In order to replace inorganic charges, which normally have an important density, a thermosetting (TS) phase was in situ created in a polypropylene (PP) matrix. The development of a reactive system within thermoplastic matrix has been already studied in the case of amorphous polymers [1] and patented in the case of semi-crystalline polymers [2]. It has been proved that many factors (kinetics, miscibility, processing, etc…) could influence the blend morphology [3]. The aim of this study is to scrutinize the chemistry and establish a relation between these chemical parameters, the morphology and finally the nanostructuration of the thermosetting/thermoplastic system. Up to now, the kinetics of several thermosetting systems were studied to evaluate the best conditions for a transposition to an in situ creation by reactive extrusion within the polyolefin matrix. The systems obtained by reactive extrusion were in particular characterized in terms of evolution of the glass transition temperature and morphology depending of the initial reagents proportions and nature. Eventually, the evolution of the PP crystallinity and the mobility of its amorphous phase were observed by WAXS and SAXS since the TS nodules can cause important strain in the matrix. [1] F. Fenouillot, H. Perier-Camby, Formation of a Fibrillar Morphology of a Crosslinked Epoxy in a Polystyrene Continuous Phase by Reactive Extrusion, Polymer Engineering and Science, Vol. 44, No. 4 (2004). [2] N. Garois, P.Sonntag, G. Martin, M. Vatan, J. Drouvroy, Procédé de préparation d’une composition thermoplastique renforcée et réactive, cette composition et son utilisation, Institut National de la Propriété Industrielle, n° 2 963 624 (2012). [3] H. Oyama, R. Nakayama, K. Takase, M. Furuta, Drastic Improvement in thermal stability of polymer alloys by formation of daughter micelles at the reactive interface, Polymer, 137, p. 107-111(2018).