Poly(ethylene terephthalate) (PET) based blends were obtained by melt blending PET with up to 30 wt% poly(ethylene-octene) either modified with maleic anhydride (mLLDPE) or not (LLDPE). Both PET/LLDPE and PET/mLLDPE blends were immiscible. The dispersed phase particle size was large in LLDPE blends, but upon mLL-DPE addition, it decreased to a small (submicron) and rather constant value with composition. This indicated compatibilization, and was attributed to specific interactions between the ester and maleic groups of PET and mLLDPE, respectively, rather than grafting reactions between components. Linear decreases in Young's modulus and yield stress, and ductility increases were observed in blends with mLLDPE. Super-toughness was achieved in blends with mLLDPE, which took place when the critical interparticle distance (IDc) was below 0.17 mu m and with only half the cross section of the specimens broken. The IDc of these blends and those of other blends from bibliography were compared with the adhesion levels estimated from the expected main interactions between the components of the blends. This comparison strongly indicated that, at least through an adhesion range, IDc depends on the adhesion level, and that IDc decreases as the adhesion level increases.