But-1-ene is an alkene, which contains a carbon-carbon double bond. Alkenes undergo addition polymerisation.

e)

(i) But-1-ene is an alkene, which contains a carbon-carbon double bond. Alkenes undergo addition polymerisation.

(ii) The monomer but-1-ene has the structure $\text{CH}_{2}=\text{CH}-\text{CH}_{2}-\text{CH}_{3}$. During addition polymerisation, the double bond breaks, and the monomers link together. The repeat unit is $\text{—CH}_{2}\text{—CH}(\text{CH}_{2}\text{CH}_{3})\text{—}$.

Here is part of the polymer molecule showing three repeat units:

$$\boxed{ \text{—}\underset{\text{H}}{\overset{\text{H}}{\text{C}}}\text{—}\underset{\text{CH}_{2}\text{CH}_{3}}{\overset{\text{H}}{\text{C}}}\text{—}\underset{\text{H}}{\overset{\text{H}}{\text{C}}}\text{—}\underset{\text{CH}_{2}\text{CH}_{3}}{\overset{\text{H}}{\text{C}}}\text{—}\underset{\text{H}}{\overset{\text{H}}{\text{C}}}\text{—}\underset{\text{CH}_{2}\text{CH}_{3}}{\overset{\text{H}}{\text{C}}}\text{—} }$$