Transcript MS PowerPoint

Metallocene based Polymerization
Catalysts
Metallocenes
Key aspects
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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
+ AlClEt2
Low PE yields
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
Vessel A
Diameter = 4.0m
Length = 20.0 m
Vessel B
Diameter = 4.0m
Length = 20.0 m
Material of
Material of
Construction = Carbon Construction =
Steel
Carbon Steel
Design Pressure = 1
atm
Design Pressure =
400 atm
Installed Cost =
$228,700
Installed Cost =
$1,840,000