Recall that radical chain-growth polymerization yields highly branched polymers, such as low-density polyethylene.

To synthesize linear polymers, Karl Ziegler and Giulio Natta developed a class of organometallic catalysts known as Ziegler–Natta catalysts.

A typical example is an organometallic complex made from titanium tetrachloride and triethyl aluminium.

The catalyst forms an active part of Ziegler–Natta polymerization, a form of addition or chain-growth polymerization.

This process yields high molecular weight and stereochemically controlled linear polymers with almost no branching.

For instance, high-molecular-weight polyethylene and ultra-high-molecular-weight polyethylene are produced using the Ziegler–Natta catalyst. These polymers find applications as underground pipes, bulletproof vests, and bearings.

Additionally, Ziegler–Natta catalysts enable the synthesis of isotactic, syndiotactic, and atactic forms of polypropylene polymers.

Likewise, polymerization of isoprene using the Ziegler–Natta catalyst yields natural rubber with a Z configuration.