Polymerization of olefins by metallocene catalysts - · PDF filePolymerization of olefins by...

Polymerization of olefins by metallocene catalysts

Pasquale Longo Università di Salerno

plongo@unisa.it

“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