The new benzylquinoxalinium salt having hexafluoroantimonate (N-BQH) was synthesized as a cationic catalyst for epoxy-cure system. The chemo-mechanical properties and volume expansion behavior of DGEBA (diglycidylether of bisphenol A)/ N-BQH system were studied for various concentration of N-BQH. This new DGEBA/ N-BQH cure system having the volume-expansion property was compared with the existed DGEBA/ amine cure system having the volume-shrinkage properties. The cure kinetics, thermal properties and rheological, mechanical, swelling behaviors were investigated by isothermal and dynamic DSC, FT-IR, TGA, TMA, DMA, rheometer, tensile and flexural test measurements. The composition of DGEBA/ N-BQH blend was varied within 99.5:0.5, 99:1, 98:2, 97:3, and 95:5 (mol%). The volume expansion rate for the various catalytic concentrations are in the range of 2.3 to 4.0%. The thermal expansion coefficient obtained by TMA increased with the increase in catalytic concentration of N-BQH until 1.0 mol%, after 2.0 mol% they decreased slightly with increasing of N-BQH concentration. The molecular weights between crosslinking points decreased linearly with the increase in the N-BQH concentration until 2.0 mol%, whereas after 3.0 mol% they increased with N-BQH concentration. The internal stress increased with the increase in N-BQH concentration. The cure reaction involves three consecutive reactions and the overall kinetic parameters for these reactions were obtained by using the isothermal DSC technique. This catalytic epoxy resin system seems to contain very complex kinetic reaction mechanisms. In this system the reaction constant k//1 and K//2 increased with increasing N-BQH concentration and curing temperature. This can be due to the good reactivity of hydroxyl group generated by the elevation of N-BQH concentration and curing temperature. The temperature dependence of the gel time is well fitted by the Arrhenius expression. The crosslinking activation energies for the various catalyst concentrations are between 56 and 57 kJ/mol; these results show that the overall curing mechanisms are nearly the same. The glass transition temperature of the 5.0 mol% sample has a lower value than 3.0 mol% sample. This result means that the excess catalyst is harmful to form fully well-developed three dimensional networks. In the dynamic mechanical analysis(DMA), one T//g were observed in all the samples. Until 2.0 mol% sample, strorage modulus and damping factor shifted to the right hand. After 3.0 mol% they shifted to the left hand. This indicates that there is optimum concentration of N-BQH. Tensile modulus behavior is similar to flexural modulus behavior and tensile strength tendency is also similar to flexural strength tendency in considering of concentration of N-BQH. The sample with 0.5 mol% has a higher value of mechanical property than the other samples. This implies that the structure of the DGEBA/ 0.5 mol% N-BQH system should have an optimally and compacted linear planar structure which has good resistance to the deformation and the crack initiation. The DGEBA/ 0.5 mol%N-BQH system for the observed concentration range has higher values of mechanical property than the DGEBA/ amine systems. The morphology of fracture surfaces was studied by SEM. The tensile fracture occurred similar to the flexural fracture. The morphology of the DGEBA/ N-BQH system showed ductile fracture property, while the morphology of the DGEBA/ amine cure system showed brittle fracture property. This catalytic epoxy cure system with 0.5 mol% concentration has lowest value of swelling degree than the other samples. This may be due to well arranged compact structure of the DGEBA/ N-BQH system like those of the density and mechanical properties of 0.5 mol% sample. The DGEBA/ N-BQH system has lower values of swelling degree than the DGEBA/ amine cure systems. The DGEBF/ amine systems have higher values of mechanical properties than the DGEBA/ amine systems. This may be due to compact structure of the DGEBF/ amine system having relatively short main and side chain length.
