Polyaniline

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Structural formula
Structure of polyaniline
General
Surname Polyaniline
other names
  • PAni
  • ORMECON
CAS number
  • 25233-30-1
  • 5612-44-2 (octamer)
Monomer aniline
Molecular formula of the repeating unit C 6 H 5 N / C 6 H 4 N (oxidation state)
Molar mass of the repeating unit 90–91 g mol −1
Brief description

dark brown solid

properties
Physical state

firmly

density

1.4 g cm −3 (20 ° C)

Electric conductivity

5-500 S / cm

safety instructions
GHS labeling of hazardous substances
no classification available
H and P phrases H: see above
P: see above
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Polyaniline , abbreviation PANI , is a conductive polymer that can be manufactured and purchased commercially without restrictions. It finds v. a. Application in the final coating of printed circuit boards and in corrosion protection. Polyaniline is also known as “intrinsically conductive polymer” (ICP), i.e. self-conductive, because it is conductive in its salt form without any additional additives. Polyaniline is sold under trade names such as ORMECON . These products even have metallic properties, which is why PAni is also referred to as "organic metal". The processing (and application) of PAni is done exclusively through dispersion .

Classification

Polyaniline is a radical - cation salt of a conjugated polymer having oxidatively coupled aniline units and an acid . In addition, the color and properties of the polyaniline differ depending on the oxidation state, three important things to be distinguished:

  • Slightly yellowish or colorless oxidation status: reduced form of the stable “green polymer”, is quickly oxidized again in air; non-conductive.
  • Green oxidation status: The most stable form of the polymer. This form of oxidation is the actually traded and used oxidation state of polyaniline; conductive or even organic metal.
  • Blue oxidation status: also stable form of the polymer, neutral, non-conductive form; can be obtained from the "green" form of PAni by neutralization with bases.

Reaction Mechanism / Production

The polyaniline is oxidative polymerization prepared, it is therefore, in addition to solvents and solubilizing agents, such as sodium dodecyl sulfate , a radical forming oxidizing agent (z. B. used peroxydisulfate ) containing the delocalized electron structure of the aniline "attack" para position and the radical ultimately on the amino group of a Attack on another aniline starts, which also forms a π bond from the nitrogen of the amino group to a carbon atom of another aniline. The radical then migrates to the amino group of the aniline that has just been attacked and the process is repeated. The resulting chain length of the polymer depends on the temperature and the starting concentration of the radical generator, which is used in the polymerization, which lasts about 24 hours. At the end of the polymer the radical is saturated.

In general:

  • The higher the temperature (approx. 220 ° C) and the concentration of the starter substance (radical generator), the shorter the average chain length of the polymer.
  • The lower the temperature (20–100 ° C) and the concentration of the starter substance, the longer the average chain length of the polymer.

Dependence on morphology, structure and conductivity

Despite nearly 30 years of research, it has not yet been possible to clarify which structure of polyaniline (and in general: which structural principles in conductive polymers) are advantageous or decisive for high conductivity. It is generally assumed that high crystallinity and linear arrangement of chains (fibrils) enable high conductivity, but at least for the technically / commercially relevant conductive polymers such as PEDOT and polyaniline, this could not be confirmed, they are largely amorphous and show differences in conductivity by one factor 1000 and more no differences in crystallinity.

A recent paper suggests a novel interpretation of the experimental data. According to this, PAni mainly consists of relatively short chain segments that are helical; Using advanced dispersion techniques, these helix elements are arranged to form longer and correlated helices.

literature

  • Terje A. Skotheim, Ronald L. Elsenbaumer, John R. Reynolds (Eds.): Handbook of Conducting Polymers . 2nd Edition. Marcel Dekker, New York 1997, ISBN 0-8247-0050-3 .
  • Li-Ming Huanga, Cheng-Hou Chena and Ten-Chin Wen: Development and characterization of flexible electrochromic devices based on polyaniline and poly (3,4-ethylenedioxythiophene) -poly (styrene sulfonic acid) . National Cheng Kung University Taiwan, 2006, doi : 10.1016 / j.electacta.2006.03.031 .
  • B. Wessling: New Insight into Organic Metal Polyaniline Morphology and Structure. In: Polymers 2, No. 4, 2010, pp. 786-798, doi: 10.3390 / polym2040786 .
  • J. Stejskal, RG Gilbert: Polyaniline. Preparation of conducting polymer (IUPAC technical report) . In: Pure and Applied Chemistry . tape 74 , no. 5 , 2002, p. 857-868 , doi : 10.1351 / pac200274050857 .

Web links

Individual evidence

  1. ↑ a b c data sheet polyaniline at AlfaAesar, accessed on April 14, 2010 ( PDF )(JavaScript required) .
  2. ↑ Seyed Hossein Hosseini, S. Jamal Gohari: Electrical field influence on molecular mass and electrical conductivity of polyaniline . In: Polymer Science Series B . tape 55 , no. 7-8 , July 2013, pp. 467-471 , doi : 10.1134 / S1560090413070087 .
  3. ^ J. Stejskal, RG Gilbert: Polyaniline. Preparation of conducting polymer (IUPAC Technical Report) . In: Pure and Applied Chemistry . tape 74 , no. 5 , 2002, p. 857-867 , doi : 10.1351 / pac200274050857 .
  4. ↑ Dispersions: Patent EP1706431A1 : Dispersions of intrinsically conductive polymers and processes for their production. ‌
  5. ↑ This substance has either not yet been classified with regard to its hazardousness or a reliable and citable source has not yet been found.
  6. ^ WS Huang, M. Angelopoulos, JR White, JM Park: Metallization of Printed Circuit Boards Using Conducting Polyaniline . In: Molecular Crystals and Liquid Crystals Incorporating Nonlinear Optics . tape 189 , no. 1 , 1990, p. 227-235 , doi : 10.1080 / 00268949008037235 .
  7. ↑ B. Wessling: Corrosion prevention with an organic metal (polyaniline): Surface ennobling, passivation, corrosion test results . In: Materials and Corrosion / Werkstoffe und Korrosion . tape 47 , no. 8 , 1996, pp. 439-445 , doi : 10.1002 / maco.19960470804 .
  8. ^ B. Wessling: New Insight into Organic Metal Polyaniline Morphology and Structure. In: Polymers 2, No. 4, 2010, pp. 786-798, doi: 10.3390 / polym2040786 .