Boron Compounds as Additives for the Cationic Polymerization Using Coumarin Derivatives in Epoxy Silicones

Abstract

This work aims at using two borane derivatives, namely Borane A: B(C6F5)3 and Borate B: C32H12BF24Na as additives for the cationic polymerization of epoxy silicones under visible light, in the presence of coumarins as photosensitizers and 4‐isopropyl‐4′‐methyldiphenyl iodonium tetrakis(pentafluorophenyl)borate (SC939). The effect of boron compounds on the absorption and the emission spectra of a coumarin is particularly outlined. These two boron compounds can improve both the polymerization rate and the final monomer conversion. Moreover, the effect of adding water on the reactivity of the system is studied. It should be noted that the studied boron additives are able to enhance in an interesting way the polymerization rate when light irradiation is switched off through a dark polymerization (DP) mechanism. This latter behavior is highly desired for practical applications. Finally, the very high photoreactivity of boron compounds is employed for the development of new cationic 3D printing resins upon exposure to a light emitting diode (LED) projector at 405 nm, as well as for direct laser write experiments, by means of a laser diode at 405 nm. The 3D polymerization occurs through a cationic process which can be quite useful in order to reduce the shrinkage usually observed in radical polymerization.

Recent advances on coumarin-based photoinitiators of polymerization

“…The crucial role of additives on the polymerization efficiency was recently demonstrated with the introduction of borates within the photocurable resins. [113] Based on the literature, it has been noted that borane A (B(C6F5)3) can complex ketones and therefore can change their absorption or emission properties and then their photochemical reactivities. [226][227][228][229] Notably, without light activation, the cationic polymerization of p-methoxystyrene was reported in the presence of borane A and water.…”

“…(B): (1) C86/SC939/Borate B (0.05%/1%/2% w/w) (when the light was continuously on for 800 s); (2) C86/SC939/Borate B (0.05%/1%/2% w/w) (when the irradiation was turned off at t = 30 s). The irradiation starts at t = 10 s. Reprinted with permission from Abdallah et al [113] Based on the polymerization results, a global photochemical mechanism could be proposed, relying on equations r9-r12.…”

Recent advances on chalcone-based photoinitiators of polymerization

“…Considering the requirement for photoinitiators to strongly absorb in the visible range, a wide range of structures have been examined over the years, as exemplified with chromones, [26][27][28] benzophenones, [29][30][31][32][33][34] pyrenes, [35][36][37][38][39][40] diketopyrrolopyrroles, [41][42][43] coumarins, [44][45][46][47][48][49][50], iron complexes, [51][52][53][54][55][56][57] 2,3-diphenylquinoxaline derivatives, [58] naphthalimides, [59][60][61][62][63][64][65][66][67][68][69][70][71] squaraines, [72][73]…”

Recent advances on benzylidene ketones as photoinitiators of polymerization

“…Reprinted with permission from Bonardi et al [34] If visible light photopolymerization seems to be an appealing and promising alternative to UV photopolymerization, the fact to use less energetic irradiation wavelengths adversely impact the reactivity of visible light photoinitiators. To address this issue, numerous families of dyes have been investigated during the last 15 years, as exemplified with coumarins, [35][36][37][38][39][40][41][42][43][44][45][46][47] chromones and flavones, [48][49][50] pyrrole derivatives, [51] iodonium salts, [52][53][54][55][56][57][58][59] thioxanthones, [60][61][62][63][64][65][66][67][68][69][70][71][72][73] iridium complexes, [74][75][76][77][78][79]…”