Discover Top Posts Tagged with #supramolecular polymers

An effective approach for preparing supramolecular polymers at high concentration

Supramolecular polymers (SPs) are molecular assemblies composed of non-covalently bonded small molecules. They show high recyclability originating from their dynamic nature of monomer binding, which is different from covalent polymers with non-biodegradable nature. The small repeating units that form SPs, called monomers, are specifically designed to construct multiple non-covalent bonds to enhance the stability of the resulting SPs. Such monomers can be organized into structurally distinct assemblies by forming various molecular arrangements depending on monomer concentration, solvent composition, and temperature. This formation of versatile self-assembled structures from a single molecule is referred to as polymorphism. However, polymorphism potentially leads to a reduction in the solubility of molecules by forming a crystalline polymorphic state. This issue is prevalent in various chemical industries, such as pharmaceuticals, where the solubility of a drug molecule affects the functionalities of the drug molecule.

Spatiotemporal segregation of chiral supramolecular polymers

In 1848, Louis Pasteur successfully segregated two types of crystals of double sodium-ammonium salt of tartaric acid, which were mirror images of each other. Back then, this was done manually through a painstaking process of observing the crystals under a microscope and utilizing a simple pair of tweezers. Following this seminal discovery, the field of stereochemistry has made great progress.

Today, advances in technology now allow chemists to explore programmable control over the helicity of chiral supramolecular polymers with molecular-level manipulation, stimuli-responsive chirality switching, etc. Unlike sub-millimeter scale stable crystals of sodium-ammonium tartrate, chiral supramolecular polymers are soft materials with dynamic structures and their size ranges from the nanometer scale to a few microns. Moreover, chiral supramolecular polymers are not uniformly present in solution due to uncontrolled diffusion.

Their distribution can be even more random and complex, especially when dealing with a mixture of supramolecular species in multicomponent self-assemblies. Manual segregation of such chiral supramolecular polymers is therefore difficult to achieve and practically impossible.

New supramolecular plastic that is degradable and highly recyclable

A research group headed by senior researcher Jianwei Li at the MediCity Research Laboratory has explored a new type of materials called supramolecular plastics that would substitute the conventional polymeric plastics with an eco-friendlier material promoting sustainable development. The mechanical properties of the supramolecular plastic created by the researchers using liquid-liquid phase separation were comparable to conventional polymers, but the new plastic decomposes much more easily and would be easier to reuse.

Plastic is one of the most important modern materials and has been integrated into all aspects of human life after a century of development. However, traditional polymer plastics degrade and regenerate poorly in nature and have become one of the greatest threats to human survival. This situation is a result of the inherent strong force of covalent bonds that link monomers for the formation of polymers.

To address the challenge, scientists have suggested making polymers connected by non-covalent bonds that are not as powerful as covalent bonds. Unfortunately, the weaker interaction is usually not strong enough to hold molecules together in materials with macroscopic sizes, which prevents the practical application of noncovalent materials.

Supramolecular adhesive with usable temperature range of 400 degrees Celsius

Researchers have developed a supramolecular adhesive that is recyclable and has outstanding gluing properties across a wide range of temperatures, from liquid nitrogen (−196 degrees Celsius) up to oven-hot temperatures (200 degrees Celsius). As the team report in the journal Angewandte Chemie, the adhesive got its efficiency from an exceptionally tight interlocking of the molecular components during curing.

Unlike standard adhesives, supramolecular adhesives do not create adhesion by the molecular components crosslinking with one another. Instead, they form a tight-knit self-assembly during curing, like puzzle pieces fitting together. Researchers are interested in such supramolecular systems because they offer sustainability and customizability and, in principle, the individual starting materials can be recovered again and their chemical behavior can be tailored. However, to date, the performance of such glues has been decent at best, not to mention highly dependent on environmental conditions.

The new supramolecular glue, developed by a research team headed by Kai Liu from Tsinghua University, Beijing, China, consists of two components, one of which is a small protein that is synthesized in bacteria modified for the purpose. The other component is a crown ether—a ring-shaped molecule which can wrap snugly around another molecule, much like a crown sitting on a queen's head.

Mussel-inspired dynamic poly(disulfides) ultra-strong underwater adhesives

Inspired by mussels' unique underwater adhesion ability, DOPA chemistry, which plays a key role in adhesive proteins, has become a typical supramolecular toolbox for designing water-resistant adhesive materials, resulting in elegant progress based on the scaffold of (hydro)gels. However, very few studies have focused on the DOPA-functionalized solvent-free network, which may enrich the supramolecular binding of DOPA moieties to the surface by avoiding solvation competition, and further boost the material performance of the bio-inspired adhesive material.

Prof. Da-hui Qu's group from East China University of Science and Technology has developed a series of solvent-free supramolecular networks by using thioctic acid (TA), a natural small molecule, as the feedstock. The reversible ring-opening polymerization (ROP) mediated by dynamic covalent disulfide bonds, together with the non-covalent crosslinking of sidechains, jointly endows the resulting network with many intriguing dynamic functions, including mechanical adaptiveness, self-healing ability, re-processability and chemical closed-loop recyclability.

Meanwhile, the resulting polymeric materials also show excellent adhesive properties, which may be attributed to (i) high interfacial penetration due to the small-molecule precursor, (ii) the high abundance of hydrogen bonds in the carboxylic sidechain and (iii) the solvent-free nature of the network. Motivated by this feature, researchers envisioned that it would be exciting if one could introduce mussel-inspired DOPA chemistry into the solvent-free network of poly(TA) so that the advantages of both adhesion chemistries could be combined in a single material that is a high-strength adhesive, while simultaneously being water-resistant, durable and dynamic.

Environmentally Friendly, Self-Templating Supramolecular Polymer Synthesis

A green method for producing crystalline supramolecular fibers promises to make polymer production more sustainable.

A polymer that catalyzes its own formation in an environmentally friendly solvent-free process has been developed by an all-RIKEN team of chemists. The discovery could lead to the development of inherently recyclable polymer materials that are made using a sustainable process.

Polymers are ubiquitous today, but they are detrimental to the environment through the accumulation of plastic waste and the unsustainable nature of conventional polymer manufacture. Polymers are generally made by linking together strings of building blocks, known as monomers, using covalent bonds. But these strong bonds make it difficult to take used, end-of-life plastic items and de-polymerize them to recover the monomers for reuse.

Chemists find a contrary effect: How diluting with water makes a solution firm

In Science, TU/e researchers have published their study on new phase transitions of solutions and gels in water, which seem to go against the basic principles of chemistry, and which they discovered by accident.

In chemistry, a hydrogel changes to a liquid by diluting it with water. For the reverse transition, you increase the hydrogel concentration. However, TU/e researchers led by Bert Meijer accidentally discovered that their liquid solution turned into a hydrogel when diluted. This phenomenon hadn't been researched or described before and could have consequences in many areas in chemistry and biology.

The research focuses on the formation of certain hydrogels. This means that it starts with an aqueous solution of, in this case, two substances (a surfactant and a monomer). The research shows that a gel is formed at a specific ratio of these two substances in water. This gel is formed by long, supramolecular networks composed of both substances. The amounts of these substances in water (the concentrations) also determine where the phase transition of the gel formation is located. When decreasing the concentration without changing the ratio between the two components, the gel dissolves and becomes liquid. So far, this is familiar territory.

Polymer that folds and unfolds under UV radiation

Polymers, the basis of all plastics, usually do not have an ordered structure, in contrast to biopolymers such as proteins. A team of researchers has now developed a polymer that can be differentiated into folded (ordered) and unfolded (disordered) domains using UV irradiation. The team's work offers new possibilities for developing functional soft materials, as they write in the journal Angewandte Chemie.

Proteins consist of long molecular chains that can fold or twist about themselves, or form an unordered cluster. The arrangement of differently ordered domains within the protein give it its ultimate form, and therefore function. However, what occurs simply and ubiquitously in nature is not always so easy to reproduce in a lab. It is difficult to give chain-like macromolecules, such as polymers, any form other than an unordered cluster.

For a particular class of polymers known as supramolecular polymers, an international team of researchers led by Shiki Yagai, Chiba University, Japan, and Giovanni M. Pavan, Politecnico di Torino, Italy, have now discovered a differentiated folding system. In supramolecular polymers, the monomers in the chain are not linked by direct chemical bonds. Instead, they are held together by non-bonding interactions such as electrostatic forces, giving researchers an interesting tool to manipulate the structure of the polymer after its formation.

Mussel-inspired dynamic poly(disulfides) ultra-strong underwater adhesives

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