Oligomers

members of homologous series occupying the region between monomers and polymers in terms of molecular size. The upper limit for the molecular weight of oligomers depends on their chemical nature and corresponds to the onset of high-elastic deformations, induced high elasticity, and other properties characteristic of macromolecular substances. Polar oligomers cover a wider range of molecular weights than do nonpolar oligomers (up to ∼ 1.5 × 10⁴, as opposed to ∼ 5 × 10³).

Most of the methods used in oligomer synthesis are based on macromolecule growth termination reactions in processes of polymerization and polycondensation. Oligomers are also obtained by degradation of macromolecular polymers and by stepwise synthesis, with the isolation of reaction products at each stage of the process; the latter method yields monodisperse oligomers.

Among the many reactive oligomers, the most important are polyester resins, epoxy resins, phenol-aldehyde resins, and alkyd resins, which have become widely used in the manufacture of laminated plastics, foam plastics, varnishes, adhesives, and sealing compounds. Oligoolefins are used as motor fuels and lubricants, in waterproofing treatment of paper, and in the preparation of polishing pastes (synthetic wax). Fluorine-substituted ethylene oligomers serve as high-boiling oils, heat-transfer agents, and fluids for hydraulic drives. Oligomers derived from an olefin oxide base are widely used as surface-active agents.

Oligomers play a relatively important role in nature. Examples are oxytocin (nonapeptide) and antibiotics (cyclooligopep-tides).