2020 Volume 56 Issue 1 Pages 20-33
In recent years, the thermal cationic polymerization initiator（ or the thermal acid generator） is expanding its use as a latent curing agent for epoxy resin mainly in the electrical and electronic fields due to several advantages including the good storage stability at room temperature, the short-time curing at relatively low temperatures around 100 ℃, and the easiness to handle. The major type cationic initiator available in the market is the combination of monoarylsulfonium cation and antimony hexafluoride anion（ SbF6-）. Because of the toxicity of heavy metal（ Sb）, however, phosphorous hexafluoride anion（ PF6-）, tetrakis（ pentafluorophenyl） borate anion（ TFPB-）, and（ Rf）nP-F6-n, in which some of the fluorine of PF6- are replaced with perfluoroalkyl groups, are also applied. TFPB- and（ Rf）nP-F6-n have the polymerization activity comparable to SbF6- although PF6- is less active. Other typical cationic components are thiophenium, quaternary anilinium, and diaryliodonium cations. As a unique type initiator different from the above salt type ones, there is a complex catalyst that combines Al-complex and alkoxysilane. Taking CAS registration number as identification mainly for the thermal cationic polymerization initiators commercially available, the article focuses on reviewing the relationship between the molecular structure and the epoxide polymerization ability of the cationic initiator.
