. "The flame retardant wherein at least one of the substituents R1, R2 and R3 is an aryl group may be a flame retardant, the substituents of which are all alkyl groups such as nonylphenyl group but only one aryl group such as a phenyl group, a benzyl group and a cumyl group or a flame retardant having a plurality of the foregoing aryl groups in all so far as the total number of carbon atoms in the su" . . . .