Amphiphilic Dendronized Copolymer-Encapsulated Au, Ag and Pd Nanoparticles for Catalysis in the 4-Nitrophenol Reduction and Suzuki-Miyaura Reactions

The branched structures of dendronized polymers can provide good steric stabilization for metal nanoparticle catalysts. In this work, an amphiphilic dendronized copolymer containing hydrophilic branched triethylene glycol moieties and hydrophobic branched ferrocenyl moieties is designed and prepared by one-pot ring-opening metathesis polymerization, and is used as the stabilizer for metal (Au, Ag and Pd) nanoparticles. These metal nanoparticles (Au nanoparticles: 3.5 ± 3.0 nm; Ag nanoparticles: 7.2 ± 4.0 nm; Pd nanoparticles: 2.5 ± 1.0 nm) are found to be highly active in both the 4-nitrophenol reduction and Suzuki-Miyaura reactions. In the 4-nitrophenol reduction, Pd nanoparticles have the highest catalytic ability (TOF: 2060 h-1). In addition, Pd nanoparticles are also an efficient catalyst for Suzuki-Miyaura reactions (TOF: 1980 h-1) and possess good applicability for diverse substrates. The amphiphilic dendronized copolymer will open a new door for the development of efficient metal nanoparticle catalysts.

Stimuli-responsive rotaxane-branched dendronized polymers with tunable thermal and rheological properties

Aiming at the creation of polymers with attractive dynamic properties, herein, rotaxane-branched dendronized polymers (DPs) with rotaxane-branched dendrons attached onto the polymer chains are proposed. Starting from macromonomers with both rotaxane-branched dendrons and polymerization site, targeted rotaxane-branched DPs are successfully synthesized through ring-opening metathesis polymerization (ROMP). Interestingly, due to the existence of multiple switchable [2]rotaxane branches within the attached dendrons, anion-induced reversible thickness modulation of the resultant rotaxane-branched DPs is achieved, which further lead to tunable thermal and rheological properties, making them attractive platform for the construction of smart polymeric materials.

Comparative Study of the U(VI) Adsorption by Hybrid Silica-Hyperbranched Poly(ethylene imine) Nanoparticles and Xerogels

Two different silica conformations (xerogels and nanoparticles), both formed by the mediation of dendritic poly (ethylene imine), were tested at low pHs for problematic uranyl cation sorption. The effect of crucial factors, i.e., temperature, electrostatic forces, adsorbent composition, accessibility of the pollutant to the dendritic cavities, and MW of the organic matrix, was investigated to determine the optimum formulation for water purification under these conditions. This was attained with the aid of UV-visible and FTIR spectroscopy, dynamic light scattering (DLS), ζ-potential, liquid nitrogen (LN₂) porosimetry, thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). Results highlighted that both adsorbents have extraordinary sorption capacities. Xerogels are cost-effective since they approximate the performance of nanoparticles with much less organic content. Both adsorbents could be used in the form of dispersions. The xerogels, though, are more practicable materials since they may penetrate the pores of a metal or ceramic solid substrate in the form of a precursor gel-forming solution, producing composite purification devices.

Dendritic Polymers in Tissue Engineering: Contributions of PAMAM, PPI PEG and PEI to Injury Restoration and Bioactive Scaffold Evolution

The capability of radially polymerized bio-dendrimers and hyperbranched polymers for medical applications is well established. Perhaps the most important implementations are those that involve interactions with the regenerative mechanisms of cells. In general, they are non-toxic or exhibit very low toxicity. Thus, they allow unhindered and, in many cases, faster cell proliferation, a property that renders them ideal materials for tissue engineering scaffolds. Their resemblance to proteins permits the synthesis of derivatives that mimic collagen and elastin or are capable of biomimetic hydroxy apatite production. Due to their distinctive architecture (core, internal branches, terminal groups), dendritic polymers may play many roles. The internal cavities may host cell differentiation genes and antimicrobial protection drugs. Suitable terminal groups may modify the surface chemistry of cells and modulate the external membrane charge promoting cell adhesion and tissue assembly. They may also induce polymer cross-linking for healing implementation in the eyes, skin, and internal organ wounds. The review highlights all the different categories of hard and soft tissues that may be remediated with their contribution. The reader will also be exposed to the incorporation of methods for establishment of biomaterials, functionalization strategies, and the synthetic paths for organizing assemblies from biocompatible building blocks and natural metabolites.

Light-Triggered Polymersome-Based Anticancer Therapeutics Delivery

Polymersomes are biomimetic cell membrane-like model structures that are self-assembled stepwise from amphiphilic copolymers. These polymeric (nano)carriers have gained the scientific community's attention due to their biocompatibility, versatility, and higher stability than liposomes. Their tunable properties, such as composition, size, shape, and surface functional groups, extend encapsulation possibilities to either hydrophilic or hydrophobic cargoes (or both) and their site-specific delivery. Besides, polymersomes can disassemble in response to different stimuli, including light, for controlling the "on-demand" release of cargo that may also respond to light as photosensitizers and plasmonic nanostructures. Thus, polymersomes can be spatiotemporally stimulated by light of a wide wavelength range, whose exogenous response may activate light-stimulable moieties, enhance the drug efficacy, decrease side effects, and, thus, be broadly employed in photoinduced therapy. This review describes current light-responsive polymersomes evaluated for anticancer therapy. It includes light-activable moieties' features and polymersomes' composition and release behavior, focusing on recent advances and applications in cancer therapy, current trends, and photosensitive polymersomes' perspectives.

Ultrahigh-Performance Optoelectronic Skin Based on Intrinsically Stretchable Perovskite-Polymer Heterojunction Transistors

The optoelectronic skin is acknowledged as the world's current cutting-edge technology in the fields of wearable healthcare monitoring, soft robotics, artificial retinas, and so on. However, the difficulty in preparing stretchable photosensitive polymers and the high-crystallization nature of most reported photosensitive materials (such as perovskites) severely restrict the development of skin-like optoelectronic devices. Herein, a surface energy-induced self-assembly methodology is proposed to form easily transferrable and flexible perovskite quantum dot (PQD) films with a worm-like morphology. Furthermore, intrinsically stretchable phototransistors (ISTPTs) are fabricated based on a stretchable photosensitive layer heterojunction consisting of worm-like PQD films and hybrid polymer semiconductors. The obtained ISTPTs display highly sensitive response to high-energy photons of X-ray (with a detection limit of 79 nGy s^-1 , that is 560 times lower than commercial medical chest X-ray diagnosis) and ultraviolet (with photosensitivity of 5 × 10⁶ and detectable light intensity of 50 nW cm^-2 among the highest performance of reported photodetectors). In addition, these ISTPTs demonstrate desirable e-skin characteristics with high strain tolerance, high sensing specificity, high optical transparency, and good skin conformability. The surface energy-induced self-assembly methodology for the preparation of ISTPTs is a critical demonstration to enable low-cost and high-performance optoelectronic skins.

Confined Microenvironments from Thermoresponsive Dendronized Polymers

Confined microenvironments in biomacromolecules arising from molecular crowding account for their well-defined biofunctions and bioactivities. To mimick this, synthetic polymers to form confined structures or microenvironments are of key scientific value, which have received significant attention recently. To create synthetic confined microenvironments, molecular crowding effects and topological cooperative effects have been applied successfully, and the key is balance between self-association of structural units and self-repulsion from crowding-induced steric hindrance. In this article, formation of confined microenvironments from stimuli-responsive dendronized polymers carrying densely dendritic oligoethylene glycols (OEGs) moieties in their pendants is presented. These wormlike thick macromolecules exhibit characteristic thermoresponsive properties, which can provide constrained microenvironments to encapsulate effectively guest molecules including dyes, proteins, or nucleic acids to prevent their protonation or biodegradation. This efficient shielding effect can also mediate chemical reactions in aqueous phase, and even enhance chirality transferring efficiency. All of these can be switched off simply through the thermally-induced dehydration and collapse of OEG dendrons due to the amphiphilicity of OEG chains. Furthermore, the switchable encapsulation and release of guests can be greatly enhanced when these dendronized polymers are used as major constituents for fabricating bulk hydrogels or nanogels, which provide a higher-level confinement.

Thermoresponsive cationic dendronized copolymers and their corresponding nanogels as smart gene carriers

Thermoresponsive dendronized copolymer nanogels show unique condensation, protection and controlled release of siRNA due to dendritic topology and spherical morphology.

Water-soluble polyglycerol-dendronized poly(norbornene)s with functional side-chains

High molecular weight polyglycerol-dendronized poly(norbornene)s (PGD-PNBs) were prepared via ring-opening metathesis polymerization of norbornene monomers containing amine functional groups on the side-chains followed by dendron growth from the olefins of PNB backbones using iterative dihydroxylation and allylation. The fourth-generation PGD-PNB with a degree of polymerization of ca. 500 is thus functionalized with 16 peripheral hydroxyl groups as well as a single amine on each repeat unit of the PNB backbone. Furthermore, the amine functionality could be used to install hydrophobic fluorophores such as coumarin and pyrene, thereby obtaining the final PGD-PNB structures which are highly water-soluble and fluorescent.

Stimuli-responsive dendronized polymeric hydrogels through Schiff-base chemistry showing remarkable topological effects

Crowded and thick dendronized polymers enhance the formation of a Schiff-base through thermally-induced collapse or freezing, resulting in hydrogels with different performances.

Tunable Supramolecular Hexagonal Columnar Structures of Hydrogen-Bonded Copolymers Containing Two Different Sized Dendritic Side Chains

Polymer structures with tunable symmetry and sizes are desired for applications such as lithography, filtration membranes, and separation. Here we report the self-assembled supramolecular hexagonal columnar (Φ_H) structures with tunable lattice size varying from 5 to 7 nm by constructing hydrogen-bonded copolymers bearing poly(4-vinylpyridine) (P4VP) and two dendritic molecular additives, 1-[4'-(3″,4″,5″-tridecyloxybenzoyloxy)phenyleneoxycarbonyl]-3-[(4″-hydroxyphenyl)oxycarbonyl]benzene (12CBP) and 4-hydroxyphenyl (3,4,5-tridecyloxy)benzoate (12CTB). Despite the distinct molecular size difference between 12CBP and 12CTB, the resulting ternary supramolecular copolymers, P4VP(12CBP)_x(12CTB)_y, possess a homogeneous Φ_H phase at x ≥ 0.1 and y ≥ 0.2. Each column is constructed with P4VP as the backbone tethered with mixed side chains. The column diameter is between the size of the corresponding P4VP(12CBP)_x+y and P4VP(12CTB)_x+y and could be easily tuned by varying x and y. The enhancement of Φ_H in supramolecular copolymers is attributed to the entropy effect of the mixed side chain and enthalpy effect from hydrogen bonding interaction of the P4VP backbone and two molecules (12CBP and 12CTB).

Preparation and Applications of Dendronized Polymer-Enzyme Conjugates

Dendronized polymer-enzyme conjugates are large, water-soluble macromolecular structures built from a linear, fully synthetic, dendronized polymer (denpol), and several copies of enzyme molecules covalently bound to the peripheral functional groups of the denpol. Since denpol chains comprise repeating units with regularly branched side chains (dendrons), denpols have a cylindrical shape and are much thicker than conventional linear polymers. Depending on the dendron generation and chemical structure, denpols may have a large number of functional groups on their surface, exposed to the aqueous medium in which they are dissolved. Enzymes (and also other molecules) can be attached to these functional groups, for example, via a stable bis-aryl hydrazone (BAH) bond. The dendronized polymer scaffold might also serve as a nanoarmor and stabilize the delicate enzymes. One of the denpols which can be used for the preparation of denpol-enzyme conjugates is de-PG2. It has a poly(methacrylate) backbone and consists of second-generation dendrons with four peripheral amino groups in each repeating unit. The synthesis of de-PG2 and the preparation of a de-PG2 conjugate carrying BAH-linked proteinase K (proK), as an example, are described here for applications in the field of enzyme immobilization on solid surfaces. The nanoarmored enzyme-polymer conjugate indicated high stability and retention of enzymatic activity.

Exploring the Loading Capacity of Generation Six to Eight Dendronized Polymers in Aqueous Solution

Aspects of size, structural (im)perfection, inner density, and guest molecule loading capacity of dendronized polymers (DPs) of high generation (6≤g≤8) in aqueous solution are studied using electron paramagnetic resonance spectroscopy on amphiphilic, spin-labeled guest molecules. The results show that the interior of the charged DPs is strongly polar, especially in comparison to their lower generation (1-4) analogues. This is a direct sign that large amounts of water penetrate the DP surface, reflecting the structural (im)perfections of these high-generation DPs and much lower segmental densities than theoretically achievable. Images obtained with atomic force microscopy reveal that the high-generation DPs do not aggregate and give further insights into the structural imperfections. Electron paramagnetic resonance spectroscopic data further show that despite their structural imperfections, these DPs can bind and release large numbers of amphiphilic molecules. It is concluded that attention should be paid to their synthesis, for which a protocol needs to be developed that avoids the relatively large amount of defects generated in the direct conversion of a generation g=4 DP to a generation g=6 DP, which had to be used here.

Solvatochromism of dye-labeled dendronized polymers of generation numbers 1-4: comparison to dendrimers

Two series of dendronized polymers (DPs) of generations g = 1-4 with different levels of dendritic substitution (low and high) and a solvatochromic probe at g = 1 level are used to study their swelling behavior in a collection of solvents largely differing in polarity as indicated by the Kamlet-Taft parameters. This is done by measuring the UV-Vis spectra of all samples in all solvents and determining the longest wavelength absorptions (λmax). The λmax values fall into a range defined by the extreme situations, when the solvatochromic probe is either fully surrounded by solvent or completely shielded against it. The former situation is achieved in a model compound and the latter situation is believed to be reached when in a poor solvent the dendritic shell around the backbone is fully collapsed. We observe that solvent penetration into the interior of the DPs decreases with increasing g and does so faster for the more highly dendritically substituted series than for the less highly substituted one. Interestingly, the swelling of the more highly substituted DP series already at the g = 4 level has decreased to approximately 20% of that at the g = 1 level which supports an earlier proposal that high g DPs can be viewed as nano-sized molecular objects. Furthermore, when comparing these two DP series with a g = 1-6 series of dendrimers investigated by Fréchet et al. it becomes evident that even the less substituted series of DPs is much less responsive to solvent changes as assessed by the solvatochromic probe than the dendrimers, suggesting the branches around the (polymeric) core in DPs to be more densely packed compared to those in dendrimers, thus, establishing a key difference between these two dendritic macromolecules.

Synthesis of Dendronized Poly(l-Glutamate) via Azide-Alkyne Click Chemistry

Poly(l-glutamate) (PGlu) was modified with a second-generation dendron to obtain the dendronized polyglutamate, P(Glu-D). Synthesized P(Glu-D) exhibited a degree of polymerization (DP_n) of 46 and a 43% degree of dendronization. Perfect agreement was found between the P(Glu-D) expected structure and the results of nuclear magnetic resonance spectroscopy (NMR) and size-exclusion chromatography coupled to a multi-angle light-scattering detector (SEC-MALS) analysis. The PGlu precursor was modified by coupling with a bifunctional building block (N₃-Pr-NH₂) in the presence of 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (DMTMM) coupling reagent. The second-generation polyamide dendron was prepared by a stepwise procedure involving the coupling of propargylamine to the l-lysine carboxyl group, followed by attaching the protected 2,2-bis(methylol)propionic acid (bis-MPA) building block to the l-lysine amino groups. The hydroxyl groups of the resulting second-generation dendron were quantitatively deprotected under mild acidic conditions. The deprotected dendron with an acetylene focal group was coupled to the pendant azide groups of the modified linear copolypeptide, P(Glu-N₃), in a Cu(I) catalyzed azide-alkyne cycloaddition reaction to form a 1,4-disubstituted triazole. The dendronization reaction proceeded quantitatively in 48 hours in aqueous medium as confirmed by ¹H NMR and Fourier transform infrared spectroscopy (FT-IR) spectroscopy.

The use of azide-alkyne click chemistry in recent syntheses and applications of polytriazole-based nanostructured polymers

The rapid development of efficient organic click coupling reactions has significantly facilitated the construction of synthetic polymers with sophisticated branched nanostructures. This Feature Article summarizes the recent progress in the application of efficient copper-catalyzed and copper-free azide-alkyne cycloaddition (CuAAC and CuFAAC) reactions in the syntheses of dendrimers, hyperbranched polymers, star polymers, graft polymers, molecular brushes, and cyclic graft polymers. Literature reports on the interesting properties and functions of these polytriazole-based nanostructured polymers are also discussed to illustrate their potential applications as self-healing polymers, adhesives, polymer catalysts, opto-electronic polymer materials and polymer carriers for drug and imaging molecules.

Hierarchical superstructures of norbornene-based polymers depending on dendronized side-chains

For understanding the self-assembly behaviours of norbornene-based main-chain polymers depending on side-chain pendants, a series of polynorbornenes containing the programmed dendrons is newly designed and successfully synthesized via ring opening metathesis polymerization.

Crosslinked dendronized polyols as a general approach to brighter and more stable fluorophores

Fluorescent, aqueous-soluble, crosslinked dendronized polyols (CDPs) are obtained through a sequential process involving ring-opening metathesis polymerization (ROMP), intra-chain ring-closing metathesis (RCM), and hydrolysis.

Highly functionalized heterogeneous dendrigraft catalysts with peripheral copper moieties for the facile synthesis of 2-substituted benzimidazoles and 2,2-disubstituted benzimidazoles

A highly functionalized heterogeneous copper loaded dendrigraft amidoamine catalyst for the synthesis of 2-substituted and 2,2-disubstituted benzimidazoles is reported.

A well-defined alternating copolymer based on a salicylaldimine Schiff base for highly sensitive zinc(ii) detection and pH sensing in aqueous solution

We report a new strategy to fabricate well-defined alternating Schiff base copolymers of poly(VBCDEG-alt-SaAEMI)s which display two distinguishable color fluorescence “OFF–ON” responses to zinc ions and pH in aqueous solution.

Dendronized Polymers: Molecular Objects between Conventional Linear Polymers and Colloidal Particles

The term molecular object (MO) is introduced to describe single, shape persistent macromolecules that retain their form and mesoscopic dimensions irrespective of solvent quality and adsorption onto a surface. The concept is illustrated with results concerning homologous series of dendronized polymers (DP). In particular, we discuss imaging experiments quantifying deformation upon adsorption, defect characterization, and atomistic molecular dynamics simulations of DP structure. We argue that MOs such as high generation DP, with their large dimensions and high internal density, provide an opportunity to address fundamental questions regarding the onset of bulk-like behavior in single molecules. Illustrative examples of such questions concern the smallest MO exhibiting a glass transition, glassy behavior or a constant bulk density. The characteristics of DP MO are highlighted by comparison to polymer beads, polymeric micelles, globular proteins, and carbon nanotubes. We discuss future research directions and speculate on possibilities involving multiarmed and toroid DP and the effect of DP on friction and rheology, as well as their utilization for nanoconstruction.