Polymer nanoparticles via intramolecular crosslinking of sulfonyl azide functionalized polymers

Reactive & Efficient: Organic Azides as Cross-Linkers in Material Sciences

The exceptional reactivity of the azide group makes organic azides a highly versatile family of compounds in chemistry and the material sciences. One of the most prominent reactions employing organic azides is the regioselective copper(I)-catalyzed Huisgen 1,3-dipolar cycloaddition with alkynes yielding 1,2,3-triazoles. Other named reactions include the Staudinger reduction, the aza-Wittig reaction, and the Curtius rearrangement. The popularity of organic azides in material sciences is mostly based on their propensity to release nitrogen by thermal activation or photolysis. On the one hand, this scission reaction is accompanied with a considerable output of energy, making them interesting as highly energetic materials. On the other hand, it produces highly reactive nitrenes that show extraordinary efficiency in polymer crosslinking, a process used to alter the physical properties of polymers and to boost efficiencies of polymer-based devices such as membrane fuel cells, organic solar cells (OSCs), light-emitting diodes (LEDs), and organic field-effect transistors (OFETs). Thermosets are also suitable application areas. In most cases, organic azides with multiple azide functions are employed which can either be small molecules or oligo- and polymers. This review focuses on nitrene-based applications of multivalent organic azides in the material and life sciences.

Strengths and limitations of size exclusion chromatography for investigating single chain folding – current status and future perspectives

Synthetic approaches for Single-Chain Nanoparticles (SCNPs) developed rapidly during the last decade, opening a multitude of avenues for the design of functional macromolecular chains able to collapse into defined nanoparticles. However, the analytical evaluation of the SCNP formation process still requires critical improvements.

Construction of Polyarylenes with Various Structural Features via Bergman Cyclization Polymerization

Synthetic polymer chemistry is a fundamental part of polymer science, and highly efficient polymerization reactions are essential for the synthesis of high-performance polymers. Development of new synthetic methods for emerging polymer science is of great importance in this regard. Bergman cyclization is a chemical process in which highly reactive aryl diradicals form from enediyne precursors, having a strong impact in a number of fields including pharmaceutics, synthetic chemistry, and materials science. Diradical intermediates stemming from enediynes can cause DNA cleavage under physiological conditions, leading to the strong cytotoxicity of many naturally occurring enediyne antibiotics. Meanwhile, diradical intermediates can quickly couple with each other to construct polyarylenes, providing a novel method to synthesize these conjugated polymers with the advantages of facile and catalyst-free operation, high efficiency, and tailored structure. Moreover, conjugated polymers generated by Bergman cyclization exhibit many remarkable properties, such as excellent thermal stability and good solubility and processability, enabling their further processing into carbon-rich materials. This review presents a brief overview of the trajectory of Bergman cyclization in polymer science, followed by an introduction to research advances, mainly from our group, in developing polymerization methods based on Bergman cyclization, taking advantages of its catalyst-free, byproduct-free, in situ polymerization mechanism to synthesize new polymeric materials with various structures and morphologies. These synthetic strategies include fabrication of rod-like polymers with polyester, dendrimer, and chiral imide side chains, functionalization of carbon nanomaterials by surface-grafting conjugated polymers, formation of nanoparticles by intramolecular collapse of single polymer chains, and construction of carbon nanomembranes on the external and internal surface of inorganic nanomaterials. These polymers with novel structural features have been used in a variety of fields, such as energy transformation, energy storage, catalyst support, and fluorescent detection. Finally, the outlook for future developments of Bergman cyclization in polymer science is presented.

Hybrid single-chain nanoparticles via the metal induced crosslinking of N-donor functionalized polymer chains

A set of single-chain nanoparticles was prepared via the intramolecular crosslinking of functionalized copolymers with various metal salts.

Characterizing single chain nanoparticles (SCNPs): a critical survey

We provide the results of a critical literature survey on the reported sizes of single chain polymer nanoparticles (SCNPs) employing different techniques.

Voltage-responsive single-chain polymer nanoparticles via host–guest interaction

Poly(N-(2-hydroxyethyl)acrylamide) with pendant β-cyclodextrin is synthesized and intramolecularly crosslinked with bridged bis(ferrocene). This supramolecular nanoparticle can be changed reversibly between a coil and a nanoparticle upon external voltage stimuli.

An unexpected route to aldehyde-decorated single-chain nanoparticles from azides

A new route towards the straightforward synthesis of aldehyde-decorated ultrafine single-chain nanoparticles from azides is described.

Supramolecular Assembly Mediates the Formation of Single-Chain Polymeric Nanoparticles

A breakthrough innovation in water-based polymeric nanoparticles has enabled significant progress in mimicking the folding of natural proteins by generating novel "single-chain polymeric nanoparticles" (SCPNs) via supramolecular interactions. In this study, a practical approach to the living polymerization of functionalized oligo(ethylene glycol) methacrylate monomers allows the incorporation of self-constituted multiple hydrogen-bonded groups into physically cross-linked polymer networks, which enables the formation of highly functionalized SCPNs in an aqueous environment. The newly developed materials are particularly attractive from a practical point of view since they have a very low critical micellization concentration and uniform particle diameters of ca. 25 nm, making them extremely stable under dilute conditions. Concentration-dependent experiments showed that SCPNs formed at polymer concentrations up to 40 mg/mL with no significant change in morphology observed. Moreover, the formed SCPNs had a very high stability in an aqueous solution containing surfactant, suggesting potential for a wide variety of applications as a promising candidate nanocarrier for bioimaging, controlled release, and drug delivery systems.

A brief user's guide to single-chain nanoparticles

In this review we outline the various methods that have been explored to synthesize architecturally defined nanoparticles from discrete polymer chains, summarize the methods of characterization that are required to prove their formation and probe their morphology, and introduce a number of potential applications.

Advances in single chain technology

This review summarizes the recent advances in single chain technology for the construction of soft nano-objects via chain compaction, and their envisioned applications.

Colored single-chain polymeric nanoparticles via intramolecular copper phthalocyanine formation

Colored single-chain polymeric nanoparticles were synthesized by intramolecular formation of copper phthalocyanines from polystyrene-co-poly[4-((4-vinylbenzyl)oxy)phthalonitrile] under diluted conditions.

How Far Are Single-Chain Polymer Nanoparticles in Solution from the Globular State?

Single-chain nanoparticles (SCNPs) are unimolecular soft nano-objects, consisting of individual polymer chains collapsed to a certain degree by means of intramolecular bonding. Many of the potential applications of SCNPs rely on their particular molecular architecture. Even if the ultimate goal is to produce globular protein-like soft nanoparticles, recent small-angle neutron scattering (SANS) and small-angle X-ray scattering (SAXS) results-supported by computer simulations-indicate that SCNPs in solution actually adopt sparse configurations. Herein we compile size data from the literature for a large number of SCNPs in solution, covering from covalent to noncovalent bonded SCNPs, and provide a comparison with the corresponding data for compact or partially swollen globules of the same nature and molar mass. This comparison gives a clear idea of how far from the compact globule limit are current SCNPs. A quantification of the departure from the globular state is provided in terms of size scaling laws. This procedure facilitates a comparison with the size scaling laws observed for folded proteins with globular conformation as well as intrinsically disordered proteins which, on average, exhibit a certain local compaction when compared to chemically denatured proteins. Lastly, the underlying physical mechanism for the noncompact morphology of SCNPs in solution is put forward, and guidelines for the potential synthesis of true SCNP globules in solution are suggested.

Multi-orthogonal folding of single polymer chains into soft nanoparticles

Efficient folding of single polymer chains is a topic of great interest due, mainly, to the challenging possibility of mimicking and controlling the structure and functionality of natural biomacromolecules (e.g., enzymes, drug delivery vehicles, and catalysts) by means of artificial single chain nano-objects. By performing extensive molecular dynamics simulations we investigate the formation of soft nanoparticles by irreversible intramolecular cross-linking of polymer precursors of different lengths. In order to optimize the folding process and to obtain more compact structures we vary the number of chemical species among the linker groups (orthogonal chemistry) which selectively form the bonds. The use of orthogonal chemistry protocols, by increasing the number of different chemical species of the linkers, leads to nanoparticles that are systematically smaller and more spherical than their homofunctional counterparts. We characterize the conformational properties of the resulting nanoparticles. These are intrinsically polydisperse in size, with a significant fraction of sparse topologies. We discuss the relevance of our results for synthesis protocols in real systems.

Exploiting the tetrazine-norbornene reaction for single polymer chain collapse

Single chain polymer nanoparticles (SCNPs) have been formed using polystyrenes decorated with pendent norbornenes and a bifunctional tetrazine crosslinker. Characterisation by size exclusion chromatography and (1)H NMR gives evidence for the formation of SCNPs by the tetrazine-norbornene reaction, whilst light scattering, neutron scattering, transmission electron microscopy and atomic force microscopy show that discrete well-defined nanoparticles are formed and their size in solution calculated.

Advances in click chemistry for single-chain nanoparticle construction

Single-chain polymeric nanoparticles are artificial folded soft nano-objects of ultra-small size which have recently gained prominence in nanoscience and nanotechnology due to their exceptional and sometimes unique properties. This review focuses on the current state of the investigations of click chemistry techniques for highly-efficient single-chain nanoparticle construction. Additionally, recent progress achieved for the use of well-defined single-chain nanoparticles in some promising fields, such as nanomedicine and catalysis, is highlighted.