This invention provides aromatic diimines where the diimines have imino groups with at least two carbon atoms, and either are in the form of one benzene ring having two imino groups on the ring, which imino groups are meta or para relative to each other, and in which each position ortho to an imino group bears a hydrocarbyl group, or are in the form of two benzene rings connected by an alkylene bridge and having one imino group on each ring, and in which each position ortho to an imino group bears a hydrocarbyl group. This invention also provides aromatic secondary diamines where the diamines have amino hydrocarbyl groups with at least two carbon atoms, and either are in the form of one benzene ring having two amino groups on the ring, which amino groups are meta or para relative to each other, and in which each position ortho to an amino group bears a hydrocarbyl group, or are in the form of two benzene rings connected by an alkylene bridge and having one amino group on each ring, and in which each position ortho to an amino group bears a hydrocarbyl group. Also provided are processes for forming diimines and secondary diamines from primary diamines, including the aromatic diimines and aromatic secondary diamines of the invention.