Any of a class of natural or synthetic substances composed of macromolecule s that are multiples of monomer s.
The monomers need not all be the same or have the same structure. Polymers may consist of long chains of unbranched or branched monomers or may be cross-linked networks of monomers in two or three dimensions. Their backbones may be flexible or rigid. Some natural inorganic materials (e.g., the minerals diamond , graphite , and feldspar ) and certain man-made inorganic materials (e.g., glass ) have polymer-like structures. Many important natural materials are organic polymers, including cellulose (from sugar monomers; see polysaccharide ), lignin , rubber , protein s (from amino acids), and nucleic acid s (from nucleotide s). Synthetic organic polymers include many plastics , including nylon s, polyurethane s, polyester s, vinyls (e.g., PVC ), and synthetic rubbers . The {{link=silicone">silicone polymers, with an inorganic backbone of silicon and oxygen atoms and organic side groups, are among the most important mixed organic-inorganic compounds.