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CHEM 121 Studioby Learn4Less · UBC CHEM 121

CHEM 121 glossary

Repeat unit

The smallest structural unit that, repeated nn times, makes up a polymer chain, written in brackets with subscript nn. For an addition polymer it has the monomer's formula; for a condensation polymer it equals the monomers minus the small molecules released.

Polymer chain and repeat unitMany ethene monomers (CH₂=CH₂) join into a long polyethylene chain. The repeat unit, –CH₂–CH₂–, is shown in brackets with subscript n for the number of repeats.n CH₂=CH₂ → –[CH₂–CH₂]ₙ–monomer → polymernrepeat unit……each vertex is a CH₂ carbon; n is often 10³–10⁵

Example

PTFE (Teflon) is [ CFX2−CFX2 ]n\left[\,\ce{CF2-CF2}\,\right]_n: the repeat unit CX2FX4\ce{C2F4} (100.01 g/mol) has the same formula as its monomer CFX2=CFX2\ce{CF2=CF2}, but no C=C.

See alsoPolymerMonomerAddition polymerCondensation polymer