Enhancing UV Photopolymerization by a Red-light Preirradiation: Kinetics and Modeling Strategies for Reduced Oxygen Inhibition

A novel strategy for red-light-controlled oxygen inhibition for improved UV-light-initiated monomer conversion is theoretically presented for the first time. The dual-wavelength kinetic equations are derived, numerically and analytically solved for the oxygen and photoinitiator concentration profiles. The UV-light-initiated Type I conversion efficacy is an increasing function of its concentration (C-20) and the light dose at transient state, but it is a decreasing function of the light intensity, scaled by [C-20/I-20](0.5), at steady state. In contrast, the red-light-initiated Type II efficacy is mainly dose dependent. Longer red-light preirradiation time (T-P) leads to a shorter UV-light T-ID of UV-light conversion, which is strongly red-light dose dependent, rather than intensity dependent. The numerical new finding is also predicted by the analytic formulas showing that oxygen and monomer conversion are strongly red-light dose dependent in a Type II mechanism. Finally, strategies for controlled initiation-inhibition switch based on two mechanisms, (a) oxygen inhibition for improved conversion and (b) radical inhibition for spatial confirmation in 3D printing, are presented. To conclude, UV-light conversion could be improved by a red-light preirradiation and more importantly and could be customizely tailored by the controlled induction time. UV-light photopolymerization conversion could be improved by a red-light preirradiation and could be customizely tailored by the controlled induction time. The UV-light-initiated Type I conversion efficacy is an increasing function of its concentration and the light dose at transient state, but it is a decreasing function of the light intensity at steady state. In contrast, the red-light-initiated Type II efficacy is mainly dose dependent. Longer red-light preirradiation time leads to a shorter UV light. (c) 2020 Wiley Periodicals, Inc. J. Polym. Sci. 2020, 58, 683-691