Photoinitiation behavior of phenothiazines containing two oxime ester functionalities (OXEs) in free radical photopolymerization and 3D printing application

Twelve one-compound photo-fragmenting (type I) photoinitiators containing two oxime esters (OXEs) func-tionalities on the terminal moiety were synthesized. These esters have high light absorptivities in the visible range, and some of them showed better photoinitiation than the commercial photoinitiator diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO), under the irradiation of a 405 nm LED. Photoinitiation mechanisms of these developed OXEs are proposed through theoretical calculations, the detection of CO2, and the ESR investigation of the free radical generation. 3D objects could be manufactured successfully by using the most reactive photoinitiators with a stereolithography 3D printer. In addition, these reactive OXEs also displayed a thermal initiation behavior, meaning that these compounds can served both as thermal or photochemical initiators.