Jacques Lalevée

Radical polymerization activity and mechanistic approach in a new three‐component photoinitiating system

A new three-component photoinitiating system (based on isopropylthioxanthone ITX, amine AH, and a bifunctional benzophenone–ketosulfone BP-SK photoinitiator) for acrylate polymerization reactions was investigated through steady-state photolysis (photodegradation, redox potentials, and acidity release determinations) and time-resolved laser spectroscopy. The photopolymerization activity has been checked. It is shown that addition of ITX to BP-SK/AH clearly enhances the efficiency of the photopolymerization of clear or pigmented coatings. This is explained (although, a direct interaction between the triplet state of ITX and BP-SK occurs to some extents) on the basis of the interaction of BP-SK with the ketyl radical of ITX.

Recent advances in sunlight induced polymerization: role of new photoinitiating systems based on the silyl radical chemistry

In the present paper, the recent development of new silyl chemistry based photoinitiating systems for sunlight induced polymerization is presented. The inherent issues of the effects of a low light intensity and oxygen inhibition are discussed. Some selected examples leading to tack free coatings in free radical photopolymerization (FRP) and cationic photopolymerization (CP) are provided. The use of the silyl radical chemistry to overcome the O2 inhibition is presented. The sunlight induced polymerization might be a promising way for practical low cost and environmentally friendly curing processes. The use of renewable epoxy monomers (such as epoxidized soybean oil (ESO), epoxidized linseed oil (ELO) or limonene dioxide (LDO)) in combination with a sunlight induced process also appears particularly worthwhile for green chemistry applications.

Investigation of cleavage processes in photoinitiators: from experiments to molecular modeling

Abstract The present paper shows an original approach combining laser induced photoacoustic calorimetry (PAC) and molecular modeling for the investigation of the cleavage process in radical photoinitiating systems. The bond dissociation enthalpies (BDE) and the enthalpies for the photodissociation reaction ΔHr diss of the photoinitiators are calculated and the quantum yields of dissociation φ diss from the excited state are determined. It appears that these quantum yields are not unity and do not correlate either with BDEs or ΔHr diss .

Investigation of the photochemical properties of an important class of photobase generators: the O-acyloximes

Abstract The influence of the molecular structure and the required conditions for bond breaking in the triplet state of 10 carefully selected O -acyloximes (eight of them are original) usable as photobase generators are deeply investigated for the first time. Ground state absorption and fluorescence spectra revealed that the transitions involved exhibit a ππ ∗ character. A clear nonvertical character in triplet–triplet energy transfer was found in compounds exhibiting a flexible arylCNO moiety. An important and new point is concerned with this effect which strongly affects the triplet sensitized decomposition process, due to the possible formation of a highly vibrationally excited triplet state from which dissociation can occur. Laser experiments enabled to detect the primary free radicals formed from both direct and sensitized dissociation and to measure the relative quantum yields in iminyl radicals. Comparison of these laser experiments with steady state quantum yields of photolysis demonstrates the involvement of in-cage reactions that influence the overall efficiency of base generation, depending on the acyl moiety. All these facts were rationalized in a global mechanism of photodissociation and found to explain well the results of photoinitiated thermal crosslinking experiments performed in a model media with the starting oxime esters.

Non-vertical energy transfer to oximes: role of structural changes

Energy transfer to aromatic ketone oximes can exhibit non-vertical behaviour depending on the planarity of ground state equilibrium geometry, a fact discussed in terms of structural changes of ground and triplet states.

Influence of the S0−T1 structural changes on the triplet–triplet sensitization of dienes

Abstract The triplet–triplet energy transfer properties of different dienes were examined through time-resolved laser spectroscopy, and the different structural changes between ground and triplet states were investigated by molecular modeling. It was found that these compounds exhibit very different behaviors depending on their molecular structure. The calculations of ground- and triplet-state potential energy surfaces (PESs) at the B3LYP/6-31+G(d) level clearly evidenced the crucial role of the thermal activation of a single bond torsion in order to decrease the energetic requirement for the transition. A recently developed model, that included the influence of such a torsional mode, was successfully used to support this hypothesis.

Chapter 8:Recent advances in photoinduced polymerization reactions under 400–700 nm light

The very recent developments of novel photoinitiators and photoinitiating systems in photoinduced radical and cationic polymerization reactions are reviewed. The use of mild irradiation conditions in the blue-to-red wavelength range (household halogen lamps, LEDs, fluorescent bulbs, sunlight; reactions under air) is particularly outlined. New opportunities in applications requiring such experimental conditions in sunlight curing, photoredox initiated polymerizations or in situ incorporation of nanoparticles in a photopolymerizable matrix are described.