21.14:
Ziegler–Natta Chain-Growth Polymerization: Overview
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.
21.14:
Ziegler–Natta Chain-Growth Polymerization: Overview
Ziegler–Natta polymerization is another form of addition or chain‐growth polymerization used for synthesizing linear polymers over branched polymers. The catalyst used for polymerization is the Ziegler–Natta catalyst, named after Karl Ziegler and Giulio Natta, who developed it in 1953. This catalyst is an organometallic complex of titanium tetrachloride and triethyl aluminum, with the active form of the catalyst being an alkyl titanium compound. Using the Ziegler–Natta catalyst, high molecular weight and stereochemically controlled linear polymers can be synthesized at a large scale. For example, high molecular weight and ultrahigh molecular weight polyethylene, used for making underground pipes and bulletproof vests, are synthesized using the Ziegler–Natta catalyst. This catalyst also facilitates the synthesis of polymers of specific tacticity. For instance, isotactic polypropylene, with chiral centers on the same side, can be synthesized using a specific Ziegler–Natta catalyst.