Metal Acetylacetonate–Bidentate Ligand Interaction (MABLI) as highly efficient free radical generating systems for polymer synthesis

Metal Acetylacetonate–Bidentate Ligand Interaction (MABLI) is presented here as a new chemical mechanism for the highly efficient generation of free radicals for polymer synthesis.

New copper(i) complex based initiating systems in redox polymerization and comparison with the amine/benzoyl peroxide reference

Novel copper complex based initiating systems for redox free radical polymerization (FRP) of methacrylate resins under mild conditions are proposed.

Mechanosynthesized copper(i) complex based initiating systems for redox polymerization: towards upgraded oxidizing and reducing agents

Significant improvements of the recently proposed Cu(i)/VitC + water/dibenzoyl peroxide (BPO) system for the redox free radical polymerization of methacrylates in air are presented here.

A novel naphthalimide scaffold based iodonium salt as a one-component photoacid/photoinitiator for cationic and radical polymerization under LED exposure

A strong drawback to overcome for photoinitiators of cationic polymerization or photoacids is their low photosensitivity for long wavelengths.

Aminoalkyl Radicals: Direct Observation and Reactivity toward Oxygen, 2,2,6,6-Tetramethylpiperidine-N-oxyl, and Methyl Acrylate

The reactivity of 11 aminoalkyl radicals toward different additives [oxygen, 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO), and methyl acrylate (MA)] has been investigated through laser flash photolysis and quantum mechanical calculations. The transient absorption spectra of the radicals were recorded: good agreement was found with the spectra calculated by using quantum mechanical calculations. All the interaction rate constants were measured. A large range of values are obtained: (0.04-3) x 10(9) M(-1) s(-1) for O2, (0.002-5) x 10(8) M(-1) s(-1) for TEMPO, and (<0.004-2) x 10(7) M(-1) s(-1) for MA. Generation of the decarboxylated aminoalkyl radical derived from N-phenylglycine was unambiguously demonstrated. It was clearly found that both the addition to oxygen and the recombination with TEMPO were strongly governed by the reaction exothermicity. On the other hand, both polar and enthalpy factors have a large influence on the rate constants of the addition reaction to the acrylate unit, which were ranging over at least 4 orders of magnitude. This paper provides a set of new data to characterize the structure/reactivity relationships of aminoalkyl radicals.

Respective Contributions of Polar vs Enthalpy Effects in the Addition/Fragmentation of Mercaptobenzoxazole-Derived Thiyl Radicals and Analogues to Double Bonds

The formation and the reactivity of three selected sulfur-centered radicals formed from mercaptobenzoxazole, mercaptobenzimidazole, and mercaptobenzothiazole toward four double bonds (methyl acrylate, acrylonitrile, vinyl ether, and vinyl acetate) are investigated. The reversibility of the addition/fragmentation reaction in these widely used photoinitiating systems of radical polymerization was studied, for the first time, through the measurement of the corresponding rate constants by time-resolved laser spectroscopy. The combination of these results with quantum mechanical calculations clearly evidences that, contrary to previous studies on other aryl thiyl radicals, the addition rate constants (ka) are governed here by the polar effects associated with the very high electrophilic character of these radicals. However, interestingly, the back-fragmentation reaction (k-a) is mainly influenced by the enthalpy effects as supported by the relationship between the rate constants and the addition reaction enthalpy DeltaHR. The addition and fragmentation rate constants calculated from the transition state theory (TST) are in satisfactory agreement with the experimental ones. Therefore, molecular orbital (MO) calculations offered new opportunities for a better understanding of the sulfur-centered radical reactivity.

Excited state processes in a four-component photosensitive system based on a bisimidazole derivative

The four component system consisting of bis[2-(o-chlorophenyl)-4,5-diphenylimidazole] (Cl-HABI), N,N'-bis(diethylamino)benzophenone (EAB), N-phenylglycine (NPG) and an iodonium salt (BIP-T) can be used for the photoinitiation of radical polymerization reactions. The excited state processes involved are reported and all the transient species, including the triplet state and ketyl radical of EAB as well as the lophyl radical, are characterized. Rate constants of interaction between the different partners in the four component system are determined. Redox potentials of the different compounds are evaluated enabling the free energies for electron transfer reactions to be calculated. An overall scheme for the evolution of the excited states and a general discussion on the role played by the different components in photoinitiating polymerization are then provided.