The Impact of Continuous Oxygen Flux in a Thin Film Photopolymerization Reaction with Peroxy‐Mediated Regeneration of Initiator

Abstract

Eosin, a photosensitizer dye that can exist in multiple oxidation states, has been shown to initiate visible‐light photopolymerizations of acrylates in open air when used in combination with tertiary amines. The exact mechanism behind this reactivity with micromolar concentrations of eosin in aqueous monomer solutions initially containing millimolar concentrations of oxygen has not been conclusively established, although pathways for regeneration of eosin in the presence of oxygen certainly play a role. In this work, a reaction–diffusion model incorporating a peroxy‐mediated eosin‐regeneration mechanism is built to explore the effects of oxygen diffusing into the system as the light‐activated reaction proceeds. An oxygen concentration‐dependent flux boundary condition is used to model the continuous replenishment of oxygen at the surface open to air as it is consumed by reaction. The model predicts the formation of a free radical concentration front that initially forms closer to the open surface and gradually moves toward the closed surface, with polymer film thickness increasing and the time required for polymerization to begin decreasing as the initial eosin concentration is increased. These results suggest that oxygen's dual role as both a free radical inhibitor and a precursor of the oxidizing species required for regeneration of eosin brings about interesting spatial variations when the reaction is carried out in a thin film geometry that is exposed to open air. In this case, an assumption of a well‐mixed system is not appropriate and the kinetics of the reaction and conversion as a function of position are likely to depend on the geometry of the system.

On the role of N-vinylpyrrolidone in the aqueous radical-initiated copolymerization with PEGDA mediated by eosin Y in the presence of O2

“…18 Recently, we used kinetic modeling to discuss the link between eosin regeneration and oxygen consumption. 36,37 We suggested that regeneration and resilience to O 2 inhibition appeared to be associated with a primary photochemical process from the excited triplet state of eosin. 38 This led us to propose a process that involves the formation of a semireduced radical trianion (EY •3− ) that can be directly oxidized back to an eosin dianion (EY 2− ) via oxidation by molecular oxygen, where excitation of the metastable intermediate further improves EY 2− regeneration.…”

“…While numerous investigations have focused on the photochemistry of eosin, [28][29][30][31][32][33][34][35] few have attempted to propose a comprehensive mechanism that integrates the photochemical reactions of eosin with the non-photochemical reactions leading to the radical copolymerization of NVP and PEGDA in the presence of excess oxygen. 18,[36][37][38] Oster and Delzenne studied the regeneration of eosin by oxygen in the solution polymerization of acrylamide. 39,40 Fouassier and coworkers later studied the regeneration of eosin in neat (meth)acrylate monomers without NVP.…”

Experimental validation of eosin-mediated photo-redox polymerization mechanism and implications for signal amplification applications

“…Models have previously been developed to study eosinmediated photopolymerization at ambient conditions, 25,31,32 and some even hypothesized a regeneration mechanism for eosin. [31][32][33] Many insights into the eosin regeneration mechanism have since been made, 26,28,34 but have yet to be combined into a kinetic model and validated with experimental results in actual diagnostic test conditions.…”