The components of Ziegler-Natta catalyst, used in the polymerisation of propylene, are

$\underset{\text{Propylene}}{{\mathrm{nCH}}_3-\mathrm{CH}={\mathrm{CH}}_2}\stackrel{{\left({\mathrm{CH}}_3{\mathrm{C}}_2\right)}_3\mathrm{Al}+{\mathrm{TiCl}}_4}{\to }$ ${\left[\underset{\text{Polypropylene}}{\begin{array}{l}C{H}_3\\ |\\ -C{H}_2-CH-\end{array}}\right]}_n$