ABSTRACT
Photopolymerization, in general, can be defined as the process whereby light is used to induce the conversion of monomer molecules to a polymer chain. One can distinguish between true photopolymerization and photoinitiation of polymerization processes. In the former, each chain propagation step involves a photochemical process [1,2] (i.e., photochemical chain lengthening process in which the absorption of light is indispensable for
2. Through direct excitation of a monomeric or polymeric molecule or of a molecular complex (A) followed by a reaction producing an initiating species:
The radicals created in (1) and (2) interact with monomer molecules to produce macroradicals, and ulti-
each propagation step); whereas in the latter, only the initial step results from the interaction of light with a photosensitive compound or system [3-6]. This chapter deals only with the photoinitiation of polymerization process or photochemical postpolymerization. This may occur in two different ways:
I . Through energy transfer of an excited sensitizer molecule (S) to either a monomer (M) or foreign molecule (A) resulting in the formation of species capable of initiation (e.g., radical):
mately, by termination of these radicals, a polymeric chain is produced:
The rate of formation of radical from the photoinitiator molecule (the only light-absorbing molecule in the system) VR-is generally given by Eq. (4):
where 10 is the incident light intensity, [In] and ~In are the photoinitiator concentration and its molar extinction coefficient, respectively, and l is the cell path length, while a is the overall quantum yield of the initiating species (R').
