Polymer
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A polymer is a material which has larger molecules made from joining together many small molecules called monomers. The word "polymer" can be broken down into "poly" (meaning "many") and "mer" (meaning "unit"). This shows how the chemical composition of a polymer consists of many smaller units (monomers) bonded together into a larger molecule. A chemical reaction bonding monomers together to make a polymer is called polymerization.
Some polymers are natural. Proteins have polypeptide molecules, which are natural polymers made from various amino acid monomer units. Nucleic acids are natural polymers made up of nucleotide units. Cellulose and starch are also natural polymers made up of glucopyranose monomer bonded together in different ways. Some polymers are man-made. Plastics, rubber, and fibers are made up of polymers.
[change] Make up of polymers
If the "units" called monomers in a polymer are all the same, then the polymer is called a "homopolymer". Homopolymers are named by adding the prefix poly- before the monomer name from which the polymer is made. For example, a polymer made by bonding styrene monomer molecules together is called polystyrene.
If the "units" are not all the same, the polymer is called a "copolymer" or a "heteropolymer".
Many polymer molecules are like chains where the monomer units are the links. Polymer molecules can be straight-chain, have branching from the main chain, or cross-linking between chains. For an example of cross-linking, sulfhydryl (-S-H) groups in two cysteine amino acid units in polypeptide chains can bond together to make a disulfide bridge (-S-S-) joining the chains together.