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

2. Soluble Metallocene Cataysts Polypropylene

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

4. Rac Ansa Catalysts
Non-superimposable Mirror Images

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

6. 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

7. 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

8. 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

9. Soluble Metallocene Cataysts Polypropylene

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

12. 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

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

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

18. … …
m m r r m m m m r r r r m m m m r

19. Unbridged metallocene catalysts
Rapid isomerization, low barriers
What kind of polymer is produced?

20. Unbridged metallocene catalysts Added phenyl group to indene
Inhibits rate of ligand rotation

22. Physical Properties of Polypropylene

23. Olefin Polymerizations with Early Metal Catalysts
~ 2 × 1011 lbs/year polyethylenes(PE), polypropylenes(PP) produced worldwide!
Metallocene Catalysts:
Technological advance
A) Incremental
B) Major:
1) New Materials
2) Detailed mechanistic understanding
Not a black box anymore…

24. Olefin Polymerizations with Early Metal Catalysts
Metallocene Catalysts:
Incremental technological advance
● Increased activities/productivities
● Many different grades of ethylene/ α-olefin copolymers
● Control of MW, MWD
bimodal, unimodal, PDI < 5.0!
Existing markets are being extended into new applications

25. Metallocene Catalysts
Major Technological Advance
New Materials
Syndiotactic polystyrene
Tm = 270 °C, 40-50% X-tal w/ good rate of x-tallization
Syndiotactic and elastomeric PP
Cyclic Olefin Copolymers
Hoechst’s TopazTM (Tg = 140 – 200 °C)

26. Chemical Review 2000, Issue 4
“FRONTIERS IN METAL-CATALYZED POLYMERIZATION”
Also
Angew. Chem. Int. Ed. 1999, 38, 428 ± 447