oligomer

An oligomer is a molecule composed of a small number of repeating units derived from monomers. The term contrasts with polymer, which comprises a much larger, often indefinite number of units. The name comes from the Greek oligos, few, and meros, part. In practice, oligomers are defined by their finite degree of polymerization, typically ranging from 2 up to about 20–40 units, though definitions vary by field.

Oligomers occur in many chemical families: oligosaccharides, oligopeptides, and oligonucleotides are common natural examples; synthetic oligomers include oligoesters and other defined oligomers used as building blocks. Their length gives them characteristic properties that are intermediate between small molecules and high-molecular-weight polymers, often with well-defined end groups and relatively narrow distributions.

They may arise as intermediates in polymerization or be prepared by stepwise synthesis or controlled polymerization, yielding molecules with specific end groups and predictable behavior. Properties such as solubility, crystallinity, and reactivity differ markedly from those of high-molecular-weight polymers, enabling precise studies of structure–property relationships.

Applications span biochemistry, materials science, and medicine: defined oligosaccharides and oligonucleotides serve as research reagents and therapeutics; oligomers provide precursors for polymers and advanced materials; short peptide or nucleic acid units are central to diagnostics, vaccines, and drug development.