ABSTRACT:Super-tough poly(butylene terephthalate) (PBT) based blends were obtained by melt blending PBT with 20 wt% poly(ethylene-octene) copolymer (PEO), and varying amounts of poly(ethylene-co-glycidyl methacrylate) (EGMA) as a compatibilizer. Partially reacted EGMA dissolved completely, mainly in the PBT-rich phase, up to 4% EGMA, at which point a crystalline EGMA phase appeared. The reaction and the consequent compatibilization led to a decrease in the particle size and to an improvement in the adhesion between the components. Two percent EGMA was the minimum content required to reach maximum super-toughness, that also corresponded to the maximum ductility. The inter-particle distance (τ) was the parameter that controlled super-toughness. The study of the parameters that τ c depends on, showed that τ c was independent of the modulus of the dispersed phase (E d ) over the τ c range studied. However, the dependence of τ c on adhesion at the interphase was seen by means of the comparison of the τ c -interfacial tension relationship of this blend with those of previous studies.