The transparency and its temperature dependence for immiscible polymer blends composed of PMMA and EVA are studied. It is found that the difference in refractive
index of each phase is the most important factor for transparency of the binary blends. However, the transparency of the binary blend depends on the ambient temperature
to a great extent, because the temperature dependence of refractive index of EVA is more pronounced than that of PMMA. Addition of TCP into the PMMA/EVA blend improves the transparency and its temperature dependence. This phenomenon can be explained by the following reasons: (1)The difference in the refractive index between both phases is reduced because of the high refractive index of TCP and (2) addition of TCP increases the thermal expansion coefficient of PMMA. In this paper, a new material design of transparent rubber-toughened polymer blends having phase separated
morphology is demonstrated. However, the thermal and mechanical properties such as heat deflection temperature, toughness, and yield stress should be checked in detail prior to application, because the addition of plasticizers always provides a negative influence on these properties. A new plasticizer having large refractive index and appropriate solubility parameter should be preferred for industrial application, because a small amount is enough to control the refractive index.