Photopolymerization initiators are divided roughly into three groups as shown above. For a photopolymerization initiator to be an excellent initiator the following properties must be considered
(1) High quantum yields in the generation of radicals, cations and anions
(2) Overlap in absorption wavelength of the photopolymerization initiators and emission wavelength of the light source
(3) High thermal stability and high stability in darkness
(4) Highly soluble in monomers and oligomersIn addition to those just developed, we have a wide assortment of initiators, such as benzoin derivatives which are already in use.