Question

Explain in detail the principles, mechanisms, and chemical structural features of electroconductive polymers.

Answer 1

Electroconductive Polymers can be defined as those organic polymers that are capable of conducting electricity. these are also known as Conductive Polymers and ICP (Intrisically Conducting Polymers).

Features of Electroconductive Polymers:

• They were first discovered in the year 1977 by Alan Heegar, Alan Mcdiarmid and Dr. H. Shirakawa.
• They are organic compounds and show properties similar to the insulating polymers.
• They have better conductivity and are considered advantegous to conductors. Due to their metallic conductance they can be categorised as semi-conductors.
• They are light in weight, and can be easily processed because of their flexibility--- These are some of the mechanical properties.
• Redox Behaviour, Photoactivity and Junction Effects are the other key chemical features.
• They have an adhesive nature.
• They are also known as non-thermoplastics and thus, do not melt upon heating.
• The electrical conductance is upto a limit of 10^-2 ohm^-1 cm^-1.
• Polyacetylene is an example of such classes of polymers.

Categories of Electroconductive Polymers:

• Inherently Conductive Thermoset, eg. polypyrolle, polyaniline, etc.
• Inherently Static-dissipative Thermoplastic, eg. polyurethenes.
• Modified or Compounded

Mechanism of Conduction followed in Electroconductive Polymers:

• Doping is performed, and after Doping, these polymers become conducting and electrically charged.

(Doping can be performed both through oxidants, eg. iodine, transition metals salt, etc. and reducing agents, like sodium naphnamide, also electrochemical methods can also be employed)

• These have p-orbital system.
• Formation of both polarons and bipolarons can be witnessed.
• The process of doping include the formation of charge carriers, named as Solitons, Polarons and Bipolarons.
• This soliton brings about R and L interconversion.
• These electroconductive polymers are synthesized through various methods, like dehyrognation and oxidative coupling reactions.
• Doping may result in increase conductivity but lowers the stability. Thus, small band-gap polymers are structured through the process named as "Band Structure Engineering".
• Band Structure Engineering includes the followinf methods:

1) Substitution or Fusion

2) Ladder Polymerization

3) Copolymerization (Random and Alternating Copolymerizations)

4) Topological Methods (includes Ionization Potential)

5) Donor-Acceptor Polymerization technique

Applications and Uses:

• Can be used as coating agents
• Biosensors
• Welding of plastic materials
• Finds use in Batteries and in display screens, etc.