Substantially Conductive Polymers Part 03

SYNTHESIS

Possible Polymerization Mechanism of Acetylene (via the metal-carbene intermediate) 3 Insoluble Infusible Intractable metallocycle metal-carbene

Solubility Improvement of Polyacetylenes (via incorporation of substituents) 4

Coplanarity is the key for gaining high conductivity Substituent Effects: Solubility Conductivity 5

6 A Molecular Orbital Description of Stability Bonding MO: constructive (in-phase) overlap Antibonding MO: destructive (out-of-phase) overlap

7 Consider the  molecular orbitals of 1,4-pentadiene: This compound has 4  e, which forming 2  bonds that are completely separated from one another 4 x 2p 2 x  * 2 x 

8 The Molecular Orbitals of 1,3-Butadiene resonance contributors resonance hybrid HOMO LUMO HOMO = the highest occupied MO LUMO = the lowest unoccupied MO 4 x 2p

9 The Molecular Orbitals of 1,3,5-Hexatriene

10 Summary of Energy Diagram h h h

Conjugation / Wavelength / Molar Absorptivity 11

Metal Semiconductor/ Insulator 12 Bands and Bandgaps Element Solids C : insulator (5.5 eV) Si : semiconductive (1.1 eV) Ge : semiconductive (0.7 eV) Sn : metal (0.1 eV) Pb : metal

13 increased attraction (nucleus  e cloud) Bond dissociation energy (bond strength) : energy required to break a bond or energy released to form a bond increased repulsion (nucleus  nucleus) Energy diagram for a H-H bond formation

14 Bonding in Hydrogen Halides

Typical Charge Carriers (via doping) 15

Energy diagrams of charge carriers 16 No. of charge carrier absorption bands: Soliton: 1 Polaron: 3 Bipolaron: 2 π band π* band

Alternative Methods for Making Polyacetylenes 17 Dehydrochlorination

Durham Route (via a processable precursor) 18

19 The Diels–Alder Reaction (1,4-addition reaction; concerted reaction) ppt a pericyclic reaction; a [4+2] cycloaddition reaction 3   2σ+ 1 

20 unstable at RT For the 2nd ring: 24 kcal/mol

Syntheses of Poly(p-phenylene) (PPP) 21 Had very low molecular weights or irregular structures Reductive polymerization (step-reaction)

22

23 Oxidative polymerization (step-reaction) 23

24 Catalyzed Chain polymerization

25 Lower the aromatization temperature via the decarboxylation

26 Free Radical Chain Reaction

Radical Chain Polymerization Mechanism 27

Radical Initiators 28

Chain Transfer 29

Syntheses of Polyphenylene Vinylene (PPV) 30