Oxygen InhibitionSuppression by Photoinduced ElectronTransfer in Oxime Ester/Triarylalkylborate Photoinitiators

Free radical photopolymerization, a pivotal technology in materials processing, is extensively utilized for radiation curing and micro/nanoscale patterning. Yet, it commonly suffers from oxygen inhibition, which diminishes curability in submicron films and degrades performance. To address this issue, we develop a novel class of (<i>Z</i>)-2-((<i>Z</i>)-2-(hydroxyimino)thiophen-3(2<i>H</i>)-ylidene)-2-(<i>o</i>-tolyl)acetonitrile-derived oxime esters (OXEs) and formulate hybrid photoinitiators by blending these OXEs with tetrabutylammonium butyltriphenylborates. Acting as electron acceptors and donors, respectively, these OXEs, along with butyltriphenylborates, enable photoinduced electron transfer, leading to the formation of triphenylborane and <i>n</i>-butyl radicals. The resultant triphenylborane reacts with oxygen or peroxyl radicals, generating radicals with initiating activity and preserving antioxygen inhibition capability throughout the photopolymerization process. Under LED@405 nm light curing, these hybrid photoinitiators significantly outperform commercial diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, achieving up to 85% retention of cured acrylate resins in air compared to only 8% for the commercial initiator. This novel OXE/triarylalkylborate system presents an exceptional antioxygen inhibition and photoinitiation ability, showcasing the potential for widespread use in radical photopolymerization.