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Polymerization of olefins by metallocene catalysts Pasquale Longo Università di Salerno [email protected]
Polymerization of olefins by metallocene catalysts
Pasquale Longo Università di Salerno
“Molecular Machine”
Ziegler – Natta catalysts “building” some plastic materials
(Poly-ethylene, Poly-propylene, Poly-styrene, etc. etc.)
This ship is made of only synthetic materials!
USA production (1960-2000) (1,000s of metric tons)
year 1960 1970 1980 1990 2000 LDPE 560 1,923 3,307 5,069 7,042 HDPE 70 728 1,998 3,780 6,333 PP - 468 1,655 3,773 7,139 PS 450 1,075 1,597 2,273 3,104 PVC 590 1,413 2,481 4,122 6,551
production went from 1.7 billion tonsm in 1960 to a massive 30.1 billion tonsm in 2000
PP strength
- very low density - high stiffness
- good tensile strength - inertness towards acids, alkalis and solvents
- cost advantage - good injection-molding characteristics
very suitable for the large-volume cost- and weight-conscious markets
(automotive)
- very low density - high stiffness - good tensile strength - inertness towards acids, alkalis and solvents - cost advantage - good injection-molding characteristics
very suitable for the large-volume cost- and weight-conscious markets
(automotive)
PP automotive applications
Battery cases Bumpers Exterior trim Interior trim Fuel tanks Instrument panels Under-the-hood applications Wires and cables
1,700 components of 5,000 are made of plastics
10% of total weight.
60% of interior weight
Glu
Ala Trp
Pro
His
Gly
Lys Arg
Ile Leu
Phe Ser
Glu
Pro His
Lys
Ile Glu Ala Trp Pro His Gly Lys Arg Ile Leu Ala Trp Gly Arg Leu Phe Ser
Proteins
Poly-propylene
Amminoacids
Propylene
Linus :
Human machine
Input (brick)
Output (building)
Classic machine (Linus Van Pelt)
Rybosom :
Natural Machine
Input (amino-acid)
Output (protein)
Molecular Machine (Rybosom)
Glu
Trp
Pro
His Gly
Lys Arg Ile
Leu
Phe Ser
Ile
Gly Gly Ile Phe Gly Ile Phe Ser Gly Ile Lys Phe Ser Gly Ile Lys Arg Phe Ser Gly Ile Trp Lys Arg Phe Ser Gly Ile Trp Pro Lys Arg Phe Ser Gly Ile Trp Pro Lys Arg Ile Phe Ser Gly Ile Trp Pro Lys Arg Ile Leu Phe Ser Gly Ile Trp Pro His Lys Arg Ile Leu Phe Ser Gly Ile Trp Pro His Gly Lys Arg Ile Leu Phe Ser Gly Ile Glu Trp Pro His Gly Lys Arg Ile Leu Phe Ser Gly Ile
Ziegler Natta Catalysts :
Artificial“Machine”
Input (propylene)
Molecular “Machine” (Ziegler-Natta catalysts)
Output (poly-propylene)
Catalysts for plastic material
production 1953-1954
Karl Ziegler Giulio Natta
Winners of the Nobel Prize
1963 http://www.nobel.se
Only italian Nobel prize winner for chemistry !
The motivations for awarding the prize to Natta
• Natural and biological catalysts had
previously dominated the synthesis of stereoregular polymers.
• Prof. Natta ended this monopoly.
Propylene : INPUT
Poly-propylene : OUTPUT
Metallocene : tools
Propylene (CH2=CHCH3)
INPUT
C
C
H3C H
HH 1
2
A
B
The faces of propene are chiral
A A*
Mirror
Chirality = asymmetry
Lord Kelvin - 1904
A chiral object does not over-lay its mirror-image
Louis Pasteur - 1848
MILESTONES REACHED
Overview, history (1) First report in September 1955 using “purple phases” of TiCl3 (α-TiCl3
and γ-TiCl3) and AlEt3 (higher activity) or AlEt2Cl (higher stereoselectivity).
Solvay 1973: Added TiCl4, which acted as a catalyst to convert β-TiCl3 into an active phase of TiCl3 (higher activity due to smaller particles).
Overview, history (2) Shell 1980: TiCl4 supported on MgCl2 in presence of AlEt3 or AlEt2Cl.
Active species still TiCl3 .
Other remarks: Awarded Nobel price in 1963. 1980’s: Process attributed to Robert Banks and J. Paul Hogan
Cerutti, L; International Journal for Philosophy of Chemistry, 1999 (5), 3-41
Mechanism
Two complications Why Cl-vacancy? Why stereospecific?
Cossee-Arlman postulate (1964)
Structure of the catalyst, overview • Three phases of TiCl3
Color Stucture Activity
α-TiCl3
Purple Hexagonal layered
structure Isotactic
β-TiCl3
Brown Needle structure Little stereospecifity
γ-TiCl3
Purple Cubic layered
structure Like α-TiCl3
Structure of the catalyst, overview
• Schematic view of the structures of α-TiCl2, α-TiCl3 and ß-TiCl3
Structure of the catalyst, active site (1)
• Cl-vacancies on the edges of the crystal.
• Electron Microscopy: active sites are on the edges
• Ti at the active sites in a square of Cl
Structure of the catalyst, active site (2)
• Square makes an angle of 55° with the base plane.
• Cl-’s not equivalent: – 3 stuck in crystal – 1 bound by 2 Ti3+
– 1 loosely bound (to 1 Ti3+)
• Vacancy and L not equivalent sites
Stereospecifity, bonding of propylene
Two possibilities: 1. Alkalyne moves back to vacancy
2. Alkalyne doesn’t move back
TiL F
B B
V
B
Ti
B
LB
V
F
B= = Ti L
V
F
AlEt3Ti V
Et
F
CH2
CH3
Ti -
Et
F CH2
HCCH3
Ti CH2
V
F
CH EtCH3
Stereospecifity, Polymerization (1)
Polymer moves back to vacancy isotactic polypropylene
Ti CH2
V
F
CH EtCH3
TiF
V
H2C
CH EtCH3
CH2
CH3
Ti -
H2C
F
CH EtCH3
CH2
HCCH3
Ti CH2
V
F
CH2
CH3CH2
CH EtCH3
CH3 CH3
R R
Stereospecifity, Polymerization (2)
Polymer doesn’t back to vacancy syndiotactic polypropylene
Experimental: Some syndiotactic PP at -70°
Ti CH2
V
F
CHEtCH3
Ti CH2
|
F
CHEtCH3
CH3
CHCH2
CH2
CH3
Ti
H2C
F
CH3
HCCH2
HCEt
CH3
V
CH3 CH3
R R
Cossee’s mechanism
X
XX
R
X
X
X
R
X
C3H6 X
X
XX
X
R
insertion
X
XX
X
R C3H6
The Polymerization reaction
Polymer
Zr
C5 C5
Polymer
Zr
C5 C5
CC
Polymer
Zr
C5 C5
CC
PolymerZr
C5 C5
CC
Polymer
Zr
C5 C5
CC
+ CH2=CH2
Piet Cossee 1964
Allegra said that …
CH2
CP
CH3
*
Zambelli found that ….
C C
C CC
C
C C
C C C C C C C C C C C
C
C C
C CC
C C C C C C C C C C C C
C C C
Steric control
a
b
Hydrocarbons monomers
Ethylene
Propylene Styrene
Conseguence of Chirality
The right foot can only wear right shoes.
A
A*
Catalyst
Better
(more reactive)
Poly-propylene :
OUTPUT
Poly-propylene
Atactic Polypropylene *
* *
*
*
* *
*
Isotactic Polypropylene * * * * * * * *
Syndiotactic polypropylene *
*
*
*
*
*
*
*
Poly-propylene
Isotactic Polypropylene
* * * * * * * *
If only one face of propylene gives co-ordination to the catalyst…
A A A A A A
Poly-propylene
Syndiotactic Polypropylene
A
A*
A
A*
A
A*
*
*
*
*
*
*
*
*
If propylene gives co-ordination to the catalyst alternatively with one and the other face …
Poly-propylene
Atactic poly-propylene
If propylene can give co-ordination to the catalyst with both the faces …
A
A*
A
A*
A
A*
*
* *
*
*
* *
*
Metallocenes : Molecular Tools
How is a Z/N metallocene catalyst made?
Ancillary Ligands
Group 4 Metal Metallocene + =
How is a Z/N metallocene catalyst made?
The metal is of group 4.
How is a Z/N metallocene catalyst made?
Which are the ligands ?
How is a Z/N metallocene catalyst made?
More than 10,000 ligands !
? ? ?
?
? ? ? ?
How is a Z/N metallocene catalyst made?
? ?
Which are the other ligands?
How is a Z/N metallocene catalyst made?
Which are the other ligands?
x x
Activators Al(CH3)3 + H2O Al
CH3
O
n
B(C6F5)3 (C6H5)3C + B(C 6F5)4 -
(C6H5)2NH + B(C 6F5)4 -
REPRESENTS A BREAKTHROUGH
Cation Cp2MX2 + MAO [Cp2M(CH3)] + + [MAOX]-
ZrC5C5
CH3+
ZrC5C5
Monomero Polimero
Monomer
How is a Z/N metallocene catalyst made?
Which are the other ligands?
Polymer chain
ZrC5C5
Ethylene
How is a Z/N metallocene catalyst made?
Which are the other ligands?
Polyethylene
ZrC5C5
Propylene
How is a Z/N metallocene catalyst made?
Whicharetheotherligands?
Polypropylene
The Tools at work:
Fundamental reaction
The Fundamental reaction
A chain of Snoopy kennels
The “Catalytic Cycle”
Polymerization reaction
One monomer insertion is going on every millionth of a second. A metallocene has a very high reactivity: it can give 10,000-20,000 monomers insertion for macromolecules A metallocene has a very high activity: 1 g of metallocene can produce more than 1,000 kg of polymer before it becomes inactive.
The Tools at work:
Formation of stereoregular polymers.
Stereoregular polymers.
The Symmetry of the King of diamonds (isospecific symmetry)
The Symmetry of the King of diamonds (isospecific symmetry)
Growing chain Growing chain
Better situation !
The Symmetry of the King of diamonds (isospecific symmetry)
Growing chain
A A*
Consequence of the Chirality
The right foot can wear only right shoes !
A
A*
Catalyst
or ? ?
Growing chain
A A*
The Symmetry of the King of diamonds (isospecific symmetry)
Growing chain
or ? ? A A*
Better situation!
The Symmetry of the King of diamonds (isospecific symmetry)
Growing chain
Growing chain
A A
?
The Symmetry of the King of diamonds (isospecific symmetry)
A metallocene having the same symmetry of the King of diamonds produces an isotactic polymer.
+ =
Isotactic Poly-propylene
Polymerization reaction as a catalytic cycle.
C2 symmetric metallocene
m m m m m m m
Mt
chainMt
chain
Allegra
By utilizing C2 symmetric stereorigid metallocene Allegra’s conclusion was verified and an isotactic polypropylene was obtained. The two sites of cationic catalyst with the C2-symmetry are homotopics, and perform isotactic polymerization of propene. An eventual back-skip reaction of the chain, before a following monomer insertion, does not influence the polymerization stereochemistry .
Mt
chainMt
chain
How is a Z/N metallocene catalyst made?
More than 10,000 ligands have been synthesized
? ? ?
?
? ? ? ?
Symmetry of Chess (syndiospecific symmetry)
Symmetry of Chess (syndiospecific symmetry)
Growing chain
Better situation
Growing chain
Symmetry of Chess (syndiospecific symmetry)
or ? ?
Growing chain
A A*
Growing chain
or ? ? A A*
Better situation !
Symmetry of Chess (syndiospecific symmetry)
Growing chain
Growing chain
Growing chain Growing chain Growing chain
Symmetry of Chess (syndiospecific symmetry)
Growing chain
A
?
A*
symmetry of Chess (syndiospecific symmetry)
A metallocene having chess symmetry produces a
syndiotactic polymer
+ =
Syndiotactic Poly-propylene
Cs Symmetric Metallocene
Mt
chain
Mt
chain
r r r r r r r
Growing chain
The comparison of the symmetries
Growing chain
King of diamonds Chess
Mechanism….
Mt Mtchain chain
The syndiospecificity of catalysts having Cs - symmetry was the first experimental evidence that Cossee’s chain migratory insertion was operative.
Mechanism …
Occasional meso (m) diads defects provide evidence for back-skip reactions of the chain, according to the hypothesis of Cossee and Arlman which suggested that “the growing alkyl group moves back to its original position after each incorporation of a new monomeric unit”.
r r m m r r r
Mechanism of Cossee and Arlman
X
XX
R
X
X
X
R
X
C3H6 X
X
XX
X
R
insertion
X
XX
X
back -sk ip
R
Cossee and Arlman
Mt
chain
The presence of tert-butyl group forbids the growing chain to be located in the inward position , close to tert-butyl group, thus, after each monomer insertion, the growing chain skips back to the less crowded outward position. Hence, insertion
always takes place with the same face, because it occurs each time on the same site of the catalyst that becomes isospecific.
m m m m m m m
Summary….
Metallocenes are molecular tools that change input molecules (alkenes) into output molecules (polymers).
Monomer Polymer
Ethylene Polyethylene Propylene Polypropylene
Summary….
Metallocenes are “intelligent” and change pro-chyral monomers (propylene) into stereoregular polymers (polypropylene iso- or syndiotactic)
Polymer
isotactic polypropylene
syndiotactic polypropylene
Symmetry King of Diamonds
Chess
Monomer
propylene
Possible polypropylene from metallocenes:
ZrX2
atactic polypropylene
ZrX2isotactic polypropylene
ZrX2syndiotactic polypropylene
ZrX2
TiPh2
ZrX2
hemisotactic polypropylene
isotactic block polypropylene
atactic - isotactic block polypropylene
C1 Symmetric Metallocene
Mt
chain
Mt
chain
R or S R R or S R R or S R R or S R
Elastomeric polypropylene
Zr P+ Zr P
+
CpTiCl3
Cp2TiCl2 [m]=0.85
(CH3)2C(Cp)(Ph)TiCl3 [m]=0.76
2-(1-cyclopentadienyl)2-(1-phenyl)propano titanium trichloride
(CH3)2C(Cp)(Ph)TiCl3(CH3)2C(Cp)(Ph)TiCl3
atattico a T = 50°Catactic at T = 50°C
Propylene
[m]=0.51
Isotactic at T = - 60°C
Longo, P.; Amendola, A.G.; Fortunato, E.; Boccia, A.C.; Zambelli, A.; Macromol. Rapid Commun. 2001, 22, 339.
+ MAO
Active specie
Longo, P.; Amendola, A.G.; Fortunato, E.; Boccia, A.C.; Zambelli, A.; Macromol. Rapid Commun. 2001, 22, 339.
Ti P
+
high temperature
P
+
Ti
low temperature
2-(1-indenyl)2-(1-naphtyl)propano zirconium trichloride
+ MAO C
CH3
CH3
ZrCl 3
Hapto-flexible catalysts
C. De Rosa, F. Auriemma, G. Circielli, A. C. Boccia, P. Longo Macromolecules, 36, 3465, 2003
Ethylene-Propylene Rubber Common uses:
Automotive applications 44% Roofing membrane 18% Oil additives 10% Wires and cables 8% (Gaskets, seals, Other coated fabric, footwear, rug underlay) 20%.
THE END
