Electron-beam Induced Structural Transformation of Bio-based Pebax: A Radical Driven Mechanistic Study

Electron-beam (E-beam) irradiation provides an effective route to modify polymer architecture, but the mechanistic connection between radical chemistry and structural evolution remains incompletely understood. Here, the irradiation-induced structural transformation of bio-based Pebax was systematically investigated over a dose range of 10–150 kGy. GPC and rheological measurements reveal a dose-dependent transition from long-chain branching (LCB) to network formation. At doses up to 60 kGy, the increase in weight-average molar mass, broadening of the high-molar-mass tail, decrease in the Mark–Houwink slope, and enhanced strain hardening consistently indicate the formation of LCB structures. At higher doses, rapid gel formation together with reduced complex viscosity indicates that crosslinking becomes dominant, while degradation increasingly contributes to the evolution of the soluble fraction. EPR spectroscopy shows that the dominant detectable radical signal is consistent with a site-confined α-oxyalkyl radical associated primarily with the polyether soft segments, and GC confirms the formation of trace H 2 , supporting hydrogen abstraction as an important elementary step. These results support a plausible radical-mediated pathway in which α-oxyalkyl radicals undergo recombination to generate branched/crosslinked structures or β-scission to produce degradation products. This work establishes a molecular-level framework linking radical processes to dose-dependent architectural evolution in irradiated bio-based Pebax.