Frontal photopolymerization under continuous UV irradiation of polyurethane dimethacrylate for centimeter-scale polymer networks

Radical frontal photopolymerization under UV irradiation was investigated using polyurethane dimethacrylate formulations to fabricate transparent centimeter-scale polymer networks. The effects of the photoinitiator Darocur 4265 and the thermal initiator Luperox 231 on front propagation were investigated by real-time FTIR spectroscopy, differential scanning calorimetry (DSC), and in situ temperature monitoring using embedded thermocouples. Under optimized conditions, formulations containing only 0.1 wt% Darocur 4265 enabled the propagation of a polymerization front through samples up to 9.5 cm long, reaching maximum temperatures of approximately 105 °C and front propagation rates up to 20 cm min -1 . Reconstruction of the front position from thermocouple measurements revealed a progressive decrease in propagation rate with increasing distance, consistent with the combined effects of light attenuation, heat dissipation and vitrification. Although Luperox 231 increased the initial heating rate, it did not significantly modify the overall propagation mechanism. These results demonstrate that transparent centimeter-scale polyurethane dimethacrylate networks can be fabricated by radical frontal photopolymerization under continuous UV irradiation without the need for a thermal initiator. They further provide new mechanistic insight into the coupled roles of light transport, photopolymerization kinetics and heat transfer governing front propagation in thick photopolymerized systems.