Odian Book Chapter 8.4 and 8.5 will cover the remaining 4 lectures.

1. Odian Book Chapter 8.4 and 8.5 will cover the remaining 4 lectures.

3. Ziegler Natta Catalysts • Too numerous to describe all variants • Two Components • Transition metal compound Group IV to VIII metals“catalyst” • Organometallic compound Group I to III metals“co-catalyst” I II III IV V VI VII VIII I II III

4. Ziegler Natta Catalysts • Prepared by mixing in a dry, inert solvent in absence of oxygen, usually at low temperatures • Usually heterogeneous • Challenges…

5. Ziegler Natta Catalyst • Example: Titanium catalyst

7. Mechanism of Ziegler Natta Polymerizations:Initiation and Propagation • Catalyst acceptsethylene as a ligand • Migratory insertion • Ethyl (alkyl) migration Cossee-Arlman Mechanism

8. Mechanism of Ziegler Natta Polymerizations:Termination

9. Chain Transfer

10. Polypropylene • 1000 kg / g Ti / hr • Heterogeneous catalysts • Chiral sites believed to be fixed on the surface of the catalyst

12. Ziegler Natta Catalyst • Better to use TiCl3 directly rather than forming in situ by reduction • TiCl3 4 different crystalline formsα, γ, δ highly stereoregular PPβ atactic PP • Tacticity • Mix of catalyst crystalline forms • Does not yield:…m m m m r m m r m m m m m r m r m m m… • But rather:…m m m m m m m m m m m m m m…mixed with …m r m m r r m r m m r m r r m r m r m r…

13. 13C NMR Characterization

14. Prochiral Relationships 1 2 3 1 3 2 • Each face is enantiotopic “si” face • Reaction with an achiral reagent will give equal quantities of enantiomers • Optically inactive product “re” face

15. Prochiral Relationships Propylene Acetaldehyde Racemic 1-deutero-ethanol R-1-deutero-ethanol

17. Analysis of i-PP made by Ziegler Natta Catalyst • 13C NMR analysis shows: • once an error occurs, corrected by the chirality of the fixed catalyst site • At the pentad levelmmmm high concentration three weak signals mmmr : mmrr : mrrm 2 : 2 : 1 … … m m m m m m m r r m m m m m m m m

18. 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

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