Self Initiating and Non Aromatic Initiators

Photopolymerizable coatings, suffer from a major disadvantage: the migration of unconsumed photoinitiator and photoproducts thereof. In the last 10 years, especially in the field of food packaging, serious concerns were addressed as isopropylthioxanthone was found in baby food and also 4-methyl benzophenone has been detected in significant amount. Therefore, in industry polymeric initiators are currently a hot topic, but diffusion limitation reduces activity significantly.

Our aim is to provide photoinitiating monomers that are able to start the radical polymerization and have polymerizable groups in their chromophore. Similar to maleimides investigated in detail by Hoyle and Jönsson, diacrylimides are able to absorb light and efficiently initiate radical polymerization similar to benzophenone/amine systems, although their absorption behaviour is significantly worse [1,2]. Also the benzoylchromophore that is omnipresent in nearly all photoinitiators always gives rise to concerns. Therefore we were interested to evaluate non-aromatic photoinitiators. a-Ketoesters such as the biocompatible a-Ketoglutaric acid have been found to be suitable to substitute classical photoinitiators [3]. Derivatives thereof can be introduced to classical (meth)acrylate oligomers [4].

[1] F. Karasu, C. Dworak, S. Kopeinig, E. Hummer, N. Arsu, R. Liska: "Photoinitiating Monomers Based on Diacrylamides"; Macromolecules, 41 (2008), 21; S. 7953 - 7958.

[2] C. Dworak, S. Kopeinig, H. Hoffmann, R. Liska: "Photoinitiating monomers based on di- and triacryloylated hydroxylamine derivatives"; Journal of Polymer Science Part A: Polymer Chemistry, 47 (2009), 2; S. 392 - 403.

[3] P. Gauss, M. Griesser, M. Markovic, A. Ovsianikov, G. Gescheidt, P. Knaack, R. Liska: "α-Ketoesters as Nonaromatic Photoinitiators for Radical Polymerization of (Meth)acrylates"; Macromolecules, 52 (2019), 7; S. 2814 - 2821.

[4] R. Taschner, P. Gauss, P. Knaack, R. Liska: "Biocompatible photoinitiators based on poly‐α‐ketoesters"; Journal of Polymer Science Part A: Polymer Chemistry, 58 (2020), 2; S. 242 - 253.