In this work, we investigate the in situ synthesis of copolymers used to improve PA / PMMA blends. Various processing conditions are evaluated using tandem extrusion. Reactive compatibilization of dual blends is a well-known approach towards new materials combining properties from two existing polymers [1]. During the melt blending of the two components bearing mutually reactive groups, a copolymer initially located at the interface can be synthesized in situ. Small amounts of these copolymers are needed to stabilize dispersion and improve properties [2]. Most tandem (also called two-stage) extrusion systems correspond to the combination of a twin-screw extruder mixing ability and a single screw extruder allowing to better dry, foam, pressurize or cool the melt in a stable way. Instead the present work focusses on the use of two twin-screw extruders connected to one another [3] allowing longer L/D with reduced torque limitations, and increased condition flexibility adapted for reactive processes scale-up. In our approach the reaction between polymethy-methacrylate-co-methacrylic acid and functional polyamide oligomers give copolymers which are then dispersed in PMMA and PA, the continuous phase. Various ratios of PA/PMMA blends are studied as a function of copolymer content and nature. Analysis of the combined effect of the reaction and the melt mixing conditions, rheology, morphology and the resulting mechanical properties are performed. 1. M. Freluche and co., Self-organized materials and graft copolymers of polymethylmethacrylate and polyamide-6 obtained by reactive blending, Polymer. 46 (2005) 6554-6562. 2. C. W. Macosko, Morphology development and control in immiscible polymer blends, Macromolecular Symposia. 149(1) (2000) 171-184. 3 J.-M. Raquez and co., In situ compatibilization of maleated thermoplastic starch/polyester melt-blends by reactive extrusion, Polym. Eng. Sci. 48 (2008) 1747-1754.