The grafting of thermosensitive amine-terminated statistical polymers onto the surface of cellulose nanocrystals (CNCs) was achieved by a peptidic coupling reaction, leading to unusual properties like colloidal stability at high ionic strength, surface activity, and thermoreversible aggregation. We have used a large variety of experimental techniques to investigate the properties of the polymer-decorated CNCs at different length-scales and as a function of the different reaction parameters. A high grafting density could be obtained when the reaction was performed in DMF rather than water. Infrared and solid-state NMR spectroscopy data unambiguously demonstrated the covalent character of the bonding between the CNCs and the macromolecules, whereas TEM images showed a preserved individualized character of the modified objects. Dynamic light scattering and zeta potential measurements were also consistent with individual nanocrystals decorated by a shell of polymer chains. Surface tension measurements revealed that CNCs became surface-active after the grafting of thermosensitive amines. Decorated CNCs were also stable against high electrolyte concentrations. A thermoreversible aggregation was also observed, which paves the way for the design of stimuli-responsive biobased nanocomposite materials.