Chemical reactions carried out by reactive extrusion usually lead to complexes created structures with mixtures of modified and non-modified polymers and in some cases to chain scissions and thus evolution of molar mass distribution. Face to such structural changes in the melt, a main challenge is to adapt physico-chemical analysis to deeply identify the new species formed. Some specific techniques can answer to such requirements: i) The use of Multi-Angle Laser Light Scattering (MALLS) for the determination of branching is usually processed on star-branched polymers synthetized from a multifunctional initiator; ii) The diffusion Ordered Spectroscopy (DOSY) is commonly used to witness the grafting of an additive or a polymer block onto polymer chains.; iii) and classically, the molar masses are measured by size-exclusion chromatography (SEC). However to our knowledge the coupling of rheology, MALLS and DOSY technics in order to observe the grafting of a multifunctional additive on a polymer and the resultant branching has never been studied. To evaluate such approach, reactive extrusion of a polymer with a multifunctional additive had been carried out with a twin screw extruder. These formulations were analyzed by frequency sweep measurements on an ARES rheometer to estimate the change of viscosity. Besides the significant drop of the copolymer molar mass confirmed by SEC, the analysis by 13C NMR and DOSY evidenced the grafting on the polymer. Hence, MALLS experiments performed on formulations obtained by playing on the functionality of the additive highlighted significant structure difference and allowed to differentiate the behavior of linear polymers from branched systems. In conclusion, these original coupling experiments demonstrate the possibility to understand in details the complexes structures created during reactive extrusion process.