Ziegler, Karl (1898-1973) was a German scientist whose improved methods of producing plastics resulted in many of the materials that revolutionized life in the 1900's. Italian chemist Giulio Natta further developed Ziegler's processes, and they were jointly awarded the Nobel Prize in chemistry in 1963.

Ziegler was born on Nov. 26, 1898, in Helsa, Germany. His mother was Caroline Helene Louise (Rall) Ziegler and his father was Carl August Ziegler, a Protestant minister. Ziegler received his Ph.D. degree from the University of Marburg in 1920. After a number of academic appointments, including nine years as a professor of chemistry at Heidelberg, Ziegler became head of the Kaiser Wilhelm Institute (now the Max Planck Institute) for Coal Research at Mulheim in 1943. As a requirement for taking the job, Ziegler received permission to research not only coal chemistry but also the chemistry of carbon compounds in general. He remained at the Institute until his retirement in 1969.

Since the early 1900's, scientists had known that certain substances could form giant molecules by linking together thousands of identical molecules in long chains. When Ziegler began looking at this process, though, chemists had been unable to control the position of molecules within the chains.

In the mid-1900's, Ziegler made his most important contribution—the discovery of the process of polymerization. He was studying reactions involving ethylene, an organic gas that is prepared by heating ethane and propane to high temperatures in the presence of steam. Ethylene may also be obtained as a by-product of petroleum refinery processes. Ethylene is a colorless, flammable gas and is slightly lighter than air.

By chance, a trace of nickel (a metallic chemical element used in alloys) was left in his apparatus from previous experiments. Ziegler found that the ethylene molecules were joined together to form a longer chain of carbon atoms. This chaining together of simpler molecules to form longer ones is called polymerization, and the product is a polymer. Plastics and rubber are examples of polymers. Ziegler found that certain compounds containing carbon and metal—especially aluminum—catalyzed (promoted) the polymerization of ethylene at atmospheric pressure and a little above room temperature. Previous polymerization processes required high pressures and temperatures, and the molecules produced could be branched or irregularly shaped in other ways. The polymers produced by Ziegler's new process had a regular structure, and were more rigid and less easily melted than the polymers produced by older methods. Ziegler's process became the basis of polymer manufacture for numerous products.

Ziegler and the Max Planck Institute licensed his process, and sold rights to use the process to numerous companies. Giulio Natta became one of many who used the process. In 1954, Natta developed polypropylene, a synthetic polymer. It is a strong, lightweight, and heat-resistant plastic. The material is durable but can be molded into a thin object that bends without breaking. Today, products made of polypropylene include such diverse items as coatings on telephone wires, carpet fibers, and margarine containers.

The processes for the polymerization of ethylene and propylene to polyethylene and polypropylene have been used since the 1950's and have been called the Ziegler-Natta catalysts. Natta further explored reactions created by the processes. Using Ziegler-Natta catalysts made it possible to create a material that was identical to natural rubber. These discoveries revolutionized the plastics industry, as well as other polymer technologies.

Ziegler and Natta shared the 1963 Nobel Prize in chemistry for their work with plastics. Ziegler also earned international honors, including the Lavoisier Medal of the French Chemical Society. In 1968, he created the Ziegler Fund and in 1970, the Ziegler Foundation. He was a member or honorary member of several German and foreign scientific societies and academies. In 1971, the Royal Society of London elected him as a foreign member. Ziegler died in 1973.