9.19C - Addition polymers from monomers with C=C bonds

The same reaction with different monomers

Many monomers containing a carbon-carbon double bond, $\ce{C=C}$, can join by addition polymerisation. The double bond becomes a single bond and new carbon-carbon bonds connect the monomer residues into a long chain. No small molecule is released.

Only the two carbon atoms originally in the double bond become the two backbone atoms of each monomer-derived repeating unit. The atoms and groups attached to them stay attached. The monomer's structure therefore determines the structure and name of the polymer.

For example, propene is $\ce{CH2=CH-CH3}$. The first two carbons form the polymer backbone; the $\ce{CH3}$ stays as a side group. Propane has no C=C bond, so it cannot form poly(propene) by this addition reaction.