Investigation of Novel Long Wavelength Photoinitiators for Radical Polymerization

Abstract

Photoinitiators (PI) for free radical polymerization have been modified using heteroatoms in the α-position to the benzoyl chromophore since the 1980s.1 At that time, acylphosphine oxides were introduced, originally for an application in the coating industry. Further investigations led to the discovery of Ge-based PIs, with diacylgermanes showing particularly good properties.2 These molecules show the desired bathochromic shift in the absorption spectra, what enables the use of light with longer wavelength. This red-shifted light is important for enhancing the curing depth of formulations. The current state-of-the-art PI is also located in the diacylgermane family with the trade name Ivocerin®. Additional advantages of Ivocerin® are thermal stability and low toxicity. Nevertheless, Ge-based PIs are higher in price compared to e.g. phosphorus based PIs, and therefore not for every application suitable. One way to overcome this disadvantage are Sn-based PIs, as this substance class is known to reach excellent bathochromic shifts in their absorbance as well as high reactivity.3 The only drawback is the poor storage stability of the so far known Sn-based PIs. In this work, novel Ge as well as Sn-based PI were successfully synthesized and photochemically investigated including UV/Vis measurements, photo-DSC measurements and steady state photolysis experiments in order to compare their photochemical properties as well as stability with literature known Sn-based PIs. Funding by the Christian Doppler Research Association (Christian Doppler Laboratory for Advanced Polymers for Biomaterials and 3D Printing), the Austrian Federal Ministry for Digital and Economic Affairs and the National Foundation for Research, Technology and Development is gratefully acknowledged. Additionally, this work was supported by Lithoz GmbH, Karl Leibinger Medizintechnik GmbH & Co. KG and Trauma Care Consult.