Reactivity and efficiency of difunctional radical photoinitiators

Abstract

Three difunctional cleavable photoinitiators based on the a-hydroxyketone structure were tested in photopolymerization reactions with Fourier transform infrared spectroscopy. The excited-state processes were investigated with time-resolved laser absorption spectroscopy and laser-induced photocalorimetry, which allowed the cleavage quantum yields to be determined and estimates of the triplet-state lifetimes and interaction rate constants with a methacrylate monomer to be given. Modeling calculations helped to describe the ground-state properties and showed that the difunctional photoinitiators exhibited different chromophoric groups than the corresponding monofunctional photoinitiator. An examination of the photochemical reactivity versus the practical efficiency observed in the polymerization showed that these difunctional photoinitiators exhibited better efficiency than the parent molecule, mainly because of their increased absorption properties. Their practical efficiency appeared to be better because of better light absorption when standard polychromatic light sources were used.

Highly Water‐Soluble Alpha‐Hydroxyalkylphenone Based Photoinitiator for Low‐Migration Applications

“…However, its absorption is only slightly increased. This nonlinear dependency of ε max has already been observed by Dietlin et al They propose that the chromophores of multifunctional initiators are able to interact with each other, explaining this unexpected absorption behavior. This observation is also confirmed by the UV–vis spectrum of Di‐PI at a concentration of 0.5 mmol (see Figure ) which shows a significantly lower absorption as the spectrum of 1.0 mmol of I2959.…”

“…However, its absorption is only slightly increased. This nonlinear dependency of ε max has already been observed by Dietlin et al [20] (4 of 6) 1700022…”

Recent advances on naphthalic anhydrides and 1,8-naphthalimide-based photoinitiators of polymerization

“…[189][190] Over the years, several strategies have been developed to overcome this drawback and low migratable photoinitiators based on oligomers, trifunctional and bifunctional architectures or photoinitiators bearing a polymerizable unit have been proposed. [104,107,[191][192][193][194][195][196][197][198][199][200][201][202][203][204][205][206][207][208] With aim at designing low migratable initiators, the best strategy is undoubtedly the introduction of a polymerizable group so that the photoinitiator is Due to the weak absorption at 405 nm, NAPHT-55 could only initiate polymerization while using a halogen lamp (12 mW/cm²). Thus, NAPHT-54/Iod/NVK (1%/2%/3%, w/w/w) could induce a faster polymerization and provide a higher EPOX conversion than its analogue three-component system NAPHT-55/Iod/NVK (1%/2%/3%, w/w/w).…”

Recent advances on pyrene-based photoinitiators of polymerization

“…Benzophenone is a well-known UV photoinitiator of polymerization and various strategies have been developed to redshift its absorption towards the visible range. In this aim, substitution of the benzophenone core with various chromophores, [193,196] its incorporation in high molecular weight arrangements such as difunctional [197,199] and trifunctional [200] structures, oligomers, [201] dendrimers [202] and even polymers [203][204][205][206] have been examined. By mean of a strong coupling of the molecular orbitals within the compounds, new chromophores that no longer resembles that of benzophenone were obtained.…”