The interfacial adhesion between PVC and nitrile rubber (NBR) can be strengthened through an increase of the acrylonitrile (AN) level in NBR in the range of 0–40% by weight [9]. Imasawa and Matsuo [10] studied the strain rate dependence of the elongation-at-break for PVC–NBR blends with various AN contents. The NBR phase as well as the PVC phase in these blends were continuous [9]. However, it was not possible to separate the effects of morphological parameters and interfacial adhesion for blends with co-continuous phases due to lack of a theoretical framework.