Soluble Metallocene Cataysts Polyethylene

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Soluble Metallocene CataystsPolyethylene

• Bis(cyclopentadienyl)zirconium dichloride
• Plus methylaluminoxane (MAO)
• 5,000 kg PE / g Zr / hr (indefinitely active)

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Soluble Metallocene CataystsPolypropylene
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Soluble Metallocene Cataysts

• Used a mixture of meso and racemic
  ansa-titanocenes
• Stereo-rigid
• Ethylene-bridged
• Rac chiral with C2-symmetric axis
• Meso achiral

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Rac Ansa Catalysts
Non-superimposable Mirror Images
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Soluble Metallocene Cataysts
Ewen J. Am. Chem. Soc. 1984
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PP from ansa-Metallocene Catalysts

• Methyl pentad region
• Fractions of iso-PP versus atactic-PP tracks with
  ratio of racemic to meso catalyst levels
• MWs on each sample were similar indicating that
  both stereo-isomers of the catalyst give rise to
  similar propagation and termination rate constants

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Soluble Metallocene Cataysts

• Confirmed Ewens proposal that it was the chiral
  ansa-metallocene that was responsible for the
  formation of isotactic PP
• Made the zirconium derivative
• 7,700 kg PP / mol Zr / hr (!)

1985 Kaminsky and Britzinger
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Mechanism for Isotactic PP

• Conformational modeling studies (Corradini 1991)
• The growing polymer chain is forced into the open
  region
• Chirality of the metallocene is relayed to the
  incoming monomer through the orientation of the
  methyl group
• Since C2-symmetry, both reactions sites are
  homotopic
• Therefore selective for the same olefin
  enantioface
• Giving rise to isotactic PP

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Soluble Metallocene CataystsPolypropylene
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Rac Ansa Catalysts
C2 Axis of Symmetry
Binding Sites are Homotopic
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1. Cs symmetry
2. Cp of different size
3. Steric bulk flanking the metallocene wedge with
   an open region in center

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How to make this?

• Hemi-isotactic
• Hemi-syndiotactic

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m m r r m m m m r r r r m
m m m r
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• Unbridged metallocene catalysts
• Rapid isomerization, low barriers
• What kind of polymer is produced?

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• Unbridged metallocene catalysts
• Added phenyl group to indene

• Inhibits rate of ligand rotation

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Physical Properties of Polypropylene
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Olefin Polymerizations with Early Metal Catalysts
2 1011 lbs/year polyethylenes(PE),
polypropylenes(PP) produced worldwide!
Metallocene Catalysts Technological advance A)
Incremental B) Major 1) New Materials 2)
Detailed mechanistic understanding Not a black
box anymore
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Olefin Polymerizations with Early Metal Catalysts
Metallocene Catalysts Incremental technological
advance ? Increased activities/productivities ?
Many different grades of ethylene/ a-olefin
copolymers ? Control of MW, MWD bimodal,
unimodal, PDI lt 5.0!
Existing markets are being extended into new
applications
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Metallocene Catalysts

• Major Technological Advance
• New Materials
• Syndiotactic polystyrene
• Tm 270 C, 40-50 X-tal w/ good rate of
  x-tallization
• Syndiotactic and elastomeric PP
• Cyclic Olefin Copolymers
• Hoechsts TopazTM (Tg 140 200 C)

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• Chemical Review 2000, Issue 4
• FRONTIERS IN METAL-CATALYZED POLYMERIZATION
• Also
• Angew. Chem. Int. Ed. 1999, 38, 428 447