Aqueous Colloidal Dispersions of Polyaniline Particles

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AQUEOUS COLLOIDAL DISPERSIONS OF POLYANILINE PARTICLES STEVEN P. ARMES* AND MAHMOUD ALDISSI, Materials Science and Technology Divi87545 sion, Los Alamos National Laboratory, P. 0. Box 1663, Los Alamos, NM *Presently at University of Sussex, School of Chemistry and Molecular Sciences, Brighton BNI 90J, United Kingdom

ABSTRACT Colloidal polyaniline has been prepared in acidic aqueous media by a modified chemical polymerization of aniline in the presence of a tailor-made polymeric surfactant. The surfactant which acts as a steric stabilizer used in this study is derivatized poly(vinyl alcohol-co-vinyl acetate). This surfactant contains pendant aniline units which participate in the aniline polymerization, resulting in the formation of sterically-stabilized polyaniline particles which have a non-spherical "rice-grain" morphology. It is shown that this novel form of polyaniline is more processable than the bulk powder that is normally obtained from a conventional chemical synthesis. The solid-state conductivity of solution-cast films or compressed pellets of these dispersions is surprisingly high (= I S/cm), despite the presence of the insulating outer layer of chemically-grafted stabilizer.

INTRODUCTION Intractability is typical of conjugated polymers because of the aggregated character associated with strong interchain interactions. To take advantage of this property, in the preparation of conducting polymers as colloidal dispersions seemed to be an excellent approach toward processability. Since 1986 several groups have described the preparation of spherical submicronic polypyrrole colloidal particles in aqueous media (1-61. The particles are sterically-stabilized by an outer layer of physically adsorbed polymeric surfactant such as methylcellulose, poly(vinyl alcohol-co-vinyl acetate), poly(vinyl pyrrolidone), poly(vinyl pyridine-co-butyl methacrylate), etc. Most of our initial attempts to produce colloidal polyaniline particles by analogous methods have resulted in macroscopic precipitation due to inefficient adsorption of the stabilizer, although in certain cases a low yield of colloidal polyaniline has been reported [7,8]. To achieve colloidal stability of polyaniline particles and avoid the problems associated with physical adsorption/desorption, we employed another synthetic approach which consisted of graft copolymerization of aniline onto the appropriate polymeric surfactant. In a recent preliminary communication [9] we described the preparation of colloidal polyaniline particles using a tailormade random copolymer poly(2-vinyl pyridine-co-p-aminostyrene) as a polymeric surfactant. Preparation of the latter and evidence of grafting were described recently [10]. In this paper, we describe the preparation and characterization of polyaniline colloids using the derivatized poly(vinyl alcohol-co-vinyl acetate) as a steric stabilizer in the graft copolymerization process.

Mat. Res. Soc. Symp. Proc. Vol. 173. @1990 Materials Research Society

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EXPERIMENTAL

Commercially available poly(vinyl alcohol-co-vinyl