Ziegler-Natta Catalysis

Presented by:

Mehrban ashiqSaad afzal

Presented To:

M.phil Inorganic- Analytical Chemistry 3rd Semester Department of Chemistry, University of Gujrat,

Pakistan.Course Title: Organo -Transition ChemistryCourse code: CHEM-529

Instructor: Dr. Muhammad Ali Mohsin

Ziegler-Natta Catalysis

Outline:

Introduction CatalysisActivation Energy Ziegler-Natta Olefin PolymerizationZiegler's DiscoveryMechanismNatta's DiscoveryPP StereochemistryDifferent Catalyst system and % yieldConclusion

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)

H2C CH2 CH2 CH2 nZiegler-Natta Catalyst

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

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

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

Al(Et)3 + NiCl2 Ni100 atm110 C

CH3CH2CH=CH2 + +AlCl(Et)2

TiCl4 1 atm20-70 C

Al(Et)3 + CH2CH2"linear"

Mw = 10,000 - 2,000,000

Problem

Idea:

Ziegler-Natta CatalystsZiegler-Natta Catalysts Combination of a transition metal compound of Combination of a transition metal compound of

an element from groups IV to VIII, and an an element from groups IV to VIII, and an organometallic compound of a metal from groups organometallic compound of a metal from groups I to III.I to III.

Catalyst Catalyst –– Transition metal Transition metal

Co-catalyst Co-catalyst –– Organometallic Compound, mainly Organometallic Compound, mainly alkyl or alkylhalides of aluminium and boron, or alkyl or alkylhalides of aluminium and boron, or methylaluminoxane.methylaluminoxane.

Ziegler-Natta Catalysis of Ziegler-Natta Catalysis of Alkene PolymerizationAlkene Polymerization

A typical Ziegler-Natta catalyst is a combination of A typical Ziegler-Natta catalyst is a combination of

TiClTiCl44 and (CH and (CH33CHCH22))22AlCl, AlCl,

or or

TiClTiCl33 and (CH and (CH33CHCH22))33Al.Al.

H2C CH2

Ziegler-Natta CatalystCH2 CH2 n

Polymerization Steps

1. Replacement of one Cl by alkyl group of Al alkyl

2. Bonding of Propylene to a vacant site

3. Insertion of propylene into Metal-alkyl bond- Initiation

4. Creation of vacant site for propylene adsorption

5. Repetition of steps 2,3 & 4 leading to chain growth/propagation

6. Catalyst configuration decides the configuration of added propylene

7. Termination of polymer chain with hydrogen- Termination

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

Mechanism of Coordination PolymerizationMechanism of Coordination Polymerization

InitiationInitiation

Mechanism of Coordination PolymerizationMechanism of Coordination Polymerization

InitiationInitiation

Al(CHAl(CH22CHCH33))33 ++ TiClTiCl44 ClAl(CHClAl(CH22CHCH33))22

++

CHCH33CHCH22TiClTiCl33

Mechanism of Coordination PolymerizationMechanism of Coordination PolymerizationInitiationInitiation

Mechanism of Coordination PolymerizationMechanism of Coordination PolymerizationInitiationInitiation

Al(CHAl(CH22CHCH33))33 ++ TiClTiCl44 ClAl(CHClAl(CH22CHCH33))22

++

CHCH33CHCH22TiClTiCl33

HH22CC CHCH22CHCH33CHCH22TiClTiCl33 ++

CHCH33CHCH22TiClTiCl33

HH22CC CHCH22

Mechanism of Coordination PolymerizationMechanism of Coordination Polymerization

InitiationInitiation

Mechanism of Coordination PolymerizationMechanism of Coordination Polymerization

InitiationInitiation

CHCH33CHCH22TiClTiCl33

HH22CC CHCH22

TiClTiCl33

CHCH33CHCH22CHCH22CHCH22

Mechanism of Coordination PolymerizationMechanism of Coordination Polymerization

propagationpropagation

Mechanism of Coordination PolymerizationMechanism of Coordination Polymerization

propagationpropagation

TiClTiCl33

CHCH33CHCH22CHCH22CHCH22

TiClTiCl33

CHCH33CHCH22CHCH22CHCH22

HH22CC CHCH22

Mechanism of Coordination PolymerizationMechanism of Coordination Polymerization

propagationpropagation

Mechanism of Coordination PolymerizationMechanism of Coordination Polymerization

propagationpropagation

TiClTiCl33

CHCH33CHCH22CHCH22CHCH22

HH22CC CHCH22

TiClTiCl33

CHCH33CHCH22CHCH22CHCH22CHCH22CHCH22

Mechanism of Coordination PolymerizationMechanism of Coordination Polymerization

propagationpropagation

Mechanism of Coordination PolymerizationMechanism of Coordination Polymerization

propagationpropagation

TiClTiCl33

CHCH33CHCH22CHCH22CHCH22CHCH22CHCH22

HH22CC CHCH22

etc.etc.

TerminationTermination

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

Natta’s Discovery• 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

CH3

TiCl3

Al(Et)2Cl

CH3 CH3 CH3 CH3

CH3

VCl4

Al(iBu)2Cl

CH3 CH3

O inCH3

- 78 CCH3

CH3

Isotactic

Syndiotactic

Ziegler and Natta won Nobel Prize in 1963

C

C

C

C

C

C

C

C

C

C

C

C

R R R R R R

C

C

C

C

C

C

C

C

C

C

C

C

R

R

R

R

R

R

C

C

C

C

C

C

C

C

C

C

C

C

R R

R

R

R

R

isotactic

syndiotactic

atactic

Automobile and appliance parts, rope, carpeting

Soft n’ sticky…not very good for anything

Polypropylene tacticity

- 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

Zieglar-Natta Catalyst

PP- Streochemistry Vs Properties PP Elastic Hardness MP Mech.props

Modulus-Gpa Mpa °C

Isotactic 1.09 125 160-170 Stiff/Brittle

Syndiotactic 125-131 Robust, transparent

Atactic 0.15 1.4 < 0

Isotactic Polymerization

Syndiotactic Polymerization

Continue………….

Continue…..

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 -96-99%

Fourth• Morphology controlled catalysts• Spherical polymer product-No extrusion

General Composition of Catalyst System and % Yield

Main Group Metal alkyl

Transition Metals Compounds % Yield of Polymer

Al2Et6 TiCl4 48

AlBu3 TiCl4 60

Al2Et6 TiCl*3 80-92

Al2Et6 VCl4 78

Al2Et6 VCl3 73

Al2Et6 CrCl3 36

Al2Et6 TiCl3 40-50

[Et2Be] n TiCl*3 94-96

[Et2Mg] n TiCl*3 78-85

Et2Zn TiCl*3 30-40

[AlClMe2] 2 TiCl*3 96-98

R.C.MEHROTRA,. A.SINGH. “Organometallic Chemistry” Revised Second Edition page(464)

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.

Move forward

homogeneous polymerization catalyst

metallocene catalysis polymerization

Ziegler – Natta olefin polymerization

homogeneous polymerization catalyst:

Reactive intermediates such as A or B, alkyl olefin complexes, should be unsaturated

Olefin insertion

Zr Me ZrCH2

H2CZr Me CH2=CH2

Me

CH2=CH2

A

ZrCH2

H2C

Me

B

Zr...

CH2=CH2

H2C

Olefin insertion

CH2

H2C

CH2

Me

PP Stereochemistry- Effect of metal & ligand

Conclusion

• Linear high density ethene polymerization

• Isotactic propylene polymerization

Thanks