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Reading (Odian Book): Chapter 8-1, 8-2

Reading (Odian Book): Chapter 8-1, 8-2. Polymer Parameters. Chemical structure Chemical composition and distribution Sequence length and distribution Molecular weight and distribution Chain isomerism Morphology Topology Additives Cost. Chain Isomerism. Regio-isomers Geometric isomers

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Reading (Odian Book): Chapter 8-1, 8-2

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  1. Reading (Odian Book): Chapter 8-1, 8-2

  2. Polymer Parameters • Chemical structure • Chemical composition and distribution • Sequence length and distribution • Molecular weight and distribution • Chain isomerism • Morphology • Topology • Additives • Cost

  3. Chain Isomerism • Regio-isomers • Geometric isomers • Stereo-isomers • Conformational isomers

  4. Geometric Isomers • 1,3-butadiene • cis-1,4-polybutadiene • Tg = - 90 °C • Tm = N/A (amorphous) • trans-1,4-polybutadiene • Tg = - 63 °C • Tm = 100 °C • 1,2-atactic-polybutadiene • Tg = 0 °C

  5. “Cis” vs. “Trans” Fats… • Animal fats and vegetable oils • Vegetable oils polyunsaturated (several double bonds) • Solid fats saturated(no double bonds) • Hardening • Convert liquid oils to solid fats…hydrogenation H2 Fat Pt

  6. Chain Isomerism • Regio-isomers • Geometric isomers • Stereo-isomers • Conformational isomers

  7. Stereoisomers Asymmetric carbons • “tacticity” • Greek: “to put in order” • Planar zig-zag conformation • Relative configurations • Isotactic

  8. Stereoisomers • Isotactic • Syndiotactic • Atactic

  9. Model Systemsmeso- and racemic 2,4-disubstituted pentane meso rac

  10. Model Systemsmeso- and racemic 2,4-disubstituted pentane a meso b a rac a

  11. “Dyad” Analysis of Polymer Chains Meso dyad (m) a b Rac dyad (r) a a

  12. “Dyad” Analysis of Polymer Chains Isotactic (mm) Syndiotactic (rr) Atactic or heterotactic (rm)

  13. Why does stereochemistry matter? Atactic polystyrene Tg = 105 °C Tm = N/A Syndiotactic polystyrene Tg = 105 °C Tm = 270 °C

  14. Why does stereochemistry matter?

  15. Why does stereochemistry matter?

  16. Stereochemistry and Synthesis 60 MHz 1H NMR spectrum ofpoly(methyl methacrylate)made using different initiators(A) Free Radical(B) Anionic

  17. “Dyad” Analysis of Polymer Chains Free radical Anionic Meso dyad (m) a b Rac dyad (r) a Methylene centered around 2.2 ppm a Free radical polymer: predominantly syndiotactic Anionic polymer: predominantly isotactic

  18. “Dyad” Analysis of Polymer Chains a b m Methyl Perspective rr Methylene Perspective Need two monomer units to “look”or to “use” methylene protons forcharacterizing stereochemistry… Need three monomer units to “look”or to “use” α-methyl group forcharacterizing stereochemistry…

  19. Chain Isomerism • Regio-isomers • Stereo-isomers • Geometric isomers • Conformational isomers

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