PAn Dispersions

The most commercially successful method of producing processable forms of CEPs has been the aqueous colloidal dispersion route pioneered by Vincent and Armes118 120 (see two recent reviews by Armes121 and Wessling122). Unlike the methods discussed earlier, which all require extensive derivatization of the aniline monomer, dispersions are readily formed from unsubstituted aniline and are readily manufactured in bulk quantities. 

The major route to colloidal (effectively water soluble) PAn has been through the chemical oxidation (S2082-) of the monomer in the presence of polymeric steric stabilizers and electrosteric stabilizers (polyelectrolytes), such as poly(vinyl alcohol), polyGV-vinyl pyrrolidone), polyethylene oxide), polystyrene sulfonate), dodecylben-zene sulfonate, and dextran sulfonate. It has been found that the stabilizer can act simultaneously as a dopant, imparting new functionality to the polymer or additional compatibility for the final application. 

We have shown that such colloids are electroactive and can be electrodeposited.126 However, the electrodeposited hints are not coherent and redissolve once the negative potential is removed. Optically active colloidal PAn nanocomposites of the type PAn/HCSA/polyacrylic acid have also recently been synthesized using the chemical oxidation route, by the oxidation of aniline with (NH4)2S208 in the presence of (+)- or (-)-HCSA as the dopant acid and polyacrylic acid as the steric stabilizer.127 

A detailed II NMR kinetic investigation132 of the polymerization of aniline in DC1/D20 solution has revealed no significant differences between the rates of dispersion polymerization using a polyethylene oxide)-based stabilizer and standard precipitation polymerization in the absence of any stabilizer. However, faster polymerization of aniline was observed in the presence of 20 nm silica particles, leading to PAn-silica nanocomposites. In contrast, slower polymerization occurred in the presence of surfactant micelles to form surfactant-stabilized PAn particles, presumably owing to the high solution viscosity. 

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