The invention of synthetic rubber
“Rubber? Yes, of course – it can be found in tires, seals, shoe soles, garden hoses...” Very good! Anything else? Well, most people would start having problems at this point. That’s not surprising, since even professionals find it difficult to name all the applications for rubber in our daily lives. That’s because no one really knows the exact number of things that owe their existence to this extremely versatile material. Bungee ropes, engine mountings, gasket rings, balloons, gym mats, print cylinders – anyone who tried to write down all the things containing rubber that we encounter every day would soon have to stop from exhaustion. It’s actually almost easier to count the things that don’t contain rubber. After all, you’re bound to find the elastic material in nearly every place where power is transmitted or stepped down, or where a liquid is transported or needs to be contained.
Nevertheless, things aren’t quite that simple, because there really is no one single elastic rubber material. Whenever rubber has to do its work under extreme conditions, engineers today rely on high-performance rubbers – special materials that have as much in common with the natural sticky stuff used by the Mayas and Aztecs to make balls and containers as a sports car has with a pushcart. And the only reason we now have these special materials is because somebody came up with a really good idea one hundred years ago.
One is sure to find people who know a great deal about rubber at the LANXESS specialty chemicals group today. That’s because the company is continuing the story of high-performance rubbers that began with a type of “contest” at the Elberfelder Farbenfabriken Friedr. Bayer & Co. dye factory in 1906. This story was then shaped by the Bayer AG company, and has been unfolding further at LANXESS since 2004. Around one hundred years ago, a man named Fritz Hofmann worked at the Elberfelder Farbenfabriken as the head chemist in the pharmaceutical department. Today, however, he is better known as the man who produced the first synthetic rubber.
Hofmann already knew what rubber was, of course. After all, Christopher Columbus and other explorers had first reported seeing Indians in South America doing things with this strange new material several centuries before Hofmann’s discovery. Then, in 1839, the process of vulcanization was invented in Europe, thereby making ít possible to transform sticky natural rubber into a solid yet elastic material. This rubber was considered for quite some time to be a high-tech material that could be used to make not only coats and boots, but also fountain pens, pipe mouthpieces, and even dentures – not to mention tires.
The natural rubber that all of these things were made of had many drawbacks, however. For one thing, it disintegrated very quickly (and still does) when exposed to air and heat – and it also had to be grown on plantations. The material was thus subject to extreme fluctuations of quality and price. The main problem, however, was that it was very difficult to modify chemically, which meant that it could not keep up with the expanding requirements of technological development.
It’s therefore not surprising that the search for a substitute material in chemists' test tubes led to some innovative ideas. One source of such ideas was Hofmann’s company, which in 1906 offered a prize of 20,000 marks to anyone who could succeed by November 1, 1909 in “developing a procedure for manufacturing rubber or an adequate substitute.” At that time, such a proposal was akin to John F. Kennedy’s call in the early 1960s for America to land a man on the moon before the end of the decade. In 1900, 20,000 marks was a lot of money; at that time, you could get a stylish suit for 50 marks, and in 1909 a worker made around 1,300 marks a year. So if Hofmann wanted to win the prize, he would have to hurry. To make matters more complicated, he only had a vague idea of the task he was facing.
Hofmann’s biggest problem was that although natural rubber was being studied in depth in many laboratories, it had only recently been discovered in 1905 that the chain molecules which make up this elastic material actually consisted of innumerable components arranged in a row, which chemists referred to as isoprenes. Actually, scientists had known about isoprenes since 1860. But no one really knew how to link isoprenes in a laboratory (polymerization) in the way that Mother Nature does. In addition, the secret “natural rubber component" isoprene was difficult to obtain in its pure form – even though it practically grew in trees in the form of latex.
Hofmann nevertheless went to work on his synthetic rubber project – and was successful: on September 12, 1909, nearly one hundred years ago, patent No. 250 690 was issued for the first-ever synthetic rubber.
It took a while before Hofmann’s idea could be transformed into a truly usable and – above all – economically exploitable rubber, however. Despite the expertise gained by Hofmann’s team, the rubber base component isoprene was still too difficult to produce. Hofmann therefore first had to learn to ignore his precious isoprene bottles and instead turn to a chemically similar substance – so-called methyl isoprene, which was somewhat easier for chemists to obtain at that time.
Hofmann put this substance into tin cans, heated it, and learned to be patient. He waited weeks and then months. What he might have said when he finally opened one of the cans remains unknown. What is clear, however, is that he found a strange substance inside, which, depending on the polymerization temperature, either became softer or harder, while always remaining elastic. This material became known as methyl rubber, or synthetic rubber, and its discovery marked the birth of rubber as we know it today.