Polymers seem to be recent materials but their origin is further away than it appears

The history of the birth of polymers is much less linear than one might think, with the intuitions of some precursors who, sometimes, remained stationary in the laboratory for decades , as the knowledge of chemical reactions or the limited technological progress of the plant hindered its development.

It is interesting to note that, for some chemical combinations which then led to the birth of a certain family of polymers, randomness could have also played a role primary role, creating unexpected situations, the result of unsought but immediately understood and exploited chemical reactions.

Surely the last century was fundamental for the development of basic polymers, as two formidable situations occurred:

- the first was the continuous progression of the knowledge of industrial chemistry, whose beginnings can be identified in the 19th century,

- the second is the great industrial progress that has been able to make available to chemists, both in the laboratory and in industrial sites, efficient and innovative machines that support the ideas of scientists.

As Michele Seppe tells us, already in the 30s of the last century, the modern rubber industry was already almost a hundred years old, celluloid was commercially available from over half a century and phenols were a dominant force in a wide variety of industries.

With few exceptions, all significant developments in polymer technology up to that point have been crosslink systems, also known as thermoset materials.

Today the industry looks very different, thermoplastics are the dominant materials and, within this group, polypropylene, polyethylene, polystyrene and PVC are the four raw materials that account for the majority of the volume consumed worldwide.

But the thermoplastic materials that can really compete with the performance, at elevated temperatures of metals and cross-linked polymers, are materials such as polyamides (nylons), polycarbonates and the PEEK.

Tracing the historical development of thermoplastics can be challenging, because many times the discovery of a material in the laboratory has not had a rapid path towards its marketing.

Polystyrene was first discovered in 1839, but was only commercially produced in 1931, due to problems with control of the exothermic polymerization reaction.

PVC was discovered in 1872, but attempts to use it commercially in the early 20th century were hampered by the limited thermal stability of the material.

In fact, the temperature required to convert the material into a melt was higher than the temperature at which the polymer began to decompose thermally.

This was solved in 1926 by Waldo Semon, at BF Goodrich, in fact, while trying to dehydrohalogenate PVC in a solvent to create a substance that binds rubber to metal, he found that the solvent had plasticized the PVC. This lowered its softening temperature and opened a window for melt processing.

Polyethylene was created for the first time in the laboratory in 1898 by the German chemist Hans von Pechmann by breaking down diazomethane, a substance he had discovered four years earlier.

But diazomethane is a toxic gas with explosive properties, therefore, it would never have been a viable commercial option for large-scale production of a polymer, which it is now used in incredibly high annual volumes.

The material was rediscovered in 1933 by Eric Fawcett and Reginald Gibson while working at ICI in England. They experimented with placing various gases under high pressure, and when they put a mixture of ethylene and benzaldehyde gas under enormous pressure, they produced a white, waxy substance that we know today as low-density polyethylene.

The reaction was initially difficult to reproduce, just two years later another ICI chemist, Michael Perrin, developed controls that made the reaction reliable enough to lead to commercialization in 1939, more than forty years after the polymer was first produced.

High-density polyethylene was synthesized with the introduction of new catalysts in the early 1950s. In 1951, while J. Paul Hogan and Robert Banks worked at Phillips Petroleum, they developed a system based on chromium oxide.

Patents were filed in 1953 and the process was commercialized in 1957, and the system is still known today as the Phillips catalyst.

In 1953, Karl Ziegler introduced a system that used titanium halides combined with organoaluminum compounds and, around the same time , an Italian chemist, Giulio Natta, made changes to Ziegler's chemistry.

Both systems allowed for a reduction in both the temperature and pressure required to produce the highly branchedLDPE and produced a much stronger linear polymer , stiffer and more heat resistant than LDPE.

These developments illustrate how different groups of chemists, who worked independently on the same problems, came to develop solutions almost simultaneously.

The new catalysts have also made it possible to produce commercially viable versions of the fourth member of the basic polymer family, polypropylene.

This was manufactured by Fawcett and Gibson in the mid-1930s. After their successful experiments with polyethylene, they naturally expanded their work to include other gas, but their results with polypropylene were disappointing.

Instead of producing a material that was solid at room temperature and exhibited useful mechanical properties, the reaction produced a sticky mass of interest only as an adhesive. Fawcett and Gibson had produced what would later be known as atactic polypropylene.

Unlike polyethylene, where all groups attached to the carbon backbone are hydrogen atoms, each propylene unit in the polypropylene backbone contains three hydrogen atoms and a much larger methyl group.

In atactic polypropylene, the methyl group can appear in any of four possible positions within the repeating unit, preventing the crystallization of the material. The new catalysts created a structure in which the methyl group was in the same position in each repeating unit.

Structural regularity led to a material capable of crystallising, indeed this crystalline form of polypropylene had strength, stiffness and a melting point even higher than HDPE .

This rapid development has created two materials that now account for more than 50% of the world's annual polymer production.

It is interesting to note that Giulio Natta's wife, Rosita Beati, who was not a chemist, coined the terms atactic, isotactic and syndiotactic to describe the different structures that could be created by polymerizing polypropylene.

Today we use these terms to refer generally to the isomeric structures that can form when polymers are produced using various types of catalysts.

Automatic translation. We apologize for any inaccuracies. Original article in Italian.