Development of the Tetrabutylphosphonium Carboxylates as Latent Curing Accelerators for Thermosetting System of Epoxy Resins and Bismaleimide Resins

Abstract

It is known that the use of phosphonium salts as curing accelerators generally results in resin compositions with excellent latent properties. In this study, various phosphonium carboxylates, ammonium carboxylates, and 2-phenylimidazole were investigated as latent curing accelerators in the anionic polymerization of epoxy resin compositions, bismaleimide resin compositions, and bismaleimide-epoxy resin compositions. The latency of each curing accelerator was observed as follows ; pyromellitate dianion > 1,2-cyclohexanedicaboxylate monoanion > 1,4-cyclohexanedicaboxylate monoanion ≒laurate ≒ 2-phenylimidazole. It was also found that the cured epoxy resins containing phosphonium salts had higher heat resistance than those containing ammonium salts. These experimental results indicate that BTBP-pyromellitate and TBP-3S (both products of HOKKO CHEMICAL INDUSTRY CO.,LTD.) are the most promising curing accelerators that can achieve both the latency of resin compositions and the heat resistance of cured materials.