Cleaving is usually required to characterize the molecular weight of grafted polymers on substrates. Here, we report on a technique to estimate the molecular weight of grafted polystyrene (PS) (Mngrafted PS) in PS-grafted cellulose nanocrystals (PS-g-CNCs) without chain cleavage. PS-g-CNCs were prepared from brominated CNC (CNC-Br) by Surface-Initiated Atom Transfer Radical Polymerization (SI-ATRP) in the presence of sacrificial initiators. (386 characters)