Molecule is made ​​up of atoms. Common compounds are made ​​up of several dozen, or dozens of atoms. Their molecular weight of more than a dozen, dozens, hundreds, not many reach thousands of fewer water molecules (H2O) is composed of two hydrogen atoms and one oxygen atom composition, its molecular weight is 18 , carbon dioxide (CO2) is the molecular weight of 44, caustic soda (NaOH) 40 molecular weight, the molecular weight of these compounds, it is call "small molecule" or "low molecular weight." Molecular weight greater than 10,000's only part of the polymer or macromolecule polymer is a polymer compound is referred to, it is very high relative molecular mass of a substance, usually a relative molecular mass of thousands or millions because these compounds exhibit with inorganic, metallic and organic small molecules of different mechanical and chemical properties. The field of chemistry and thus become an important branch.

Materials used in human society are mainly three types: hand-metallic materials of inorganic materials and polymer materials. The first two categories have long been well known material. Their use dates back to thousands of years. Polymer materials more closely with humans. It can be said, since the origin of mankind on the indissoluble bond with the polymer. Because life on Earth fundamental research are made ​​of a polymer material. Polymer is also inseparable from the basic necessities of mankind. However, due to the limitations of scientific knowledge on human recognition of the polymer is only thing in the early 20th century. The advent of synthetic polymer material to today from less than a century. However, in this short span of a few decades, the pace of development of synthetic polymer material is far more than other traditional materials. In the past 40 years the United States jumped 100 times plastics production, steel production in the same period is almost negative growth, as calculated by volume, the world's plastic production in the early "era has more than steel, shows the development of polymer materials in the world economy the role has become increasingly important.

Production of polymer materials developed so rapidly obtain reasons: one is due to the material itself has a very good performance. It is not as heavy metal, like a sturdy metal as brittle as glass and ceramics it is not, just like they are as transparent and corrosion;. Polymer materials like metal and ceramic processing that require high temperatures of thousands of degrees, does not require a lot of manual labor. Therefore, the process convenient, high degree of automation, the other polymer material resources are very rich, very low prices of raw materials, refined from petroleum refinery after oil can not directly use gasoline J diesel and lubricants. Exhaust gas and heavy oil and tar generated during coking coke plant is to produce the best raw material polymer. This makes the polymer production and processing of the required investment and Qi lower than other materials, there are very significant economic and market competitiveness.

Today, a large number of synthetic polymeric materials have replaced the metal, wood, ceramics, glass and other natural materials, are more and more into our lives, to enter all areas of the national economy. Even some still extensive use of metal or other materials production sector, the amount of synthetic polymer materials also increased. For example, in the automotive industry, to 1990, the share of plastics in weight per army has reached 10.3%, accounting for about half of the vehicles with the volume of material, so that the weight reduction of more than four cars. In the machinery and textile industries, the use of plastic bearings and plastic gears instead of noise corresponding metal parts, military bed and weaving machine operation is greatly reduced, improving the working conditions of workers. There is a composite material made ​​of plastic with fiberglass fiberglass one to use, because it is more robust than steel. In recent years, the building materials industry, the use of plastic doors and windows not only beautiful, but also save a lot of timber resources. Today accounts for about 50% of synthetic fibers in the amount of civil fiber, in industrial fibers, replacing almost all natural fibers. Although the slow development of the rubber industry, production of synthetic rubber has greatly exceeded natural rubber, accounting for two-thirds of the amount of rubber in the world.