Gelation behavior of thermoplastic-modified epoxy systems during polymerization-induced phase separation

The rheological behavior and gelation characteristics of epoxy blends are of critical importance to property study and industrial application. In this work, we studied the rheological behavior and structural transition of different thermoplastics, including polyetherimide, polymethylmethacrylate, and polyethersulfone (PES), modified epoxy systems by using rheometry instrument, differential scanning calorimetry, time-resolved light scattering, and scanning electronic microscopes. At the same molecular weight level of thermoplastics, different epoxy blends show profound diversities on the rheological and gelation behavior due to the large differences in phase separation and curing process. For early phase-separation systems of PES-modified epoxy blends, two gel points are identified, which correspond to physical gelation and chemical gelation, respectively. With the variation of the PES molecular weight and curing rate, dramatic changes in gel time and critical exponent were observed. As the molecular weight of thermoplastics is increased, the gelation time becomes shorter and the gel strength gets lower, while the faster curing rate would increase the physical gel strength significantly.