In this study, we systematically investigated 39 secondary amines as additives in concentrated EB/NMP solutions for gelation and degradation. We discovered that when both the width (defined as the longest distance between two hydrogens in the plane perpendicular to the NH bond of the amine) and depth (defined as the longest distance between two atoms in a plane perpendicular to the width) of the amines are <4.53 Angstrom and their pK(a) is >7.7, the amines significantly extend the gelation times of 20 mass % EB/NMP solutions for more than 12 h. However, some of these amines also significantly degrade the polymer, Amines with small width and depth and strong basicity, such as azetidine and pyrrolidine, can significantly destroy the EB structures. This was evidenced by order-of-magnitude decreases in doped film conductivity, by significantly changed T TV-vis spectra, and by significantly reduced molecular weights of the aged EB solutions as measured by gel permeation chromatography (GPC). However, when both the width and depth of amines are >4.53 Angstrom, these amines neither prolong gelation. time nor appreciably degrade EB.