Introduction to the themed collection on photopolymer science dedicated to Ewa Andrezejewska

Research in the field of photopolymer science is witnessing a steady advance, driven by both academic enthusiasm and industrial pragmatism. The numerous environmental and economic benefits of light induced chemistry make this technology highly interesting for manufacturers and fabricator within a wide range of different industrial sectors.

The light-curing process is continuously growing in conventional areas, such as coatings, varnishes, inks and adhesives, as well as in more advanced domains, such as dental filling materials, 3D-printing and nanotechnology.

Reasons for the growing importance of the light-curing technique is its peculiar characteristics that include the fast transformation of a liquid monomer formulation into a solid crosslinked polymeric material, which has distinctive physical–chemical and mechanical properties. This polymerization process provides the advantage of curing on demand, with the reaction rate readily manipulated by the appropriate combination of various polymerization parameters, such as the photoinitiator type and concentration, intensity and wavelength of light, temperature, and monomer and oligomer structures. The process can be considered to be environmentally friendly, owing to the solvent-free methodology, and the fact that it is usually carried out at room temperature, thus conferring energy saving advantages and the possibility of curing coatings on thermal-sensitive materials. In contrast to thermal curing, photopolymerization also allows the efficient tempospatial control of the curing process, thereby making imagewise curing or the fabrication of 3D objects possible.

Photochemistry is strongly involved in the photopolymerization process, since the first step of the process is the adsorption of a photon by a molecule, the photoinitiator, which induces the formation of reactive species, such as radicals, strong acids or bases. The photogenerated reactive species are prone to promote classical chain growth or, in the case of thiol–ene, step-growth polymerization reactions.

This themed collection on photopolymerization is a collection of papers by authors who actively participated at the last European Symposium of Photopolymer Science (ESPS), which was organized with strong support from TU Vienna and held as a virtual conference in 2021. The ESPS meeting is the largest biennial international symposium in Europe dedicated to all aspects of photopolymer science and technology, emphasizing the fundamental scientific aspects of this technology. The ESPS meeting aims to bring together recent achievements and challenges in photopolymer science and technology from both academia and industry, with topics addressing critical issues such as photochemistry, reaction kinetics, photoinitiators, monomer and oligomer synthesis, structure–property relationships, polymer processing and applications.

The first ESPS meeting was organized in Mulhouse, France, in 2010. The subsequent meetings took place in Torino, Italy in 2012, then in Vienna, Austria in 2014, in Leipzig, Germany in 2016, and again in Mulhouse in 2018. A following meeting was supposed to be held in Istanbul, Turkey in 2020. Unfortunately, this meeting had to be cancelled due to COVID restrictions, and was therefore organized online as vESPS 2021. The meeting united 500 participants from all over the world. More then 45 invited lectures, nearly 70 oral presentations and 60 posters of high quality were presented at this conference.

This themed collection is dedicated to Ewa Andrzejewska, who was an outstanding scientist in the photopolymer community, contributing excellent work and having a very kind personality. With deep regret, we have to announce that Prof. Ewa Andrzejewska passed away in June 2019.

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