ormula (X2 PN)m where m is 3-7, wherein X is a halogen selected from the group consisting of F, Cl, and Br and all of the X's are not required to be identical, at temperatures of about 130??? C. to 220??? C. in the presence of at least one catalyst which is selected from the group consisting of phosphazene derivatives consisting of the reaction product formed by reacting (1) at least one cyclic ol