Editing Ziegler–Natta catalyst (section)

==Stereochemistry of poly-1-alkenes==
Natta first used polymerization catalysts based on titanium chlorides to polymerize [[propylene]] and other 1-alkenes. He discovered that these polymers are crystalline materials and ascribed their crystallinity to a special feature of the polymer structure called [[stereoregularity]]. 
[[Image:Polypropylene tacticity.svg|thumb|upright=1.8|left|Short segments of polypropylene, showing examples of isotactic (above) and syndiotactic (below) [[tacticity]].]]
The concept of stereoregularity in polymer chains is illustrated in the picture on the left with polypropylene. Stereoregular poly(1-alkene) can be [[isotactic]] or [[syndiotactic]] depending on the relative orientation of the [[alkyl]] groups in polymer chains consisting of units −[CH<sub>2</sub>−CHR]−, like the CH<sub>3</sub> groups in the figure. In the isotactic polymers, all stereogenic centers CHR share the same configuration. The stereogenic centers in syndiotactic polymers alternate their relative configuration. A polymer that lacks any regular arrangement in the position of its alkyl substituents (R) is called atactic. Both isotactic and syndiotactic polypropylene are crystalline, whereas atactic polypropylene, which can also be prepared with special Ziegler–Natta catalysts, is amorphous. The stereoregularity of the polymer is determined by the catalyst used to prepare it.