Dual-Function Enhancer for Near-Infrared Photopolymerization: Kinetic Modeling for Improved Efficacy by Suppressed Oxygen Inhibition

Abstract

There are many strategies for improved conversion efficacy such as the reduction of oxygen inhibition effects (OIH). Three-component system using the phosphine to reduce the OIH effects during the free radical polymerization of (meth)acrylate monomers has been reported. Addition, near-infrared (NIR) photopolymerization offers advantages of safer, less light diffusion and scattering, and deeper penetration into the materials. This study presents the detailed kinetics, and modeling the conversion efficacy associated with the experimental results of Bonardi et al. (Macromolecules, 2018(Macromolecules, , 51, 1314(Macromolecules, -1324. The dual function of the enhancer additive includes: (i) regenerating the photoinitiator, and (ii) producing extra reactive radical. The temporal profiles of the concentration of each of the 3-component system and the associate conversion efficacy are numerically produced. In this study, several new findings showing unique features of various factors influencing the conversion will be demonstrated. For examples, reverse trends (roles) are found in: (i) the light intensity and enhancer concentration, and (ii) the coupling rate constants of radical-oxygen and radical-monomer. The monomer conversion is an increasing function of enhancer, oxygen concentration, and the light intensity. However, they have significantly different steady state features. The steady-state conversion increases from 10% without the enhancer (with enhancer concentration [B] 0 = 0) to (30%, 50%, 80%) for [B] 0 = (0.5, 1.0, 2.0)%. High conversion also requires a long lifetime of the free radical. Finally, the measured conversion profiles at various conditions reported by Bonardi et al. (Macromolecules, 2018, 51, 1314-1324) are compared and analyzed by our modeling.

Coumarin Derivatives as Photoinitiators in Photo-Oxidation and Photo-Reduction Processes and a Kinetic Model for Simulations of the Associated Polymerization Profiles

“…The proposed photochemical mechanisms shown by Scheme 1 may be further summarized The kinetic equations for our previous system [41][42][43][44] are revised to include the enhancer, electron-donor molecule, [B], as the co-initiator for additional radical R produced from initiator [A]. The so-called quasi-steady state assumption [13,14] was used to model the experimental results.…”

Unified Theory for Hybrid-Photocatalysts: A Review on New Strategies for Synergic, Enhanced Conversion Efficacy and Photoredox Cycle

“…The kinetic equations for 3-component system (A/B/N) with 2-monomer M' (for FRP) and M (for CP) are given by the following, under the so-called quasi-steady-state conditions: dT/dt=dR/dt=dS'/dt=dS/dt=0, In addition, the inttiator [A] rgeneration term (RGE) compensates its light depeltion, i.e, d [A]/dt=0, or [A]=A0, is a constant [ ]. The monomer conversions for FRP and CP are given by Lin et al [19,20] = −( + ′ + ′ ′)…”

“…For cost effective with long-living excited states, copper complexes have been used as a new polymerization for the formation of acetylacetonate radicals by redox reaction with a phosphine and to initiate the free radical polymerization (FRP) of acrylates or the free radical promoted cationic polymerization (CP) of epoxides [14][15][16][17]. Recently, Coumarin having dual function of photoinitiators in photooxidation or photo-reduction in visible light were reported [18][19][20]. The efficiency of copper complex (G1) based photoinitiating systems (G1/iodonium salt (Iod)/N-vinylcarbazole (NVK) was investigated by Mokbel et al [16] for FRP of acrylates and CP of epoxides using light source (LEDs at 375, 395, 405 nm).…”

“…The efficiency of copper complex (G1) based photoinitiating systems (G1/iodonium salt (Iod)/N-vinylcarbazole (NVK) was investigated by Mokbel et al [16] for FRP of acrylates and CP of epoxides using light source (LEDs at 375, 395, 405 nm). Recently, Rahal et al [18,19] also reported the difunction of Coumarin for 3D printing, and modeling was proposed by Chiu et al [20] to analyze their data. Bonardi et al [21] reported high performance near-Infrared photoinitiating systems in the presence of oxygen.…”

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This article presents, for the first time, comprehensive model based on the proposed mechanism of Rahal et al [17], Bonardi {20], Tar et al [20], and Mau et al [24], for 3-component systems of G1/Iod/EDB, G1/Iod/amine (in gold chloride), and Iod/Benzoic/Borate (for reduced oxygen inhibition) for the hybri free radical (FRP) and cationic (CP) photopolymerization of interpenetrated polymer network (IPN) systems. Analytic formulas are developed to explore the new features including: (i) conversion efficacy(CE) of FRP is an increasing function of the light intensity (I), the effective absorption coefficient (b), for transient state, whereas, CE at steady-state is independent to the light intensity; (ii) initiator regeneration (RGE)provides a catalytic cycle for improved CE for FRP and CP; (iii) in the IPN system, the synergic effects due to the co-exist of FRP and CP include: (i) CP can increase the medium viscosity limiting the diffusional oxygen replenishment, such that OIH is reduced; (ii) the cationic monomer also acts as a diluting agent for the radical polymer network, and (iii) the exothermic property of the CP polymerization.

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