Novel self-initiating UV-curable acrylate monomers

Based on the addition reaction of hydroxyl groups and the isocyanate groups in the bi-functional monomer acroyloxyethyl isocyanate (AOI), two novel self-initiating ultraviolet (UV)-curable acrylate monomers were synthesized from benzoin and 2-hydroxy-4 '-(2-hydroxyethoxy)-2-methylpropiophenone (commercial-available Irgacure (R) 2959), and the products were denoted as Benzoin-AOI and 2959-AOI, respectively. The chemical structures of the products were confirmed by nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy (FTIR). The UV-visible absorption spectrum showed that the self-initiating acrylates exhibited similar maximum absorption wavelengths to both benzoin (250 nm) and Irgacure (R) 2959 (270 nm). When the products were continually exposed to a mercury lamp, the maximum absorption peak gradually blue shifted, showing that the products decomposed under the UV radiation. The photo differential scanning calorimetry (Photo-DSC) analysis showed that the self-initiating monomers could initiate the polymerization of 1,6-hexanediol diacrylate (HDDA) as quickly as the original photo-initiator, and the efficiency of Benzoin-AOI was slightly lower than that of benzoin, while for 2959-AOI, the efficiency remained stable after being linked to the AOI moiety. The cytotoxicity assay against fibroblasts cell line L929 showed that 2959-AOI exhibited lower cytotoxicity at low dosages but higher cytotoxicity at high dosages compared to Irgacure (R) 2959 after the introduction of the AOI structure.