June 30, 2022

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Science and History / Hermann Staudinger and the Discovery of Large Molecules

There are scientific discoveries that not only radically changed the course of research, but also led to it happening They also greatly influenced the habits of daily life; This is the case of the discovery of organic macromolecules that has led to the possibility of designing polymers to produce materials with the most diverse properties and multiple applications. The author outlines both the scientific profile of Hermann Staudinger and his human standing, which is especially distinguished by his resolute and vocal opposition to the First and Second World Wars and the possible military use of chemical weapons.

Hermann Studinger was born in Worms in 1881; His father, who was studying philosophy in high school, was a socialist and pacifist and this influenced his rule over the two world wars. He graduated in chemistry at the University of Halle in 1899, and in 1905 was the first to make chitin (R’R” C = C = O) and study its applications in organic synthesis; From 1912 to 1926 he taught at the Federal Institute of Technology in Zurich (ETH Zürich). Since Switzerland was neutral, this allowed him, being deeply pacifist, given the education he had received from his father, to criticize in a very harsh manner the conduct of war by Germany both in the interventions in the newspapers and in the private sector; In particular, he argued with chemist Fritz Haber (1868-1934). He was a giant of German chemistry who found a way to synthesize ammonia (for this he was awarded the Nobel Prize in 1918), a material essential for the production of fertilizers, but also of explosives; At the outbreak of World War I, he was a huge supporter of the war and led the production of aggressive chemicals, and also directed their use in the war zone. When the United States entered the war in 1917, Studinger, who had prepared a careful analysis of the impact of the technical and industrial potential of a belligerent country, declared that Germany had lost the war. In 1926 he moved to the University of Freiburg im Breisgau where he stayed for the rest of his career. In 1953 he was awarded the Nobel Prize in Chemistry “for his discoveries in the field of macromolecular chemistry”. He died in Freiburg in 1965.

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Quantum leap

Molecules are aggregates of atoms held together by very strong chemical bonds, usually covalent, while other types of weaker bonds, called intermolecular forces, cause molecules to clump together in solids. Organic macromolecules are molecules with a molecular weight that can range from 50,000 atomic mass units to several million uma, while other molecules such as alcohol, sugar, benzene hydrocarbons or many drugs have a weight of 50 uma to 500 uma; Examples of macromolecules are plastics, cellulose and starch, as well as proteins and DNA, which in the human case reach a mass of 1.9 1012 Uma. Due to their large size, large particles do not give clear solutions but are colloidal: they are thus as turbid as for example milk, because particles with dimensions between 0.01 μm and 1 μm dissipate visible light; Moreover, it does not precipitate because the forces of interaction with the solvent prevail with respect to gravity, pass through filter paper and undergo Brownian motion.

Until the early twentieth century, the dispersed colloidal phase was thought to always consist of clumps of molecules ( micelles), even if abnormally high molecular weights were measured in the nineteenth century for rubber, cellulose, and proteins. At that time the prevailing view was that molecules of this weight were not stable, so some chemists, including Wolfgang Ostwald (1853-1932), hypothesized the existence of aggregates of small molecules where the intermolecular forces are so high that the measurement of molecular weight changes.

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Hermann Staudinger strongly opposed this view, arguing that all physical and chemical properties are determined by molecular structure rather than by forces outside the individual molecule. He thus argued that the specific properties of materials such as rubber and paper, which are very different from those of the isoprene and glucose of which they are composed, could be derived from the simple assembly of the latter without involving true chemical bonds. Beginning in 1920, he published a series of articles in which he presented evidence that molecules such as rubber and polystyrene were in fact covalently bound molecules. In 1922 in an article on Helvetica Chemica Acta coined the term “macromolecule” (macromolecular) to identify these long chain molecules. The precise definition was: “colloidal particles in which the molecule is identical to the particle and in which the atoms are linked by covalent bonds.”

Already in the nineteenth century it was proved that natural rubber consists of isoprene (C.5 h.8) and in 1909 in Germany it was possible to produce a synthetic form that became an industrial product during the First World War.

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