1. Ziegler-Natta Catalysis
Presented by:
Mehrban ashiq
Saad afzal
Presented To:
M.phil Inorganic- Analytical Chemistry 3rd Semester
Department of Chemistry, University of Gujrat, Pakistan.
Course Title: Organo -Transition Chemistry
Course code: CHEM-529
Instructor: Dr. Muhammad Ali Mohsin

2. Ziegler-Natta Catalysis
Outline:
Introduction
Catalysis
Activation Energy
Ziegler-Natta Olefin Polymerization
Ziegler's Discovery
Mechanism
Natta's Discovery
PP Stereochemistry
Different Catalyst system and % yield
Conclusion

3. Branched/low-density = (LDPE)
Ziegler-Natta Catalyst
most popular plastic.
Grocery bags, shampoo bottles, toys, etc.
Simple structure than all polymers.
Branched/low-density = (LDPE)
Easier to make
Linear/high-density = (HDPE)

4. Catalysis
Catalysts increase reaction rate without themselves being changed
Can accelerate a reaction in both directions
Do not affect the state of equilibrium of reaction
simply allow equilibrium to be reached faster

5. Activation energy
Molecules must be activated before they can undergo a reaction
Reactants must absorb enough energy from surroundings to destabilize chemical bonds (energy of activation)
Transition state
Intermediate stage in reaction where the reactant molecule is strained or distorted but the reaction has not yet occurred

6. Ziegler’s Discovery 1953 K. Ziegler, E. Holzkamp, H. Breil & H. Martin
Angew. Chem. 67, 426, 541 (1955); 76, 545 (1964).
Problem
Idea:

7. Ziegler-Natta Catalysts
Combination of a transition metal compound of an element from groups IV to VIII, and an organometallic compound of a metal from groups I to III.
Catalyst – Transition metal
Co-catalyst – Organometallic Compound, mainly alkyl or alkylhalides of aluminium and boron, or methylaluminoxane.

8. Ziegler-Natta Catalysis of Alkene Polymerization
Ziegler-Natta Catalyst
A typical Ziegler-Natta catalyst is a combination of
TiCl4 and (CH3CH2)2AlCl, or
TiCl3 and (CH3CH2)3Al.

9. Polymerization Steps Replacement of one Cl by alkyl group of Al alkyl
Bonding of Propylene to a vacant site
Insertion of propylene into Metal-alkyl bond- Initiation
Creation of vacant site for propylene adsorption
Repetition of steps 2,3 & 4 leading to chain growth/propagation
Catalyst configuration decides the configuration of added propylene
Termination of polymer chain with hydrogen- Termination

10. Conventional Ziegler-Natta Catalyst
Catalyst components TiCl4 & AlEt3
Organo aluminium compound reduces TiCl4 to generate TiCl3
Active phase TiCl3
Different crystalline forms- α , β, γ , & δ
β Chain structure; α , γ , & δ have layer structure
Activity & Isotacticity differs
α – Hexagonal Close packed – hcp of Cl ions
γ - Cubic close packed –ccp of Cl ions
Ti ions occupy Octahedral holes of Cl- matrix

11. Mechanism of Coordination Polymerization
Initiation
Al(CH2CH3)3 +
TiCl4
ClAl(CH2CH3)2 +
CH3CH2TiCl3

12. Mechanism of Coordination Polymerization
Initiation
Al(CH2CH3)3 +
TiCl4
ClAl(CH2CH3)2 +
CH3CH2TiCl3
CH3CH2TiCl3 +
H2C
CH2
CH3CH2TiCl3
H2C
CH2

13. Mechanism of Coordination Polymerization
Initiation
TiCl3
CH3CH2CH2CH2
CH3CH2TiCl3
H2C
CH2

14. Mechanism of Coordination Polymerization
propagation
TiCl3
CH3CH2CH2CH2
H2C
CH2
TiCl3
CH3CH2CH2CH2

15. Mechanism of Coordination Polymerization
propagation
TiCl3
CH3CH2CH2CH2CH2CH2
H2C
CH2
TiCl3
CH3CH2CH2CH2

16. Mechanism of Coordination Polymerization
propagation
TiCl3
CH3CH2CH2CH2CH2CH2
H2C
CH2
etc.

17. Termination

18. Catalytic cycle for polymerization of ethylene - Cossee-Arlman mechanism
- Direct insertion of olefin across M-alkyl bond

19. Natta’s Discovery Isotactic Syndiotactic
1954 Giulio Natta, P. Pino, P. Corradini, and F. Danusso
J. Am. Chem. Soc. 77, 1708 (1955) Crystallographic Data on PP
J. Polym. Sci. 16, 143 (1955) Polymerization described in French
Isotactic
Syndiotactic
Ziegler and Natta won Nobel Prize in 1963

20. Automobile and appliance
Polypropylene tacticity
Automobile and appliance
parts, rope, carpeting
Soft n’ sticky…not very good for anything

21. Zieglar-Natta Catalyst
- Before Z-N Catalyst invention, PP composites were only atactic form
- After that, isotactic PP composites of extraordinary MW(>106) is synthesized
LDPE
HDPE PP
This has less hardness, stiffness and strength compared to HDPE, but better ductility, Free radical
10 billion lb/yr
Use chromium compounds.
Zieglar-Natta process is recent application.
A few number of branches
AlR3, AlHR2
Natta
4 billion lb/yr

22. PP- Streochemistry Vs Properties
PP Elastic Hardness MP Mech.props
Modulus-Gpa Mpa °C
Isotactic Stiff/Brittle
Syndiotactic Robust, transparent
Atactic < 0

23. Isotactic Polymerization

25. Syndiotactic Polymerization

26. Continue………….

27. Continue…..

28. Z-N catalysts- Generations catalyst
First
TiCl3 and AlEt2Cl
Second
TiCl3 + AlEt2Cl + Mono/Di ethers, Mono/Di esters
Third
TiCl4 supported on MgCl2 + Al-Alkyl + Phthalate esters -3rd component
MgCl2 has layered structure; Ionic radii of Mg2+ & Ti3+ similar
Structural compatibility
Polymer yield > 30 Kg/g ; Isotacticity index %
Fourth
Morphology controlled catalysts
Spherical polymer product-No extrusion

29. General Composition of Catalyst System and % Yield
Main Group Metal alkyl
Transition Metals Compounds
% Yield of Polymer
Al2Et6
TiCl4 48
AlBu3 60
TiCl*3
80-92
VCl4 78
VCl3 73
CrCl3 36
TiCl3
40-50
[Et2Be] n
94-96
[Et2Mg] n
78-85
Et2Zn
30-40
[AlClMe2] 2
96-98
R.C.MEHROTRA,. A.SINGH. “Organometallic Chemistry” Revised Second Edition page(464)

30. Limitations
we can't make poly(vinyl chloride) by Ziegler-Natta polymerization. When the catalyst and cocatalyst come together to form the initiating complex, radicals are produced during intermediate steps of the reaction. These can initiate free radical polymerization of the vinyl chloride monomer.
Acrylates are out, too, because Ziegler-Natta catalysts often initiate anionic vinyl polymerization in those monomers.

31. Move forward homogeneous polymerization catalyst
metallocene catalysis polymerization

32. Ziegler – Natta olefin polymerization
homogeneous polymerization catalyst:
Reactive intermediates such as A or B, alkyl olefin complexes, should be unsaturated

33. PP Stereochemistry- Effect of metal & ligand

34. Conclusion Linear high density ethene polymerization
Isotactic propylene polymerization

35. Thanks