α-Ketoesters as Nonaromatic Photoinitiators for Radical Polymerization of (Meth)acrylates

Abstract

Photopolymerization of (meth)­acrylate-based formulations has become a widespread method for industry due to the high energy efficiency and low curing times of this technology. Various products from simple coatings to more complex applications such as additive manufacturing technologies are based on this versatile method. Common industrial radical photoinitiators are generally based on aromatic ketones with the benzoyl chromophore as the key constituent. In medical or food packaging applications, residual photoinitiator or photoproducts migrating into the product have to be avoided, particularly for toxicological reasons. In this paper we present a new generation of nonaromatic initiator systems. Besides their good reactivity in (meth)­acrylic formulations, they show good bleaching properties and high biocompatibility.

1-(2-Naphthyl)-2-(1-pyrrolidinyl)ethanone as a Photoinitiator for Methyl Methacrylate Polymerization

“…These initiators produce the initiating radicals by reacting with co-initiators like thiols, amines, ethers and alcohols. Type 1 initiators require high energy for bond cleavage and they need to use high-energy light sources that have short wavelengths [14][15][16][17].…”

Biocompatible photoinitiators based on poly‐α‐ketoesters

“…). By combining these two theoretical concepts, a nonaromatic photoinitiator, the aliphatic α‐ketoester was successfully introduced recently . α‐Ketoesters, ethyl pyruvate for example, are sensitive to UV‐light with an absorption maximum at around 330 nm (n‐π*).…”

“…α‐Ketoesters, ethyl pyruvate for example, are sensitive to UV‐light with an absorption maximum at around 330 nm (n‐π*). However, the molar extinction coefficient of α‐ketoesters is much lower compared to aromatic ring containing photoinitiators, the quantum yield as well as the radical reactivity is much higher …”

“…Besides acrylates, methacrylates and polyethylene glycol (PEG) diacrylate‐based hydrogels also were cured using α‐ketoesters as photoinitiators. Ethyl pyruvate was compared to benzophenone/amine in terms of reactivity and achieved nearly double the rate of polymerization with around 200 mmol L −1 s −1 in a diacrylate system …”

“…Esters of α‐ketoacids, for example ethyl pyruvate and its photoproducts, were tested in terms of cytotoxicity in a previous study. For the highest concentration tested (18 mmol L −1 ), there was no drop in metabolic activity of mouse fibroblast cells and still above 80% activity for the cells that were irradiated for 10 min by UV‐light . For the present study, α‐ketoglutaric acid was selected for the preparation of polymerizable, macromolecular and polymerizable, macro‐molecular derivatives to ensure a low‐migration photoinitiator compared to a low molecular weight reference (co)initiator based on the benzophenone/amine system.…”