Preludium 20

Project title:

Photochemical fine-tuning of iodonium salts' photoinitiation ability by using easily modifiable chromophores:  Unlocking the Potential of Easily Fabricating an Efficient Cationic Photoinitiators Active in Visible Light

Principal investigator: mgr Filip Petko

Obtained funds: 210 000 PLN

Project duration:

Start day: 2022-01-01

End day: 2025-01-01

Project cooperation:

Prof. Jacque Lalevee from the Institut Universitaire de France - Institut de Science des Matériaux de Mulhouse (IS2M)

Short description of the project:

The main goal of this research project is to synthesis and determine the spectroscopic characteristics of new compounds based on an hypervalent iodine(III) structure (iodonium salts) which will be able to effectively dissociate after an absorption of light from UV-A and visible region of the electromagnetic spectrum and efficiently generate superacid. They could act as one component photoinitiators of the cationic polymerisation process. Another important research goal is to determine the factors and in which way they affect the efficiency of photoacid generators (PAGs) in the new obtain cationic photopolymerisation initiators and how the efficiency of this photoinitiators can be improved through structural modification.

Currently, there is still the problem of a poor match between absorption characteristics of unimolecular cationic photoinitiators and the emission range of light sources used from practical applications which still needs to be solved. The effect of this project will be the development of more efficient iodonium photoinitiators and the development of a set of rules for the design of new more efficient unimolecular cationic photoinitiators than those are used currently. The newly development iodonium salts which are able to dissociate and generate superacid after absorption of light from the near-visible region of the spectrum can find numerous applications e.g. in stereolithography (3D printing).

Cationic photopolymerisation processes require the use of efficient generators of non-nucleophilic strong acids (PAGs) capable for the initiation of the polymerisation process. Iodonium salts have numerous advantages such as high photoreactivity - high quantum yield of photodissociation and undergo the photodecomposition in nearly every conditions. Therefore, finding a new precursors/substrate for iodonium salts synthesis, with a more sophisticated structure ensuring better absorption properties is desired. New, easy to obtain iodonium salts, photodissociating at a lower energy of excitation will be responding to today’s demand and they could find new applications. A key goal for basic research aimed at the experimental clarification of the issues raised will not only contribute to a better understanding of the mechanisms of action of the initiators themselves but will also enable the development of guidelines for the design of new, more effective initiating systems for cationic polymerisation.

In order to carry out this task, the core structure of benzylidene chromophores has been selected and two schemes of modification have been proposed. Molecules obtain according to both schemes will exhibit push-pull effect. The general research plan is divided into two main parts, synthesis of new iodonium salts and characterising them in terms of their photochemical and photophysical properties as well as their ability to photoinitiate cationic polymerisation of electron-rich monomers.

Therefore the proposed project will be accomplished in the following way:

  1. Chemical compounds selected for the photoinitiators will be synthesized and studied. These will involve suitable iodonium salts, chromophores as well as the organic iodine(III) precursors.
  2. A detailed study of photochemical, photophysical, and electrochemical properties of the developed cationic photoinitiators and their components will be carried out.
  3. A comprehensive study of the kinetics of the cationic photopolymerization initiated with photoinitiators will be performed using photo DSC, photo-rheology, and real time-FTIR. 
  4. Mechanisms of photo-generation of strong protic acids by the direct photolysis of the newly developed iodonium photoinitiators will be elucidated

Many aspects concerning cationic polymerization photoinitiators are still not known and require thorough study both for better understanding of their nature and for their applications. These fundamental research are aimed not only on elucidation of the reaction mechanisms by which these photoinitiators work, but also on determination of criteria for design of new more effective and sensitive photoinitiators that will provide additional advantages. On the other hand, to-date limited of knowledge about effects of structural factors of cationic photoinitiators on quantum yield of photo-generation of the strong protic acids being the proper cationic polymerization initiators. This aspect is crucial for design of efficient initiating systems and requires sophisticated thorough study.