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Ziegler-Natta Catalysis

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Presentation on theme: "Ziegler-Natta Catalysis"— Presentation transcript:

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

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