SYNTHESES AND CHARACTERISATION OF ELECTRICALLY CONDUCTING POLYMERS

Abstract

Conducting polymers, in particular, polyaniline and polythiophene, have both been well studied for their electroconductive as well as NLO properties. Most functionalisation studies involve incorporation of pendent groups at the arylene rings and little has been done to study the effect of hetero-moieties along polymer backbone. In this project, a series of polymerisations involving di-arylenic monomers based on polythiophene and polyaniline has been undertaken. The first of this series involves the polymerisation of aminobiphenyl to yield PABP, in which a comparison between chemical synthesis and electropolymerisation is performed. Results show that protonation of the amine moiety is insufficient to bring about high conductivity and that back-bone oxidation is required. This can be brought about by electrical or chemical oxidation. Together with poly(bithiophene ), which has been well investigated and documented, PABP acts as a basis of comparison with the second group involving monomers in which an acetylenic group has been introduced between the arylene rings. The latter has been relatively Iittle studied compared to the parents due to unavailability of the monomers commercially. In order to study the latter, a series of diarylene ethynylene monomers are synthesised. Two major subgroups are studies here: ethynylene benzenamine type and bisthienyl ethynylene type of which the parents are poly(aminobiphenyl) and poly(bithiophene) respectively. A study of the effect of polymer derivatisation and stereoregularity is also initiated. A heterogeneous polymer, poly(thienyethynyl)benzenamine has also been analysed. This work has demonstrated that incorporation of acetylenic moiety along the polymer backbone can cause varying characteristic depending on whether the parent is phenylamine-based or thiophene based. In the former group, the stability of the extended conjugation has greatly increased the polymerisation potential of the monomer so much so that during electropolymerisation, degradation occurs before polymerisation can occur. Chemical polymerisation has also failed to produce a long linear chain. This contrasted with the results for the parent polymer, PABP. On the other hand, poly(thieny ethynylene) can be obtained using the conventional chemical polymerisation to yield linear conductive samples, except in the case of P(5,4'-EBT), which has restricted conjugation. The results contradicted with the low conductivity reported in the published literature for this type of polymers. More importantly, it demonstrated the effect of the heteroatom which not only enhances the polymerisability of the monomer (as compared to benzenamine), but also affects the conductivity of the polymer by contribution to the density of the delocalised electrons.