Weakening and Recovery of Radical‐Induced Cationic Polymerization Fronts Through Finite Constrictions

ABSTRACT We investigated how finite constrictions affect front propagation, post‐exit recovery, and reaction‐progress distribution in an epoxy/oxetane radical‐induced cationic frontal polymerization (RICFP) system. We combined differential scanning calorimetry, infrared thermography, and thermochemical finite element analysis. The model was calibrated in a rectangular channel and applied without refitting to a 2:1 dumbbell channel, predicting uninterrupted propagation and thermal‐zone narrowing. Richardson extrapolation of the three‐dimensional dumbbell model gave a front speed of 52.1 mm min −1 , compared with an experimental value of 58.0 mm min −1 . The fine‐grid convergence index for front speed was 2.2%. In a separate three‐dimensional steel‐mold simulation at a neck‐width ratio of 0.10, speed fell by 31.4% in the neck and recovered to 98.2% of its pre‐neck value after exit. The regional mean peak temperature decreased by 55.1°C and returned close to its pre‐neck value. Narrowing increased the steel‐contact perimeter per resin cross‐sectional area to 3.6 times its wide‐region value, intensifying heat loss. At 200 s, after front exit, modeled reaction progress ranged from 0.023 near the sidewall to 0.921 at the center. Front recovery did not imply uniform reaction progress within the neck.