Polymers are substances containing a large number of structural units joined by the same type of linkage. These substances often form into a chain-like structure. Polymers in the natural world have been around since the beginning of time. Starch, cellulose, and rubber all possess polymeric properties. Man-made polymers have been studied since 1832. Today, the polymer industry has grown to be larger than the aluminum, copper and steel industries combined.
Polymers already have a range of applications that far exceeds that of any other class of material available to man. Current applications extend from adhesives, coatings, foams, and packaging materials to textile and industrial fibers, composites, electronic devices, biomedical devices, optical devices, and precursors for many newly developed high-tech ceramics.
Plastics are synthetic materials called polymers, which are long-chain molecules made up of repeating units joined together. These units contain various combinations of oxygen, hydrogen, nitrogen, carbon, silicon, chlorine, fluorine, and sulfur. Although plastics are soft and moldable and approach a liquid condition during manufacture, they are solid in their finished state. As more repeating units are added, the plastic’s molecular weight increases. Addition of more repeating units to the chain makes the molecule heavier.
The mechanical and physical properties of plastics are directly related to the bonds between molecular chains, as well as to the chain length and composition. Plastic properties can also be modified both by alloying and blending with various substances and reinforcements.
