A high-molecular-weight organic compound, natural or synthetic, whose structure can be represented by a repeated small unit, the monomer (e.g., polyethylene, rubber, cellulose). Synthetic polymers are formed by addition or condensation polymerization of monomers. If two or more different monomers are involved, a copolymer is obtained. Some polymers are elastomers, some plastics. (Plastics Engineering Handbook of the Society of the Plastics Industry, Inc., edited by Michael L. Berins, 1991).