Surlyn is the sodium salt of ethylene/methacrylic acid copolymer. The phase separation behavior of blend of Surlyn and Poly(ethylene terephthalate)(PET) has been studied by Scanning Electron Microscope and IR. It is shown that particles of Surlyn are dispersed in PET matrix
and this phase separation is controlled by heat-treated condition of blend. When the thermal treatment temperature is higher
more reaction is occurred between Surlyn and PET
thus the compatibility of Surlyn with PET' enhances and less particles of Surlyn are found.