New iodonium salts in NIR sensitized radical photopolymerization of multifunctional monomers

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-CH2=CH-Ph-SO3-, p-C12H15-Ph-SO3-, CF3SO3-, C4F9SO3-, B(CN)(4)(-), B(Ph)(4)(-), B(PhF5)(4)(-), N(CN)(2)(-), (SO2-CF3)(2)N-) 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.