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

Abstract

Three novel visible-light absorbing benzophenone-based hydrogen acceptors (BPD-D, BPDM-D and BPDP-D) were designed on the basis of a donor–benzophenone–donor structural backbone. Mono or diketone units and double diphenylamine electron-donating groups in para-or meta-positions were introduced to comprehend the electronic and structural effects on free radical photopolymerization (FRPP). Such a structural change leads not only to a red-shift of the absorption maxima but strongly enhances their molar extinction coefficients compared to the commercial phototinitiators such as benzophenone (BP) and 4,4′-bis(diethylamino) benzophenone (EMK). In addition, excellent melting points and thermal decomposition temperatures were achieved for those novel compounds. Further, the photochemical reaction behavior was studied by cyclic voltammograms (CV), photolysis and electron spin resonance (ESR) spectroscopy. Finally, benzophenone derivatives in combination with an amine (TEA, triethylamine) as a co-initiator were prepared and initiated the FRPP of trimethylolpropane trimethacrylate (TMPTMA) using a UV lamp as a light source. When used in stoichiometric amounts, the BPDP-D/TEA had the best double bond conversion efficiency among all the compounds studied, and were even superior to the reference compounds of BP/TEA and EMK/TEA. The results and conclusions could provide the fundamental rules applicable for the structural design of benzophenone derivative-based photoinitiators.

Effects of the number and position of methoxy substituents on triphenylamine-based chalcone visible-light-absorbing photoinitiators

“…Scan rate = 100 mV s −1 ; electrolyte = n Bu 4 NPF 6 .dThe bandgap, E g , was derived from the intersection of the absorption and emission spectra.eThe free energy changes between CY1–CY5 and the TEOA bimolecular system followed the equation Δ G ET = E ox − E red − E g + C .fTemperature at 5% weight loss recorded through TGA performed at a heating rate of 15 °C min −1 in N 2 .gMelting point.hRef. 41.…”

“…Therefore, we also investigated the effect of substitutions of the TPA unit and discovered that these substitutions strongly affected the photoreactivity. 15,27,[40][41][42] TPA and chalcone moieties were also combined by Lalevée et al to yield a series of symmetric and asymmetric photoinitiators; these compounds exhibited broad and red-shifted absorption that would make them suitable for visible light irradiation. 31,[43][44][45] Although monochalcones offer greater flexibility in structure design, their poor light harvesting may limit their application to visible light irradiation.…”

Photocrosslinking of ethylene‐vinyl acetate (EVA)–polyethylene‐octene (POE) copolymer containing halogen‐free flame retardants

“…So far, the most common light sources that have been used to activate the photoinitiators are mercury UV lamps [ 27–30 ] ; however, due to the high costs, reduced depth of penetration and environmental concerns, the research is focusing on their replacement with near‐UV emitting LEDs. [ 31 ]…”

High potential of new dyeing photoinitiators for fast curing of (meth)acrylate compositions under low intensity UV–Vis light

“…12 Photoinitiated polymerization reactions belong to the commonly used methods of production of various types of novel smart and multifunctional polymer materials with specific functional properties and multiple conventional applications. 1,[9][10][11][12][13] Photopolymerization processes have found applications in many fields of science and technology. [14][15][16][17][18][19][20][21][22] Several examples of the use of photopolymerization reactions are presented in Fig.…”