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P. Knaack, D. Bomze, I. Krossing, R. Liska:
"Advances in Cationic Photopolymerization";
Vortrag: 4th European Symposium of Photopolymer Science, Leipzig; 11.09.2016 - 14.09.2016; in: "ESPS 2016", (2016), S. O-9.

Cationic photopolymerization is an, long time underestimated, alternative to the classical radical photopolymerization. Various vinyl and cyclic monomers, like vinyl ethers and epoxides can be cured via a cationic mechanism. To start the curing process so called Photo Acid Generators (e.g. iodonium and sulphonium salts) are used which liberate the active acid upon irradiation. Here the invention of a new aluminum based PAG1 allows not only to avoid the classical, highly toxic, arsenic and antimony compounds or the expensive boron based PAG, but also to increase the reactivity drastically.
Since some PAGs are also cleavable via a redox reaction with radicals an elegant alternative for bulk curing of epoxides namely the Radical Induced Cationic Frontal Polymerization (RICFP)2 can be realized. Fig. 1 shows a schematic view of this method where in the first step the PAG liberates the acid upon irradiation, which initiates the exothermic polymerization in step two. The generated polymerization heat cleaves a thermal initiator and the radical generates in a redox reaction with the PAG again the active acid.

This reaction circle will keep itself alive until
. the heat loss towards the surroundings is too high and prevents therefore the cleavage of the thermal initiator, or
. the whole formulation has been cured.
With this process the energy consumption of the curing process can be reduced significantly and the timescale shrinks from hours to minutes.

Cationic photopolymerization, vinyl and cyclic monomers