2,4,6-Tris(2,2'-biphenylylenedioxy)cyclotriphosphazene 6800-71-1 NSC117812 Tris(2,2'-dioxybiphenyl)cyclotriphosphazene Trispiro[1,3,5,2,4,6-triazatriphosphorine-2,6':4,6'':6,6'''-trisdibenzo[d,f][1,3,2]dioxaphosphepin]