High‐Performance Photoinitiating Systems for Free Radical Photopolymerization. Application to Holographic Recording

Abstract

The photoinitiating systems (PIS) usable in free radical photopolymerization are briefly reviewed. Apart conventional Type I and Type II photoinitiators, three-component PIS exhibiting a photocyclic behavior are discussed. The mechanisms of photoreaction are presented, highlighting the role of a redox additive which reacts with the photoinitiator photoproduct. Recent applications in holography recording are described showing that the selection of a PIS plays a crucial role in this application.

Photocyclic Initiating System for Free Radical Photopolymerization Studied Through Holographic Recording

“…Type I photoinitiator systems is extremely efficient systems because back electron transfer step does not occur and produce high rate of cleavage [2]. Another important advantage of type I is the short life time of the excited state [1,2].…”

“…Another important advantage of type I is the short life time of the excited state [1,2]. One-component photoinitiator systems are only active for UV wavelength and UV light sources [2]. Two-component photoinitiator systems are more versatile initiators for both ultra violet (UV) curing systems and visible light induced systems because the choice of the light absorbing molecule (the photosensitizer) is not limited to UV absorbing molecule and can be selected in organic dyes.…”

“…Another important advantage of type I is the short life time of the excited state [1,2]. One-component photoinitiator systems are only active for UV wavelength and UV light sources [2].…”

“…Photoinitiator systems can be classified according to the number of components involved. Type I systems contain a single-component photoinitiator (unimolecular fragmentation mechanism), while type II systems are based on two components (bimolecular electron transfer or hydrogen abstraction mechanism) and finally three components initiator systems were developed to enhance the efficiency of type II systems [1,2].…”

Triazine‐Based Type‐II Photoinitiating System for Free Radical Photopolymerization: Mechanism, Efficiency, and Modeling

“…Three main families of PIS have been developed, each with their own advantages and limitations. [2,[4][5][6][7][8][9] Type-I PIS rely on the photoinduced dissociation of the initiator to produce primary radicals. Despite a high quantum yield of radical production, typical bond dissociation energies require the use of UV lamps that are known to be harmful and to release ozone in the atmosphere.…”