Cationic Cure of Epoxy Resin by an Optimum Concentration of N - benzylpyrazinium Hexafluoroantimonate

Cure behavior of an epoxy resin was investigated at different cure temperatures (110, 120, 130, 140, and 150°C) and cure times in the presence of 2 wt% of an N-benzylpyrazinium hexafluoroantimonate (BPH) cationic catalyst by means of differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The glass transition temperature (T g ) and chemical conversion (x) at the different temperatures were determined from DSC thermograms. TheT g andx vs. ln time data were superposed up toT g = 100°C andx = 0.70 by shifting horizontally at a reference temperature ofT g = 130°C. It is interesting that theT g andx of the superposed data increase rather slowly in the early stage of cure and rapidly thereafter. Therefore, the increase of theT g andx can be divided into two regions;R I = −18.4(=T g ) ∼ 5°C andR II= 5 ∼ 100°C inT g , andR I = 0 ∼ 0.24 andR II= 0.24 ∼ 0.70 in x. TheR I is closely related to the initiation reactions between BPH and epoxy and between hydroxy group and epoxy in this epoxy/catalyst system. From the kinetic analysis of theT g -shift, activation energy was 12.5 kcal/mol. The relationship betweenT g andx was also considered. The gelation and vitrification times for different cure temperatures were obtained from DMA curves.