New iodonium salts in NIR sensitized radical photopolymerization of multifunctional monomers

Abstract

Reactivity of new iodonium salts [A-I-B]⁺X⁻ was studied with near infrared (NIR) initiated radical polymerization by photo-DSC using the polymethine dye S1 (5-(6-(2-(3-ethyl-1,1-dimethyl-1H-benzo[e]indol-2(3H)-ylidene)ethylidene)-2-(2-(3-ethyl-1,1-dimethyl-1H-benzo[e]indol-3-ium-2-yl)vinyl)cyclohex-1-en-1-yl)-1,3-dimethyl-2,6-dioxo-1,2,3,6-tetrahydropyr-imidin-4-olate) as sensitizer. The iodonium salt [A-I-B]⁺X⁻ functioned as a radical initiator bearing a different substitution pattern for the cation and the anion, respectively. Electron transfer of the excited state of S1 to [A-I-B]⁺X⁻ (X⁻: benzilate, lactate, NO₃⁻, PF₆⁻, SbF₆⁻, p-CH₂CH-Ph-SO₃⁻, p-C₁₂H₁₅-Ph-SO₃⁻, CF₃SO₃⁻, C₄F₉SO₃⁻, B(CN)₄⁻, B(Ph)₄⁻, B(PhF₅)₄⁻, N(CN)₂⁻, (SO₂-CF₃)₂N⁻) results in initiating radicals. The reactivity of S1/[A-I-B]⁺X⁻ correlated with the conductivity of the salt in acrylate monomers such as hexane-1,6-diol diacrylate, tripropylene glycol diacrylate, poly(ethylene glycol) diacrylate and trimethylolpropane triacrylate. A high conductivity related always to a better reactivity in the monomer chosen. The solubility of [A-I-B]⁺X⁻ determined ranged between several g L⁻¹ up to well mixable systems (>2000 g L⁻¹). Particular the bis(trifluoromethylsulfonyl) imide anion (N(SO₂-CF₃)₂⁻) resulted in giant solubilities depending on the [A-I-B]⁺ cation. A high solubility did not always lead to a high reactivity. Furthermore, iodonium salts comprising the bis(trifluoromethylsulfonyl) imide anion exhibited a lower cytotoxicity compared to those with the tetraphenyl borate anion as determined by the MTT-test using CHO-9-cells.