Modeling the dual-function effects of hybrid-1 photopolymerization in Iodonium / Amine and two 2 monomers system 3

The synergetic features of a three-component photoinitiating systems (A/B/C) based on the 8 measured data and proposed mechanism of Liu et al are analyzed. The co-initiators/additives B and 9 C have dual-functions of : (i) regeneration of photoinitiator A, and (ii) generation of extra radicals for 10 enhanced conversion efficacy (CE), the synergic effects lead to higher CE for both free radical 11 polymerization (FRP) and cationic polymerization (CP). The CE of FRP has 3 terms due to the direct 12 (tyep-I) coupling and two radicals. Therefore, it is always higher than that of CP having only one 13 radical. The CE of CP has a transient state proportional to the effective absorption constnat (b), the 14 light intensity (I) and initiator concentration (A0), but a steady state given independent to the light 15 intensity (I). For the CE of FRP, the contribution from radical R could have two cases: (i) linear 16 dependence on T'=bIA0, or (ii) nonlinear square root dependence T0.5. The nonlinear feature is due to 17 the bimolecular termination term of k'R2. The key factors influencing the conversion efficacy are 18 explored by analytic formulas. The synergetic effects lead to higher conversion of FRP and CP are 19 consistent with the measured work. However, there are other theoretically predicted new features 20 (findings) which are either not identified or explored experimentally including: (i) co-initiator [C] 21 always enhances both FRP and CP conversions, whereas co-initiator [B] leads to more efficient FRP, 22 but it also reduces CP. The specific systems analyzed are: benzophenone derivatives (A) ethyl 423 (dimethylamino)benzoate (B), and (4-tert-butylphenyl)iodonium hexafluorophosphate (C) under a 24 UV (365 nm) LED irradiation; and two monomers of trimethylolpropane triacrylate (TMPTA, for FRP) 25 and (3,4epoxycyclohexane)methyl 3,4-epoxycyclohexylcarboxylate (EPOX, for CP). 26


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Comparing to the conventional thermal-initiated polymerization, there are several advantages 30 for photopolymerization such as fast and controllable reaction rates, and spatial and temporal control 31 over the formation of the material, without the need for high temperatures or harsh conditions [1]. under two wavelengths to eliminate the oxygen inhibition effects was also reported experimentally 40 [9][10][11]. Sequential network formation has also been achieved with many different types of common type-II PI for the polymerization of (meth)acrylates under visible light [15,16].

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Various strategies to reduce oxygen inhibition in photoinduced polymerization have been 49 proposed such as using co-initiators or addition of oxygen scavengers, and the thiol-ene and thiol-50 acrylate-Michael systems which are insensitive to oxygen [8,9]. Dual-wavelength (red and UV) 51 photopolymerization was also reported, in which pre-irradiation of the red light eliminated the 52 oxygen inhibition effect and thus enhanced the conversion efficacy of the UV light [10].

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The classical diaryliodonium salts, such as diaryliodonium, suffer low solubility in monomers 54 and formation of side products due to the release of HF. To overcome this drawback, Kirschner et al.

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[15] recently reported a new counter anion-free and fluoride-free aryliodonium ylides (AY) to avoid 56 the formation of HF and to enhance their solubility. They reported (CQ)/amine/AY as a new and 57 efficient PI system for the polymerization of methacrylates under air and blue light (477 nm) 58 irradiation for additional reactions and initiating radicals for improved conversion efficacy.

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Example of dual-wavelength (UV 365 nm and blue 470 nm) system for enhanced conversion by 62 reducing the oxygen inhibition was reported by de Beer et al [8,9] for the photopolymerization of ZnTTP/DEGEEA has distinct absorption peak at UV-365 nm and red-635 nm, respectively, and thus 72 it can be independently excited by a UV and a red light, respectively. Lin et al [19] reported the 73 theoretical modeling for the above described 2-wavelength system [13]. The novel strategy using 3-74 wavelength of uv, blue and red lights was recently proposed by Lin et al [21] -11,19,20) and three-wavelength [21]; and three-component, one-wavelength system 79 [13,23]. We note that all these systems have been theoretically and experimentally studied, except the 80 3-wavelength systems which was recently proposed theoretically by Lin et al [21]. The synergetic 81 effects lead to higher monomer conversion can be achieved by co-initiators extra radicals and 82 multiple wavelengths for reduced oxygen-inhibition.

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This article will present, for the first time, the kinetics of the synergetic features of the 3-initiator,

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However, we note that our Figure 1 is more general than the following Scheme of Liu et al [22] 125 which ignored the termination scheme due to the couplings of R+R (bimolecular), R+S, and R+S'.

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The CE of CP defined by CE'=1-M'/M0', which is the time integral of Eq.

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(iii) enhancing FRP by producing radical S (as shown by Figure 1).

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For analytic formulas, we will consider a perfect catalytic cycle of the initiator, or when G"=0,