Blends of 80/20 CPE/NR filled with various silica loadings were prepared, and their properties were determined. It was found that cure properties are influenced significantly by the addition of precipitated silica. Scorch time and cure time decrease with increasing silica loading, which could be explained by the thermal history attributed to the shear heating in the blending stage. An increase in crosslink density as a function of silica loading is believed to be caused by a migration of curatives to the NR phase. In terms of phase morphology, with increasing silica loading, the NR dispersed phase size decreases due to the increase in compound viscosity and, thus, the shear stress available for efficient blending. An increase in silica loading also enhances resistance to oil due to the decrease in the NR dispersed phase size associated with the dilution effect, but gives no significant impact on thermal aging resistance. According to the change in damping peak height associated with the shift in T-g of the CPE phase, silica appears to preferentially migrate to the CPE phase due to the strong interaction between CPE and silanol groups of the silica surfaces. (c) 2005 Wiley Periodicals, Inc.