Photopolymerization mechanisms of acrylates in poly(methyl methacrylate) films

Photoinitiation processes for photopolymer coating layers have been investi gated with respect to quenching rates by a laser flash photolysis using a t otal reflection cell, as well as to the decomposition-quantum yield of a se nsitizer dye and a radical-generating reagent by a gel permeative chromatog raphic analysis (GPC); the sensitizer dye, 2-[p-(diethylamino)styryl]naphth o[1,2-d]-thiazole (DNT) and the radical-generating reagent, 2,2'-bis(2-chlo ro-phenyl)-4,4',5,5'-tetraphenyl-1, 1'-bi-1H-imidazole (BI). From experimen ts using flash photolysis, strong fluorescence was observed at excitation o f 355 nm laser pulse, though no transient absorption was observed. The fluo rescence was statically quenched by BI with a quenching distance, R=11 Angs trom. From the experiments using GPC, the high-quantum yield of decompositi on (Phi) was obtained as Phi (DNT) = 3 and Phi (BI)=9 for DNT and BI in the presence of acrylate monomers, trimethyrolpropanetri-acrylate (TMPTA), at 488 nm exposure of 3.36 mJ/cm which was required to form a photo-hardened i mage, however no decomposition of DNT and BI was detected in the absence of TMPTA. The results imply that the photoinitiator system undergoes efficien t static-dye sensitization and efficient polymerization of the acrylate mon omers accompanied with the chain decomposition of DNT and BI. Copyright (C) 1999 John Wiley & Sons, Ltd.