The aim of this study is to use industrially available polymers, PMMA, PHA and PLA for the preparation of PMMA-g-PHA and PMMA-g-PLA by transesterification reactive extrusion in a corotative twin screw extruder. Nevertheless, can the reactive system be adapted to obtain good yields and consequently compatibilized polymers and in extreme conditions only graft copolymers by reactive extrusion? This study aims to answer this question positively by providing efficient catalysts and adequate reaction and extrusion conditions. Poly(lactic acid) (PLA) and poly(3-hydroxybutyrate) PHB were grafted onto Poly(methyl methacrylate) (PMMA) by reactive extrusion. Two catalysts were used, 1.5.7-triazabicyclodec-5-ene (TBD) and tin (II) bis(2-ethylhexanoate) (SnOct2). Such catalysts are efficient for alcoholysis or transesterification reaction at high temperature in the melt. 1H NMR spectroscopy was used to characterize the structures of the products of the reactive blends. A higher amount of graft copolymer is obtained by increasing the temperature. Grafting is also influenced by the type of catalyst. TBD is more efficient than (SnOct2) for PHB grafting onto PMMA (substitution rate 19% at 230°C). Likewise, when grafting PLA, significantly lower grafting is obtained and SnOct2 is more efficient than TBD. Thermal analyses showed that amorphous and miscible products were obtained. In the case of PMMA-g-PHB synthesis, increasing temperature improves the substitution rate from 5% to 11% with SnOct2 and from 14% to 24% with TBD. The same effect was observed in the case of PMMA-g-PLA synthesis. The results obtained by SEC confirm both the results obtained by 1H NMR analysis and the possibility to synthesize the copolymer by reactive extrusion with a sho