Novel benzyl sulfonium salt having an aromatic group on sulfur atom as a latent thermal initiator

Three benzyl p‐hydroxyphenyl methylsulfonium salts with different counter anions were synthesized as novel latent thermal initiators. Syntheses of the sulfonium salts (2) were performed by the reaction of p‐hydroxyphenyl methyl sulfide with benzyl chloride followed by exchange of the counter anion (Cl−) with SbF−6 (2a), PF−6 (2b), or BF−4 (2c). In the bulk polymerization of glycidyl phenyl ether (PGE) with 2, initiator activity of the sulfonium salts was evaluated by comparison with that of benzyl tetramethylenesulfonium hexafluoroantimonate (1, R = H). Among the initiators, 2a showed the highest activity, and was much more active than 1 (R = H). Since the polymerization of PGE with 2a proceeded efficiently at more than 80°C but not at all at less than 60°C, 2a was suggested to be a good latent thermal initiator.