A molecule is made up of atoms. Common compounds are composed of several, a dozen, or dozens of atoms. Their molecular weight is more than ten, tens to hundreds, not thousands, even less, water molecules (H2O) composed of two atoms of hydrogen and one atom of oxygen, 18 is its molecular weight, carbon dioxide (CO2) 44 is the molecular weight, caustic soda (NaOH) 40 is the molecular weight, the molecular weight of these compounds, people call it "small molecule" or "low molecular". Molecular weight greater than 10000 belong to the macromolecule or macromolecular polymer compound, polymer is short, the relative molecular mass of it is very high relative molecular mass of material, usually tens of thousands or millions, because these compounds exhibit mechanical and chemical properties are completely different from inorganic, metal and organic small molecular compounds. So it becomes an important branch in the field of chemistry.

The human society the materials used are of three main types: inorganic material hand metal materials and polymer materials. The first two kinds of materials already known. Their use of history can be traced back to thousands of years ago. Polymer materials with human relations more closely. Can say, the human from the origin has the indissoluble bound with polymer. Because life on earth and the fundamental is composed of polymer materials. Human basic necessities of life also cannot do without polymer. But due to the limitations of scientific understanding of human identity, the polymer is only the beginning of twentieth Century. The synthesis of polymeric materials from being published today is less than 1 of a century. However, in this short span of several decades, the development speed of synthetic polymeric material is far more than other traditional materials. In the past 40 years USA plastic production jumped 100 times, in the iron and steel production during the same period is almost negative growth, such as the calculation of the volume of the whole world, plastic production in "in the early 1990s has more than steel, the effect of polymer materials in the development of the world economy has become more and more important.

Polymer materials production was so rapid development: on the one hand is due to the material itself has high performance. It is not as heavy metal materials, like metals. It is not as strong as crisp as glass and ceramics, but like a transparent and corrosion; high polymer material processing unlike metal and ceramic that need thousands of degrees hot, do not need a lot of manual labor. Therefore, the processing is convenient, high degree of automation, on the other hand, polymer material is very rich in resources, raw material price is very low, the refinery refining gasoline J diesel oil and lubricating oil from the oil can not directly use. Waste gas and heavy oil coking coke plant waste gas and tar are the best raw material for the production of polymer. This makes the polymer production and processing required investment and cost than other material low, notable economic benefits and market competitiveness.

Today, synthetic polymers have largely replaced the metal, wood, ceramics, glass and other natural materials, are more and more into our life, in all fields of the national economy. Even some still in the extensive use of metal or other material production departments, synthetic polymer material consumption is also increasing. For example, in the automobile industry, to 1990, plastic for every car army weight reached 10. 3%, accounting for about half of the vehicle material volume, the weight of more than four cars. In machinery and textile industry, because of the use of plastic bearings and plastic gear to replace the metal parts of the corresponding noise army, bed and loom operation is greatly reduced, improving the working conditions of workers. There is a kind of composite material with plastic and glass fibres one one glass steel, because of its stronger than steel. In recent years, in the building materials industry in the use of plastic steel windows and doors, not only beautiful, but also save a lot of timber resources. Today, synthetic fiber in the civil fiber dosage has accounted for about 50%, in the fiber industry, almost entirely replaced the natural fiber. The development of rubber industry although slower, synthetic rubber production has greatly exceeded the natural rubber, of the world rubber consumption 2/3.