Polymer

Polymer, substance composed of very large molecules (macromolecules) built up by repeated linking of small molecules (monomers). Natural polymers include proteins, nucleic acids, polysaccharides, resins, rubber, and many minerals. The ability to make synthetic polymers (e.g., plastics and synthetic fibers) lies at the heart of modern technology. Polymerization, which requires that each monomer have two or more functional groups capable of linkage, takes place by condensation, with elimination of small molecules, or by simple addition. Catalysis is usually required, or the use of an initiator to start a chain reaction of free radicals. If more than one kind of monomer is used, the result is a copolymer with the units arranged at random in the chain.