Polymer, also known as an addition polymer, is a product formed by polymerization (addition) of a monomer, and its molecules have repeating structural units. Low molecular weight polymers are called oligomers, such as paraformaldehyde. Polymers with molecular weights up to thousands or even millions are called high polymers or high molecular compounds. There are two types of polymers, natural products and synthetics. Natural polymers, such as polymers where proteins are amino acids, starch, and cellulose are cyclic polyhydroxy polymers (sugars), also known as biological polymers. There are many types of synthetic polymers, and the products are widely used, such as polyvinyl chloride and polystyrene plastics, resins, polyester, and rubber. High molecular polymers are high molecular weight compounds composed of one or several structural units mainly connected by covalent bonds. For example, the structural units of polyethylene [-CH2-CH2-]n and nylon 6 [-NH(CH2)5CO-]n are -CH2-CH2- and -NH(CH2)5CO-, and the degree of polymerization is n.
Figure 1. Macromolecule polymer.
The application of polymers is extremely extensive, covering clothing, food, housing, transportation, various sectors of the national economy, and cutting-edge technology. The advent of functional macromolecule polymers extended the application of synthetic polymers to a more sophisticated and advanced level, not only for promoting industrial and agricultural production and cutting-edge technology but also for exploring the mysteries of life, conquering cancer, and treating genetic diseases.
- General polymer materials: Polyethylene, polypropylene, polyvinyl chloride, and polystyrene in plastics, nylon, polyester, acrylic acid and vinylon in fiber, styrene-butadiene rubber, cis-butadiene rubber, isoprene rubber, and ethylene-propylene rubber are widely used polymer materials and are general-purpose polymers.
- Engineering polymer materials: Engineering plastics refer to high molecular polymers with special properties (such as high-temperature resistance and radiation resistance). Polyoxymethylene, polycarbonate, polystone, polyimide, polyarylene ether, polyamide, fluorine-containing polymer, boron-containing polymer, etc. are relatively mature varieties, which have been widely used as engineering materials.
Figure 2. Structural formula of engineering plastic polyamide.
- Functional polymer materials: Ion exchange resins, photosensitive polymers, polymer reagents, and polymer catalysts are all functional polymers. Medical polymers and medicinal polymers have special requirements in medicine and physiology and hygiene, which are also regarded as functional polymers.
Figure 3. Responsive polymers for biosignal molecules.
According to the structure of the main chain, the polymer can be divided into carbon chain polymer, hetero chain polymer, and element organic polymer.
- Carbon chain polymer: The main chain of the carbon chain polymer macromolecule is entirely composed of carbon atoms. Most olefinic and diene polymers belong to this category, such as polyethylene, polystyrene, and polyvinyl chloride.
- Hetero chain polymer: In addition to carbon atoms, there are heteroatoms like oxygen, nitrogen, and sulfur in the main chain of heterochain polymer macromolecules, such as polyether, polyester, polyamide, polyurethane, and polysulfide rubber. Engineering plastics, synthetic fibers, and heat-resistant polymers are mostly heterochain polymers.
- Element organic polymer: Elemental organic polymer macromolecules have no carbon atoms in the main chain, mainly composed of silicon, boron, aluminum and oxygen, nitrogen, sulfur, phosphorus, and other atoms, but the side groups are composed of organic groups, such as methyl, ethyl, and ethylene base. Silicone rubber is a typical example.
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