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Keywords

Keywords. Derive from title Multiple word “keywords” e.g. polysilsesquioxane low earth orbit Brain storm synonyms Without focus = too many unrelated hits If you haven’t already, get it to me today. Homework. Name files with your last name, and HWK#

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Keywords

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  1. Keywords • Derive from title • Multiple word “keywords” • e.g. polysilsesquioxane low earth orbit • Brain storm synonyms • Without focus = too many unrelated hits • If you haven’t already, get it to me today.

  2. Homework • Name files with your last name, and HWK# • Within file, your name, HWK title, descriptive information (like the title of you paper topic) -Never make your audience work

  3. Bibliography homework • Due on 27th at 11:59 PM • Based on your keyword search • J. Am. Chem. Soc. format with title e.g. Doe, J., Smith, J. “Proper bibliographies for Professor Loy’s class,” J. Obsc. Academ. B. S. 2012, 1, 234. Recommend endnote or pages or biblio.

  4. Chapter 2 Continued Highly Crosslinked Materials Then Addition Polymerizations

  5. Step Growth Polymers • Polyesters, polyamides, engineering plastics such as polysulfones, polyetherether ketones (PEEK), polyurethanes. • Condensation often occurs. • Polymerization affords high MW late in the game

  6. Step-Growth Non-Condensation Polymerization Polyurethanes [RCO2]2SnBu2 1,4-toluenediisocyanate + 1,3-propanediol

  7. Functionalities > 2: Crosslinking into networks Polyurethanes (thermoset) f = 3

  8. Thermosets • Urethanes • Epoxies • Polyesters (2-stage) • Formaldehyde-aromatic • Melamine-formaldehyde Generally: Start as low viscosity liquids (low Mw) And set or cure to form glassy “vitrified” solids.

  9. Gelation: f > 2 • If f > 2 • No cyclics form then an infinite network is possible (unless it phase separates!!!)

  10. Functionality Higher than Two Phase separation = gels, glasses, or precipitates Due to chemical bonding

  11. Functionality = Two: Linear polymers Physical gels may form due to poor solubility of polymer

  12. Functionality = Three: Cyclization Lowers functionality & delays (or even prevents) gelation Gel point = 1/(f -1) = 1/2 or 50% conversion If cyclics present, gel point is higher.

  13. Addition Polymerizations 1) Catalyzed polymerization free radical cationic anionic coordination 2) Active group on end of polymer 3) MW increases more rapidly 4) Cheap & easier than step growth 5) Enthalpically favorable

  14. Free Radical Polymerizations • Initiators (catalyst): • Thermal: azo compounds, peroxides, • Redox: persulfates • Photochemical: azo, peroxides, amine/ketone mixtures • Monomers

  15. Free radical Mechanism Initiation: Ea = 140 – 160 kJ mol-1 Kd = 8 x 10-5 s-1 t1/2 = 10 h at 64 °C Propagation: kp = 102 - 104 L/mol s Termination: kt = 106 - 108 L/mol s

  16. Free Radical Polymerization Kinetics Rp ∝ [M]; Rp ∝ [I]1/2 MW •MOST POLYMERS FORM IN SECONDS OR LESS • POLYMERIZATIONS TAKE HRS TIME

  17. Living Radical Polymerizations: MW increases linearly with time Narrow Mw distributions Block copolymers • Atom TransfeR Polymerization (ATRP) • Polymerization (RAFT) • TEMPO Lower concentration of propagating species Lower termination rate

  18. Cationic Polymerizations: Vinyl polymerization Ring opening polymerization

  19. Anionic Polymerizations:

  20. Anionic Polymerizations:

  21. Anionic Polymerizations:

  22. Coordination Polymerizations: Transition Metal Mediated Polymerizations -Ziegler Natta polymerizations (Early TM) -ring opening metathesis polymerization (metal Alkylidenes) -Insertion polymerizations (mid to late TM’s)

  23. Ziegler Natta Polymerizations • ZN are heterogeneous; solid catalysts • Catalytic polymerizations • Early TM halide, AlR3 on MgCl2 • Polypropylene and HDPE • Highly productive: 106g polymer/gram catalyst-hour • 10,000 turn overs/second (enzyme like speed)-diffusion limited • Stereochemical control: Karl Ziegler (1898-1973) iso or syndiotactic polymers Giulio Natta (1903-1979)

  24. Ziegler Natta Monomers Not compatible with heteroatoms (O,N,S,etc)

  25. Plastics Polyethylene, high density (HDPE) Polypropylene, isotactic Polystyrene, syndiotactic Polymers Synthesized with Complex Coordination Catalysts Bottles, drums, pipes, sheet, film, etc. Automobile and appliance parts, rope, carpeting Specialty plastics

  26. Ring Opening Metathesis • Strained Rings with C=C bonds • Metal alkylidene catalysts • Ti, Mo, W alkylidenes (Schrock catalysts) • Ruthenium alkylidenes (Grubbs catalysts) • Living polymerizations

  27. Examples of ROMP

  28. Acyclic Diene Metathesis Polymerization Coordination-Condensation polymerization Ethylene gas is produced Not commerciallized

  29. Redox Polymerizations Polypyrrole

  30. Redox Polymerizations Polyaniline When acid doped: conducting polymer

  31. Polymerization Techniques • Bulk-no solvent just monomer + catalysts • Solution Polymerization-in solvent • Suspension-micron-millimeter spheres • Emulsion-ultrasmall spheres

  32. Less Common Polymerization Techniques • Solid state polymerization • Polymerization of crystalline monomers • Diacetylene crystals • Gas Phase polymerization • Parylene polymerizations • Plasma polymerization • Put anything in a plasma

  33. Plasma Polymerization

  34. Characterization of Polymers • 1H & 13C Nuclear Magnetic Resonance spectroscopy (NMR) • Infrared spectroscopy (Fourier Transform IR) • Elemental or combustion analyses • Molecular weight

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