New Approach for the Controlled Cross-Linking of Polyaniline:  Synthesis and Characterization

A new strategy has been employed to control the cross-linking of polyaniline that allows the synthesis of high molecular weight, conducting copolymers. The new method utilizes aniline−formaldehyde condensates (AFC) to establish the upper limit of possible cross-link sites in an AFC−polyaniline copolymer. By changing the ratio of AFC to aniline during the polymerization reaction, it is possible to control the number of cross-linking sites, and in turn the bulk conductivity and molecular weight. The copolymer is obtained by oxidizing aniline in the presence of AFC, where the aniline is oxidized to form polyaniline through a cation radical mechanism. The AFC present in the mixture terminates the propagation of polyaniline chains while at the same time binding it to the AFC backbone. In essence, the AFC polymer molecules tether together polyaniline chains to form much larger molecular weight molecules. Varying the ratio of AFC to aniline monomer prior to chemical polymerization allows control over the conductivity, molecular weight, and solubility of the copolymer. Under appropriate conditions, high molecular weight copolymers (weight-average molecular weight of 106) with conductivities on the order of pure polyaniline (k = 10 Ω-1 cm-1) and similar redox behavior can be obtained. Adhesion measurements on glass demonstrate that of the copolymers have a significantly higher strength of adhesion compared to that observed for pure polyaniline.