The Mooney viscosities of the compounds with ENR-10 as compatibilizer show almost no change when the amount of ENR-10 is increased from 2.5 to 15 phr: Fig. 2. Incorporation of ENR-38 and ENR-51 decreases the Mooney viscosities of the compounds to match the level of that of the TESPT-containing compound when the amount of ENRs used is ⩾10 phr. The decrease of compound viscosity when ENR is used as compatibilizer implies an improvement of silica dispersion due to the interaction between epoxide groups and silanol groups of the silica resulting in better compatibility. However, the compound viscosities can be affected by various factors including the NR/ENR blend incompatibility. The presence of polar epoxy groups in the ENRs leads to the difference between the solubility parameters of NR and ENR, and increases interfacial tension. It has been reported that the NR/ENR blends exhibit two distinct glass transition temperatures (Tg) corresponding to the original polymers, as analyzed by differential scanning calorimetry (DSC) [30], and dynamic mechanical analysis (DMA) [31].