hich was bath sonicated for 2 h to achieve a good dispersion. Then, specimens were cured at 130 °C in vacuum for 24 h. The maximum loading of the additives, MDI (7.8 wt %) and FS (10 wt %), was limited by experimental difficulties during the prepation. Namely, both MDI and FS significantly increased the viscosity of PGS prepolymer solutions. The increased viscosity caused the generation of trapped bubbles in the prepolymer that could not be effectively removed in subsequent processes. After curing, the resulting samples had rough surfaces and trapped bubbles, thus were not suitable for tensile testing.