POCl3 was reacted with phenol to phenyl dichlorophosphate (I) at diphenyl chlorophosphate (II) at 120 degrees C, under N in presence of MgO or Mg catalyst. The I and II intermediates were sepd. by vacuum distn. and reacted with bisphenol A to some oligomeric products proposed as flame retardants for plastics. The reaction was followed by mass spectroscopy.