Scientific News #2

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For previously presented topics have a look at Scientific News #1 – Lab-layered Latte Edition

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Topic #4: Processable crosslinked polymers

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Modern society demands polymer materials and composites that are easy to process, assemble and recycle, while exhibiting outstanding mechanical, thermal and chemical properties. Vitrimers, which are are polymer networks that can shift their chemical bonds through exchange reactions, could meet these requirements. In principle they can replace traditional thermoplastics without their disadvantages such as low mechanical strength, instability at high temperatures or lack of solvent resistance! The group of Nicolaÿ and Leibler used the metathesis of dioxaborolanes to make vitrimers from polymers such as poly(methyl methacrylate) (PMMA), polystyrene (PS) and high density polyethylene (HDPE).

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Synthesis of vitrimers: (A) shows the synthesis of copolymers with dioxaborolanes from functional monomers. (B) illustrates the grafting of dioxaborolanes onto perexisting thermoplastic polymers by means of reactive processing. (C) depicts the cross-linking process of functional polymers containing the pendant dioxborolane units by means of metathesis with a bis-bioxaborolane (green-red-green feature). The free dioxaborolanes formed during the cross-linking process may stay in the system as plasticizers or may be removed through evaporation. - Illustration taken from Ref.

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Although permanently networked, these polymers can be processed several times through typical reshaping processes such as extrusion or injection molding! The developed strategy works for polymers with a backbone of C-C single bonds. Furthermore their work did not end with providing a kind of new polymere type, but they also investigated their mechanical and chemical stabilities, hereby showing the superior properties of vinyl and olefin vitrimers!

This is a truly awesome scientific work!
I warmly recommend checking out the original literature!

Reference:
M. Röttger, T. Domenech, R. v. d. Weegen, A. Breuillac, R. Nicolaÿa and L. Leibler: High-performance vitrimers from commodity thermoplastics through dioxaborolane metathesis, Science, 2017, 356, pp. 62-65

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Topic #5: Nanoparticle size determination with AAS

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Leopold and co-workers have developed a method to determine the sizes of gold nanoparticles using high-resolution graphite furnace atomic absorption spectrometry. Normally, atomic absorption spectrometric analysis works as follows:

• The analyte is usually supplied in an aqueos form.
• In an atomizer unit (either a flame, furnace or plasma) the sample is evaporated, pyrolized and finally atomized.
• The free atoms can absorb wavelengths of well-defined energy according to their energetic shell structure.
• Radiation of the relevant wavelength is radiated through the sample space.
• The decrease in radiation intensity can then be related to an analyte concentration via the Lambert-Beer law. (For more see: Lambert-Beer law)

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The standard application of AAS thus allows the qualification and quantification of analyte elements. In order to be able to read out this completely new information about the size of nanoparticles from the measurement data, a novel data analysis technique was developed. This technique is based on the fact that the nanoparticles are atomized in a time-delayed manner depending on their size. Thus, it is possible to distinguish between ionic gold and monomodal gold nanoparticle suspensions with particles in the range of 2 and 100 nm. As the authors show, after deconvolution of the AAS data their method is in principle also suitable for investigating multimodal mixtures!

Reference:
K. Leopold, A. Brandt and H. Tarren: Sizing gold nanoparticles using graphite furnace atomic absorption spectroscopy, J. Anal. At. Spectrom., 2017, 32, pp. 723-730

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Topic #6: News from the chemistry of Xenon

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Schrobilgen and co-workers present the first isolatable compounds with xenon-bromine binding. The number of isolatable compounds which do have different noble-gas/element bonds is limited strongly for xenon and even more for krypton. You can hardly find any Xe-Cl bond containing compounds, and prior to this work no Xe-Br bonded compounds were isolated in macroscopic quantities:
The combination of XeO3 and Ethyl- or Methylbromide in acetonitrile gave monocrystals of the Bromoxenates [N(C2H5)4]3[Br3(XeO3)3] and [N(CH3)4]4[Br4(XeO3)4]. According to the authors, the anionic parts of these complexes exhibit the following structures:

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Illustration taken from Ref.

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The isostructural chloroxenates are accessible via the same synthetic pathway. The initially simple appearing synthetic route towards those air-stable compounds is hampered by the detonation sensitivity of XeO3.
The found Xe-Br distances of 3.1 to 3.3 Å are well below the sum of the Van der Waals radii (4.0 Å). According to quantum mechanical investigations, the Xe-halogen bond in the bromo- and chloroxenates is weakly covalent and can be described as a halogen-bridging-bond.

For more, have a look at the reference:
James T. Goettel, Veit G. Haensch and Gary J. Schrobilgen: Stable Chloro- and Bromoxenate Cage Anions, J. Am. Chem. Soc., 2017, 139 (25), pp 8725-8733

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Economic-scientific Notes

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The German petroleum AG, short DEA, won - together with the Mexican state-owned company Pemex - the tendering for the extraction of light oil and natural gas within an area of 549 square kilometers off the Mexican East Coast. - Ref.

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The US government imposed a fine of $ 2 million on the oil giant Exxon Mobil for doing business with Russia's competitor Rosneft in May 2014. Although the Russian company was not on the US sanction list itself, but its CEO Igor Sechin was! All this took place while Rex Tillerson was the CEO of Exxon Mobil. - Ref.

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mountain.phil28