Polymers
Polymers are a long chain of large organic molecules with high molecular mass that are assembled from many smaller molecules called as the monomers. These polymers contain long chains of repeating units that often tend to form a chain-like structure. The word polymer has been derived from the Greek words TTOλu meaning Poly (many) and μέρος meaning meros (parts). The study of the manmade polymers started since 1832 and today, the polymer industry has grown larger than the aluminum, steel and copper industries. Some of the very common and simple examples of polymers include DNA, proteins and plastic.
The term polymer refers to a large number of natural and synthetic manmade materials having a variety of properties and uses.
The polymers can be classified based on their structure, mode of reaction and the change in the physical properties due to heat. These classifications have been discussed in brief here below.
· Structure based classification: The polymers can be classified based on the structures into Homopolymers and Copolymers. Homopolymers consist of a chain of identical bonds that links to each monomer unit. These are usually the polymers that are made of identical monomer molecules e.g. [a-a-a-a-a-a-a-a-a-a-a]-. While the copolymers are made of chains with two or more linkages of different types of monomer units e.g. [a-c-c-c---c-c-a-a-]-.
· Reaction based classification: Based on their mode of reaction, polymers can also be classified into Addition polymers and the Condensation polymers. The monomer molecules that bond to each other without losing any atoms are termed as the Addition Polymers. Alkene monomers are the largest groups of additional polymers. While when two different monomers combine, there occurs a loss of small molecules usually water, this kind of polymers is termed as the condensation polymers. Polyesters, polyamides like nylon are the examples of the condensation polymers.
· Classification based on physical properties: Based on their changes in the physical properties due to heat, the polymers can again be classified into thermoplastics and thermosets. The plastics that soften or melt on heating and again become rigid when cooled, are termed as thermoplastics e.g. polyethylene and the polypropylene. Most of the thermoplastics are polymers with high molecular weight that are associated through the van der waals forces, dipole-dipole interactions etc. While the plastics that soften on heating and can be molded into any shape are termed as the thermosets. Thermoset materials are mainly in the liquid or malleable form before being molded into any final structure. The curing process transforms the resin into a plastic or rubber by a simple cross-linking process using catalysts. Some examples of the thermosets are vulcanized rubber, Bakelite, melamine resin etc.
Natural polymers: The natural polymers are considered very important. The DNA and RNA are the examples of natural polymers. The messenger RNA is responsible for making a large number of all possible peptides, enzymes and proteins in our body. The enzymes helps to do the chemistry inside the organisms and the peptides make the interesting structural components like the skin, hair, cuticles etc. Proteins are the basic and most essential structural components of the human and animal tissues that are made of a long chain of monomer units of amino acids. Cellulose is a natural polymer which is the main structural component of plants. Rubber is another fine example of natural polymers made of carbon and hydrogen.
Synthetic polymers: The synthetic polymers are usually referred to as plastics such as polyethylene and nylon. All the synthetic polymers can be largely classified under three groups namely, thermoplastics, thermosets and the elastomers. These manmade polymers are used in various applications, like food packaging, fibers, films, pipes etc.
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