Four series of photocrosslinkable‐cum‐flame retardant poly(benzylidene phosphoramide ester)s were synthesized from bis(4‐hydroxy‐3‐methyoxybenzylidene) acetone, 2,5‐bis(4‐hydroxy‐3‐methoxybenzylidene)cyclopentanone, 2,6‐bis(4‐hydroxy‐3‐ methoxybenzylidene)cyclohexanone and 2,7‐bis(4‐hydroxy‐3‐methoxybenzylidene) cycloheptanone with various arylphosphorodichloridates by interfacial polycondensation using a phase transfer catalyst. The resultant polymers were characterized by gpc, FTIR, 1H, 13C and 31P‐NMR spectroscopy. Thermal behavior of the polymers was evaluated by differential scanning calorimetry and thermogravimetry. Flame retardant properties were ascertained by Limiting Oxygen Index. The photocrosslinking ability of the polymers was studied by ultraviolet spectroscopy. The crosslinking proceeds via 2π + 2π cycloaddition reaction of the benzylidene groups. The rate of crosslinking decreases with increase in the size of cycloalkanone ring, while the thermal stability increases with increase in the size of the alkanone ring. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3285–3291, 1999