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Homogeneous Catalysis HMC-8- 2013

Homogeneous Catalysis HMC-8- 2013. Dr. K.R.Krishnamurthy National Centre for Catalysis Research Indian Institute of Technology,Madras Chennai-600036. Metallocene based Polymerization Catalysts-Part 1. Metallocenes. Key aspects Why metallocenes ? Metallocenes - Structure & Features

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Homogeneous Catalysis HMC-8- 2013

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  1. Homogeneous CatalysisHMC-8- 2013 Dr. K.R.Krishnamurthy National Centre for Catalysis Research Indian Institute of Technology,Madras Chennai-600036

  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 sitecatalyst 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 1951 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 – 1000 -1500 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

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

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

  18. 6- 60,900/62000 6-140/2000/15 7-170/3000/59 8- 3330/18000 8-180/3000/49 11- 12,000/352000 12-2900/480000 13- 36900/260000 11-1700/32000/95 13-1900/79000/97 9- 22,200/1000000 9-1200/24000/98 Polyethylene Polypropylene 18- 2000/500000 18-1500/160000/Synd 19-130/750000/Synd 20-2000/730000/Synd 15- 111900/250000 14-750/420000/>99 [Me2Si(2-Me-4,5 BenzInd)2 ]ZrCl2 26-26-14000/680000/98 Activity- Kg PE/mole of Zr.hr.cmon Metallocenes-Metals/Structure.Vs.Activity/MW/Isotacticity

  19. Neo menthyl acetate

  20. 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 (0.1 -2 mole%) Structure-6 Every Zr atom produces 46000 polymer chains /hr Time for insertion of one ethylene unit- 3 X10-5 Sec Structures-14-17 &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.

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