monomer

schematic diagram of the emulsion-polymerization methodSchematic diagram of the emulsion-polymerization method. Monomer molecules and free-radical initiators are added to a water-based emulsion bath along with soaplike materials known as surfactants, or surface-acting agents. The surfactant molecules, composed of a hydrophilic (water-attracting) and hydrophobic (water-repelling) end, form a stabilizing emulsion before polymerization by coating the monomer droplets. Other surfactant molecules clump together into smaller aggregates called micelles, which also absorb monomer molecules. Polymerization occurs when initiators migrate into the micelles, inducing the monomer molecules to form large molecules that make up the latex particle.

monomer, a molecule of any of a class of compounds, mostly organic, that can react with other molecules to form very large molecules, or polymers. The essential feature of a monomer is polyfunctionality, the capacity to form chemical bonds to at least two other monomer molecules. Bifunctional monomers can form only linear, chainlike polymers, but monomers of higher functionality yield cross-linked, network polymeric products.

functional group: monomers and polymers
functional group: monomers and polymersFunctional groups in monomers and polymers.

Addition reactions are characteristic of monomers that contain either a double bond between two atoms or a ring of from three to seven atoms; examples include styrene, caprolactam (which forms nylon-6), and butadiene and acrylonitrile (which copolymerize to form nitrile rubber, or Buna N). Condensation polymerizations are typical of monomers containing two or more reactive atomic groupings; for example, a compound that is both an alcohol and an acid can undergo repetitive ester formation involving the alcohol group of each molecule with the acid group of the next, to form a long-chain polyester. Similarly, hexamethylenediamine, which contains two amine groups, condenses with adipic acid, which contains two acid groups, to form the polymer nylon-6,6.

The Editors of Encyclopaedia Britannica This article was most recently revised and updated by Adam Augustyn.
Citation Information
Article Title: monomer
Website Name: Encyclopaedia Britannica
Publisher: Encyclopaedia Britannica, Inc.
Date Published: 05 March 2020
URL: https://www.britannica.comhttps://www.britannica.com/science/monomer
Access Date: November 21, 2024