A monomer is the small molecule that repeats to build a polymer; in an addition polymer it is an unsaturated molecule with a carbon-carbon double bond.
A monomer is the small molecule that repeats to build a polymer. In an addition polymer the monomer is an unsaturated molecule that contains a carbon–carbon double bond, C=C, which opens so the units can join. Malay: monomer · Chinese: 单体.
Monomers are the building blocks of every polymer, and the whole chain is nothing more than the same monomer written again and again. The exam recognises two kinds. An addition monomer has one C=C double bond, and examples include ethene, propene and chloroethene (vinyl chloride). A condensation monomer instead carries two reactive functional groups, one at each end, so it can bond on both sides; amino acids and the diol-plus-dicarboxylic-acid pair are the standard examples. Knowing which kind of monomer you have tells you at once which type of polymerisation will follow and whether a small molecule is given off.
Example. Ethene, CH₂=CH₂, is the monomer of polythene: thousands of ethene molecules add together into one long chain. Isoprene is the monomer of natural rubber, an amino acid is the monomer of protein, and glucose is the monomer of the carbohydrates starch and cellulose.
Confusion to avoid. Do not confuse the monomer with the repeating unit. The monomer is the free starting molecule, still holding its double bond; the repeating unit is the part left in the chain after the double bond has opened, so the two look similar but are not identical. Nor is the monomer the same as the polymer, the monomer is small and single, the polymer is the giant product.
Because every polymerisation question begins by identifying the monomer, this term underpins the whole Form 5 Polymers chapter and is worth fixing exactly for SPM Chemistry.
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