g/mol), 4,4′-methylenedianiline (M = 198.27
g/mol), and hexamine (M = 140.18 g/mol) were obtained
from Sigma-Adrich, India. Trifluoroacetic acid (99.5%) was purchased
from Alfa Aesar. Anhydrous N,N-dimethylformamide
(DMF) was obtained from Spectrochem, India, and was used without further
purification. All other organic substrates and hydrochloric acid (analytical
grade) were procured from E-Merck, India.