Benzophenone derivatives as novel organosoluble visible light Type II photoinitiators for UV and LED photoinitiating systems

Abstract

Five organosoluble visible light benzophenone derivatives (BPs), incorporated different arylamine as electron donating groups have been synthesized and investigated for their roles as photoinitiating systems for free radical photopolymerization of acrylate monomer upon the UV and LED exposure. All the target compounds (BP-1-5) have confirmed through 1 H NMR, HR-MS/EI-MS spectra and elemental analysis. BPs displayed red-shifted absorption, higher molar extinction coefficient and better thermal properties as compared to reference benzophenone (BP) compound. BP and BPs in combination with hydrogen donor, triethylamine (TEA), are prepared and investigated their electron spin resonance (ESR) spectroscopy and photo-DSC (photo-differential scanning calorimetry). ESR spectra of BP-1/TEA package showed the highest radical intensity among the test photoinitiator packages. In addition, BP-1-based formulation exhibited the best double bond conversion efficiency than other BPs and comparable to the BP for the free radical polymerization (FRP) of TMPTA under similar UV light source. We then selected BP-1/TEA and BP/TEA package for FRP under LED light irradiation. Interesting, the BP-1/ TEA system exhibited better efficiency and shorter time at maximum heat flow than BP/TEA. This result indicates BP-1 photoinitiator not only displays good light harvesting, thermal property, but exhibits conversion efficiency under the irradiation of UV and LED.

Ketone Number and Substitution Effect of Benzophenone Derivatives on the Free Radical Photopolymerization of Visible-Light Type-II Photoinitiators

“…BPDP-D exhibited the broadest absorption spectra due to the diketone with para electron-donation substituents, which might be beneficial for light absorption with good photoreactivity. In addition, BPD-D sample containing double arylamine substituents was also compared to the mono-arylamine substituent (i.e., BP-1) [ 25 ]. The BPD-D has longer λ max and higher molar extinction coefficient than that of BP-1 congener.…”

“…Electron spin resonance (ESR) experiments on the photoinitiator were carried out using a Bruker EMX Plus X-Band spectrometer (Billerica, MA, USA) using ultrahigh pressure mercury (MUV-250U-L, λ: 250–450 nm, intensity: 250 W) as irradiation source for generating radicals. The radicals were trapped by N-tert-Butyl-α-phenylnitrone (PBN) according to a procedure described according to the literature [ 25 ]. All the experiments were carried out at room temperature under nitrogen atmosphere in t-butylbenzene as solvent.…”

“…g Melting point. h The reduction potential were tabulated from the literature [ 25 ]. i Data from materials safety data sheet document.…”

“…However, initiation of photopolymerization is still a challenge and require more suitable photoinitiators to meet the needs of industry. Previously, we showed that a series of type II benzophenone derivative based photoinitiators containing various mono-electron donating groups in their molecule structures could undergo different photoreactivity under similar light irradiation [ 25 ]. There are current reports of the synthesis and characterization of a series of benzophenone derivatives with mono or diketone units at para-or meta-positions with similar diphenylamine electron-donating groups.…”

Chemical engineering around the 5,12-dihydroindolo[3,2-a]carbazole scaffold: Fine tuning of the optical properties of visible light photoinitiators of polymerization

“…[18][19][20] However, considering that these chromophores were UVcentered, shift of their absorptions towards the visible range can only be obtained at the cost of difficult syntheses and most of the dyes only absorb not far from the near-UV/visible range. [21][22][23][24][25][26][27][28][29] Face to these considerations, a second approach consists in developing new molecules totally disconnected from these historical structures. [30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48] Considering that visible light photoinitiators of polymerization should exhibit a strong absorption over the visible range, long-living excited state lifetimes but also appropriate electrochemical properties in order to efficiently interact with the different additives introduced into the photocurable resins, structures commonly used in Organic Electronics are candidates of choice for photoinitiation.…”