Unravelling the initiator‐only stage in alginate grafting: Radical‐induced depolymerization and its impact on acrylamide grafting efficiency

Free‐radical grafting of natural polymers often assumes that initiators only create active sites before monomer addition. We tested this by exposing sodium alginate to potassium persulphate (KPS) under typical grafting conditions without monomer (acrylamide). Structural changes ( 1 H NMR, FTIR), chain size (intrinsic viscosity), and heat flow (calorimetry) revealed rapid random scission of glycosidic bonds and formation of new reducing ends, with little oxidation. Molecular weight declined steeply in the first 20 min, faster at higher temperatures. Pretreatment with KPS significantly increased acrylamide grafting efficiency (37%–77%) but progressively reduced chain length, showing that initiator radicals act as both activators and degraders. Graft efficiency is gained only at the cost of chain length, underscoring that the initiator‐only stage is never neutral.