Phenothiazine-based oxime ester as a photobase generator for thiol-acrylate reactions

Abstract

In this work, a previously designed and synthesized phenothiazine-based oxime ester was investigated as a photobase generator for the formation of thiol-acrylate networks through the polymerization of thiol-acrylate reactions and more appealingly the base-catalyzed thiol-acrylate Michael addition reactions. This system accomplished a complete disappearance and a full conversion of the characteristic acrylate peak within 10 min of irradiation with a light-emitting diode (λ = 405 nm) or within 1 or 2 min of the same irradiation source and 24 h of heat exposure (T = 60 °C). Photobase generation was evidenced using phenol red as a pH-indicator, enabling to confirm the production of methyl amine (CH3NH2) as initiating species. Photoinitiation mechanism through which base reactive species are produced and the reactions by which the thiol-acrylate polymerization proceeds were investigated according to the base detection experiments, the obtained real-time Fourier transform infrared spectroscopy results, and according to the general photochemical base-generation reactions of oxime-esters. Finally, differential scanning calorimetry scans and Shore A and Shore D hardness experiments have been performed on the polymers obtained to examine their thermal properties and surface hardness features.