Metallocene based Polymerization Catalysts

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

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

PE- Molecular weight distribution - Effect of metallocene

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

Metallocene-The race for supremacy

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

Polyolefins catalysts- Phenomenal growth

Propylene polymerization cycle on metallocene catalyst

Ferrocene Discovered in 1951 by reaction between Cyclopentadienyl Magnesium bromide & FeCl3 With 6 lectrons from each ring & six fron Fe, a totall of 18 electrons ensures stable noble gas configuration Bond distance between sandwiched Fe & CPD rings is 2.04Å Nickelocene,Cobaltocene & Titanocene were synthesized later

Metallocenes- Structural features 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

Search for homogeneous Z-N catalysts Bis (cyclopentadienyl) Ti4+ Tetrabenzyl Titanium Tetraallyl Zr & Hf Low PE yields + AlClEt2 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

Methyl Aluminoxane - MAO- Co-catalyst for Metallocenes MAO- Formed by controlled hydrolysis of Al(CH3)3 with water, with evolution of methane Mixed oligomers with Mol.mass – 1000 -1500 g/mol Gen formula Me2-Al-O[AlMeO]n-OAlMe2- n= 5-20 Highly reactive, stored & transported as solution in toulene Structures in solution

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

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