Cross-linking in polypyrrole and poly(N-methylpyrrole): Comparative experimental and theoretical studies

A comparative study about cross-linking in electrogenerated polypyrrole and poly(N-methylpyrrole) is presented. Experimental studies on polymer films prepared under a constant potential of 1.4 V but considering different polymerization times as well as quantum mechanical calculations on model oligomers indicated that cross-linking is very low in polypyrrole, while cross-links are frequently formed by poly(N-methylpyrrole) chains. These behaviors have been attributed to the architecture of the molecular chains, which is completely different for the two systems under study. Thus, polypyrrole forms linear chains with some irregularities in the inter-ring linkages, while branched molecules with many irregularities are the most stable for poly(N-methylpyrrole). These remarkable differences are fundamentally due to the steric repulsions induced by the methyl groups of poly(N-methylpyrrole).