For me research I cannot use any cationic photoinitiator / photoacid generator, but Irgacure PAG 103.
So my question only applies to this single product of BASF. Has anyone used it for cationic photopolymerization?
I tried it in 1 wt-% with Epoxides (ECC), divinylether and oxetanes, but in no case I observed any curing.
When checking the IR spectra, then there is no decrease in the epoxide signal at ECC (790 cm^-1), for example.
Nevertheless, when I irradiate Irgacure PAG 103 in Acetonitrile at 415 nm, I get the same results like in literature - the absorption spectrum shifts exactly like in this paper, indicating that the photocleavage works in Acetonitrile:
Article Photochemical Fragmentation of Irgacure PAG 103
Anyone knows why the PAG can be cleaved in Acetonitrile, but does not cause any polymerization with the suitable monomers?
Dear Christof Rein, hope this time you get answers from more spécialisés RG Scholars. Again I just provide you with some references. My Regards
https://doi.org/10.1021/acsomega.9b02621
https://doi.org/10.1002/(SICI)1099-0518(20000201)38:33.0.CO;2-G
DOI:10.1039/C7PY00855D
BOOK:
Photoinitiators for Polymer Synthesis: Scope, Reactivity and Efficiency
Author(s): Prof. Jean Pierre Fouassier Prof. Jacques Lalevée
First published:4 July 2012
Print ISBN:9783527332106 |Online ISBN:9783527648245 |DOI:10.1002/9783527648245
I finally got the answer, so just in case anybody else may stumble upon a similar problem:
The Photoacid generated by Irgacure PAG 103 is Propanesulfone acid. This is a very strong acid of course and will deprotonate 100 %ly. Still, the nucleophily of the anion is extremely small, but not 0. And that is why the Sulfonate anion will ultimately react with a growing polymer chain and lead to a termination. Thats why you will always get oligomers or small polymers, that will never fully harden - the Sulfonate will terminate every chain at some point.
Therefore Irgacure PAG 103 can only be used for photoacid applications outside of polymerization. Thats also why it never worked for me and also never will.
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