Photoinitiation mechanisms of novel phenothiazine-based oxime and oxime esters acting as visible light sensitive Type I and multicomponent photoinitiators
Résumé
In this work, three new photoinitiators, based on the phenothiazine scaffold as a chromophore and potentially bearing the oxime ester functionality as an initiating group were designed and synthesized for the free radical polymerization of acrylates, the cationic polymerization of epoxides, and the formation of interpenetrated polymer networks upon irradiation with a light emitting diode emitting at 405 nm. These phenothiazine-based oxime and oxime esters revealed impressive photoinitiation ability manifested by excellent polymerization rates and high final reactive function conversions. Significantly, they can be used as both; one-component (Type I) and two-component photoinitiating systems. Photoinitiation mechanisms through which reactive species are produced were investigated by means of different complementary techniques including real-time Fourier transform infrared spectroscopy, UV-visible absorption spectroscopy, electron spin resonance spectroscopy, fluorescence (steady state and time resolved), cyclic voltammetry, and molecular modelling calculations. Thermal initiation behavior of the different oxime esters was also studied by using differential scanning calorimetry, highlighting their dual thermal/photochemical initiation ability. Finally, 3D printed objects were successfully fabricated by conducting both direct laser write and 3D printing experiments.
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