasonably designed unimolecular nanoreactors in a programmable way. In this review, we provide a brief introduction of the properties and types of unimolecular nanoreactors, a condensed summary of representative methodologies of nanofabrication within various unimolecular nanoreactors and a predicted outlook of the potential further developments of this charming nanofabrication approach.

Precision Anisotropic Brush Polymers by Sequence Controlled Chemistry

The programming of nanomaterials at molecular length-scales to control architecture and function represents a pinnacle in soft materials synthesis. Although elusive in synthetic materials, Nature has evolutionarily refined macromolecular synthesis with perfect atomic resolution across three-dimensional space that serves specific functions. We show that biomolecules, specifically proteins, provide an intrinsic macromolecular backbone for the construction of anisotropic brush polymers with monodisperse lengths via grafting-from strategy. Using human serum albumin as a model, its sequence was exploited to chemically transform a single cysteine, such that the expression of said functionality is asymmetrically placed along the backbone of the eventual brush polymer. This positional monofunctionalization strategy was connected with biotin-streptavidin interactions to demonstrate the capabilities for site-specific self-assembly to create higher ordered architectures. Supported by systematic experimental and computational studies, we envisioned that this macromolecular platform provides unique avenues and perspectives in macromolecular design for both nanoscience and biomedicine.

Preparation of a novel sandwich-type electrochemical immunosensor for AFP detection based on an ATRP and click chemistry technique

It is extremely important to explore the synthesis methodology and application scope of functional polymer brush-based nanocomposites.

Amphiphilic multicomponent molecular brushes

Multicomponent molecular brushes containing amphiphilic polymer moieties are promising objects of research of macromolecular chemistry. The development of stimulus-responsive systems sensitive to changes in environmental parameters, based on the molecular brushes, opens up new possibilities for their applications in medicine, biochemistry and microelectronics. The review presents the current understanding of the structures of main types of amphiphilic multicomponent brushes, depending on the chemical nature and type of coupling of the backbone and side chains. The approaches to the controlled synthesis of multicomponent molecular brushes of different architecture are analyzed. Self-assembly processes of multicomponent molecular brushes in selective solvents are considered.

The bibliography includes 259 references.

Manipulation and Deposition of Complex, Functional Block Copolymer Nanostructures Using Optical Tweezers

Block copolymer self-assembly has enabled the creation of a range of solution-phase nanostructures with applications from optoelectronics and biomedicine to catalysis. However, to incorporate such materials into devices a method that facilitates their precise manipulation and deposition is desirable. Herein we describe how optical tweezers can be used to trap, manipulate, and pattern individual cylindrical micelles and larger hybrid micellar materials. Through the combination of TIRF imaging and optical trapping we can precisely control the three-dimensional motion of individual cylindrical block copolymer micelles in solution, enabling the creation of customizable arrays. We also demonstrate that dynamic holographic assembly enables the creation of ordered customizable arrays of complex hybrid block copolymer structures. By creating a program which automatically identifies, traps, and then deposits multiple assemblies simultaneously we have been able to dramatically speed up this normally slow process, enabling the fabrication of arrays of hybrid structures containing hundreds of assemblies in minutes rather than hours.

Electrostatic attraction of nanoobjects – a versatile strategy towards mesostructured transition metal compounds

This highlight summarizes current challenges of mesostructuring and focuses on the scope and the potential of the ELAN – (electrostatic attraction of nanoobjects) strategy in mesostructuring of transition metal compounds.

Hybrid Silicon-Based Organic/Inorganic Block Copolymers with Sol-Gel Active Moieties: Synthetic Advances, Self-Assembly and Applications in Biomedicine and Materials Science

Hybrid silicon-based organic/inorganic (multi)block copolymers are promising polymeric precursors to create robust nano-objects and nanomaterials due to their sol-gel active moieties via self-assembly in solution or in bulk. Such nano-objects and nanomaterials have great potential in biomedicine as nanocarriers or scaffolds for bone regeneration as well as in materials science as Pickering emulsifiers, photonic crystals or coatings/films with antibiofouling, antibacterial or water- and oil-repellent properties. Thus, this Review outlines recent synthetic efforts in the preparation of these hybrid inorganic/organic block copolymers, gives an overview of their self-assembled structures and finally presents recent examples of their use in the biomedical field and material science.

Polymer brush guided templating on well-defined rod-like cellulose nanocrystals

Precisely grafted polymer brushes on cellulose nanocrystals guide the formation of silica and yield uniform CNC-based hybrid nanomaterials which are subsequently used in the fabrication of hollow and highly porous silica nanorods.

UV-responsive amphiphilic graft copolymers based on coumarin and polyoxazoline

A series of amphiphilic photo-responsive heterografted copolymers have been successfully synthesized. The random copolymers were composed of a methacrylate backbone, with various compositions of hydrophilic oligomeric 2-methyl-2-oxazoline side chains (OMOx) and hydrophobic long alkyl chains terminated by a coumarin moiety (Cm). Using dynamic (DLS) and static light scattering (SLS), and transmission electron microscopy (TEM), their self-assembling behavior was studied in water using the nanoprecipitation method. Depending on the system, one, two or three particle size distributions co-exist in solution. However, DLS measurements showed that monomodal and slightly polydisperse self-assemblies were obtained with the more hydrophobic copolymers (i.e., 85% of hydrophobic monomers with a long alkyl chain terminated by a coumarin moiety (MCm) per molecule) with hydrodynamic diameters ranging from ca. 130 to 300 nm. Morphological information on these self-assembly structures was obtained using SLS: a Gaussian behavior has thus been evidenced. Finally, these heterografted copolymers were illuminated using UV light at λ = 350 nm inducing photo-crosslinking of the coumarin units. The influence of UV illumination on the thus-formed nanoparticles was investigated by carrying out complementarily DLS-measurements and UV spectroscopy.

Supramolecular Graft Copolymerization of a Polyester by Guest-Selective Encapsulation of a Self-Assembled Capsule

Repeating guest units of polyesters poly-(R)-2 were selectively encapsulated by capsule 1(BF₄ )₄ to produce supramolecular graft polymers. The encapsulation of the guest units was confirmed by ¹ H NMR spectroscopy. The graft polymer structures were confirmed by the increase in the hydrodynamic radii and the solution viscosities of the polyesters upon complexation of the capsule. After the capsule was formed, atomic force microscopy showed extension of the polyester chains. The introduction of the graft chains onto poly-(R)-2 resulted in the main chain of the polymer having an M-helical morphology. The complexation of copolymers poly-[(R)-2-co-(S)-2] by the capsule gave rise to the unique chiral amplification known as the majority-rules effect.

A CTA-shuttled R-group approach: a versatile synthetic tool towards well-defined functional cylindrical polymer brushes via RAFT polymerization

We report a novel three-step strategy toward polyCTA for the synthesis of cylindrical polymer brushes via “CTA-shuttled” RAFT R-approach polymerization. Post functionalizations on the CTA residue are also discussed.