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 Hardening H2
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 “tacticity” Planar zig-zag conformation
Asymmetric carbons
“tacticity”
Greek: “to put in order”
Planar zig-zag conformation
Relative configurations
Isotactic

8. Stereoisomers
Isotactic
Syndiotactic
Atactic

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

10. Model Systems meso- and racemic 2,4-disubstituted pentane

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?
Isotactic
Syndiotactic
Atactic Tm
(°C)
165
135
N/A
Density
(g/mL)
0.92 – 0.94
0.89 – 0.91
0.85
Solubility
(Hydrocarbons at Room Temp)
none
medium
high
Strength
low

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

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

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

22. Chain Isomerism Regio-isomers Stereo-isomers Geometric isomers
Conformational isomers