Benzylidene ketones as visible light radical photoinitiator: The effects of electron-donating group and co-initiator

Recent advances on benzylidene ketones as photoinitiators of polymerization

“…Recently, influence of the electron-donating groups of benzylidene ketones on the photoinitiating ability was examined with a series of four dyes (C3PH, C3PO, C3PS and C3PN) in which ethoxy, methylthio and dimethylamino groups were used as electron donating groups (See Figure 19). [317] Figure 19. Chemical structures of C3PH, C3PO, C3PS and C3PN.…”

“…Reproduced with permission of Ref. [317] Noticeably, irrespective of the irradiation wavelength, only low monomer conversions were obtained with the different dyes when used as monocomponent systems. Conversely, upon addition of TEOA, a significant enhancement of the monomer conversion could be evidenced.…”

“…Reproduced with permission of Ref. [317] Photobleaching of the photocurable resins is a major concern of visible light photopolymerization. Indeed, due to the fact that dyes absorbing in the visible range are used, the photosensitizer is often responsible of an undesired colour imposed to the final coatings, adversely affecting the development of visible light photopolymerization.…”

“…Figure 20. UV-visible absorption spectra of C3PH, C3PO, C2PS and C3PN in acetonitrile.Reproduced with permission of Ref [317]. …”

Two- and three-photon processes in photoinitiators for 3D laser printing

“…Upon photoactivation of DETC and the formation of T 1 state, energy barrier significantly decreases up to 5.8 and 3.1 kcal/mol allowing HAT with the rate of 7x10 08 s -1 and 4x10 10 s -1 , calculated employing the Eyring equation 30 at room temperature and pressure, in ACN and gas phase, respectively. However, recently, Xue et al 31 have reported that the reaction of benzylidene ketone PIs during the reaction with the amine-based co-initiators is predominantly controlled by material diffusion rather than by an activation process. We believe this is the reason why resists with DBA show no two-photon scaling during 3D printing of PETA using DETC, reported in Fig.…”