New iodonium salts in NIR sensitized radical photopolymerization of multifunctional monomers

Abstract

Reactivity of new iodonium salts [A-I-B] + X À 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 À 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 À (X À : benzilate, lactate, NO 3, (SO 2 -CF 3 ) 2 N À ) results in initiating radicals. The reactivity of S1/[A-I-B] + X À 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 À determined ranged between several g L À1 up to well mixable systems (>2000 g L À1 ). Particular the bis(trifluoromethylsulfonyl) imide anion (N(SO 2 -CF 3 ) 2 À ) 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.

Comparison between NIR and UV-Sensitized Radical and Cationic Reactivity of Iodonium Salts Comprising Anions with Different Coordination Behavior

“…The salts 1c and 2e were synthesized according to a previous procedure based on anion exchange [19]. Thus, the corresponding potassium salts…”

“…Each sample went through a syringe filter before used in the experiment. The light generated was collected with a lens and projected into a y-fiber, which was connected with the head of the DSC (Q2000 from TA-Instruments) [19]. The output of each fiber arm was adjusted with radiometric sources (HR4000 from Ocean Optics).…”

“…A regular photo-DSC setup was used to determine the photo initiation efficiency of the NIR photoinitiator systems in the monomers [19]. Each sample went through a syringe filter before used in the experiment.…”

“…Alternative anions may be fluorinated phosphates with fluorinated alkyl groups ([PF 6-x (C n F 2n+1 ) x ] -; x>0, x<6) showing from our best knowledge no HF release under conditions where this phenomenon was observed in the case of PF 6 interesting alternative anion in iodonium salts. It exhibited in some cases a giant solubility in many monomers while the reactivity in NIR-photopolymers was remarkable [8,19] --anion as counter ion. Thus, such methides would form an interesting alternative compared to imides since they should exhibit according to their structure a less nucleophilicity [8,19,20].…”

“…It exhibited in some cases a giant solubility in many monomers while the reactivity in NIR-photopolymers was remarkable [8,19] --anion as counter ion. Thus, such methides would form an interesting alternative compared to imides since they should exhibit according to their structure a less nucleophilicity [8,19,20].…”