Multibranched triarylamine end-capped oxime esters as visible-light absorbing type I photoinitiators for free radical photopolymerization

Abstract

A series of oxime esters (TPA-DP, TPA-CZ and TPA-PT) have been developed and synthesized, in which three electron-donating groups (diphenylamine, carbazole, and phenothiazine) are connected to the 4,4′-positions of the triphenylamine to form three triarylamine oxime ester photoinitiators. All the compounds were prepared successfully; in addition, for reference the electron-donating free oxime ester (TP-1M) was also prepared for comparison. The influence of different electron-donating groups on the absorption region, theoretical calculations, and photochemical properties of oxime esters was studied. In addition, photo-DSC experiments under UV, LED@365 nm and LED@405 nm exposures were carried out to realize the corresponding photoreactivity. Although compound TPA-DP exhibits a rather red-shifted and broader absorption region, TPA-CZ and TPA-PT based formulations showed better photochemical and photoreactive properties. Furthermore, two-component photoinitiating systems of oxime ester/iodonium salt (Iod) showed an efficient free radical and cationic photopolymerization behavior under irradiation with a 405 nm LED. Finally, these oxime esters also displayed thermal initiation characteristics, indicating that these compounds are capable of acting as both thermal and photochemical initiators.