How are platinum-group metal catalysts used to make plastics such as polyethylene and polypropylene?

Platinum-group metals are utilized in the production of plastics such as polyethylene and polypropylene primarily through the use of organometallic complexes.1

These complexes, such as alkylplatinum compounds, act as catalysts in the process of olefin polymerization. In this catalytic mechanism, alkenes coordinate to a metal center and subsequently insert into a hydrocarbon chain. This process repeats, effectively building extremely long-chain hydrocarbon polymers.12

While the most common industrial catalysts for these specific plastics—developed by Karl Ziegler and Giulio Natta—rely on titanium and aluminum compounds, platinum-group metal complexes are specifically employed in these polymerization processes as well as in related industrial applications, such as the oxidation of ethylene to acetaldehyde. Generally, these metals are valued for their ability to readily accelerate or control the rates of various chemical reactions, including oxidation and hydrogenation, despite being highly resistant to chemical attack themselves.123