1. Analysis of i-PP made by Ziegler Natta Catalyst
13C NMR analysis shows: … …
m m m m m m m r r m m m m m m m m
Enantiomorphic Site Control … …
m m m m m m m r m m m m m m m m m
Chain - end Control

2. Soluble Metallocene Cataysts Polyethylene
Bis(cyclopentadienyl)zirconium dichloride
Plus methylaluminoxane (MAO)
5,000 kg PE / g Zr / hr (indefinitely active)

3. Soluble Metallocene Cataysts Polypropylene

4. Soluble Metallocene Cataysts
Used a mixture of meso and racemic ansa-titanocenes
Stereo-rigid
Ethylene-bridged
Rac: chiral with C2-symmetric axis
Meso: achiral

5. Rac Ansa Catalysts
Non-superimposable Mirror Images

6. Soluble Metallocene Cataysts
Ewen J. Am. Chem. Soc. 1984

7. PP from ansa-Metallocene Catalysts
Methyl pentad region
Fractions of iso-PP versus atactic-PP tracks with ratio of racemic to meso catalyst levels
MWs on each sample were similar indicating that both stereo-isomers of the catalyst give rise to similar propagation and termination rate constants

8. Soluble Metallocene Cataysts
Confirmed Ewen’s proposal that it was the chiral ansa-metallocene that was responsible for the formation of isotactic PP
Made the zirconium derivative
7,700 kg PP / mol Zr / hr (!)
1985 Kaminsky and Britzinger

9. Mechanism for Isotactic PP
Conformational modeling studies (Corradini 1991)
The growing polymer chain is forced into the open region
Chirality of the metallocene is relayed to the incoming monomer through the orientation of the methyl group
Since C2-symmetry, both reactions sites are homotopic
Therefore selective for the same olefin enantioface
Giving rise to isotactic PP

10. Soluble Metallocene Cataysts Polypropylene

12. Rac Ansa Catalysts
C2 Axis of Symmetry
Binding Sites are Homotopic

13. H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H

16. Cs symmetry
Cp of different size
Steric bulk flanking the metallocene wedge with an open region in center

17. How to make this?
Hemi-isotactic
Hemi-syndiotactic

19. … …
m m r r m m m m r r r r m m m m r