A quantitative analysis of peroxy-mediated cyclic regeneration of eosin under oxygen-rich photopolymerization conditions

Abstract

a b s t r a c tEosin, a photoreducible xanthene, reacts with tertiary amines and initiates the free radical photopolymerization of aqueous solutions of acrylate monomers. This reaction proceeds even in the presence of a large excess (~1000Â) of inhibiting oxygen via a mechanism that has not been established conclusively. This chemistry has proven useful in the area of biosensing, where the formation of a hydrogel on the time scale of seconds serves as a macroscopic, amplified signal that can be connected to molecular recognition events. In this work, we built a kinetic model to quantitatively explore a mechanism in which eosin is regenerated through the reaction of eosin-based radicals with peroxy-radicals formed from oxygen-inhibition reactions. To determine whether the predictions of this model are consistent with conversion profiles measured using real-time FTIR, we refrained from fitting rate constants or other unknown parameters associated with individual steps in the mechanism to the conversion profile. Rather, we considered physical upper bounds and performed sensitivity analyses spanning several orders of magnitude to predict the reactivity of the system. We explored the effects of the peroxymediated regeneration rate constant, k regen , and the initial eosin concentration on the irradiation time that is required to reach a C]C bond conversion of 0.2 (t 0.2 ). At this C]C bond conversion, the aqueous monomer solutions studied herein have become hydrogels. The predictions of the model capture several trends that we have observed experimentally. However, even when the rate constants associated with eosin regeneration via reaction with peroxy-species are set at the physical upper bounds, the values of t 0.2 predicted by the model are much larger than those that we observed experimentally. The results presented herein motivate and provide a framework for future work to more fully elucidate the mechanism of this interesting and useful photopolymerization reaction.

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

“…Both fi gures show that a higher initial eosin concentration requires a shorter period of time before polymerization starts while also resulting in a higher overall averaged conversion. This trend matches that of the results obtained experimentally, [ 24,30 ] whereby the conversion, as measured using spectroscopic techniques, follows a similar shape with experiments at higher initial eosin concentrations polymerizing faster. Furthermore, comparing both conversion profi les also indicate that the continuous fl ux of oxygen into the system as in the reaction-diffusion case slows down the overall polymerization process as inhibition times are increased.…”

“…Plots of conversion obtained a) from a model consisting of a system of ordinary differential equations for all the reactions that excludes diffusion effects and continuous flux of oxygen from the open surface, and b) from the reaction–diffusion model averaged over the whole spatial dimension at each time step.…”

“…In the initial stages when the light is fi rst turned on, the inhibition reactions are much faster than the oxygen fl ux into the system due to the dissolution of atmospheric oxygen into the aqueous reaction mixture, resulting in an oxygen gradient where oxygen diffuses from the surface representing the open air to the closed solid surface. Due to the dual roles of oxygen as both a free radical inhibitor Plots of conversion obtained a) from a model consisting of a system of ordinary differential equations for all the reactions that excludes diffusion effects and continuous fl ux of oxygen from the open surface, [ 30 ] and b) from the reaction-diffusion model averaged over the whole spatial dimension at each time step.…”

UV-Vis/FT-NIR in situ monitoring of visible-light induced polymerization of PEGDA hydrogels initiated by eosin/triethanolamine/O2

“…10,13 However, recent theoretical evidence suggests that despite its kinetic feasibility, this reaction alone appears insufficient to explain eosin’s extraordinary resistance to excess O 2 . 14 …”

Triazine‐Based Type‐II Photoinitiating System for Free Radical Photopolymerization: Mechanism, Efficiency, and Modeling

“…Experimental procedures have then been proposed to determine some of them using a Type-I PIS, while the others can be reasonably approximated. [48][49][50]54] It was decided to determine these parameters with the Type-I photoinitiator diphenyl 2,4,6-TPO. Complete explanations of the parameter determination as well as the description of the Type-I PIS kinetic model for TPO (mechanism, differential equations, fit to experimental data…) are given in the Supporting Information.…”