Bis(4-cyanophenyl) phenyl phosphate (CPP) is introduced for the first time as a viscosity reducing comonomer for phthalonitrile resins. In comparison to the common phthalonitrile resins, the blends of CPP with 4,4'-[benzene-1,3-diylbis(oxy)] diphthalonitrile demonstrated advanced processing properties suitable for cost-effective injection processing (eta as low as to 180 mPa.s at 100 degrees C). Thermal copolymerization was performed indicating complete inclusion of bis-benzonitrile CPP into the phthalonitrile network resulting in formation of thermosets with great thermal performance. Hydrolysis of CPP at pH 4, 7, and 10 was studied to confirm its suitability as a reactive diluent for phthalonitrile. Conversion vs. time plots were obtained via HPLC analysis, and pseudo-first order rate constants were determined in the range of 25-80 degrees C. The activation parameters were calculated from the Arrhenius equation.