Photopolymerization Reactions Initiated by a Visible Light Photoinitiating System: Dye/Amine/Bis(trichloromethyl)-Substituted-1,3,5-Triazine

Abstract

Addition of a bis(trichloromethyl)‐substituted‐1,3,5‐triazine (Tz) to a dye/amine photoinitiating system leads clearly to an increased efficiency of polymerization under visible light irradiation. The polymerization rates obtained with three triazine derivatives with either phenosafranine, eosin or Rose Bengal as light absorbing species, were measured. Whatever the investigated dye/amine mixture, the addition of Tz led to a strong synergistic effect: the inhibition time decreased and the polymerization rate increased significantly when the three components were used jointly. The spectroscopic and redox properties of the Tz were measured. The system dye/amine/Tz was investigated through time‐resolved laser spectroscopy and steady state fluorescence experiments. A detailed reaction mechanism was elaborated which shows that Tz acts mainly as an inhibitor scavenger. The involved inhibitor is the reduced dye (DH∗︁) arising from the first photochemical reaction between the excited states of the dye and the amine.

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

“…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.…”

Triazine‐Based Type‐II Photoinitiating System for Free Radical Photopolymerization: Mechanism, Efficiency, and Modeling

“…It has three main advantages: (i) the fundamental state of the PI is regenerated and can participate to a new cycle, (ii) supplementary initiating radicals are produced, (iii) potential terminating agents are consumed. Among the numerous PCIS redox additives reported in the literature, triazine derivatives (Tz) have been extensively used as electronacceptors in combination with amines, [12][13][14][15][16][17] thiols, [18] or borate salts. [18][19][20][21] They have been found to enhance final conversion and rate of polymerization by reacting with the semi-reduced form of the PI.…”

“…It has been reported that triazine A (TA) is not able to initiate acrylate photopolymerization when combined to several different dyes. [12,13] However, recent studies have proved that triazine derivatives are actually efficient to act as co-initiators, via a photoinduced electron transfer from the singlet state of pyrromethene derivatives. [15][16][17] Interestingly, isopropylthioxanthone (ITX) which is one of the most versatile photoinitiator for free radical photopolymerization (FRP) [23] has never been combined with triazine derivatives in a two-component photoinitiating system for FRP, although that such a combination has been studied for photoacid generation.…”

“…The interaction between triazine derivatives and ITX triplet state has been reported to occur through an energy transfer with a resulting triazine triplet state undergoing a homolytic dissociation of the CCl bond followed by a consecutive electron transfer between the radical moieties. [24] The triplet state energy E T of TS is 3.2 eV, [12] a value much higher than that of ITX (E T = 2.71 eV [24] ). Therefore, the triplet-triplet energy transfer from ITX to TS appears thermodynamically disfavored, the Gibbs free energy variation of energy transfer being ΔG PEneT = 0.49 eV.…”

“…Because TA highly absorbs around 355 nm, it was not possible to analyze its photosensitized mechanism with ITX by LFP. However, positive ΔG PEneT value of 0.19 eV (E T = 2.9 eV [12] ) compared to ΔG PEleT of −0.08 eV (E red = −1.12 V vs. SCE [16] ) tends to indicate that a photoinduced electron transfer is also operating for ITX/TA system. The Type-II PIS model was used with parameters specific to TA (initial concentrations, k et extracted with Equation (9) from the k q = 3.7 × 10 9 m −1 s −1 reported value [64] ) and a k bet value of 7.5 × 10 5 s −1 was found ( Figure 6) for a ΔG bet value of −2.63 eV.…”