New Push–Pull Dyes Derived from Michler’s Ketone For Polymerization Reactions Upon Visible Lights.

Abstract

Among other photoinitiating systems, aromatic ketone based compounds have been largely exploited as photoinitiators (PIs). However, none of these compounds efficiently absorb above 420 nm. The search of novel architectures of PIs for getting an important red-shift of the absorption is crucial for the use of visible lights for polymer synthesis. Novel bifunctional dyes derived from the Michler's ketone structure are proposed here as photoinitiators for the free radical polymerization of acrylates and the cationic polymerization of epoxides upon exposure to 457, 473, and 532 nm laser diodes and even to a green LED bulb at 514 nm. Excellent polymerization profiles are obtained. These original dyes exhibit a push−pull molecular character for a remarkable covering of the visible lights. The formation of the radicals and the ions in the two-and three-component photoinitiating systems is described and the initiation steps are discussed.

Visible light sensitive photoinitiating systems: Recent progress in cationic and radical photopolymerization reactions under soft conditions

“…The large number of BP derivatives [e.g., 4,4 -diethylaminobenzophenone (EAB), benzophenonesulfonyl ketone (BPSK), 4-benzoyl-4 -methyl diphenyl sulphide (BMS), 2,4,6-tri(4-benzoylphenylamino)-1,3,5-triazine (Tz BP), silylated benzophenone, etc.] have already been prepared and investigated [1,16,25,152,153], but mainly remained sensitive to UV lights. Recently, some UV light sensitive BP derivatives [28,32,38,[154][155][156][157][158][159][160][161] with specific properties (e.g., migration stability or anti-oxygen inhibition effect) have also been developed.…”

“…To the contrary, a real progress has been made in the synthesis of new chemical skeletons and new modifications of existing structures, as well as in the use of new additives: this has allowed the proposal of a large number of novel PIs and PISs. The mechanisms encountered in these systems are schematically depicted in reactions (1)-(7) [10][11][12][13][14][15][16]: after light absorption, PI interacts with one or two additives (e.g., iodonium salt, amine, N-vinylcarbazole, silane, chloro triazine, etc. ; Scheme 1) to generate initiating radicals for free radical polymerization (FRP; reactions (1)-(3a) and (6)) of (meth)acrylates or thiol-ene polymerization (TEP; reactions (1), (2) and (5)), cations or radical cations for cationic polymerization (CP; reactions (1) and (2)) or free radical promoted cationic polymerization (FRPCP) of epoxides (reactions 1-3) or vinyl ethers (reactions (1), (2) and (4)); the concomitant cationic/radical polymerization CCRP (hybrid cure) of a cationic monomer/radical monomer blend can also be achieved for the manufacture of interpenetrated polymer networks IPNs.…”

A new role of curcumin: as a multicolor photoinitiator for polymer fabrication under household UV to red LED bulbs

“…42,43 It is well known that curcumin can act as a free radical scavenger, 44 but its role as a photoinitiator (but not a free radical scavenger) predominates in the relevant photoinitiating systems based on the ESR results. Based on the above investigation, phenyl radicals and aminoalkyl radicals can be generated in the CCM/Iod and CCM/EDB systems respectively during LED irradiation, through the photochemical mechanisms presented in Scheme 1.…”

Unprecedented Nucleophilic Attack of Piperidine on the Electron Acceptor during the Synthesis of Push‐Pull Dyes by a Knoevenagel Reaction

“…During the past decades, push‐pull dyes have been extensively studied with regards to their numerous applications ranging from sensors, energy conversion, field effects transistors, organic light‐emitting diodes, nonlinear optics or photoinitiators of polymerization . To access to these structures consisting in an electron donor connected to an electron acceptor by means of a conjugated or none‐conjugated spacer, the Knoevenagel reaction is undoubtedly the most popular reaction, opposing an aldehyde with an electron acceptor bearing an activated methylene group, in the presence of a catalytic amount of a base.…”