Synthesis of Arylmethylpyridinium Tetrakis(pentafluorophenyl)borates and Their Application to Cationic Thermally-Latent Curing Agents for Epoxy Resins

Abstract

Various arylmethylpyridinium tetrakis(pentafluorophenyl)borates were synthesized and their properties as cationic thermally-latent curing agents for epoxy resins were studied. Arylmethylpyridinium chlorides were prepared by reaction of arylmethylchlorides with cyanopyridines. The desired arylmethylpridinium borates were obtained by the successive ionexchange of these salts with sodium tetrakis(pentafluorophenyl)borate. Catalytic activity of the pyridinium borates toward bisphenol A diglycidyl ether (BAGE) and difunctional alicyclic epoxy resin (Celoxide) were examined by differential scanning calorimetry (DSC). Storage stability of the epoxy resins/salt mixture at room temperature for one month was examined by ¹H-NMR measurements. We found that p-methoxybenzyl-3-cyanopyridimium tetrakis(pentafluorophenyl) borate (pMB3CPB) has high curing activity with good storage stability toward epoxy resins. We also found that the cured BAGE possessed higher glass transition temperatures and higher adhesion strength to stainless steel than the resin cured with a conventional sulfonium antimonate.