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^-F_6-n, in which some of the fluorine of PF₆^- are replaced with perfluoroalkyl groups, are also applied. TFPB^- and（ Rf）_nP^-F_6-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.

To evaluate the effect of wettability of pressure-sensitive adhesive（ PSA） to probe surface, the probetack test was done under the condition of light compression pressure（ 5.0 kPa）. It is about half of ASTMrecommended condition. The crosslinked poly（n-butyl acrylate-acrylic acid） random copolymer was used asPSA. The debonding behavior was observed using a high speed microscope from upper and side directionswith a probe made of stainless steel. As a result, peeling of edge part was hardly occurred from the test startto the peak in the stress-displacement curve and the debonding occurred drastically at the peak with theformation of cavitation and the decrease of stress. The cavitation and the fibrillation were observed only afterdebonding took place. That is, these never contributed to the tack rising. Tack value is equal to the stress fordebonding start. The debonding behavior was also observed using three probes made of poly（vinyl chloride）（higher tack）, polyoxymethylene（ medium tack） and high density polyethylene（ lower tack）. The debondingmechanism was the same as that with a probe made of stainless steel. It

Butyl acrylate - acrylic acid copolymers with different molecular weights / molecular weight distributions（PDI） were synthesized, and the effect of the degree of crosslinking on the gel fraction, the degree of swelling,and the molecular weight distribution of the sol fraction, were studied. It was revealed that the PDI greatlycontributed to the onset of gel formation at low concentration of the crosslinking agent. PDI also related to thesaturation of the gel fraction at high concentration of the crosslinking agent. The gel fraction and the degree ofswelling could be evaluated from the identical specimen. The degree of swelling largely depended on the PDIof the raw material copolymer, even if the gel fraction was about the same. In addition, it was clarified that thedistribution of a molecular weight of 1,000,000 or more increased in the sol of the low equivalent compositionof crosslinking agent（ ie. 0.001 eq and 0.002 eq.）. In the same time, the distribution in the low molecularweight region decreased. It means that the copolymer and the crosslinking agent dimerized first to give a highmolecular weight polymer, and then the formation of a crosslink（ gel formation） occurred.