22 November Lecture

1
Polymer History

• Polymer generation
• natural
• synthetic fibers
• engineering plastics
• conducting

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2
Requirement for Polymer to Become Electrically
Conducting

• Conjugated polymers with alternating single and
  double bonds or conjugated segments coupled with
  atoms providing p-orbitals for continuous orbital
  overlap

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3
Electrical Properties

• Polymers traditionally been used as insulators
• Conductivity (s) is expressed in units of siemens
  (S) per cm (siemen is a reciprocal ohm)
• s lt 10-8 S/cm insulator s 1/p
  (resistivity)
• 10-7-10-1 S/cm semiconductor
• gt 102 S/cm conductor

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4
Comparison of Electrical Conductivities
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5
Opportunities for Conducting Polymers

• Properties of electrical, electrochemical and
  chemical
• corrosion prevention of metals
• anti-static floor tiles
• rechargeable batteries
• chemical sensors
• photo-voltaics (solar cells)
• light emitting diodes (LED)
• photochromic devices
• lasers

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6
Polyacetylene

• H. Shirakawa
• Ziegler Natta catalysis
• p-doping

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Doping

• Charge injection (transfer) into conjugated
  systems
• chemicalp-type doping (oxidation)
  (p-polymer)n-type doping (reduction)
  (p-polymer)-
• electrochemicalelectrodes supply redox charge to
  the conducting polymer doping level determined
  by voltage

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8
Doping

• photochemical

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9
Doping

• Semiconducting polymer interface e- and holes
  can be injected from metallic contractspolymer
  is oxidized or reduced however, nocounterion

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10
Application Depends upon Property
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11
Example of Conducting Polymers
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Example of Conducting Polymers
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13
Light-Emitting Application of Conjugated Polymers

• Single-layer electroluminescent polymer LED device

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14
Light-Emitting Application of Conjugated Polymers

• Balancing e- and hole injection from electrodes
  in order to balance charge transport
• bilayers(1) electron-transport layer (ETL) with
  a combined hole-transport (HTL) and emission
  layer (2) hole-transport layer and a combined
  electron transport and emission layer
• trilayer(1) HTL, emission layer, ETL

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Light-Emitting Application of Conjugated Polymer

• Going to bilayer and trilayer usually increases
  device efficiency lowers threshold and operating
  voltage because balancing charge injection and
  transport with recombination of the e- and hole
  taking place at the interface between layers and
  not at the interface between the organic material
  and one of the electrodes.

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16
Polymer Structure and Color Emitted

• Controlling band gap between LUMO and HOMO

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Polymerization

• Chain reaction
• free radical
• cationic
• anionic
• group transfer
• Ziegler Natta
• Step reaction
• linear polymers can be synthesized from
  difunctional monomers
• AB AB ABAB
• or
• AA BB AABB

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18
Control of Polymer Structure

• Polymer synthesis
• Suzuki cross coupling
• (2) Heck reaction
• McMurry reaction
• Knoevenagle reaction
• Wittig reagents
• (6) Grignard coupling
• (7) Yamamoto coupling by Ni(O)
• (8) Metathesis (ROMP)
• (9) Other

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19
Heck Chemistry

• Heck reaction

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20
Heck Chemistry

• Example

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21
Coupling by Suzuki Reaction

• Cross coupling of organic boronic acids or esters
  with organic/halides
• Mechanism

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Coupling by Suzuki Reaction

• Example

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Coupling by Suzuki Reaction
carried out in 2-phases - organic solution/Pd
complex/monomer/polymer - water and Na2CO3 to
remove acidic byproducts
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Coupling by Suzuki Reaction
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Coupling by Suzuki Reaction
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McMurry Chemistry

• McMurry reaction
• Mechanism

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McMurry Chemistry

• Example

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Knoevenagle Chemistry

• Knoevenagle reaction
• in general

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Knoevenagle Chemistry

• Example

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30
Wittig

• Wittig reagentsPhosphorus ylids react with
  aldehydes and ketonesto form an alkene product
  through a betaine intermediate which collapsed to
  an oxaphosphetane. Driving force is formation of
  f3PO.

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Wittig

• Variations called Hornes-Wadsworth-Emmons. Use
  of phosphonate ester derivatives

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Wittig

• Examples

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Grignard Coupling

• Diorgano nickel (11) complexes, NiR2Ln undergo
  reductive coupling reactions to give R-R
• Mechanism

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Grignard Coupling

• Example

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Grignard Coupling

• Intermediates

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Polyphenylene

• Problems with making PPP
• poor solubility
• if put groups to help solubility of polymer then
  decreases reactivity of dibromoarene

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Coupling by Zero-Valent Nickel

• Yamamoto reactionDrawback with Grignard reagents
  is that these react with ketone and ester groups.
  Therefore, Grignard coupling cannot be employed
  with certain groups.
• Mechanism

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Coupling by Zero-Valent Nickel

• Example

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Coupling by Zero-Valent Nickel

• Intermediates

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Coupling by Zero-Valent Nickel

• Intermediate Why not?

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Coupling by Zero-Valent Nickel

• Intermediate Why not? (maybe steric)

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42
Coupling by Zero-Valent Nickel
L2 2,2-bipyridine
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43
Metathesis

• ROMP (ring-opening metathesis polymerizationc
  arbon-carbon double bonds of the monomer are
  retained in the polymer

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Metathesis

• Metathesis

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45
Other

• Soluble Polymer Precursor Synthesis

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