Polyaniline emeraldine base in N-methyl-2-pyrrolidinone containing secondary amine additives: B. Characterization of solutions and thin films

Secondary amines are added to emeraldine base (EB)/N-methyl-2-pyrrolidinone (NMP) solutions to stabilize the EB solution. However, amines can interact with the EB molecule either by physical interaction, such as with the hydrogen bond (H-bond), or by chemical reaction. Several amines with different basicity and geometry were investigated. The UV–VIS–NIR, FT-IR, GPC, and TGA results reveal that secondary amines, due to their different basicity and molecular size, can chemically degrade EB in two different ways. Secondary amines with strong basicity and small size, such as azetidine (AZ) and pyrrolidine (PY), attack both the quinoid ring and the NC site in the EB backbone immediately. The attacked EB not only loses its conjugated structure due to ring substitution, but also loses its molecular weight because the chain breaks down. Secondary amines with moderate or strong basicity and large geometry, such as heptamethyleneimine (HPMI), reduce most of the quinoid ring to form a ring-substituted material. The final product loses its conjugated structure, but its molecular weight does not appreciably change. However, amines with weak basicity, such as 2-methyl-aziridine (2MA), form H-bonds with EB but do not appreciably degrade the EB structure.