polypropene

Polypropene, commonly called polypropylene (PP), is a versatile thermoplastic polymer produced by the polymerization of propylene. It is a polyolefin composed of repeating propylene units with a methyl substituent on every second carbon, and its properties depend on the arrangement of these units.

The rate and stereochemistry of polymerization yield isotactic PP, syndiotactic PP, or atactic PP. Isotactic and syndiotactic PP are crystalline and provide higher stiffness, strength, and melting points, while atactic PP is largely amorphous and has poorer mechanical properties. Isotactic PP typically melts around 160–170°C and has a density of about 0.90 g/cm³; its glass transition temperature is near −20°C.

PP is resistant to many chemicals and offers good fatigue resistance, electrical insulation, and a favorable balance of stiffness and toughness. Its properties can be tuned by processing, copolymerization with ethylene to produce random copolymers (which improve clarity and flexibility), blending with fillers, or adding stabilizers for weather resistance.

Industrial production relies on coordination polymerization using Ziegler–Natta or metallocene catalysts. Processing methods include injection molding, extrusion, blow molding, film, and fiber manufacture. Major applications include packaging films and containers, automotive parts, textiles and nonwovens, consumer goods, and medical devices. Polypropylene is recyclable, commonly represented by recycling code 5.

Historically, PP was developed in the mid-20th century by Giulio Natta and Karl Ziegler, leading to widespread commercial use.