PHOTOPOLYMERIZATION IN AQUEOUS-SOLUTIONS INITIATED BY THE INTERACTION OF EXCITED PYRENE DERIVATIVES WITH ALIPHATIC-AMINES

The photolysis of pyrene derivatives in the presence of amines has been employed as a source of free radicals in the polymerization of 1-vinyl-2-pyrrolidinone in aqueous solution. The photoinitiation efficiency strongly depends on the amine and the sensitizer employed. With regard to the amine, only tertiary amines are efficient cocatalysts, hydroxyethanolamines being particularly efficient. For a given amine the initiation efficiency is high for pyrene and its cationic derivatives, while pyrenebutyric acid is a poor photoinitiator and pyrenesulfonic acid does not initiate the polymerization. The active radicals are produced in the interaction between the singlet excited state and the additive, the photoinitiation rate being proportional to the fraction of singlets quenched by the amine. The photoinitiation efficiency at total singlet quenching correlates with the rate constant of the quenching process, the photobleaching rate, and the pyrene radical anion yield. Photobleaching yield and the lifetime of the pyrene-derived radical anion decrease in the presence of 1-vinyl-2-pyrrolidinone. All these results are compatible with an initiation mechanism involving the interaction of the pyrene radical anion with the monomer.