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

• Published in: Polymer chemistry Vol. 14; no. 3; pp. 3421 - 3432
• Main Authors: Wu, Yu-Hao, Noon, Adel, Hammoud, Fatima, Hamieh, Tayssir, Toufaily, Joumana, Graff, Bernadette, Lalevée, Jacques, Chen, Yung-Chung
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 01.08.2023
• Subjects: Carbazoles; Electromagnetic absorption; Esters; Formulations; Free radicals; Light emitting diodes; Photoinitiators; Photopolymerization; Polymer chemistry
• ISSN: 1759-9954; 1759-9962
• DOI: 10.1039/d3py00682d

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. Compounds ( TPA-DP , TPA-CZ and TPA-PT ) had been developed and synthesized, in which three electron-donating groups (diphenylamine, carbazole, or phenothiazine) are connected to the 4,4′-positions of the triphenylamine to form three triarylamine oxime ester photoinitiators.