PHOTOPOLYMERIZATION STUDIES USING VISIBLE-LIGHT PHOTOINITIATORS

We have synthesized six esters of decarboxylated Rose Bengal and employed them as electron-donor photoinitiators at 514 nm. Photoreduction of the dyes by triphenyl n-butyl borate ion in ethyl acetate yields decarboxylated Rose Bengal (RB) as well as products that do not adsorb in the visible region. The yield of RB is approximately 8% of total dye consumption and is produced by cleavage of the radical anion formed in the initial electron-transfer step. We have studied the photopolymerization of polyol acrylates initiated by the RB esters plus electron donor under steady-state irradiation with the Ar+ laser, lambda = 514 nm. Photopolymerization results in thin films as well as in thick samples indicate the order with respect to light intensity is 0.5 at both low and relatively high conversions (40%). The ratio k(p)/k(t)0.5 depends on the identity of the RB ester employed as photoinitiator. On the basis of our results, we conclude that the initiating radical is derived from the electron donor whereas the radical released by cleavage of the semireduced dye acts as the predominant terminator of polymer chains.