|Polymers are large molecules consisting of many repeating structural units. Rubber is a natural polymer. Celluloid is the first plastic. The first synthetic polymer was a substance called Bakelite, which is used in stovetop appliances because of its ability to resist heat. Since the beginning of the 20th century, hundreds of polymers have been synthesized. They are easy to manufacture, starting materials used to make them are inexpensive, and they have a wide range of properties. They can be drawn into wire and be molded into shapes. Children’s toys are made of a polymer called polyethylene, which is made from synthesizing ethene under pressure.
Monomers are molecules from which polymers are made. Monomers bond together one after another in a rapid series of steps. Catalysts are required for the reaction to take place. With other polymers, such as nylon and Dacron, two or more kinds of monomers bond to each other in an alternating sequence. These reactions are called polymerization reactions.
There are two classes of polymers: thermoplastic and thermosetting. Thermoplastic polymers can be melted and molded repeatedly into shapes that are retained when cooled. Thermosetting polymers can be molded when first prepared, but once cool, cannot be re-melted.
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