Composite polyamide membranes are prepared using in-situ interfacial polymerization using mixed amine system comprising 1,4-phenylene diamine and pipperazine. Separation performance of the membranes are studied as a function of the concentration of amine and acid chloride, the concentration ratio of the amines, nature of the acid chloride, and the presence of surfactant and acid acceptor in the aqueous reagent. The effect of esterification and hydrazide reactions involving residual carboxylic acid groups in the polymeric membranes on the co-polymeric composite membrane performance is also studied. The membrane performance can be tailored easily by conversion of the residual reactive functional groups in post-treatment.