Progress in the development of polymeric and multifunctional photoinitiators

UV-curing technology has been developed and widely used in industry for 6 decades. However, the migration of low-molecular-weight photoproducts is today an important drawback in many application fields such as food packaging materials, leading to unpleasant secondary features such as odor, blooming and contamination. Therefore, many efforts have been devoted to design polymeric photoinitiators (PPIs) and multifunctional photoinitiators (MFPIs) to overcome these drawbacks. This review introduces the development and the challenges of UV-curing technology and the state of the art of PPIs and MFPIs, in which methodologies of synthesis and characterization are meticulously discussed. Moreover, a novel classification, based on the molecular structure, has been drafted for all the PPIs conventionally reacting through photodissociation or photoreduction. Most of the PPIs and MFPIs have excellent photochemistry properties, some of which have extra properties such as amphiphile, self-floating and biocompatibility. Examples of well-defined structures are discussed in the section on MFPIs.