Macromolecules, Vol.27, No.25, 7454-7458, 1994
Laser Flash-Photolysis Study of the Photoinitiator System Safranine-T Aliphatic-Amines for Vinyl Polymerization
The polymerization of a-hydroxyethyl methacrylate, in a methanol solution, proceeds efficiently using the photoinitiator safranine T in the presence of tertiary aliphatic amines. Polymerization rates were measured at several amine concentrations. These values increase with the amine concentration, reaching a maximum, and further amine addition slowly reduces the polymerization rate. The quenching of the dye excited states by amines was analyzed by static fluorescence and laser flash photolysis. The excited singlet quenching involves a charge-transfer process with rate constants near the diffusional limit. Flash photolysis studies of safranine in the presence of amines, in a methanol solution, yield the triplet species (SH+)-S-3 and S-3(+) and the unprotonated semireduced radical. This latter transient follows a dependence with the amine concentration similar to that found for polymerization rates. Al these results indicate that polymerization involves the interaction of the excited triplet with the amine, while quenching of the excited singlet inhibits the polymerization.