Abstract

Polypropylene is one of the most widely used thermoplastics, accounting for 26% of total consumption. Many automobiles, textile appliances, and other everyday items contain substantial amounts of these polymers. The ability to manufacture a broad variety of polypropylenes having properties tailored for specific applications is the primary factor in its widespread use. Comonomers, usually ethylene, are often used to provide impact-modified or lower melting polymers. The types of polymers produced, economics of processes and product, and end use of products are discussed.

Highly stereoselective Ziegler-Natta catalyst systems are the basis for all propylene polymerization processes. The development of these catalysts, from the early TiCl₃ systems to the modern, high yield MgCl₂-supported systems, including polymerization mechanisms, is discussed. These catalysts enabled the evolution of these polymerization processes from the early slurry process, to the current liquid monomer or gas-phase processes. The Spheripol and Spherizone processes are discussed in detail.