Wide processing window-oriented phosphorous containing bis-phthalonitrile resins, bis[3-(3,4-dicyanophenoxy)phenyl] phenyl phosphate (2c), and bis[4-(3,4-dicyano phenoxy)phenyl] phenyl phosphate (2d) have been prepared by the reaction of monophthalonitrile precursors, 4-(3-hydroxyphenoxy)phthalonitrile (1c) and 4-(4-hydroxyphenoxy)phthalonitrile (1d) with phenyl phosphoridate dichloride in anhydrous aprotic solvents. The monophthalonitrile precursors were synthesized via nucleophilic substitution reaction of 4-nitrophthalonitrile with resorcinol (1c) and hydroquinone (1d) respectively in dry polar aprotic solvents preferably in dimethyl sulphoxide (DMSO) at ambient temperature under N2-atmosphere. The Differential Scanning Calorimetry (DSC) thermogram of uncured resins 2c and 2d showed onset of curing at 206°C and 236°C, respectively, with a processing window of 181°C and 136°C along with a curing window of 120°C and 131°C on 10°C/min heating rate, respectively. The enthalpies of curing reactions for the resins 2c and 2d were found to be 33 J/g and 55 J/g, respectively. These resins 2c and 2d were then cured in presence of 5 wt% bis[4,4’-bis(3-aminophenoxy)diphenyl] sulphone (m-BAPS) to form corresponding oligomers and further post-curing at the programmed heating schedule to achieve fully cross-linked thermosetting networks, 3c and 3d, respectively. The thermogravimetric analysis (TGA) of the fully cured polymers 3c and 3d has shown the onset of thermal degradation (Tons) at 389°C and 404°C along with char yield of 78 wt% and 79 wt% at 800°C with 20°C/min heating rate, respectively, in N2 -atmosphere. The corresponding limiting oxygen index (LOI) values of these cured polymers were found to be 48.7 and 49.1 (calculated by Krevelen’s equation). Both the cured polymers 3c and 3d have not shown any glass transition temperature (Tg ) up to 350°C (via DSC analysis).

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