Structure-property relationships in polyanilines

Anjan Ray, University of Pennsylvania

Abstract

The work presented in this dissertation was undertaken with the following objectives in view: (1) synthesis and characterization of alkyl ring-substituted polyanilines for the purpose of ascertaining the effect of steric and electronic properties of the substituents on the electrical, electronic, magnetic and spectroscopic properties of polyaniline; (2) evaluation of nitrogen-15 NMR spectroscopy as a probe for determination of the chemical structure and oxidation state of polyanilines; (3) determination of the distribution of protons between semiquinone and protonated amine sites in the salt forms of polyaniline, formed by protonation ("doping") of the corresponding base forms by an aqueous acid; (4) rationalization of the enhancement of conductivity of "doped" polyaniline salts (in their half-oxidized "emeraldine" oxidation state) by traces of water vapor. Significant conclusions are: (1) Seven variables have been shown experimentally to be of major importance in determining the electrical, electronic, chemical and mechanical properties and the environmental stability of polyanilines, viz., oxidation state, protonation level, extent of hydration, ring-substitution, N-substitution, counterion and molecular weight; (2) nitrogen-15 NMR studies have shown that the "emeraldine" oxidation state of polyaniline, in its base form, exhibits small but significant clustering of oxidized and reduced repeat units; (3) cyclic voltammetry and electronic spectral studies indicate that the steric effect of alkyl substituents on the ($-$C$\sb6$H$\sb4-$) rings dominates over their electronic effect, leading to a progressive decrease in the conductivity of the doped polymers with increasing steric bulk of the alkyl substituent; (4) a semi-empirical model, developed for describing the protonation behavior of polyaniline in terms of its oxidation state and the acidity of the environment, shows that some protonation of amine sites always occurs in addition to imine protonation in aqueous acids; (5) this model, together with nitrogen-15 NMR results, supports the hypothesis that the conducting state of polyaniline consists of "metallic" regions of polysemiquinone radical cations separated by insulating regions of protonated amines; (6) The enhancement of conductivity in the emeraldine salt forms of polyaniline upon exposure to water vapor depends on the "dopant" acid, "emeraldine" trifluoroacetate being more stable to water exposure-desorption cycling than "emeraldine" hydrochloride.

Subject Area

Polymers|Materials science

Recommended Citation

Ray, Anjan, "Structure-property relationships in polyanilines" (1989). Dissertations available from ProQuest. AAI8922589.
https://repository.upenn.edu/dissertations/AAI8922589

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