Composition-resolved multi-response design of UV-triggered radical-induced cationic frontal polymerization in epoxy/oxetane thermosets

FTIR-derived BADGE conversion alone poorly predicts tensile strength. • Strength spans 19.1–44.7 MPa within 78–81% BADGE conversion. • Multi-response optimization balances front velocity, strength, and conversion. • UV settings tune ignition but have little effect on steady front velocity. • A thermochemical model verifies self-sustained curing beyond velocity fitting. UV-triggered radical-induced cationic frontal polymerization enables epoxy/oxetane thermosets to continue curing after brief UV exposure. However, formulations that support faster front propagation do not necessarily maximize tensile strength. We combined single-factor screening, central composite design, desirability optimization, and orthogonal UV experiments to examine the relations among formulation, process, and properties. In situ infrared thermography recorded front propagation. A thermochemical finite-element model described the thermal field. Across the formulation space, FTIR-derived BADGE conversion poorly predicted tensile strength. The single-variable model gave R 2  ≈ 0.08, while tensile strength ranged from 19.1 to 44.7 MPa as BADGE conversion ranged from 78% to 81%. The selected formulation yielded a front velocity of 51.6 mm·min −1 , a tensile strength of 37.7 MPa, and a BADGE conversion of 82.3%. All three results were within the prediction intervals. UV wavelength, irradiance, and exposure time affected tensile strength and BADGE conversion. The steady front velocity changed by less than 10%. The model reproduced continued propagation after UV removal and the axial cooling gradient. The thermochemical analysis supported self-sustained propagation. These results establish a composition-resolved multi-response strategy. Composition determines the attainable properties, while UV settings tune ignition. Download: Download high-res image (95KB) Download: Download full-size image