Novel hydrazinium salts, N,N-dimethyl N-benzyl N'-benzyl N'-benzoyl hydrazinium hexafluoroantimonate (2) and N,N-dimethyl N-benzyl N'-(2-propyl) N'-benzoyl hydrazinium hexafluoroantimonate (3) were synthesized from hydrazinium salt (1) with the corresponding alcohol. Their initiator activities were examined in the polymerization of glycidyl phenyl ether (GPE). The polymerization of GPE did not proceed with 2 and 3 below 60 and 100degreesC but proceeded rapidly above those temperatures, respectively. It was found that 1-3 served as thermally latent initiators in the polymerization of GPE. The initiators species and terminating species were identified as the proton or alkyl cation and aminimide, respectively. (C) 2005 Wiley Periodicals, Inc.