2. Photoinitiators

To be effective, a photoinitiator must satisfy a number of criteria:

• it must have high absorption in the emission range of the light source used, usually a mercury vapor lamp;

• singlet and triplet excited states must have short lifetimes (a few nanoseconds) to avoid quenching by molecular oxygen or monomer;

• ions or radicals from excited states must be produced with the highest possible quantum yield and be reactive towards the monomer group.

The various photophysical processes involved after absorption of a photon by an initiator molecule are shown schematically in figure 1 . The initiation rate is given by the relation...