1. Coordination Polymerization
Ziegler Natta Processes

2. Stereoregular Polymerization
Cationic Initiation of Vinyl Ethers
Schildknecht et al. Ind. Eng. Chem. 39, 180, (1947)
Isotactic vinyl ether

3. Stereoregular Polymerization
Anionic Polymerization of Methyl Methacrylate,
H. Yuki, K. Hatada, K.Ohta, and Y. Okamoto, J. Macromol. Sci. A9, 983 (1975)
Isotactic
Syndiotactic

4. POLYETHYLENE (LDPE) Molecular Weights: 20,000-100,000; MWD = 3-20
density = g/cm3
Highly branched structure—both long and short chain branches
Tm ~ 105 C, X’linity ~ 40%
15-30 Methyl groups/1000 C atoms
Applications: Packaging Film, wire and cable coating, toys, flexible bottles, housewares, coatings

5. Ziegler’s Discovery
1953 K. Ziegler, E. Holzkamp, H. Breil and H. Martin
Angew. Chemie 67, 426, 541 (1955); 76, 545 (1964).
+ Ni(AcAc) Same result
+ Cr(AcAc) White Ppt. (Not reported by Holzkamp)
+ Zr(AcAc) White Ppt. (Eureka! reported by Breil)

6. Polypropylene (atactic)
Formation of allyl radicals via chain transfer limits achievable molecular weights for all a-olefins

7. Natta’s Discovery Isotactic Syndiotactic
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
Isotactic
Syndiotactic
Ziegler and Natta awarded Nobel Prize in 1963

8. Polypropylene (isotactic)
Density ~ g/cm3—very high strength to weight ratio
Tm = 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

9. Polyethylene (HDPE) Essentially linear structure
Few long chain branches, methyl groups/ 1000 C atoms
Molecular Weights: 50, ,000 for molding compounds
250,000-1,500,000 for pipe compounds
>1,500,000 super abrasion resistance—medical implants
MWD = 3-20
density = g/cm3
Tm ~ C, X’linity ~ 80%
Generally opaque
Applications: Bottles, drums, pipe, conduit, sheet, film

10. Polyethylene (LLDPE) Copolymer of ethylene with a-olefin
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

11. UNIPOL Process
N. F. Brockman and J. B. Rogan, Ind. Eng. Chem. Prod. Res. Dev. 24, 278 (1985)
Temp ~ °C, Pressure ~ 2-3 MPa

12. 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 kg polypropylene/g Ti with isospecificity of > 90%

13. 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

14. General Composition of Catalyst System
Group I – III Metals
Transition Metals
Additives
AlEt3
TiCl4 H2
Et2AlCl
EtAlCl2
a,g, d 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

15. Adjuvants used to control Stereochemistry
Phenyl trimethoxy silane
Ethyl benzoate
2,2,6,6-tetramethylpiperidine
Hindered amine (also antioxidant)

16. Nature of Active Sites Bimetallic site Monometallic site
Active sites at the surface of a TiClx crystal on catalyst surface.

17. Monometallic Mechanism for Propagation
Monomer forms π -complex with vacant d-orbital
Alkyl chain end migrates to π -complex to form new σ-bond to metal

18. Monometallic Mechanism for Propagation
Chain must migrate to original site to assure formation of isotactic structure
If no migration occurs, syndiotactic placements will form.

19. 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

20. Modes of Termination 1. β-hydride shift
2. Reaction with H2 (Molecular weight control!)

21. Types Of Monomers Accessible for ZN Processes
1. -Olefins
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

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

23. Development of Single Site Catalysts
Z-N multisited catalyst, multiple site reactivities depending upon specific electronic and steric environments
Single site catalyst—every site has same chemical environment

24. Kaminsky Catalyst System W. Kaminsky et. al. Angew. Chem. Eng. Ed
Kaminsky Catalyst System W. Kaminsky et.al. Angew. Chem. Eng. Ed. 19, 390, (1980); Angew. Chem. 97, 507 (1985)
Linear HD PE
Al:Zr = 1000
Activity = 107 g/mol Zr
Me = Tl, Zr, Hf
Atactic polypropylene, Mw/Mn =
Activity = 106 g/mol Zr

25. Methylalumoxane: the Key Cocatalyst
MAO
Proposed structure

26. Nature of active catalyst
Transition metal alkylation
MAO
Ionization to form active sites
Noncoordinating Anion, NCA

27. 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

28. Evolution of single site catalysts
Date
Metallocene
Stereo control
Performance
1950’s
None
Moderate Mw PE
Some comonomer incorporation
Early
1980’s
High MW PE
Better comonomer incorporation

29. Synthesis of Syndiotactic Polystyrene N. Ishihara et. al
Synthesis of Syndiotactic Polystyrene N. Ishihara et.al. Macromolecules 21, 3356 (1988); 19, 2462 (1986)
Styrene
syndiotactic polystyrene
m.p. = 265C

30. Evolution of single site catalysts
Date
Late 1980’s
Metallocene
Stereo control
Slight
Performance
Very High Mw PE, excellent comonomer incorporation
Highly
Syndio-
tactic
Used commercially for PP
Early
1990’s
Isotactic

31. Technology S-curves for polyolefin production