We have investigated the effectiveness of chemical crosslinking modification of P84 co-polyimide membranes using diamine compounds for pervaporation dehydration and developed the scheme to enhance separation performance of asymmetric polyimide membranes. Two diamine cross-linking agents; namely, p-xylenediamine and ethylenediamine (EDA) were used in this study for both dense and asymmetric P84 membranes. Experimental results suggest that the cross-linking reaction induced by EDA is much faster than that by p-xylenediamine because the former has smaller and linear structure than the latter. However, membranes cross-linked by p-xylenediamine are thermally more stable than that by EDA. Membranes modified by p-xylenediamine or ethylenediamine (EDA) have increased hydrophilicity. An increase in the degree of cross-linking reaction initially results in an increase in separation factor with the compensation of lower flux for pervaporation dehydration of isopropanol (IPA). However, further increase in the degree of cross-linking reaction may swell up the polymeric chains because of hydrophilic nature of these diamine compounds, thus results in low separation performance. It is found that post treatment after cross-linking reaction can significantly enhance as well as tailor membrane performance because of the formation of charge transfer complexes (CTCs) and the enhanced degree of cross-linking reaction. A low-temperature heat treatment may develop pervaporation membranes with high flux and medium separation factor, while a high-temperature heat treatment may produce membranes with high separation factor with medium flux.