In chemistry and biochemistry , an oligomer about this sound) is a molecule that consists of few homologous or double units which can be obtained, actually or conceptually, from copies of a smaller molecule, its monomer . The name is derived from the Greek elements oligo- , “something” and -mer , “parts”. An adjective form is oligomeric .
The oligomer concept is in contrast to a polymer which is usually understood to contain a large number of units, possibly thousands or even millions. However, there is no sharp difference between these two concepts. One proposed criterion is whether the properties of the molecule differ significantly with the removal of one or a few units. 
An oligomer with a specific number of units is known from that number denoted with the Greek prefix ending -mer Thus: dimer , trimer , tetramer , pentamer refer to molecules with two, three, four, and five units, respectively. . The units of an oligomer can be arranged in a linear chain (as in melam , a dimer of melamine , a closed ring (as) trioxane , a cyclic trimer of formaldehyde (as), or the more complex structure of tellurium tetrabromide , a tetramer of TeBr
4with a cube -like core). If the units are the same, then is a homo-oligomer ; Otherwise one can use hetero-oligomers . An example of a homo-oligomeric protein is collagen , which is composed of three identical protein chains.
Some biologically important oligomers contain macromolecules such as proteins or nucleic acids ; For example, hemoglobin is a protein tetramer. An oligomer of an amino acid is called an oligopeptide or just a peptide . An oligosaccharide is an oligomer of a monosaccharide (simple sugar) . An oligonucleotide is a short single-stranded fragment of nucleic acid such as DNA or RNA , or similar fragments of nucleic acid analogues such as peptide nucleic acids or morpholinos .
The units of an oligomer may be linked by covalent bonds, which may result from bond rearrangements or condensation reactions or weak forces such as hydrogen bonds. Span multimer ( / m l t m r _ _ / ) is used in biochemistry for oligomers of proteins that are not covalently bound. The major capsid protein VP1 that comprises the shell of poliovirus is a self-assembling multimer of 72 pentamers bound by local electric charge.
Many oils are oligomeric, such as liquid paraffin. Plasticizers are oligomeric esters that are widely used to soften thermoplastics such as PVC. They can be made from monomers by bonding them together, or by separating them from higher fractions of crude oil. Polybutene is an oligomeric oil used for making putties.
Oligomerization is a chemical process that converts monomers into macromolecular complexes through a limited degree of polymerization.  Telomerization is an oligomerization performed under conditions that result in chain transfer, which limits the size of the oligomers.   (This concept should not be confused with telomere formation, a region of highly repetitive DNA at the end of a chromosome.)
In the oil and gas industry, green oil refers to the oligomers formed in all C2, C3, and C4 hydrogenation reactors of ethylene plants and other petrochemical production facilities; It is a mixture of C4 to C20 unsaturated and reactive components consisting of approximately 90% aliphatic dienes and 10% alkanes plus alkanes.  Various heterogeneous and homogeneous catalysts are active in the production of green oil through the oligomerization of alkene.