Coordination Polymerization

Ziegler Natta Processes

Stereoregular PolymerizationCationic Initiation of Vinyl Ethers

Schildknecht et al. Ind. Eng. Chem. 39, 180, (1947)

OBF3.Et2O

Propane

OR OR OR OR

CH2

H3CCH3

- 80-60 C

Isotactic vinyl ether

Stereoregular Polymerization

CH3

OO

MgBr

Toluene-78-0 C

H3C OR OR OR OR

BuLiTHF -78 C

H3C OR OROR OR

BuLi or

Anionic Polymerization of Methyl Methacrylate,

H. Yuki, K. Hatada, K.Ohta, and Y. Okamoto, J. Macromol. Sci. A9, 983 (1975)

Isotactic

Syndiotactic

POLYETHYLENE (LDPE)

H2C CH2

RH2C CH2

x20-40,000 psi150-325° C

Molecular Weights: 20,000-100,000; MWD = 3-20 density = 0.91-0.93 g/cm3

Highly branched structure—both long and short chain branches

15-30 Methyl groups/1000 C atoms

Tm ~ 105 C, X’linity ~ 40%

Applications: Packaging Film, wire and cable coating, toys, flexible bottles, housewares, coatings

CH2

H3CCH3

CH3

H3C

CH3

H3C

H3C

H3C

H3C

Ziegler’s Discovery• 1953 K. Ziegler, E. Holzkamp, H. Breil and H. Martin• Angew. Chemie 67, 426, 541 (1955); 76, 545 (1964).

Al(Et)3 + NiCl2 Ni100 atm110 C

CH3CH2CH=CH2 + +AlCl(Et)2

+ Ni(AcAc) Same result

+ Cr(AcAc) White Ppt. (Not reported by Holzkamp)

+ Zr(AcAc) White Ppt. (Eureka! reported by Breil)

TiCl4 1 atm20-70 C

Al(Et)3 + CH2CH2"linear"

Mw = 10,000 - 2,000,000

Polypropylene (atactic)

CH3 CH3

* n

R

CH2Low molecular weight oils

Formation of allyl radicals via chain transfer limits achievable molecular weights for all -olefins

Natta’s Discovery• 1954 Guilio Natta, P. Pino, P. Corradini, and F. Danusso• J. Am. Chem. Soc. 77, 1708 (1955) Crystallographic Data on PP

• J. Polym. Sci. 16, 143 (1955) Polymerization described in French

CH3

TiCl3

Al(Et)2Cl

CH3 CH3 CH3 CH3

CH3

VCl4

Al(iBu)2Cl

CH3 CH3

O inCH3

- 78 CCH3

CH3

Isotactic

Syndiotactic

Ziegler and Natta awarded Nobel Prize in 1963

Polypropylene (isotactic)

CH3

TiCl3

Al(Et)2Cl

CH3 CH3 CH3 CH3

Density ~ 0.9-0.91 g/cm3—very high strength to weight ratio

Tm = 165-175C: Use temperature up to 120 C

Copolymers with 2-5% ethylene—increases clarity and toughness of films

Applications: dishwasher safe plastic ware, carpet yarn, fibers and ropes, webbing, auto parts

Polyethylene (HDPE)

CH3

Essentially linear structure

Few long chain branches, 0.5-3 methyl groups/ 1000 C atoms

Molecular Weights: 50,000-250,000 for molding compounds250,000-1,500,000 for pipe compounds >1,500,000 super abrasion resistance—medical implants MWD = 3-20 density = 0.94-0.96 g/cm3Tm ~ 133-138 C, X’linity ~ 80%

Applications: Bottles, drums, pipe, conduit, sheet, film

Generally opaque

Polyethylene (LLDPE)

• Copolymer of ethylene with -olefin

Density controlled by co-monomer concentration; 1-butene (ethyl), or 1-hexene (butyl), or 1-octene (hexyl) (branch structure)

CH3

CH3 CH3

CH3

CH3

x y

Applications: Shirt bags, high strength films

UNIPOL ProcessN. F. Brockman and J. B. Rogan, Ind. Eng. Chem. Prod. Res. Dev. 24, 278 (1985)

Temp ~ 70-105°C, Pressure ~ 2-3 MPa

CATALYST PREPARATION

Ball mill MgCl2 (support) with TiCl4 to produce maximum surface area and incorporate Ti atoms in MgCl2 crystals

Add Al(Et)3 along with Lewis base like ethyl benzoateAl(Et)3 reduces TiCl4 to form active complexEthyl Benzoate modifies active sites to enhance stereoselectivity

Catalyst activity 50-2000 kg polypropylene/g Ti with isospecificity of > 90%

Catalyst Formation

AlEt3 + TiCl4 → EtTiCl3 + Et2AlCl

Et2AlCl + TiCl4 → EtTiCl3 + EtAlCl2

EtTiCl3 + AlEt3 → Et2TiCl2 + EtAlCl2

EtTiCl3 → TiCl3 + Et. (source of radical products)

Et. + TiCl4 → EtCl + TiCl3

TiCl3 + AlEt3 → EtTiCl2 + Et2AlCl

General Composition of Catalyst SystemGroup I – III Metals

Transition Metals Additives

AlEt3 TiCl4 H2

Et2AlCl

EtAlCl2

TiCl3

MgCl2 Support O2, H2O

i-Bu3Al VCl3, VoCL3,

V(AcAc)3

R-OH

Phenols

Et2Mg

Et2Zn

Titanocene dichloride

Ti(OiBu)4

R3N, R2O, R3P

Aryl esters

Et4Pb (Mo, Cr, Zr, W, Mn, Ni)

HMPA, DMF

R C CH

Adjuvants used to control Stereochemistry

OCH2CH3

O

N

H

SiO

O

O

Ethyl benzoate2,2,6,6-tetramethylpiperidine

Hindered amine (also antioxidant)

Phenyl trimethoxy silane

Nature of Active Sites

Ti

R ClCl

Cl Cl

AlR R

Monometallic site Bimetallic site

Active sites at the surface of a TiClx crystal on catalyst surface.

TiCH2

Cl

H3C

AlR

R

Cl

Cl

Monometallic Mechanism for Propagation

Ti

CH2ClCl

Cl Cl

CH3

Ti

CH2ClCl

Cl Cl

CH3

Ti

CH2ClCl

Cl Cl

CH3Ti

H2CClCl

Cl Cl CH2

CH3

Monomer forms π -complex with vacant d-orbital

Alkyl chain end migrates to π -complex to form new σ-bond to metal

Monometallic Mechanism for Propagation

Ti

CH2ClCl

Cl Cl

H3CTi

H2CClCl

Cl Cl CH2

CH3

Chain must migrate to original site to assure formation of isotactic structure

If no migration occurs, syndiotactic placements will form.

Enantiomorphic Site Control Model for Isospecific Polymerization

Stereocontrol is imposed by initiator active site alone with no influence from the propagating chain end, i.e. no penultimate effect

Demonstrated by: 13C analysis of isotactic structures

not

Stereochemistry can be controlled by catalyst enantiomers

Modes of Termination

TiCH2

R

C H

Al

CH2

TiR

Al

H

TiCH2

R

CH2

Al

1. β-hydride shift

2. Reaction with H2 (Molecular weight control!)

TiCH

R

C H

Al

CH3

TiR

Al

H

TiCH2

R

CH2

AlHH

2

Types Of Monomers Accessible for ZN Processes

H2C CH2CH3 CH2CH3 R

1. -Olefins

2. Dienes, (Butadiene, Isoprene, CH2=C=CH2)

1.2 Disubstituted double bonds do not polymerize

trans-1,4 cis-1,4 iso- and syndio-1,2

Ethylene-Propylene Diene Rubber (EPDM)S. Cesca, Macromolecular Reviews, 10, 1-231 (1975)

CH3

.4-.8

.5-.1 0.05

+ +

VOCl3 Et2AlClV(AcAc)3

Catalyst soluble in hydrocarbons

Continuous catalyst addition required to maintain activity

Rigid control of monomer feed ratio required to assure incorporation of propylene and diene monomers

Development of Single Site Catalysts

Ti

R ClCl

Cl Cl Me

Z-N multisited catalyst, multiple site reactivities depending upon specific electronic and steric environments

Single site catalyst—every site has same chemical environment

MeX

X

+ Al O

CH3

* *n

CH3

Al:Zr = 1000

Me = Tl, Zr, Hf

Linear HD PE

Activity = 107 g/mol Zr

Atactic polypropylene, Mw/Mn = 1.5-2.5

Activity = 106 g/mol Zr

Kaminsky Catalyst SystemW. Kaminsky et.al. Angew. Chem. Eng. Ed. 19, 390,

(1980); Angew. Chem. 97, 507 (1985)

Methylalumoxane: the Key Cocatalyst

Al(CH3)3 + H2Otoluene

0 C Al O

CH3

* *n

n = 10-20

O

Al

AlAl

CH3

OO

O

Al

OAl

OAl

AlCH3

CH3 Proposed structure

MAO

Nature of active catalyst

Cp2MeX

X+ Al O

CH3

* *n

Cp2MeCH3

X+ Al O

CH3

Al

X

Om

Cp2MeCH2

+Al O

CH3

Al

X

Om

X

Transition metal alkylation

Ionization to form active sites

MAO

Noncoordinating Anion, NCA

Homogeneous Z-N Polymerization

Advantages:

High Catalytic Activity

Impressive control of stereochemistry

Well defined catalyst precursors

Design of Polymer microstructures, including chiral polymers

Disadvantages:

Requires large excess of Aluminoxane (counter-ion)

Higher tendency for chain termination: β-H elimination, etc.

Limited control of molecular weight distribution

Evolution of single site catalysts

Date Metallocene Stereo control

Performance

1950’s None Moderate Mw PE

Some comonomer incorporation

Early

1980’s

None High MW PE

Better comonomer incorporation

Me

Me

Synthesis of Syndiotactic PolystyreneN. Ishihara et.al. Macromolecules 21, 3356 (1988); 19, 2462 (1986)

*Al

O*

CH3

n

TiCl

Cl

Ti Cl

ClCl

Ti Cl

Cl

+

44.1%

99.2%

1.0%

syndiotactic polystyrene

m.p. = 265C

Styrene

Evolution of single site catalysts

Date

Late 1980’s

Metallocene Stereo control

Slight

Performance

Very High Mw PE, excellent comonomer incorporation

Late 1980’s

Highly

Syndio-

tactic

Used commercially for PP

Early

1990’s

Highly

Isotactic

Used commercially for PP

N Me

R

Me

RR

Me

Technology S-curves for polyolefin production