Effect of mesoscopic fillers on the polymerization induced viscoelastic phase separation at near- and off-critical compositions.

We have investigated the effect of mesoscopic fillers on the polymerization induced viscoelastic phase separation of thermoplastic modified thermosets at near- and off-critical concentrations using optical microscopy, time-resolved light scattering, dynamic mechanical analyses, and rheological instrument. Mesoscopic fillers including sepiolite and nanosized silica showed a significant enhancement effect in viscoelastic phase separation, and resulted in pronounced differences in the phase structures at all concentrations of polyetherimide modified epoxy resins with dynamic asymmetry. For blends near critical concentration, the introduction of fillers led to much finer phase structure with smaller characteristic length scale. At off-critical composition (i.e., blends with low concentration of slow dynamic component), the strong polymer chain entanglement resulted in enwrapped mesoscopic fillers within a slow dynamic phase. The rheological behavior of the blends clearly demonstrated the significant enhancement effect of mesoscopic fillers in the viscoelastic phase separation. The apparent activation energy of polymer chain mobility obtained from dynamic mechanical study of glass transition reflected strong wrapping behavior of polymer chains on mesoscopic fillers, which were consistent with the rheological and light scattering study.