1. Anatomy of Addition Polymerizations Initiation –Generation of active initiator –Reaction with monomer to form growing chains Propagation –Chain extension by incremental monomer addition Termination –Conversion of active growing chains to inert polymer Chain Transfer –Transfer of active growing site by terminating one chain and reinitiating a new chain.

2. Polymerizability of Vinyl Monomers Active Centers must be stable enough to persist though multiple monomer additions Typical vinyl monomers

3. Polymerizability of Vinyl Monomers MonomersRadicalCationicAnionicComplex Metal Ethylene +-++ Propylene -+/--+ 1,1-Dialkyl olefins -+-- 1,2-Dialkyl olefins -+-+ 1,3-Dienes ++++ Styrenes ++++

4. Polymerizability of Vinyl Monomers MonomersRadicalCationicAnionicComplex Metal VCl +--+/- Vinyl esters +--- Acylates/ methacrylat es +-+- Acrylonitrile s/ Acrylamides +-+- Vinyl ethers -+-- Substituted Styrenes ++/-

5. Types of Vinyl Polymerization MethodAdvantagesDisadvantages Bulk (Neat)Simple equipment Rapid reaction Pure polymer isolated Heat buildup Gel effect Branched or crosslinked product SolutionGood mixing Ready for application Lower mol. Wt. Low R poly Solvent Recovery Suspension (Pearl) Low viscosity Direct bead formation Removal of additives EmulsionHigh R poly Low Temperatures High Mol. Wt. High surface area latex Removal of additives Coagulation needed Latex stability Inverse EmulsionWater in oil latex formed Inversion promotes dissolution in water

6. Commodity Vinyl Polymers Polystyrene (1920) PS Styrofoam, clear plastic cups envelop windows, toys Poly(vinyl chloride) (1927) PVC garden hose, pipe, car trim, seat covers, records, floor tiles

7. Semi-Commodity Polymers Poly(methyl methacrylate) (1931) PMMA plexiglas, embedding resin, resist for X-ray applications Polytetrafluoroethylene. (1943) teflon, non stick cookware, no grease bearings, pipe-seal tape

8. Suspension Polymerization Equivalent to a "mini-bulk" polymerization Advantages Aqueous (hydrocarbon) media provides good heat transfer Good particle size control through agitation and dispersion agents Control of porosity with proper additives and process conditions Product easy to recover and transfer Disadvantages Suspending Agents contaminate product Removal of residual monomer necessary

9. Suspension (Pearl) Polymerization Process TypeAqueous PhaseMonomers UsedProduct BEAD Polymer Soluble in Monomer  1% Sol. Polymer Suspending Agents Cu++ Inhibitors Styrene Methyl Methacrylate Vinyl Acetate Clear Beads POWDER Polmer Insoluble in Monomer Suspending Agents Electrolytes Vinyl Chloride Acrylonitrile Fluoroethylene Opaque Beads or Powders INVERSE Hydrocarbon Media Monomer Initiator Acrylamide Acrylic Acids Beads  Emulsions

10. Suspension Polymerization of Styrene Temp Polymerization Time. Hours Aqueous Phase: 16.6 Kg of H2O 0.24 kg Ca3PO4 0.14 kg Na+ Naphthalene sulfonate 0.077 kg. 15% Sodium Polyacrylate Monomer Phase 16.6 Kg. Styrene (0.5 kg Methacrylic Acid) 0.012 kg AIBN 0.006 kg Benzoyl Peroxide 0.015 kg tert-Butyl Perbenzoate

11. EMULSION POLYMERIZATION Advantages: High rate of polymerization ~ kp[M] N part /2 High molecular weights, ( )   of particles/  R. sec-1 = N kp [M] / Ri Few side reactions High Conversion achieved Efficient heat transfer Low viscosity medium Polymer never in solution Low tendancy to agglomerate Emulsified polymer may be stabilized and used directly Disadvantages: Polymer surface contaminated  by surface active agents Coagulation introduces salts; Poor electrical properties

12. Components of Emulsion Polymerization R.R. Water soluble initiator

13. POLYMERS PRODUCED USING EMULSION PROCESSES PolymerApplications Styrene-Butadiene Rubber (SBR) Tires, Belting, Flooring, Molded goods, Shoe soles, Electrical insulation Butadiene-Acrylonitrile (nitrile rubber) Fuel tanks, Gasoline hoses, Adhesives, Impregnated paper, leather and textiles Acrylonitrile-Butadiene- Styrene (ABS) Engineering plastics, household appliances, Automobile parts, Luggage Polyacrylates Water based latex paints

14. Ziegler-Natta (Metal-Coordinated) Polymerization Stereochemical Control Polydisperse products Statistical Compositions and Sequences Limited set of useful monomers, i.e. olefins SINGLE SITE CATALYSTS

15. Polyolefins Polypropylene (1954) PP dishwasher safe plastic ware, carpet yarn, fibers and ropes, webbing, auto parts

16. Tacticity Isotactic All asymmetric carbons have same configuration Methylene hydrogens are meso Polymer forms helix to minimize substituent interaction Syndiotactic Asymmetric carbons have alternate configuration Methylene hydrogens are racemic Polymer stays in planar zig-zag conformation Heterotactic (Atactic) Asymmetric carbons have statistical variation of configuration

17. 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)

18. 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

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

20. Polypropylene (isotactic) Density ~ 0.9-0.91 g/cm 3— 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

21. 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% Applications: Bottles, drums, pipe, conduit, sheet, film Generally opaque

22. 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) Applications: Shirt bags, high strength films

23. CATALYST PREPARATION Ball mill MgCl 2 (support) with TiCl 4 to produce maximum surface area and incorporate Ti atoms in MgCl 2 crystals Add Al(Et) 3 along with Lewis base like ethyl benzoate Al(Et) 3 reduces TiCl 4 to form active complex Ethyl Benzoate modifies active sites to enhance stereoselectivity Catalyst activity 50-2000 kg polypropylene/g Ti with isospecificity of > 90%

24. Catalyst Formation AlEt 3 + TiCl 4 → EtTiCl 3 + Et 2 AlCl Et 2 AlCl + TiCl 4 → EtTiCl 3 + EtAlCl 2 EtTiCl 3 + AlEt 3 → Et 2 TiCl 2 + EtAlCl 2 EtTiCl 3 → TiCl 3 + Et. (source of radical products) Et. + TiCl 4 → EtCl + TiCl 3 TiCl 3 + AlEt 3 → EtTiCl 2 + Et 2 AlCl

25. 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

26. General Composition of Catalyst System Group I – III Metals Transition MetalsAdditives AlEt 3 TiCl 4 H2H2 Et 2 AlCl EtAlCl 2  TiCl 3 MgCl 2 Support O 2, H 2 O i-Bu 3 AlVCl 3, VoCL 3, V(AcAc) 3 R-OH Phenols Et 2 Mg Et 2 Zn Titanocene dichloride Ti(OiBu) 4 R 3 N, R 2 O, R 3 P Aryl esters Et 4 Pb(Mo, Cr, Zr, W, Mn, Ni) HMPA, DMF

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

28. Nature of Active Sites Monometallic site Bimetallic site Active sites at the surface of a TiCl x crystal on catalyst surface.

29. 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

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

31. 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

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

33. Types Of Monomers Accessible for ZN Processes 1.  -Olefins 2. Dienes, (Butadiene, Isoprene, CH 2 =C=CH 2 ) 1.2 Disubstituted double bonds do not polymerize trans-1,4cis-1,4 iso- and syndio-1,2

34. 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

35. 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

36. Al:Zr = 1000 Me = Tl, Zr, Hf Linear HD PE Activity = 10 7 g/mol Zr Atactic polypropylene, Mw/Mn = 1.5-2.5 Activity = 10 6 g/mol Zr Kaminsky Catalyst System W. Kaminsky et.al. Angew. Chem. Eng. Ed. 19, 390, (1980); Angew. Chem. 97, 507 (1985)

37. Methylalumoxane: the Key Cocatalyst n = 10-20 Proposed structure MAO

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

39. 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

40. Evolution of single site catalysts DateMetalloceneStereo control Performance 1950’sNoneModerate Mw PE Some comonomer incorporation Early 1980’s NoneHigh MW PE Better comonomer incorporation

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

42. Evolution of single site catalysts Date Late 1980’s MetalloceneStereo 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

43. Technology S-curves for polyolefin production