Poly(ethylene-co-vinylalcohol)-grafted-poly(3-hydroxybutyrate-co-hydroxyvalerate) ( EVOH-g-PH BV) was prepared by a catalyzed grafting of PHBV onto immiscible EVOH. These reactions were performed at high temperature in the molten state. The choices of Tin(II) bis(2-ethylhexanoate) (Sn(Oct)(2)) and 1,5,7-Triazabicyclo vertical bar 4.4.0 vertical bar dec-5-ene (TBD), as catalyst, were justified by a first study in an internal mixer. The catalyst quantity, reaction temperature and reaction time were optimized to apply them in the conditions of a reactive extrusion process with a co-rotating twin screw extruder. High reaction temperature, from 180 degrees C to 220 degrees C, associated to intensive mixing led to efficient grafting of PHBV onto EVOH, compatible with short residence times required. Rheological, thermal and morphological analyses were conducted to characterize the obtained copolymers. Molecular weights were determined by SEC. SEM imaging were made on cryo-fractured surfaces of blends extruded with and without catalyst. In most of reaction conditions, a compatible blend was obtained with a fine micro phase separation. Grafted copolymers were only obtained when well defined and controlled conditions are applied. (C) 2012 Elsevier Ltd. All rights reserved.