Prof. Natta extended the research conducted by Ziegler on organometallic catalysts to the stereospecific polymerization, thus discovering new classes of polymers with a sterically ordered structure, viz. isotactic, syndiotactic and di-isotactic polymers and linear non branched olefinic polymers and copolymers with an atactic (or sterically nonordered) structure.    From Wordnik.com.  [Giulio Natta - Biography] Reference