Mecanistic investigation of new visible light photoinitiating systems for free radical photopolymerization

XAVIER ALLONAS; OLGA TARZI; JEAN PIERRE FOUASSIER; CHRISTIAN LEY; AHMAD IBRAHIM

Toledo, España

Conferencia; XXIV International Conference on Photochemistry; 2009

Comité Organizador

Free radical photopolymerization is a very versatile and powerful technique for the formation of solid polymer under excitation by light. Applications such as photo-imaging, holography, computer-to-plate, etc..., are highly demanding in term of sensitivity of the photopolymerizable medium. Therefore, it is of prime importance to develop highly reactive photoinitiating systems (PIS) that can work in the visible region of the electromagnetic spectrum. Among these PIS, the so-called three-component photoinitiating systems are known to be very reactive. Pyrromethene dyes (Py) have been previously studied in our laboratory as an example of an application to printing technology, in which they interact by a sensitization mechanism with a photoacid generator to produce a “positive working photopolymer”. The present paper reports the use of Py as part of a photoinitiating system for radical polymerization in the visible region of the spectrum. We examined the ability of the systems formed by Py / amine, Py / triazine and Py / amine / triazine, to initiate the polymerization of a diacrylate under visible light, using 1,3,5,7,8-pentamethyl pyrromethene BF2 complex (HMP) and 2,6-diethyl-8-phenyl-1,3,5,7-tetramethyl-pyrromethene BF2 complex (EPP) as dyes,  ethyl-4-dimethylaminobenzoate (EDB) as amine and 2-(4-methoxyphenyl)-4,6-bis(trichloromethyl)-1,3,5-triazine (triazine A, TA). In order to understand their efficiency in terms of monomer conversion, the photochemistry of these systems was investigated by means of steady state and time resolved spectroscopies. The fluorescence quenching by the amine and triazine, as well as laser flash photolysis to investigate the electron transfer process that occurs in these photoinitiating systems. Experiments show that the main interaction between the dye and both coinitiators is through its excited singlet state and the process is more efficient when TA is present. A mechanistic scheme is proposed to account for these results.