Polyamide-6 was modified by reactive extrusion using a triamine as a structuring agent. To scrutinize the reactive medium after the chemical modification and to characterize the new structures obtained, the coupling of several physico-chemical analyses was necessary and applied to either model molecules or polyamide chain. By correlation of liquid NMR, matrix assisted laser desorption ionisation/time of flight mass spectrometry (MALDIToF MS), and size-exclusion chromatography (SEC) analyses, it was possible to observe both grafting and polyamide chain scissions that led to randomly branched and linear molecules. One of the most noticeable modifications regarding the properties was a decrease in the amorphous phase mobility with a very small amount of triamine (0.7 wt%). A comprehensive study by X-ray scattering techniques (small and wide angle X-ray scattering, SAXS and WAXS, respectively) allowed us to highlight the noticeable size evolution of the crystalline and amorphous parts at the lamellar scale. In conclusion, these multi-scale experiments demonstrate the possibility of modifying the amorphous phase mobility by controlling the nanostructure morphology of the material, particularly the crystalline lamellae thickness and the rigid amorphous fraction (RAF) content. Thus, an increase in the RAF content of around 6 % induced more restricted mobility in the amorphous phase as the glass transition temperature (T-g) shifted to higher temperature (approximate to+ 7 degrees C).