polymerization synthesis of polyaniline occurred directly on the surface of the indium-tin-

oxide glass. The chemical polymerization method of synthesis was also employed by Cao

et al. [2] to synthesize polyaniline. This study involved the polymerization of aniline, in

which different oxidizing agents and protonic acid were used to synthesize polyaniline. The

plasma polymerization method was used by Cruz et al. [3] to synthesize polyaniline film.

This involved the use of RF glow discharges that has restrictive coupling between the

stainless electrodes to fabricate polyaniline film. The report stated that polyaniline was

formed at a frequency and pressure range of 13.5 MHz and (2–8) × 10⁻² Torr, respectively.

Interfacial polymerization, a method in which polymerization occurs at the boundary be­

tween the two immiscible phases of the liquid used, was employed by Zang et al. [4] to

synthesize polyaniline using aniline in toluene as the upper organic phase and acidic

ammonium peroxidisulphate as the lower aqueous phase.

19.3.2 Polyacetylene (PA)

Polyacetylene is a type of conducting polymer which consists of a long molecular chain of

repeating C2H2 patterns and shows alternating patterns of single and double bonds

(Figure 19.3c). Polyacetylene is referred to as a conjugate molecule due to the alternating

nature of the single and double bonds in its structure. Two isomeric forms of polyacetylene

(trans – polyacetylene and cis – polyacetylene) are available. The conductivity of poly­

acetylene is enhanced greatly when doped with dopants such as iodine. Despite the high

electrical conductivity of this conducting polymer, polyacetylene is unstable and en­

counters processing challenges in the presence of humidity and other gases. But among the

two isomeric forms of polyacetylene, the trans-isomer shows more thermodynamic stability

at room temperature than the cis-isomer. The stability of polyacetylene is greatly improved

when it is in the form of nanoparticles. Nanoparticles of polyacetylene are fabricated when

acetylene is polymerized in a solution saturated with certain polymers [5].

The synthesis of polyacetylene has seen the application of various methods such as

catalytic polymerization, non-catalytic polymerization, and precursor-assisted synthesis.

The catalytic-polymerization method involves the use of a catalyst such as Ziegler–Natta

catalyst or Luttinger catalyst in the synthesis of polyacetylene. Shirakawa [6] used a

Ziegler–Natta catalyst solution in the interfacial polymerization method to synthesize

polyacetylene from acetylene monomers. Non-catalytic synthesis of polyacetylene en­

compasses approaches in which catalysts are not used. One such approach is the elec­

trochemical polymerization method. This method was employed by Ma et al. [7] to

synthesize poly(o-dihydroxybenzene), a polyacetylene analog. The process involved di­

rect anodic oxidation of o-dihydroxybenzene in boron trifluoride diethyl etherate.

19.3.3 Poly(3,4-Ethylene Dioxythiophene) (PEDOT)

Poly(3,4-ethylene dioxythiophene) is a derivative of polythiophene with a shorter side

chain (Figure 19.3d). To improve the stability of polythiophene, the monomer, thiophene

is substituted with alkoxyl groups (such as ether). Polymerization of the alkoxyl groups

substituted thiophene results in the formation of poly(3,4 ethylene dioxythiophene). Poly

(3,4-ethylene dioxythiophene) is more stable than polythiophene. The improved stability

of poly(3,4-ethylene dioxythiophene) resulting from the inclusion of alkoxyl group in the

thiophene monomer, helps to reduce the oxidizing potential. Owing to the stability and

high conductivity of poly(3,4-ethylene dioxythiophene), poly(3,4-ethylene dioxythio­

phene) is applied in supercapacitors and bioelectronics.

Conducting Polymer Composites

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