Rheological properties and cure kinetics of siloxane-modified epoxy resins

Copolymerization of siloxane-containing oligomer and diglycidylether of bisphenol A (DGEBA) epoxy was carried out to improve the thermal stability and toughness of inherently brittle epoxy resin. The compositions of siloxane-containing oligomer in this system were varied within 0, 3, 5 and 10 phr for the measurements of rheological properties and cure kinetics. Rheological properties were investigated using a rheometer under an isothermal condition. The gel time was obtained from the values of storage modulus (G′) and loss modulus (G′). The cross-linking activation energies were also determined from the Arrhenius plot based on the gel times and reaction temperatures. As a result, the maximum gel time and cross-linking activation energy were observed in the 5 phr siloxane-containing oligomer to DGEBA. In this work, another activation energy for cure was obtained by the Kissinger equation using dynamic differential scanning calorimeter (DSC). This cure activation energy increased with increasing the siloxane oligomer content and showed a maximum value in the case of 5 phr siloxane oligomer content. It revealed that the optimum condition to make a compact cross-linking structure without side reaction is 5 phr siloxane-containing oligomer content in this system.