1. Ziegler Natta catalyst Submitted to Dr. Afzal Qamar Submitted by Kainat Rafiq Roll number 1750(21406) Semester BS Chemistry 8 th (E 2 )

2. Ziegler Natta catalyst

3. Ziegler Natta Catalyst is a type of a catalyst made from a mixture of chemical compound that are mainly used in the synthesis of polymers belonging to 1- alkenes such as alpha-olefins which are hydrocarbons containing a double carbon-carbon bong. A typical Ziegler Natta Catalyst system usually contains two parts.  A transition metal (Group IV metals, like Ti, Zr, Hf)  An organoaluminum compound (Co- catalyst)

4. Ziegler Natta catalyst Example: The common example of Ziegler Natta Catalyst system includes:

5. Ziegler Natta catalyst In 1953 German chemist Karl Zieglar discovered a catalyst system able to polymerize ethylene into linear, high molecular weight polyethylene which conventional polymerization techniques could not make, the system contained a transition metal halide with main group element alkyl compound.

6. Ziegler Natta catalyst

7. Following the catalyst design, Italian chemist Giulio Natta found that polymerization of α-olfeins resulted in stereo regular structure, either syndiotactic or isotactic depending on the catalyst used.

8. Ziegler Natta catalyst Because of these important discoveries Karl Ziegler and Giulio Natta shared the noble prize in chemistry in 1963.

9. Ziegler Natta catalyst Advantages over traditional polymerization method: Traditionally, polymerization of α -olefins was done by radical polymers problem with this technique was the formation of undesired allylic radical leaded to branched polymers for example, radical polymerization of propene give branched polymers with large molecular weight distribution, also, radical polymerization had no control over stereochemistry.

10. Ziegler Natta catalyst Linear unbranched polyethylene and stereo regulated polypropylene could not be fabricated by free radical polymerization.

11. Ziegler Natta catalyst Mechanism of Ziegler Natta catalytic polymerization: Activation of Ziegler Natta catalyst Herein, TiCl4 + AlEt3 catalyst system is taken as an a example. The titanium chloride compound has a crystal structure in which each Ti atom is coordinated to 6 chlorine atoms.on the crystal surface, a Ti atom is surrounded by 5 chlorine atoms with one empty orbital to be filled.

12. Ziegler Natta catalyst When Et3 Al comes in it donates on ethyl group to Ti atom and and the Al atom is coordinated to one of the chlorine atoms. Meanwhile, one chlorine atom from Latium is kicked out during this process. Thus the catalyst system still has an empty orbital. The catalyst is activated by the coordinate of AlEt3 to Ti atom.

13. Ziegler Natta catalyst

14. Initiation step: The polymerization reaction is initiated by forming alkene metal complex. When a vinyl monomer like propylene comes to the active metal center, it can be coordinate to Ti atom by overlapping their orbitals. There is an empty orbital and a filled dx2-y2 orbitals in Ti’s outermost shell.

15. Ziegler Natta catalyst The carbon-carbon double bond of alkene has pi-bond, which consist of a filled pi-bond orbital and an empty pi-antibonding orbital,so the alkene’s pi- bonding orbital and Ti’s dxy orbital come together that Ti’s dx2-y2 orbital come mighty close to the pi-antibonding orbital, sharing another pair of electrons.

16. Ziegler Natta catalyst

17. The formed alkene-metal complex (1) than goes through electron shuffling, with several pairs of electrons shifting their positions. The pairs of electron from carbon-carbon pi-bond shifts to form Ti-carbon bond, while the pairs of electrons form the bond between the ethyl group and the methyl-substituted carbon of propylene.

18. Ziegler Natta catalyst The pairs of electron from carbon-carbon pi-bond shifts to form Ti-carbon bond, while the pairs of electrons form the bond between the ethyl group and the methyl-substituted carbon of propylene. After electron shuffling, Ti is back with an empty orbital again, needing electrons to fill it.

19. Ziegler Natta catalyst

20. Propagation step: When other propylene molecules come in the process starts over and over, giving linear polypyrene.

21. Ziegler Natta catalyst Termination step: Termination is the final step of a chain growth polymerization forming dead polymers (desired product). Several termination approaches developed with aid of cocatalyst AiEt3.

22. Ziegler Natta catalyst

23. Three termination approaches: β-elimination form the polymer chain forming metal hydride. β-elimination with hydrogen transfer to monomer. Hydrogenation.

24. Ziegler Natta catalyst Regio and stero selectivity (a)Regio selectivity: For propene polymerization, most Ziegler Natta catalyst are catalyst are highly regio selective favoring 1,2 primary insertion.

25. Ziegler Natta catalyst

26. (b)Stereo- selectivity: Stereo- selectivity of polymers made from Ziegler Natta catalyst can be well regulated by rational designof ligands. By using different ligand systems, either syndiotactic polymers can be obtained.

27. Ziegler Natta catalyst The relative stereochemistry of adjacent chiral centers within a macromolecule is defined as tacticity. Three kinds of stereochemistry are possible: (a)Isotactic (b)Syndiotactic (c)Atactic

28. Ziegler Natta catalyst In isotactic polymers substituents are located on the same side of the polymer backbone, whole substituents on Syndiotactic polymer have alternate positions. In atactic polymers substituents are placed randomly along the chain.

29. Ziegler Natta catalyst Application: the polyethylene fabricated by Ziegler Natta catalysts, there are three major classes: High density polyethylene (HDPE) Linear low density polyethylene(LLDPE) Ultra-high molecular weight polyethylene(UHMWPE)

30. Ziegler Natta catalyst High density polyethylene (HDPE) It is a liner homopolymer is widely applied in garbage containers detergent bottles and water pipes because of its high tensile strength. High density polyethylene (HDPE) have very low branching degree.

31. Ziegler Natta catalyst Linear low density polyethylene(LLDPE): It has many short branches. Its better toughness, flexibility and stress- cracking resistance makes it suitable for material like cable coverings, and so on.

32. Ziegler Natta catalyst Ultra-high molecular weight polyethylene(UHMWPE): It is polyethene with a molecules weight between 3.5 and 7.5 million. This material is extreme tough and chemical resistant. Therefore, it is often used to make gears and artificial joints.