\^▐tsē-glәr ^▐ka-t^әl-әst\ Any of a large group of catalysts made by reacting a compound of a transition metal chosen from groups IV through VIII of the periodic table with an alkyl, hydride, or other compound of a metal from groups I through III. A typical example is the reaction product of an aluminum alkyl with titanium tetrachloride or titanium trichloride. These catalysts were first discovered by the German chemist K. Ziegler (late 1940s) for the low-pressure polymerization of ethylene. Subsequent work by G. Natta (early 1950s) showed that these and similar catalysts are useful for preparing stereoregular polyolefins; thus, the family of catalysts is sometimes called Ziegler-Natta catalysts. (Odian, G. C., Principles of Polymerization, John Wiley and Sons, Inc., New York, 2004; Elias, H. G., Macromolecules Vol. 1–2, Plenum Press, New York, 1977).