PHOTOREDOX

In recent years, photopolymerizations have witnessed intense research effort due to the constant growth of industrial applications associated with the synthesis of new photoinitiators PI and monomers. The use of photoinitiated polymerization is continuously growing in industry as reflected by the large number of applications in not only conventional areas such as coatings, inks, and adhesives but also high-tech domains, optoelectronics, laser imaging, stereolithography, and nanotechnology. Photopolymerization offers many stricking advantages over traditional thermo-polymerization such as temporal and spatial control of initiation, cost efficiency and solvent-free systems. In contrast to thermally based applications which usually require elevated temperatures, photopolymerization can advantageously be performed at room temperature and even below. A wide range of different monomers, including (meth)acrylates, epoxides, vinyl ethers, oxetanes, and many others, can be employed in photopolymerizations leading to a large variety of final polymer properties. However, in order to cut cost, use of soft irradiation conditions is required and the development of new photoinitiators strongly absorbing in the visible region and exhibiting high molar extinction coefficients are actively researched by the academic and industrial communities. For industrial applications, minimization of the risk for the operator has to be considered and use of light sources emitting beyond the UV region or as expected in the following years in the visible range is of crucial importance for the operator safety. Another requirement for industry is the possibility to use low-power consumption LEDs to cut cost and avoid the use of expensive photochemical equipments. In the present project, a new approach based on the photoredox catalysis will be proposed for the development of new systems active upon soft visible light conditions. Two families of photocatalysts fulfilling the aforementioned requirements will be proposed: i) from pure organic molecules i.e. organophotocatalysts and ii) from transition metal complexes. i) The first series of PI will concern purely organic photoinitiators that will be designed starting from well-known PI (pyrene, anthracene, perylene, perinones, rhodamine, fluorescein or other dyes). Strong coupling of the molecular orbitals MO of a given PI with the central polyaromatic structure led to improved absorption properties (red-shifted wavelengths, higher molar extinction coefficients) of the macro PI compared to that of the parent PI. ii) The second series of PI that will be examined will concern the transition metal complexes. Iridium (III) and ruthenium (II) complexes have recently been investigated as exceptional initiators of photopolymerization. A low-cost alternative using non-toxic metal would be an asset for industrial applications. Thus, the second series of photoinitiators will incorporate metals such as Cu, Al, Zn, Fe, Ni, Co,… This project perfectly fits this CD2i call and particularly the axis “Réactions et procédés efficients”. Indeed, the search for efficient polymerization initiating systems usable upon very soft irradition conditions is highly desirable. In addition to the academic partners (IS2M - Mulhouse; ICR-Marseille), an industrial partner (Photon & Polymers - PnP) is also involved in this project (Task 3) for the evaluation of the performance of the best systems developed for industrial irradiation conditions and particularly LEDs. Indeed, these LED irradiation devices are 60-80% more energy efficient than conventional Mercury UV lamps and have environmental, health and safety benefits for industries. The proposed systems provide solutions to the industrial problems by combining both optimized productivity and respect of the environment.