ELSEVIER Synthetic Metals 66 (1994) 3341 SYliilTIHI[TIIC m|TRLS FT-IR studies on thermal degradation of electrically polymers F. Mohammad 1, P.D. Calvert, N.C. Billingham School of Chemistry and Molecular Sciences, University of Sussex, Brighton BN1 9QU, UK Received 26 October 1993; in revised form 1 March 1994; accepted 7 March 1994 conducting Abstract The degradation behaviour of electrochemically prepared polythiophene has been studied by the FT-IR spectroscopic technique. Studies show that it is more stable than polyacetylene but still undergoes degradation reactions which involve two steps, namely, loss of dopant and then degradation of polymer backbone. The general features of degradation mechanisms are discussed. Keywords." Degradation; Spectroscopy 1. Introduction 1.1. General background Polymers undergo chemical reactions just like any typical low molecular weight compound, provided the reactants are made available at the reaction site. The process of deterioration of the useful polymer properties involving chemical reactions is defined as 'degradation'. There are many external causes of degradation of polymeric materials such as heat, light, mechanical stress, oxygen, ozone, moisture, atmospheric pollutants, etc., along with the factors effective at the time of processing. Also, the presence of reactive sites in the polymers, e.g., superoxides, defects, chemically reactive groups, etc., may degrade the polymer properties with or without the combination of external factors. The degradation behaviour of traditional polymers has been studied very widely and has been extensively reviewed [1--4]. Unfortunately, conducting polymers were known to exist only in the form of intractable and non- processible black powders with very little knowledge of their molecular, structural and physical properties and little reason for study of their degradation. Recently, the emergence of direct and precursor routes to XPresent address: Department of Applied Chemistry, Z.H. College of Engineering and Technology, Aligarh Muslim University, Aligarh 202002, India. polyacetylene (PA) films [5,6] and electrochemical polymerization of heterocyclics into polymer films, such as polythiophene (PTh) [7,8] and polypyrrole (PPy) [9-11], has triggered the investigation of these materials due to somewhat easier fabrication of experimental samples. The knowledge and broader understanding of the environmental stability and degradation behaviour are pre-qualifications for their use in many practical ap- plications. This has led us to try to develop some chemical understanding of their long-term stability and degradation behaviour under different atmospheric and chemical conditions. The impact of degradation on chemical structure and electrical conductivity of doped and compensated PTh has been studied. PPy has also been studied for comparison. 1.2. Intrinsic degradation At their best, conducting polymers are long chain molecules with a very high degree of conjugation and few defects. For a perfect chain in a perfect lattice this implies an electronic structure, in which the ~-- electrons occupy a filled valence band and there is an empty conduction band, with no available sites between the two. Such a structure has two properties of interest, the bandgap (i.e., the energy difference between the highest occupied and lowest unoccupied molecular or- 0379-6779/94/$07.00 © 1994 Elsevier Science S.A. All rights reserved SSDI 0379-6779(94)02134-K