Conducting Polymers
22-2-96
CONDUCTING POLYMERS
By Colin Pratt
INTRODUCTION
Until about 30 years ago all carbon based polymers were rigidly regarded as insulators. The idea that plastics could be made to conduct electricity would have been considered to be absurd. Indeed, plastics have been extensively used by the electronics industry because of this very property. They were utilized as inactive packaging and insulating material. This very narrow perspective is rapidly changing as a new class of polymer known as intrinsically conductive polymer or electroactive polymers are being discovered. Although this class is in its infancy, much like the plastic industry was in the 30 's and 50 's, the potential uses of these are quite significant. In 1958, polyacetylene was first synthesised by Natta et al. as a black powder. This was found to be a semi-conductor with a conductivity between 7 x 10-11 to 7 x 10-3 Sm-1, depending upon how the polymer was processed and manipulated. This compound remained a scientific curiosity until 1967, when a postgraduate student of Hideki Shirakawa at the Tokyo Institute of Technology was attempting to synthesise polyacetylene, and a silvery thin film was produced as a result of a mistake. It was found that 1000 times too much of the Ziegler-Natta catalyst, Ti(O-n-But)4 - Et3Al, had been used. When this film was investigated it was found to be semiconducting, with a similar level of conductivity to the best of the conducting black powders. Further investigations, initially aimed to produce thin films of graphite, showed that exposure of this form of polyacetylene to halogens increased its conductivity a billion fold. Undoped, the polymer was silvery, insoluble and intractable, with a conductivity similar to that of semiconductors. When it was weakly oxidised by compounds such as iodine it turned a golden colour and its conductivity increased to about 104 Sm-1.In the 1980 's polyheterocycles were first developed. Polyheterocycles were found to be much
CONDUCTING POLYMERS
By Colin Pratt
INTRODUCTION
Until about 30 years ago all carbon based polymers were rigidly regarded as insulators. The idea that plastics could be made to conduct electricity would have been considered to be absurd. Indeed, plastics have been extensively used by the electronics industry because of this very property. They were utilized as inactive packaging and insulating material. This very narrow perspective is rapidly changing as a new class of polymer known as intrinsically conductive polymer or electroactive polymers are being discovered. Although this class is in its infancy, much like the plastic industry was in the 30 's and 50 's, the potential uses of these are quite significant. In 1958, polyacetylene was first synthesised by Natta et al. as a black powder. This was found to be a semi-conductor with a conductivity between 7 x 10-11 to 7 x 10-3 Sm-1, depending upon how the polymer was processed and manipulated. This compound remained a scientific curiosity until 1967, when a postgraduate student of Hideki Shirakawa at the Tokyo Institute of Technology was attempting to synthesise polyacetylene, and a silvery thin film was produced as a result of a mistake. It was found that 1000 times too much of the Ziegler-Natta catalyst, Ti(O-n-But)4 - Et3Al, had been used. When this film was investigated it was found to be semiconducting, with a similar level of conductivity to the best of the conducting black powders. Further investigations, initially aimed to produce thin films of graphite, showed that exposure of this form of polyacetylene to halogens increased its conductivity a billion fold. Undoped, the polymer was silvery, insoluble and intractable, with a conductivity similar to that of semiconductors. When it was weakly oxidised by compounds such as iodine it turned a golden colour and its conductivity increased to about 104 Sm-1.In the 1980 's polyheterocycles were first developed. Polyheterocycles were found to be much
References: M. F. Rubner, Molecular Electronics, Research Studies Press, 1992, chapter 2 Luis Alcacer, Conducting Polymers, D. Reidel Publishing Company, 1987 Herbert Naarmann, Polymers to the Year 200 and Beyond, John Wiley & Sons, 1993, Chapter 4 Ian M. , Introduction to Synthetic Polymers, Oxford Science Publications, 1994, Chapter 10 W. R. Salaneck D. T. Clark E. J. Samuelsen, Science and Application of Conducting Polymers, IOP Publishing, 1991 Richard B. Kaner and Alan G. MacDiarmid, Scientific America, February 1988, 60 – 65 G. Natta, G. Mazzanti, P. Corradini, Atti. Acad. Naz. Lincei, Cl. Sci. Fis. Mat. Rend., 25, 8, 3, 1958 M. Hatano, S. Kambara, S. Okamoto, J. Polym. Sci., 51, S26, 1961 H. Shirakawa, E.J. Louis, A.G. MacDiarmid, C.K. Chiang, A.J. Heeger, J. Chem. Soc., Chem. Commun., 578, 1977 J. Margolis, Conductive Polymers and Plastics, Chapman and Hall, 2-11, 1989 I.M. Cambell, Introduction to Synthetic Polymers, Oxford Science Publications, 196, 1994 Home