Competition Between Steric Hindrance and Hydrogen Bonding in the Formation of Supramolecular Bottle Brush Polymers

Photo-responsive supramolecular polymer bottle-brushes: The key role of the solvent on self-assembly and responsiveness

HYPOTHESIS

Supramolecular polymer bottlebrushes (SPBs) consist in the 1D self-assembly of building blocks composed of a self-assembling core with pendant polymer arms. Kinetic hurdles often hinder their stimuli-responsiveness in solution. Changing the nature of the solvent should alleviate these hurdles by modulating the self-association strength, leading to stimuli-responsive SPBs.

EXPERIMENTS

The SPBs were formed, in various solvents, by hydrogen bond-driven self-assembly of an azobenzene-bisurea decorated with poly(ethylene oxide) polymer arms. The photo-isomerization of the azobenzene unit was studied by UV/visible spectroscopy and proton NMR spectroscopy, whereas the consequences on supramolecular self-assembly were studied by small angle neutron and X-ray scattering.

FINDINGS

In water, the assembly was previously shown to be driven by both hydrogen-bonds and strong hydrophobic effects, the latter rendering the system kinetically frozen and the disassembly irreversible. Here we show that in organic solvents such as toluene or chloroform, reversible light-responsive dissociation is achieved. Solvophobic effects in these solvents are expected to be much weaker than in water, which probably allows reversibility of the light-response in the former solvents. The key role of the solvent on the reversibility of the process opens up new perspectives for the design of stimuli-responsive SPBs and their applications in various fields.

Beyond Traditional Stimuli: Exploring Salt-Responsive Bottlebrush Polymers-Trends, Applications, and Perspectives

Bottlebrush polymers represent an important class of high-density side-chain-grafted polymers traditionally with high molecular weights, in which one or more polymeric side chains are tethered to each repeating unit of a linear polymer backbone, such that these macromolecules look like "bottlebrushes". The arrangement of molecular brushes is determined by side chains located at a distance considerably smaller than their unperturbed dimensions, leading to substantial monomer congestion and entropically unfavorable extension of both the backbone and the side chains. Traditionally, the conformation and physical properties of polymers are influenced by external stimuli such as solvent, temperature, pH, and light. However, a unique stimulus, salt, has recently gained attention as a means to induce shape changes in these molecular brushes. While the stimulus has been less researched to date, we see that these systems, when stimulated with salts, have the potential to be used in various engineering applications. This potential stems from the unique properties and behaviors these systems show when exposed to different salts, which could lead to new solutions and improvements in engineering processes, thus serving as the primary motivation for this narrative, as we aim to explore and highlight the various ways these systems can be utilized and the benefits they could bring to the field of engineering. This Review aims to introduce the concept of stimuli-responsive bottlebrush polymers, explore the evolutionary trajectory, delve into current trends in salt-responsive bottlebrush polymers, and elucidate how these polymers are addressing a variety of engineering challenges.

Influence of Polymer Side Chain Size and Backbone Length on the Self-Assembly of Supramolecular Polymer Bottlebrushes

Hydrogen bonds are a versatile tool for creating fibrous, bottlebrush-like assemblies of polymeric building blocks. However, a delicate balance of forces exists between the steric repulsion of the polymer chains and these directed supramolecular forces. In this work we have systematically investigated the influence of structural parameters of the attached polymers on the assembly behaviour of benzene trisurea (BTU) and benzene tris(phenylalanine) (BTP) conjugates in water. Polymers with increasing main chain lengths and different side chain sizes were prepared by reversible addition-fragmentation chain-transfer (RAFT) polymerization of hydroxyethyl acrylate (HEA), tri(ethylene glycol) methyl ether acrylate (TEGA) and oligo(ethylene glycol) methyl ether acrylate (OEGA). The resulting structures were analyzed using small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). Both BTU and BTP formed fibres with PHEA attached, but a transition to spherical morphologies was observed at degrees of polymerisation (DP) of 70 and above. Overall, the main chain length appeared to be a dominating factor in inducing morphology transitions. Increasing the side chain size generally had a similar effect but mainly impeded any aggregation as is the case of POEGA. Interestingly, BTP conjugates still formed fibres, suggesting that the stronger intermolecular interactions can compensate partially for the steric repulsion.

Amphiphilic Block Copolymers PEG-b-PMTCs: Synthesis, Self-Assembly, Degradation Properties and Biocompatibility

As a hydrophilic cyclic ketene acetal (CKA), 2-methylene-1,3,6-trioxocane (MTC) has recently attracted a lot of attention owing to its ability to promote a quicker (bio)degradation as compared to other heavily studied CKAs. Here, we prepared amphiphilic block copolymers based on poly-MTC with varying chain lengths by radical ring opening polymerization. Self-assemblies of these amphiphiles were performed in PBS buffer to generate nanoparticles with sizes from 40 to 105 nm, which were verified by dynamic light scattering, electron microscopy, and static light scattering (Zimm plots). Subsequently, fluorescence spectroscopy was applied to study the enzymatic degradation of Nile red-loaded nanoparticles. By performing a point-by-point comparison of fluorescence intensity decline patterns between nanoparticles, we demonstrated that lipase from Pseudomonas cepacia was very efficient in degrading the nanoparticles. Hydrolysis degradations under basic conditions were also carried out, and a complete degradation was achieved after 4 h. Additionally, cytotoxicity assays were carried out on HEK293 cells, and the results affirmed cell viabilities over 90% when incubated with up to 1 mg/mL nanoparticles for 24 h. These biodegradable and biocompatible nanoparticles hence hold great potential for future applications such as drug release.

Reconfiguration of Langmuir Monolayers of Thermo-Responsive Branched Ionic Polymers with LCST Transition

Thermo-responsive ionic polymers have the ability to form adaptive and switchable morphologies, which may offer enhanced control in energy storage and catalytic applications. Current thermo-responsive polymers are composed of covalently attached thermo-responsive moieties, restricting their mobility and global dynamic response. Here, we report the synthesis and assembly at the water-air interface of symmetric and asymmetric amphiphilic thermo-responsive branched polymers with weakly ionically bound arms of amine-terminated poly(N-isopropylacrylamide) (PNIPAM) macro-cations. As we observed, symmetric branched polymers formed multimolecular nanosized micellar assemblies, whereas corresponding asymmetric polymers formed large, interconnected worm-like aggregates. Dramatic changes in localized and large-scale chemical composition confirmed the reversible adsorption and desorption of the mobile PNIPAM macro-cations below and above the low critical solution temperature (LCST) and their non-uniform redistribution within polymer monolayer. Increasing the temperature above LCST led to the formation of large interconnected micellar aggregates because of the micelle-centered aggregation of the hydrophobized PNIPAM macro-cationic terminal chains in the aqueous subphase. Overall, this work provides insights into the dynamic nature of the chemical composition of branched ionic polymers with weakly ionically bound thermo-responsive terminal chains and its effect on both morphology and local/surface chemistry of monolayers at LCST transition.

Crystalline lamellar films with honeycomb structure from comb-like polymers of poly(2-long-alkyl-2-oxazoline)s

Comb-like copolymers are usually structured by grafting polymeric side chains onto main polymer chain. There are few reports of comb-on-comb polymers in which dense secondary side chains are grafted onto primary side chain. In this work, we synthesized comb polymers with grafted-on-graft side chains (c-PEI-g-Acyl) via an effective acylation reaction of comb polymers possessing polyethyleneimine (PEI) side chain with long-alkyl acyl chlorides. For comparison, we also synthesized homopolymers l-PEI-g-Acyls via reaction of linear PEI with long-alkyl acyl chlorides. Then, we investigated their crystalline feature in the film formation by XRD, DSC and SEM, and found that the polymers tend to form hexagonal lamella structures with bilayer alkyl spacing. The comb polymers c-PEI-g-Acyls and linear polymers l-PEI-g-Acyls were used in preparation of honeycomb film by the "breath-figure" process by dropping chloroform solution of the polymers on substrate. Different to many honeycomb polymeric films which are supported by amorphous phase, interestingly, our polymers easily afford honeycomb films which are supported by crystalline lamellae frames under higher humidity condition. It was found that the comb polymers of c-PEI-g-Acyls with longer PEI primary side chain and long alkyl secondary side chain have advantages in producing honeycomb film than linear polymers of l-PEI-g-Acys.

Regulation of Inflammatory Response and Osteogenesis to Citrate-Based Biomaterials through Incorporation of Alkaline Fragments

A proper pH microenvironment is crucial to mobilizing regeneration function of biomaterials. Neutralizing the acidity in bone defects with alkaline substances is a promising strategy to create favorable environments for cell proliferation and bone repair. In this study, to neutralize the acidity and reduce the inflammation caused by the rapid release of citric acid, a novel citrate-based biodegradable elastomeric poly(citric acid-1,8-octanediol-1,4-bis(2-hydroxyethyl)piperazine (BHEp)) (POPC) is synthesized with the introduction of the alkaline fragment BHEp, and then POPC/β-tricalcium phosphate (β-TCP) porous scaffolds are fabricated by 3D printing technique. The results reveal that the alkaline fragment BHEp effectively corrects the acid environment and improves the biocompatibility, cells affinity and promoted cell adhesion, and proliferation of POPC. Furthermore, the improved pH of POPC15/β-TCP (PTCP15) enhances the adhesion and the proliferation of rabbit bone marrow mesenchymal stem cells, and the expression of osteogenesis-related genes. Moreover, PTCP15 scaffolds relieve inflammatory response and switch RAW 264.7 toward a prohealing extreme. The rat femoral defect model further demonstrates good biocompatibility and enhanced bone regeneration of PTCP15. In conclusion, the results offer a promising approach for biodegradable polymers to address the degradation acidity issue. Meanwhile, a positive regulation strategy is provided for biopolymer to enhance cell proliferation, osteogenic differentiation, and bone repair.

AIE Featured Supramolecular Tubisomes for Imaging-Guided Drug Delivery

Polymeric cylinders, a fascinating type of nanostructures with high surface area, internal volume and rigidity, have been exploited as novel drug delivery vehicles over the past decade. However, it's still an open challenge to afford cylindrical nanostructures using polymeric building blocks via traditional self-assembly processes. Herein, we report a hierarchical self-assembly strategy of preparing cylindrical aggregates (tubisomes) from an amphiphilic supramolecular bottlebrush polymer in which cyclic peptide nanotube is employed as the noncovalent backbone. Additionally, aggregation induced emission effect was introduced into the tubisomes to endow them with excellent fluorescent property. Intriguingly, encapsulation of anticancer drug doxorubicin (DOX) can inactivate the fluorescence of both tubisome and DOX due to the energy transfer relay (ETR). The release of DOX can interrupt the ETR effect and light up the silenced fluorescence, thereby permitting the in-situ visualization of drug release. The supramolecular tubisomes described here paves an alternative way for fabricating polymeric cylindrical nanostructures, and holds great potential in imaging-guided drug delivery.

Overcoming the Necessity of a Lateral Aggregation in the Formation of Supramolecular Polymer Bottlebrushes in Water

The assembly of supramolecular polymer bottlebrushes in aqueous systems is, in most cases, associated with a lateral aggregation of the supramolecular building blocks in addition to their axial stacking. Here, it is demonstrated that this limitation can be overcome by attaching three polymer chains to a central supramolecular unit that possesses a sufficiently high number of hydrogen bonding units to compensate for the increased steric strain. Therefore, a 1,3,5-benzenetrisurea-polyethylene oxide conjugate is modified with different peptide units located next to the urea groups which should facilitate self-assembly in water. For a single amino acid per arm, spherical micelles are obtained for all three tested amino acids (alanine, leucine, and phenylalanine) featuring different hydrophobicities. Only a slight increase in size and solution stability of spherical micelles is observed with increasing hydrophobicity of amino acid unit. In contrast, introducing two amino acid units per arm and thus increasing the number of hydrogen bonds per unimer molecule results in the formation of cylindrical structures, that is, supramolecular polymer bottlebrushes, despite a suppressed lateral aggregation. Consequently, it can be concluded that the number of hydrogen bonds has a more profound impact on the resulting solution morphology than the hydrophobicity of the amino acid unit.

Supramolecular polymer bottlebrushes

The field of supramolecular chemistry has long been known to generate complex materials of different sizes and shapes via the self-assembly of single or multiple low molar mass building blocks. Matching the complexity found in natural assemblies, however, remains a long-term challenge considering its precision in organizing large macromolecules into well-defined nanostructures. Nevertheless, the increasing understanding of supramolecular chemistry has paved the way to several attempts in arranging synthetic macromolecules into larger ordered structures based on non-covalent forces. This review is a first attempt to summarize the developments in this field, which focus mainly on the formation of one-dimensional, linear, cylindrical aggregates in solution with pendant polymer chains - therefore coined supramolecular polymer bottlebrushes in accordance with their covalent equivalents. Distinguishing by the different supramolecular driving forces, we first describe systems based on π-π interactions, which comprise, among others, the well-known perylene motif, but also the early attempts using cyclophanes. However, the majority of reported supramolecular polymer bottlebrushes are formed by hydrogen bonds as they can for example be found in linear and cyclic peptides, as well as so called sticker molecules containing multiple urea groups. Besides this overview on the reported motifs and their impact on the resulting morphology of the polymer nanostructures, we finally highlight the potential benefits of such non-covalent interactions and refer to promising future directions of this still mostly unrecognized field of supramolecular research.

A Critical Approach to Polymer Dynamics in Supramolecular Polymers

Over the past few years, the concurrent (1) development of polymer synthesis and (2) introduction of new mathematical models for polymer dynamics have evolved the classical framework for polymer dynamics once established by Doi-Edwards/de Gennes. Although the analysis of supramolecular polymer dynamics based on linear rheology has improved a lot recently, there are a large number of insecurities behind the conclusions, which originate from the complexity of these novel systems. The interdependent effect of supramolecular entities (stickers) and chain dynamics can be overwhelming depending on the type and location of stickers as well as the architecture and chemistry of polymers. This Perspective illustrates these parameters and strives to determine what is still missing and has to be improved in the future works.

The influence of directed hydrogen bonds on the self-assembly of amphiphilic polymers in water

HYPOTHESIS

Molecules forming directed intermolecular hydrogen bonds, such as the well-known benzene-1,3,5-tricarboxamides (BTA) motif, are known to self-assemble into long fibrous structures. However, only a few of these systems have so far demonstrated the ability to form such anisotropic nanostructures, if they are combined with hydrophilic polymers to create an amphiphilic material. Here, we designed BTA-polymer conjugates to investigate whether the directionality of the hydrogen bonds or the ratio of hydrophobic to hydrophilic parts of the molecule, and thus the packing parameter, is decisive for obtaining anisotropic supramolecular structures in water.

EXPERIMENTS

Poly(ethylene glycol) was conjugated to BTA moieties with varying lengths of hydrophobic alkyl spacers ranging from two to twelve methylene units. The resulting amphiphilic materials were characterized in aqueous solution by light and small-angle neutron scattering, analytical ultracentrifugation, and cryo-transmission electron microscopy.

FINDINGS

While spherical micelles were observed for C₆ and C₁₀ alkyl spacers, anisotropic structures were only present in case of the C₁₂ spacer. The comparison to an analogous material, which lacks the directed hydrogen bonds, revealed that the BTA motif cannot provide a sufficient driving force to induce anisotropic structures, but increases the packing density in the hydrophobic part. Therefore, the packing parameter governs the appearance of anisotropic aggregates.

Supramolecular nanoscale drug-delivery system with ordered structure

Supramolecular chemistry provides a means to integrate multi-type molecules leading to a dynamic organization. The study of functional nanoscale drug-delivery systems based on supramolecular interactions is a recent trend. Much work has focused on the design of supramolecular building blocks and the engineering of supramolecular integration, with the goal of optimized delivery behavior and enhanced therapeutic effect. This review introduces recent advances in supramolecular designs of nanoscale drug delivery. Supramolecular affinity can act as a main driving force either in the self-assembly of carriers or in the loading of drugs. It is also possible to employ strong recognitions to achieve self-delivery of drugs. Due to dynamic controllable drug-release properties, the supramolecular nanoscale drug-delivery system provides a promising platform for precision medicine.

Identification of Critical Surface Parameters Driving Lectin-Mediated Capture of Bacteria from Solution

Lectin-functional interfaces are useful for isolation of bacteria from solution because they are low-cost and allow nondestructive, reversible capture. This study provides a systematic investigation of physical and chemical surface parameters that influence bacteria capture over lectin-functionalized polymer interfaces and then applies these findings to construct surfaces with significantly enhanced bacteria capture. The designer block copolymer poly(glycidyl methacrylate)- block-poly(vinyldimethyl azlactone) was used as a lectin attachment layer, and lectin coupling into the polymer film through azlactone-lectin coupling reactions was first characterized. Here, experimental parameters including polymer areal chain density, lectin molecular weight, and lectin coupling buffer were systematically varied to identify parameters driving highest azlactone conversions and corresponding lectin surface densities. To introduce physical nanostructures into the attachment layer, nanopillar arrays (NPAs) of varied heights (300 and 2100 nm) were then used to provide an underlying surface template for the functional polymer layer. Capture of Escherichia coli on lectin-polymer surfaces coated over both flat and NPA surfaces was then investigated. For flat polymer interfaces, bacteria were detected on the surface after incubation at a solution concentration of 10³ cfu/mL, and a corresponding detection limit of 1.7 × 10³ cfu/mL was quantified. This detection limit was 1 order of magnitude lower than control lectin surfaces functionalized with standard, carbodiimide coupling chemistry. NPA surfaces containing 300 nm tall pillars further improved the detection limit to 2.1 × 10² cfu/mL, but also reduced the viability of captured cells. Finally, to investigate the impact of cell surface parameters on capture, we used Agrobacterium tumefaciens cells genetically modified to allow manipulation of exopolysaccharide adhesin production levels. Statistical analysis of surface capture levels revealed that lectin surface density was the primary factor driving capture, as opposed to exopolysaccharide adhesin expression. These findings emphasize the critical importance of the synthetic interface and the development of surfaces that combine high lectin densities with tailored physical features to drive high levels of capture. These insights will aid in design of biofunctional interfaces with physicochemical surface properties favorable for capture and isolation of bacteria cells from solutions.

Robust supramolecular nanocylinders of naphthalene diimide in water

Long and robust NDI-containing nanocylinders formed by supramolecular self-assembly via hydrogen bonds and aromatic interactions in aqueous medium.

Effect of the Strength of Stickers on Rheology and Adhesion of Supramolecular Center-Functionalized Polyisobutenes

In order to systematically investigate the effect of the strength of the supramolecular interactions on the debonding properties of associative polymers, a series of model systems have been characterized by probe-tack tests. These model materials, composed of linear and low dispersity poly(isobutylene) chains ( M_n ≈ 3 kg/mol) center-functionalized by a single bis-urea sticker, are able to self-assemble by four hydrogen bonds. Three types of stickers are used in the present study: a bis-urea with a methylene diphenyl (MDI) spacer, a bis-urea with a tolyl (TOL) spacer, and a bis-urea with a xylyl (XYL) spacer. In order to investigate the influence of stickers in depth, both the nanostructure of the materials and the linear rheology were investigated by small-angle X-ray scattering (SAXS) and oscillatory shear, respectively. For two types of stickers (TOL and XYL), the association of polymers via hydrogen bonds induces the formation of bundles of rodlike aggregates at room temperature and the behavior of a soft elastic material was observed. For bis-urea MDI, no structure is detected by SAXS and a Newtonian behavior is observed at room temperature. In probe-tack experiments, all these materials show a cohesive mode of failure, a signature of flowing materials as previously observed for tri-urea center-functionalized poly(butylacrylate) (PnBA3U). However, XYL center-functionalized polyisobutene shows much higher debonding energies than PnBA3U, revealing the importance of the strength of noncovalent bonds in the scission/recombination dynamics. On the basis of the analysis of the debonding images, this effect is discussed via the mechanical behavior at large deformation.

Cyclic peptide-poly(HPMA) nanotubes as drug delivery vectors: In vitro assessment, pharmacokinetics and biodistribution

Size and shape have progressively appeared as some of the key factors influencing the properties of nanosized drug delivery systems. In particular, elongated materials are thought to interact differently with cells and therefore may allow alterations of in vivo fate without changes in chemical composition. A challenge, however, remains the creation of stable self-assembled materials with anisotropic shape for delivery applications that still feature the ability to disassemble, avoiding organ accumulation and facilitating clearance from the system. In this context, we report on cyclic peptide-polymer conjugates that self-assemble into supramolecular nanotubes, as confirmed by SANS and SLS. Their behaviour ex and in vivo was studied: the nanostructures are non-toxic up to a concentration of 0.5 g L^-1 and cell uptake studies revealed that the pathway of entry was energy-dependent. Pharmacokinetic studies following intravenous injection of the peptide-polymer conjugates and a control polymer to rats showed that the larger size of the nanotubes formed by the conjugates reduced renal clearance and elongated systemic circulation. Importantly, the ability to slowly disassemble into small units allowed effective clearance of the conjugates and reduced organ accumulation, making these materials interesting candidates in the search for effective drug carriers.

pH-Responsive, Amphiphilic Core-Shell Supramolecular Polymer Brushes from Cyclic Peptide-Polymer Conjugates

The synthesis and self-assembly of pH-responsive, amphiphilic cyclic peptide-polymer conjugates are described. The design relies on the introduction of a poly(2-(diisopropylamino)ethyl methacrylate) (pDPA) block between the cyclic peptide and a hydrophilic block. These conjugates are disassembled and protonated at low pH but assemble into core-shell nanotubes at physiological pH, as determined by a combination of titration experiments and scattering techniques.

Opposing Phase-Segregation and Hydrogen-Bonding Forces in Supramolecular Polymers

Phase segregation between different macromolecules and specific weak interactions are the basis of molecular organization in many biological systems, which are held together by attractive hydrogen bonds (H-bonds) and dissociated by phase segregation. We report significant changes in the association behavior of covalent H-bonds by the phase of attached polymer chains. Depending on the aggregation state, we observed either intact H-bonds despite segregation of the phases, or macrophase separation with a larger amount of H-bonding dissociation.

Patchy Supramolecular Bottle-Brushes Formed by Solution Self-Assembly of Bis(urea)s and Tris(urea)s Decorated by Two Incompatible Polymer Arms

In an attempt to design urea-based Janus nanocylinders through a supramolecular approach, nonsymmetrical bis(urea)s and tris(urea)s decorated by two incompatible polymer arms, namely, poly(styrene) (PS) and poly(isobutylene) (PIB), were synthesized using rather straightforward organic and polymer chemistry techniques. Light scattering experiments revealed that these molecules self-assembled in cyclohexane by cooperative hydrogen bonds. The extent of self-assembly was limited for the bis(urea)s. On the contrary, reasonably anisotropic 1D structures (small nanocylinders) could be obtained with the tris(urea)s (Nagg ∼ 50) which developed six cooperative hydrogen bonds per molecule. (1)H transverse relaxation measurements and NOESY NMR experiments in cyclohexane revealed that perfect Janus nanocylinders with one face consisting of only PS and the other of PIB were not obtained. Nevertheless, phase segregation between the PS and PIB chains occurred to a large extent, resulting in patchy cylinders containing well separated domains of PIB and PS chains. Reasons for this behavior were proposed, paving the way to improve the proposed strategy toward true urea-based supramolecular Janus nanocylinders.

Dynamic Ordering and Phase Segregation in Hydrogen-Bonded Polymers

Hydrogen bonds (H-bonds) constitute highly relevant structural units of molecular self-assembly. They bridge biological and synthetic sciences, implementing dynamic properties into materials and molecules, not achieved via purely covalent bonds. Phase segregation on the other hand represents another important assembly principle, responsible for, e.g., cell compartimentation, membrane-formation, and microphase segregation in polymers. Yet, despite the expanding elegant synthetic strategies of supramolecular polymers, the investigation of phase behavior of macromolecules driven by H-bonding forces still remains in its infancy. Compared to phase segregation arising from covalently linked block copolymers, the generation of phase segregated nanostructures via supramolecular polymers facilitates the design of novel functional materials, such as those with stimuli-responsive, self-healing, and erasable-material properties. We here discuss the phase segregation of H-bonding polymers in both the solution and solid state, wherein the molecular recognition elements are based on multiple H-bonding moieties, such as thymine/2,6-diamino-pyridine (THY/DAP), thymine/diamino triazine (THY/DAT), and barbiturate/Hamilton wedge (Ba/HW) elements. The specific aggregation of a series of different H-bonding polymers in solution, both linear and dendritic polymers, bearing heterocomplementary H-bonding moieties are described, in particular focusing on the issue of phase segregation. The exploitation of H-bonded supramolecular dendrons with segregating polymer chains leads to the formation of three-phase segregated hierarchical micelles in solution, purely linking the components via H-bonds, in turn displaying a versatile spectrum of segregated morphologies. We also focus on segregation effects of H-bonded amorphous and crystalline polymers: thus the formation of nanostructures, such as disordered micelles and well-ordered body centered cubic (BCC) packed spheres from telechelic polymers bearing H-bonding moieties at the chain ends is observed. Finally, we discuss the discovery of novel functional microphase separated self-healing supramolecular architectures, illustrating dynamic and self-healing properties with an almost complete recovery of the initial mechanical performances healing within 24h at 30 °C. Collectively, our studies prove that phase segregation in H-bonding polymers is an important principle, capable to generate nanostructures and dynamic properties not achieved in covalently linked polymers. The results discussed illustrate that a rational architectural design within H-bonding polymer systems in interplay with phase segregation in both the amorphous and crystalline state opens perspectives to develop artificial supramolecular systems approaching the level of complexities and properties present in nature's biomaterials.

SiC Nanowires with Tunable Hydrophobicity/Hydrophilicity and Their Application as Nanofluids

In this paper, several methods including HF, NaOH, TEOS, and PVP treatment were adopted to modify the wettability of silicon carbide (SiC) nanowires switching from hydrophobic to hydrophilic. The phase and microstructure investigated by XRD, FT-IR, XPS, TGA, SEM, and TEM demonstrated SiC nanowires switching from hydrophobic to hydrophilic due to the surface-tethered hydrophilic layer as well as increasing interspace between nanowires. Besides this, SiC nanowires with hydrophilicity may effectively improve the thermal conductivity of a fluid. The thermal conductivity of aqueous SiC nanowires after TEOS treatment with just 0.3 vol % was remarkably improved up to ca. 13.0%.

A supramolecular brush polymer via the self-assembly of bridged tris(β-cyclodextrin) with a porphyrin derivative and its magnetic resonance imaging

Accurate imaging of soft tissues is one of the ultimate goals in biomedical imaging. Different imaging modalities can improve their disadvantages, and promote the imaging ability. However, once an imaging agent has been prepared, it is usually hard to adjust it according to the actual needs. Herein, we developed a supramolecular brush polymer (SBP) as a versatile imaging agent platform. The SBP platform (SBPP) is constructed by the intermolecular inclusion complexation of bridged tris(β-cyclodextrin) (1) with Mn(iii)-porphyrin-bearing poly(ethylene glycol) (PEG) side chains (Mn(iii)-TPP), and can further bind other functional groups by host-guest interactions of cyclodextrin and adamantine. The SBPP is characterized by UV/vis absorption spectroscopy, NMR, dynamic light scattering (DLS), atomic force microscopy (AFM) and transmission electron microscopy (TEM). We demonstrated that this SBPP not only has no cellular toxicity against NIH 3T3 cells in in vitro cell experiments, but it also shows an efficient enhanced T₁ relaxivity in in vitro MR imaging experiments. When used as multifunctional imaging agents, different imaging probes and/or targeting agents can be introduced to this SBPP as needed through simple host-guest interactions. In in vitro imaging experiments, it shows accurate imaging of different kinds of cancer cells by choosing on-demand targeting agents. These results suggest a promising strategy for engineering multifunctional imaging agents with SBPs.

One-pot synthesis and self-assembly of supramolecular dendritic polymers

A X–Y₂ type heterotropic single-chain polymer, Ba-(PnBuA-HW)₂, is prepared in a one-pot two-step reaction, subsequently self-assembling into supramolecular dendrimers, which are displaying solvent-dependent disc-like hierarchical nanoscopic structures as evidenced by AFM.

Exploiting nucleobase-containing materials – from monomers to complex morphologies using RAFT dispersion polymerization

The synthesis of nucleobase-containing polymers was successfully performed by RAFT dispersion polymerization in both chloroform and 1,4-dioxane and self-assembly was induced by the polymerizations.