New kinetic and mechanistic aspects of photosensitization of iodonium salts in photopolymerization of acrylates

Abstract

a 1,3-Bis(p-bromophenylamino)squaraine which functions as an electron-transfer photosensitizer for a wide range of diphenyliodonium salts radical photoinitiators of triacrylate polymerization under UV-blue light irradiation is presented. The functionality of the photosensitizer is determined by the presence of a suitable co-initiator. For this purpose, several different diphenyliodonium salts were used as a source of active species for radical polymerization. The reactivity of the new iodonium salts was studied with ultraviolet-blue light initiated radical polymerization by photo-DSC using squaraine dye as a sensitizer.The iodonium salts functionated as radical initiators bearing different substitution patterns. Electron transfer from the excited state of the sensitizer to the iodonium salt results in initiating radicals. The ability to initiate free radical polymerization of TMPTA by iodonium salts studied is similar. Most of the iodonium salts exhibit no large differences regarding the reactivity in initiation of TMPTA polymerization.However, an introduction of a nitro group in the para position of the phenyl ring of the co-initiator results in a significant increase in the rate of polymerization and degree of monomer conversion. The dye-sensitized photoreaction mechanism of the SQ/I system was also confirmed.

Iodonium sulfonates as high‐performance coinitiators and additives for CQ‐based systems: Toward aromatic amine‐free photoinitiating systems

“…After excitation of the PI or PS, the iodonium salt is reduced and diaryliodine radicals are formed. Aryl radicals are generated through the cleavage of the CI bond …”

“…Aryl radicals are generated through the cleavage of the C I bond. 9,[17][18][19][20] In many fields such as dentistry, the most employed two component PIS is CQ/amine. 6,21 Due to its visible light absorption properties in the 400-500 nm spectral region, CQ is the reference system for the free-radical polymerization of methacrylate under visible light.…”

Development of New High-Performance Biphenyl and Terphenyl Derivatives as Versatile Photoredox Photoinitiating Systems and Their Applications in 3D Printing Photopolymerization Processes

“…Nevertheless, cationic photopolymerization is applied mainly to epoxy monomers, vinyl ethers, and their derivatives in the industry [30,31]. In the photochemical industry, onium salts and mainly diaryliodonium and triarylsulfonium salts [32,33], in which protons are the particles initiating the process and active centers are carbocations or onion ions [34], are used as efficient photoinitiators for the cationic photopolymerization process. In contrast to free-radical photopolymerization, which experiences rapid termination of the polymerization process when the light is turned off (due to radical-radical termination reactions), the cationic polymerization processes proceeds long after irradiation has ceased, until nearly all of the monomer has been consumed [35].…”

Sunlight photodepolymerization of transient polymers

“…The sensitization of iodonium salts has been used in cationic photopolymerizations to achieve faster rate with anthracene derivatives . Near infrared sensitization of iodonium salts has been assessed previously with cyanines; however, the basic functionality is likely not compatible with acid‐catalyzed processes . Wallraff et al .…”