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Coordination Polymerization

Coordination Polymerization. Ziegler Natta Processes. Stereoregular Polymerization. Cationic Initiation of Vinyl Ethers Schildknecht et al. Ind. Eng. Chem. 39 , 180, (1947). Isotactic vinyl ether. Stereoregular Polymerization. Anionic Polymerization of Methyl Methacrylate ,

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Coordination Polymerization

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  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 = 0.91-0.93 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 • 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 ~ 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

  9. Polyethylene (HDPE) 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

  10. Polyethylene (LLDPE) • Copolymer of ethylene witha-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 ~ 70-105°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 50-2000 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

  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. Cesca, Macromolecular Reviews, 10, 1-231 (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 SystemW. 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 = 1.5-2.5 Activity = 106 g/mol Zr

  25. Methylalumoxane: the Key Cocatalyst n = 10-20 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

  29. Synthesis of Syndiotactic PolystyreneN. Ishihara et.al. Macromolecules21, 3356 (1988); 19, 2462 (1986) Styrene syndiotactic polystyrene m.p. = 265C

  30. Evolution of single site catalysts

  31. Technology S-curves for polyolefin production

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