Humans have used natural rubber for centuries. On his voyage to discover the new continent, Columbus discovered that a ball played by South American aborigines was made of hardened plant juice. Columbus and later explorers were surprised by this elastic ball. Some samples were brought back to Europe as treasures. Later, people found that this kind of elastic ball can erase the traces of pencils, so they gave it a common name "eraser". This is also the English name of this substance. This substance is rubber.

But it was not until 1839 that American CharlesGoodyear successfully vulcanized natural rubber that rubber became a valuable material. By heating with sulfur for vulcanization, the crosslinking of rubber molecular chain is realized, which makes rubber have good elasticity. Why is rubber elastic? Let's analyze the molecular structure of rubber. The monomer of natural rubber molecule is isoprene. We know that the intermolecular forces between chains in polymers determine their physical properties. In rubber, the intermolecular force is weak, because isoprene is not easy to interact with other links. For example, two friends want to shake hands, but everyone has a lot of things in their hands, so it is difficult to shake hands. The force between rubber molecules determines the softness of rubber. Rubber molecules are easy to rotate and have a lot of room for movement. The arrangement of molecules presents an irregular and random natural state. When subjected to external influences such as bending and elongation, molecules are forced to show certain regularity. When the external force is removed, the rubber molecules return to their original irregular state. This is why rubber is elastic. Because of the weak intermolecular force, molecules can rotate freely, and there is not enough binding force between molecular chains, so molecules will slide each other and elasticity will not be shown. This sliding will be weakened by the entanglement of molecules. The entanglement between molecules is unstable and will gradually loosen with the increase of temperature or the passage of time, so it is necessary to establish a solid connection between molecular chains. This is a vulcanization method invented by Goodyear. The vulcanization process is generally carried out at the temperature of 140- 150 degrees Celsius. At that time, Goodyear's small stove only played a role in heating. The main function of vulcanization is simply to form cross-links between molecular chains, thus enhancing the interaction between molecular chains.

In the past thousands of years, people have been using wooden wheels in cars or adding metal rims around the wheels. After Goodyear invented the practical vulcanized rubber in 1845, the British engineer R.W. Thomson put a suitable inflatable rubber tube on the wheel and obtained the patent for this equipment. By 1890, tires were officially used on bicycles, and by 1895, they were used on various old cars. Although rubber is a soft and fragile substance, it is more wear-resistant than wood or metal. The durability and shock absorption of rubber, coupled with the ingenious design of pneumatic tires, make passengers feel unprecedented comfort. With the increasing number of cars, the demand for rubber used to make tires has reached astronomical figures. Such a wide range of applications makes the supply of natural rubber in short supply. Facing the grim situation of rubber production, countries are competing to develop synthetic rubber.

People first thought of making synthetic rubber from isoprene, the structural unit of natural rubber. As early as 1880, chemists found that isoprene would soften and start after being left for too long, and it would become a rubber-like substance after acidification.

Kaiser Wilhelm II once used this substance to make a tire of a royal car to show German superb chemical technology. However, there are two difficulties in using isoprene as the raw material of synthetic rubber: first, the main source of isoprene is natural rubber itself; Second, in the long chain of natural rubber, all isoprene units face the same direction; In the long chain of gutta percha, they are strictly arranged in a positive and negative direction, while isoprene units are often irregularly polymerized together during artificial polymerization to obtain a substance that is neither rubber nor gutta percha. This substance lacks the elasticity and flexibility of rubber, and will soon become sticky, so it can't be used to make car tires (except Royal Cars, which are only used for national activities, of course). During the First World War, due to the shortage of rubber patches, Germans adopted methyl rubber polymerized from dimethyl butadiene, which can be produced in large quantities and at a low price. During World War I, Germany produced about 2500 tons of methyl rubber. Although this kind of rubber was eliminated after the war because of its unsatisfactory pressure resistance, it is the first synthetic rubber with practical value after all.

In about 1930, Germany and the Soviet Union synthesized a rubber called sodium butadiene with butadiene as monomer and sodium metal as catalyst. As a kind of synthetic rubber, sodium cis-polybutadiene rubber is satisfactory for solving the shortage of rubber patches. Polymerization with other monomers can improve the properties of sodium rubber. For example, butadiene-styrene rubber (Buna-S) is obtained by polymerization with styrene, and its properties are very similar to those of natural rubber. In fact, during the Second World War, the German army did not have a serious shortage of rubber supply because of the existence of styrene-butadiene rubber. The Soviet Union supplied rubber to its own army in the same way.

The United States vigorously studied synthetic rubber after the war. Firstly, chloroprene rubber was synthesized. Chlorine atoms made chloroprene rubber have some corrosion resistance that natural rubber did not have. For example, it has high corrosion resistance to organic solvents such as gasoline, which is far less easy to soften and expand than natural rubber. Therefore, chloroprene rubber is actually more suitable for applications like oil hose than natural rubber. For the first time, chloroprene rubber clearly shows that, just like in many other fields, in the field of synthetic rubber, the products in test tubes can not only be used as substitutes for natural substances, but also have better performance than natural substances.

1955 Americans use Ziegler catalyst (also called Ziegler-Natta catalyst) to polymerize isoprene. Synthetic natural rubber with the same structure as natural rubber was synthesized by artificial method for the first time. Soon, ethylene-propylene rubber, which is made of ethylene and propylene, the two simplest monomers, was also successful. In addition, various kinds of rubber with special properties have appeared, and the total output of synthetic rubber has greatly exceeded that of natural rubber.