1. Homogeneous Catalysis HMC-8- 2013
Dr. K.R.Krishnamurthy
National Centre for Catalysis Research
Indian Institute of Technology,Madras
Chennai 1

2. Metallocene based Polymerization
Catalysts-Part 1

3. Metallocenes Key aspects Why metallocenes ?
Metallocenes - Structure & Features
Methyl Aluminoxane (MAO) - Structure & Features
Activation of Metallocenes by MAO
Polymerization with Metallocenes

4. Why Metallocenes ?
Need for homogeneous catalyst system- Well-defined structure-activity correlations
Metallocenes- Well known organometallics- Can function as Single site catalyst
Tunable structure- rings, substituents, ligands
High degree of stereoregulation –Isotactic / Syndiotactic
High productivity
Narrow molecular weight distribution
Better co-monomer distribution
Chain termination by β- Hydrogen elimination→ Vinyl end group→ Facile grafting of functional monomers
Pathway to designer catalysts

5. PE- Molecular weight distribution - Effect of metallocene

6. PE- Density Vs Co-monomer content :
Effect of metallocene

7. Ferrocene First metallocene to be discovered
Discovered in by reaction between
Cyclopentadienyl Magnesium bromide & FeCl3
With 6 electrons from each ring & six from Fe,
a total of 18 electrons ensures stable noble
gas configuration
Bond distance between sandwiched Fe & CPD
rings is 2.04Å
Nickelocene, Cobaltocene & Titanocene were
synthesized later

8. Metallocenes- Structural features
Tetrahedral structure
Orientation of CPD rings
Zr may be replaced with Ti,Hf &
CPD with Indenyl / Fluorenyl rings
with or without substituents
Ethylene bridge holds both rings rigid
retarding swiveling – helps in proper
approach of monomer to metal centre
Ethylene Bis-Indenyl Zirconocene
Cyclopentadienyl,Indenyl, Fluorenyl ligands with & w/o substituents

9. Metallocene-The race for supremacy

10. Organometallics- Vital components in polymerization catalysts
Polymerization- Controlled making & breaking metal-alkyl bonds

11. Polyolefins catalysts- Phenomenal growth

12. Search for homogeneous Z-N catalysts
Bis (cyclopentadienyl) Ti4+
Tetrabenzyl Titanium
Tetraallyl Zr & Hf
Low PE yields +
AlClEt2
Inactive for propylene polymerization
Al alkyls are not effective as co-catalysts for metallocenes
Methyl aluminoxane was discovered by Kaminski in
as the most effective co- catalyst for metallocenes

13. Methyl Aluminoxane - MAO- Co-catalyst for Metallocenes
MAO- Formed by controlled hydrolysis of Al(CH3)3
Tri methyl aluminium(TMA) with water, with
evolution of methane
Mixed oligomers with Mol.mass – g/mol
Gen formula Me2-Al-O[AlMeO]n-OAlMe2 with n= 5-20
Highly reactive, stored & transported as solution
in toulene
Structures in solution

14. Activation of Metallocene by MAO
Substitution of Cls with methyl groups followed by ion-pair formation &
creation of a vacant site

15. Propylene polymerization cycle on metallocene catalyst

17. Applied Homogeneous Catalysis with Organometallic. Compounds, Vols
Applied Homogeneous Catalysis with Organometallic Compounds, Vols. 1 & 2, edited by
B. Cornils and W.A. Herrmann, VCH, Weinheim,New York, 1996.

18. Applied Homogeneous Catalysis with Organometallic. Compounds, Vols
Applied Homogeneous Catalysis with Organometallic Compounds, Vols. 1 & 2, edited by B. Cornils and W.A. Herrmann, VCH, Weinheim,N ew York, 1996.

19. Metallocenes-Metals/Structure.Vs.Activity/MW/Isotacticity
6- 60,900/62000
6-140/2000/15
7-170/3000/59
/18000
8-180/3000/49
11- 12,000/352000
/480000
/260000
/32000/95
/79000/97
9- 22,200/
9-1200/24000/98
Polyethylene
Polypropylene
/500000
/160000/Synd
19-130/750000/Synd
/730000/Synd
/250000
14-750/420000/>99
[Me2Si(2-Me-4,5 BenzInd)2 ]ZrCl2
/680000/98
Activity- Kg PE/mole of Zr.hr.cmon
Metallocenes-Metals/Structure.Vs.Activity/MW/Isotacticity

20. Neo menthyl acetate

21. Metallocene polymerization- Features
Zr catalysts more active than Ti or Hf
Methyl aluminoxane more active than ethyl/isobutyl aluminoxane
Mol. Wt lowered by increasing temp., raising metallocene/ethylene
ratio or adding more hydrogen ( mole%)
Structure-6
Every Zr atom produces polymer chains /hr
Time for insertion of one ethylene unit- 3 X10-5 Sec
Structures &26
Introduction of methyl/ethyl group in position 2 of Indenyl rings
prevents β hydrogen transfer elimination increases mol wt
Phenyl or naphthyl groups enhances stereospecificity & MW
Applied Homogeneous Catalysis with Organometallic Compounds, Vols. 1 & 2, edited by
B. Cornils and W.A. Herrmann, VCH, Weinheim, New York, 1996.