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P. Gauss, P. Knaack, R. Liska:
"Replacing aromatic type II photoinitiators with aliphatic compounds";
Poster: 5th European Symposium of Photopolymer Science, Mulhouse, France; 03.09.2018 - 06.09.2018; in: "5th European Symposium of Photopolymer Science", 5th European Symposium of Photopolymer Science, (2018), S. P9.

Photopolymerization, as a versatile method, became a well-known method for industry due to high energy efficient and fast curing processes. A wide range of industrial products, from coatings to the most complex applications, such as 3D printing of biomaterials are based on this useful method. The vast majority of industrial radical photoinitiators are founded on aromatic ketones with a benzoyl-chromophore responsible for the light absorption.
Of course when it comes to food packaging and medicinal products, regulations are especially strict for substances migrating through cured network into the product. Low molecular weight photoinitiators and sensitizers as well as their photoproducts can be dangerous for the environment and are able to harm the human body.
Benzophenone derivatives are one of the most common photoinitiators for UV curing in the range of 230-350 nm. Cost efficiency and the rather good performance makes these compounds attractive for industrial applications.
In 2013 the International Agency for Research on Cancer (IARC) published a monograph about the health risks and carcinogenity of benzophenones.1 In this study it is evident that benzophenone, its derivatives and photoproducts act as estrogenic endocrine disruptors in mammals.2 Also some indications that orally consumed benzophenone can induce cancer growth in rhodents was found. Benzophenone is categorized as "possibly carcinogenic to humans (Group 2B)" by the IARC. Investigations on the cancerogenity of benzophenones are ongoing in a REACH study by the European Chemical Agency ECHA.
Generally benzoyl chromophores of cleavable photoinitiators are problematic as various aromatic recombination products are generated during the curing process. Volatile and odorous compounds such as benzaldehyde, acetone or isopropanol can be a risk during production. A lot of degradation and recombination products of aromatic initiators can be potentially mutagenic or toxic to the human body. Therefore, even nontoxic initiators can lead to dangerous migrating substances in the final product.
Looking for new benzoyl-free concepts, nontoxic aliphatic structures were found, which may be able to replace common type II initiators and provide good reactivity, no discoloration and safe photoproducts.

Photopolymerization, 3D printing of biomaterials, aromatic ketones with a benzoyl-chromophore responsible for the light absorption, new benzoyl-free concepts, nontoxic aliphatic structures