Transcript Coordination Polymerization - Louisiana State University

Coordination Polymerization
Ziegler Natta Processes
Stereoregular Polymerization
Cationic Initiation of Vinyl Ethers
Schildknecht et al. Ind. Eng. Chem. 39, 180, (1947)
O
CH2
H3C
CH3
BF3.Et2O
OR
OR
OR
Propane
- 80-60 C
Isotactic vinyl ether
OR
Stereoregular Polymerization
Anionic Polymerization of Methyl Methacrylate,
H. Yuki, K. Hatada, K.Ohta, and Y. Okamoto, J.
Macromol. Sci. A9, 983 (1975)
CH3
O
O
BuLi or
MgBr
H3C OR
Toluene
-78-0 C
OR
OR
OR
Isotactic
H3C OR OR
OR
BuLi
THF -78 C
Syndiotactic
OR
POLYETHYLENE (LDPE)
R
H2C
CH2
20-40,000 psi
150-325° C
H2C CH2
x
Molecular Weights: 20,000-100,000; MWD = 3-20
density = 0.91-0.93 g/cm3
H3C
Highly branched
structure—both long and
short chain branches
Tm ~ 105 C, X’linity ~ 40%
H3C
CH3
H3C
H3C
C
H2
H3C
15-30 Methyl groups/1000 C atoms
Applications: Packaging Film, wire and cable coating, toys,
flexible bottles, housewares, coatings
CH3
H3C
CH3
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
CH3CH2CH=CH2 + Ni + AlCl(Et)2
100 atm
110 C
+ Ni(AcAc)
+ Cr(AcAc)
+ Zr(AcAc)
Same result
White Ppt. (Not reported by Holzkamp)
White Ppt. (Eureka! reported by Breil)
Al(Et)3 + TiCl4
CH2CH2
1 atm
"linear"
20-70 C Mw = 10,000 - 2,000,000
Polypropylene (atactic)
CH3
CH3
R
*
CH2
n
Low molecular weight oils
Formation of allyl radicals via chain transfer limits achievable
molecular weights for all a-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
CH3
CH3
CH3
CH3
Al(Et)2Cl
Isotactic
CH3
VCl4 - 78 C
Al(iBu)2Cl
O
in
CH3 CH3
CH3
CH3
CH3
Syndiotactic
Ziegler and Natta awarded Nobel Prize in 1963
Polypropylene (isotactic)
CH3
TiCl3
CH3
CH3
CH3
Al(Et)2Cl
Density ~ 0.9-0.91 g/cm3—very high strength to weight ratio
Tm = 165-175C: 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
CH3
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 compounds
250,000-1,500,000 for pipe compounds
>1,500,000 super abrasion resistance—medical implants
MWD = 3-20
density = 0.94-0.96 g/cm3
Tm ~ 133-138 C, X’linity ~ 80%
Generally opaque
Applications: Bottles, drums, pipe, conduit, sheet, film
Polyethylene (LLDPE)
• Copolymer of ethylene with a-olefin
CH3
CH3
CH3
CH3
CH3
x
y
Density controlled by co-monomer concentration; 1-butene (ethyl), or
1-hexene (butyl), or 1-octene (hexyl) (branch structure)
Applications: Shirt bags, high strength films
UNIPOL Process
N. 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 benzoate
Al(Et)3 reduces TiCl4 to form active complex
Ethyl 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 System
Group I –
III Metals
AlEt3
Et2AlCl
EtAlCl2
i-Bu3Al
Et2Mg
Et2Zn
Et4Pb
Transition Metals
Additives
TiCl4
a,g, d TiCl3
MgCl2 Support
VCl3, VoCL3,
V(AcAc)3
Titanocene dichloride
Ti(OiBu)4
H2
O2, H2O
(Mo, Cr, Zr, W, Mn,
Ni)
HMPA, DMF
R C CH
R-OH
Phenols
R3N, R2O, R3P
Aryl esters
Adjuvants used to control Stereochemistry
O
O
Si
CH2CH3
O
O
O
N
H
Ethyl benzoate
2,2,6,6-tetramethylpiperidine
Hindered amine (also
antioxidant)
Phenyl
trimethoxy
silane
Nature of Active Sites
R
R
Al
R Cl
Cl Ti
Cl Cl
Monometallic site
H3C
d
CH2
Cl d
Ti
Cl
Cl
Al
R
R
Bimetallic site
Active sites at the surface of a TiClx crystal on catalyst
surface.
Monometallic Mechanism for Propagation
Monomer forms π -complex with vacant d-orbital
CH2
Cl Ti Cl
Cl Cl
CH3
CH2
Cl Ti Cl
Cl Cl
CH3
Alkyl chain end migrates to π -complex to
form new σ-bond to metal
H2C
CH3
Cl Ti Cl
Cl Cl
CH2
CH2
Cl Ti Cl
Cl Cl
CH3
Monometallic Mechanism for Propagation
Chain must migrate to original site to assure
formation of isotactic structure
H2C
CH3
Cl Ti Cl
Cl Cl
CH2
H3C
CH2
Cl Ti Cl
Cl Cl
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
1. β-hydride shift
C H
CH2
Ti
CH2
CH2 H
Al
R
Ti
Al
CH2
Ti
R
Al
R
2. Reaction with H2 (Molecular weight control!)
C H
H H
CH2
Al
Ti
R
CH2
CH3 H
Ti
Al
R
CH2
Ti
R
Al
Types Of Monomers Accessible for ZN Processes
1. a-Olefins
H2C CH2
CH2CH3
CH3
R
2. Dienes, (Butadiene, Isoprene, CH2=C=CH2)
trans-1,4
cis-1,4
iso- and syndio-1,2
1.2 Disubstituted double bonds do not polymerize
Ethylene-Propylene Diene Rubber (EPDM)
S. Cesca, Macromolecular Reviews, 10, 1-231 (1975)
+
+
CH3
Catalyst
soluble in
hydrocarbons
VOCl3
Et AlCl
V(AcAc)3 2
.4-.8
.5-.1
0.05
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
R Cl
Cl Ti
Cl Cl
Z-N multisited catalyst, multiple
site reactivities depending upon
specific electronic and steric
environments
Me
Single site catalyst—
every site has same
chemical environment
Kaminsky Catalyst System
W. Kaminsky et.al. Angew. Chem. Eng. Ed. 19, 390,
(1980); Angew. Chem. 97, 507 (1985)
Me
X +
X
CH3
*
Al O
*
n
Al:Zr = 1000
Linear HD PE
Activity = 107 g/mol Zr
Me = Tl, Zr, Hf
CH3
Atactic polypropylene, Mw/Mn = 1.5-2.5
Activity = 106 g/mol Zr
Methylalumoxane: the Key Cocatalyst
CH3
toluene
Al(CH3)3 + H2O
0C
Al
O
O
O
O
Al
Al
O
O
Al
Al
Al
Al O
*
n
n = 10-20
CH3
Al
*
CH3
CH3
MAO
Proposed structure
Nature of active catalyst
CH3
X
Cp2Me
+
*
X
Al O
*
n
MAO
Cp2Me
CH3
CH3
+
Al O
X
CH3
Cp2Me
CH2
+
Transition metal
alkylation
X
Al
m
O
X X
Al O Al O
m
Ionization to
form active sites
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
1950’s
Stereo
control
Performance
None
Moderate Mw PE
Some comonomer
incorporation
Me
Early
1980’s
None
Me
High MW PE
Better comonomer
incorporation
Synthesis of Syndiotactic Polystyrene
N. Ishihara et.al. Macromolecules 21, 3356 (1988); 19, 2462 (1986)
Ti
*
Al
O
CH3
+
n*
Cl
Styrene
Cl
44.1%
Ti Cl
Cl
Cl
Ti
99.2%
syndiotactic polystyrene
Cl
Cl
1.0%
m.p. = 265C
Evolution of single site catalysts
Date
Metallocene
Late
1980’s
N
Stereo
control
Slight
Performance
Very High Mw PE,
excellent comonomer
incorporation
Highly
Syndiotactic
Used commercially
for PP
Me
R
Late
1980’s
R
R
Me
Early
1990’s
Highly
Used commercially
Isotactic for PP
Me
Technology S-curves for polyolefin
production