In chemistry, an oligomer is a molecule that consists of a few monomer units (ολιγος, or oligos, is Greek for "a few"), in contrast to a polymer that, at least in principle, consists of an unlimited number of monomers. Dimers, trimers, and tetramers are oligomers. Many oils are oligomeric, such as liquid paraffin. Plasticizers are oligomeric esters widely used to soften thermoplastics such as PVC. They may be made from monomers by linking them together, or by separation from the higher fractions of crude oil. Polybutene is an oligomeric oil used to make putty. Greek prefixes are often used to designate the number of monomer units in the oligomer, for example a tetramer being composed of four units and a hexamer of six.
In biochemistry, the term oligomer is used for short, single-stranded nucleic acid fragments, such as DNA or RNA, or similar fragments of analogs of nucleic acids such as peptide nucleic acid or Morpholinos. Such oligos are used in hybridization experiments (bound to glass slides or nylon membranes), as probes for in situ hybridization or in antisense experiments such as gene knockdowns. It can also refer to a protein complex made of two or more subunits. In this case, a complex made of several different protein subunits is called a hetero-oligomer or heteromer. When only one type of protein subunit is used in the complex, it is called a homo-oligomer or homomer.
Oligomerization is a chemical process that converts monomers to a finite degree of polymerization. The actual figure is a matter of debate, often a value between 10 and 100.
When an oligomer forms as a result of chain transfer the oligomer is called a telomer and the process telomerization. A telomere is a region of highly repetitive DNA at the end of a linear chromosome.