Cationic Photoinitiators

Cationic photopolymerization offers not only wide range of polymerizeable monomers (e.g. epoxides, oxetanes, vinyl ether) but also a clear advantage compared to the classical free radical photopolymerization, which is the insensitivity to oxygen inhibition and the dark curing process.

The state of the art cationic photoinitiators (so called photo acids) are usually iodonium or sulfonium salts of fluorometallate anions (e.g. BF4-; PF6-; AsF6-; SbF6-) or [BAr4F]--anions. These anions suffer from different drawbacks like toxicity, hydrolysis or tough synthesis.

Very recently we have developed a new class of photoinitiators (sulphonium as well as iodonium salt) based on a fluorinated alkoxyaluminate [1], that

   •     is expected to have a low toxicity,

   •     has a high stability against hydrolysis,

   •     is easy to synthesize and

   •     shows a high reactivity.

Especially the high reactivity towards the usually rather inactive glycidylethers (e.g. bisphenol A diglycidyl ether BADGE) is remarkable. Especially in frontal polymerization outstanding reactivity has been found [2]. Based on these results we have synthesized and evaluated different anions and cations to seek for new classes of cationic initiators [3,4].


[1] N. Klikovits, P. Knaack, D. Bomze, I. Krossing, R. Liska: "Novel photoacid generators for cationic photopolymerization"; Polymer Chemistry, 30 (2017), 30; S. 4414 - 4421.

[2] P. Knaack, N. Klikovits, A.D. Tran, D. Bomze, R. Liska: "Radical induced cationic frontal polymerization in thin layers"; Journal of Polymer Science Part A: Polymer Chemistry, 57 (2019), 11; S. 1155 - 1159.

[3] R. Taschner, R. Liska, P. Knaack: "Evaluation of suitable onium tetrafluoroborates for cationic polymerization of epoxides"; Polymer International, 71 (2021), 1; 13 S.

[4] R. Taschner, P. Knaack, R. Liska: "Bismuthonium- and pyrylium-based radical induced cationic frontal polymerization of epoxides"; Journal of Polymer Science Part A: Polymer Chemistry, 59 (2021), 16; S. 1841 - 1854.