New synthesis method opens up possibilities …

New synthesis method opens up possibilities for organic electronics

Semiconducting polymers, large, chain-like molecules made from repeating subunits, are increasingly drawing the attention of researchers because of their potential applications in organic electronic devices. Like most semiconducting materials, semiconducting polymers can be classified as p-type or n-type according to their conducting properties. Although p-type semiconducting polymers have seen dramatic improvements thanks to recent advances, the same cannot be said about their n-type counterparts, whose electron conduction (or ‘electron mobility’) is still poor.

Unfortunately, high-performance n-type semiconducting polymers are necessary for many green applications, such as in types of solar cells. The main challenges holding back the development of n-type semiconducting polymers are the limited molecular design strategies and synthesis procedures available. Among the existing synthesis methods, DArP (which stands for ‘direct arylation polycondensation’) has shown promising results for producing n-type semiconducting polymers in an environmentally friendly and efficient way. However, until now, the building blocks (monomers) used in the DArP method were required to have an orienting group in order to produce polymers reliably, and this severely limited the applicability of DArP to make high-performance semiconducting polymers.

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The similarities between a Van Gogh painting…

The similarities between a Van Gogh painting and a golf ball

On a molecular scale, there are surprising similarities between the outer shell of a golf ball and the white oil paint used by Van Gogh and his contemporaries. In both cases, the interactions between zinc ions and polymer chains are at the basis of important material properties. In a recent publication in the scientific journal Science Advances, Rijksmuseum and University of Amsterdam researchers describe the role of zinc ions in the molecular network of oil paint. Their studies could explain why paintings made with zinc white pigment are so sensitive to high humidity conditions.

Vincent van Gogh and other painters of his day often used zinc white (zinc oxide, ZnO), a white pigment that yields a good opaque oil paint. However, zinc white can easily react with the oil binder as it polymerises and transform into a network of molecular chains during paint drying. As a consequence, zinc ions nestle themselves between the molecular chains of the oil. Previous research showed that this process is not without danger—the ions can speed up the breakdown of the oil, and they form problematic chemical compounds with the degradation products.

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Researchers create uniform-shape polymer nan…

Researchers create uniform-shape polymer nanocrystals

A team of researchers from the University of Konstanz has demonstrated a new aqueous polymerization procedure for generating polymer nanoparticles with a single chain and uniform shape, which, by contrast to previous methods, involves high particle concentrations. A corresponding paper titled “Uniform shape monodisperse single chain nanocrystals by living aqueous catalytic polymerization” is set for publication in Nature Communications.

To build nanomaterials, nanoparticles with uniform shapes and sizes are required. While inorganic metal or metal oxide nanoparticles suitable for assembly can be generated in a variety of shapes, it has been very difficult until now to manufacture polymer nanoparticles in shapes other than spheres. Stefan Mecking, professor of chemical materials science at the University of Konstanz says, “In previous approaches, single-chain particles were prepared by post-polymerization collapse or assembled from solutions of separately synthesized chains. What we have managed to do is to demonstrate direct polymerization to single-chain uniform-shape monodisperse nanocrystals for polyethylene, which is the largest and most important synthetic polymer material.”

One major challenge associated with this approach is to achieve living chain and particle growth that can be sustained for several hours and up to very high molecular weights, ideally yielding single-chain nanocrystals of ultra-high molecular weight polyethylene. To achieve this, the researchers developed advanced catalysts. “We then conducted a series of pressure reactor tests to identify ideal conditions for maintaining catalytic activity over longer periods of time and to gain insights into the chain and particle growth process,” explains Mecking. “In addition to the novel catalysts, control of the colloidal state of the reaction mixture is another key element in obtaining the desired aqueous particle dispersions.”

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Suspension polymerization ( 2 ) is a form of r…

Suspension polymerization ( 2 ) is a form of radical polymerization in which the monomers are added to a solvent (often water) in which they are soluble, then reacted kinetically (i.e. mixed together to prompt a reaction). It is a widely used technique that is fairly easy to control, simply the various components of the reaction such as stirring speed or the volume fraction of the monomer present.

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Interfacial polymerization ( 2 ) is a form of …

Interfacial polymerization ( 2 ) is a form of step-growth polymerization that creates thin film (or other nanostructured) polymers at the interfaces of two materials. These two materials are usually two immiscible liquids, with a different monomer in each liquid, reacting at the interface, but liquid-solid interactions as well as liquid-in-liquid emulsion reactions are also possible. 

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Precipitation polymerization ( 2 ) is a method…

Precipitation polymerization ( 2 ) is a method of polymerization in which a monomer and initiator are added to a solvent in which they are soluble in, but in which the resulting polymer is insoluble. As a result, particles of the polymer grow within the solution as the reaction proceeds, precipitating from the solvent.

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Solution polymerization ( 2 ) is a method of p…

Solution polymerization ( 2 ) is a method of polymerization in which a monomer and initiator are added to a solvent in which they (and the resulting polymer) are soluble in, creating a solution. When using this method the remaining solvent must then be removed at the end of the reaction, so solution polymerization is common with polymers in which the presence of a solvent is desired, such as varnishes or adhesives. 

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Emulsion polymerization ( 2 ) is a form of pol…

Emulsion polymerization ( 2 ) is a form of polymerization in which a surfactant is mixed in water with a water soluble initiator and (typically) a non-water soluble monomer, ensuring that the polymerization reaction is carried out within the micelles formed by the surfactants. (Other materials can be used, but the oil-in-water form of emulsion polymerization is the most common.) Emulsion polymerizations are always radical polymerizations. 

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Bulk (or mass) polymerization ( 2 ) is a form …

Bulk (or mass) polymerization ( 2 ) is a form of polymerization in which only a monomer and an initiator are present for the reaction (i.e. no solvents are added). It can be used for step growth and chain growth polymers, though it is more commonly used for step growth. These factors make bulk polymerization a very easy, simple, and inexpensive method, but the reaction can be difficult to control, particularly since viscosity increases as the reaction nears completion. 

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