Substituent effects on the photoinitiation ability of coumarin-based oxime-ester photoinitiators for free radical photopolymerization

Abstract

In this study, a series of coumarin chromophore-based oxime-esters were designed and synthesized as visible light photoinitiators (PIs).

5,12‐Dialkyl‐5,12‐dihydroindolo[3,2‐a]carbazole‐Based Oxime‐Esters for LED Photoinitiating Systems and Application on 3D Printing

“…The trend of efficiency of the OXEs in the one‐component system in thin samples (25 µm, in laminate) is (3) > (4) > (2) > (8) > (5) > (6) > (10) > (9) > (1) > (7) , which is not directly linked to their absorption properties. Indeed, we have notably shown in our previous work (devoted to a series of coumarin‐based oxime‐esters) [ 10 ] the importance of other factors in the photopolymerization process, such as the cleavage reaction, the decarboxylation reaction, and the reactivity of the generated radicals. For example, the decarboxylation reaction is affected by the ester group and the reaction is energetically more favorable in the case of methyl substituent (Δ H decarboxylation = −4.94 kcal mol −1 ).…”

“…For example, the decarboxylation reaction is affected by the ester group and the reaction is energetically more favorable in the case of methyl substituent (Δ H decarboxylation = −4.94 kcal mol −1 ). [ 10 ] In addition, solubility can also affect the photoinitiation ability. For example, compound (9) which possesses the highest absorption properties, is not efficient in photopolymerization, due to its poor solubility in acrylate monomers.…”

“…[ 4–8 ] Their high efficiency is assigned to the direct photocleavage of the NO bond, enabling to generate iminyl and acyloxy radicals, which in turn can undergo further decarboxylation reactions and generate aryl or alkyl radicals ( Scheme ). [ 9,10 ]…”

Recent advances on coumarin-based photoinitiators of polymerization

“…In 2022, a series of eleven coumarin-based oxime esters C138-C148 was synthesized and influence of the substitution of the oxime esters on the photoinitiating ability was examined (See Figure 42). [265] Interestingly, aliphatic and aromatic groups were used to produce oxime esters. Markedly, a crosslinkable group, namely an acryloyl group, was also used (See C139).…”

“…Photopolymerization profiles of TMPTA (acrylate function conversion vs. irradiation time) in laminate (thickness= 25 µm) upon exposure to LED light λ= 405 nm in the presence of: (1) C138/Iod (0.5%/1% w/w); (2) C139/Iod (0.5%/1% w/w); (3) C140/Iod (0.5%/1% w/w); (4) C141/Iod (0.5%/1% w/w); (5) C142/Iod (0.5%/1% w/w); (6) C143/Iod (0.5%/1% w/w); (7) C144/Iod (0.5%/1% w/w); (8) C145/Iod (0.5%/1% w/w); (9) C146/Iod (0.5%/1% w/w); (10) C147/Iod (0.5%/1% w/w); and (11) C148/Iod (0.5%/1% w/w); respectively. The irradiation starts for t = 10 s. Reprinted with permission from Hammoud et al[265]…”