Publisher's Synopsis
The demand for photoinitiators has been steadily increasing since benzoin ethers, latent radical sources activated by UV light, were first industrially employed in particle-board finishing in the 1960s. Among the factors con tributing to the continuing success of photoinitiators are the widespread adoption of dry coatings which eliminate the environmental problems as sociated with solution polymerisation and the development of new printing and resist applications. All of the early commercial photoinitiators were organic compounds, primarily derivatives of benzil or acetophenone. But as research in organo metallic chemistry gained momentum, the potential advantages of organo metallic complexes as photoinitiators became evident. Not only would the use of metal-based compounds allow polymerisation to be initiated by lower energy, and, therefore, more economical visible light but the absorption characteristics and reactivity of these complexes could be fine tuned to fit the specific application requirements by manipulation of the metal ligands. In fact, the recent commercialisation of the first two organo-metallic photoinitiators, a titanocene (see p. 347) and a (cyclopentadienyl)(arene)iron(II) salt (see p. 359), bears testimony to the mounting importance and versatility of metal complexes as latent sources of radicals and/or Lewis acids. The purpose of this chapter is to provide an overview of photopolymerisation with metal species, whether they be metal ions, inorganic or organo-metallic complexes.
