Glycidyl azide polymer (GAP) has been evaluated for use as binder for solid propellants. The effects of various parameters like cross-linking conditions, concentration of crosslinker, and the ratio of isocyanate to hydroxyl functional groups (NCO/OH ratio) on the mechanical properties were studied in detail. It was observed that the type of curing agent and the NCO/OH ratio have a strong influence on the gum-stock properties. Similar impact was seen for cross-linker concentration also. The swelling characteristics of the cross-linked binder prepared with different NCO/OH ratios were evaluated with toluene and tetrahydrofuran (THF). The polarity and the solubility parameter of the solvents were found to influence the swelling of GAP. The NCO/OH ratio and cross-linker concentration of the polymer were also found to affect the swelling characteristics. The sol fraction determined for the polymer was found to follow a similar pattern. The cross-link density and average molecular weight between crosslinks (Mc) were determined from the swelling studies and also from the stress-strain relationship. The Mc values were found to be influenced by the NCO/OH ratio. Finally, the Mc values determined from the swelling data were correlated to the gum-stock properties, and the model parameters were estimated. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 114: 3360-3368, 2009