Coordination Polymerization Ziegler Natta Processes
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