13 October 2015
Year: 2013
Price: 10.00
As the number of applications of visible light-induced photopolymerizable materials increases, the need of development of efficient PIS for the visible becomes more and more evident. Some of the applications of this technology are dental materials, laser imaging, and holography [1-4].

LED sources are commercially available in a wide variety of wavelengths in the visible light spectrum. Dyes capable of absorbing light at these wavelengths can react from their excited states with either an electron donor or an electron acceptor. This reaction leads to the generation of radicals, which can later react with acrylate monomers to initiate polymerization (Figures 1 and 2). These are two-component photoinitiating systems, 2C-PIS.
2C-PIS have some disadvantages that may limit its efficiency as photoinitiators. One is that the amount of radicals generated is limited by the amount of dye in the formulations, which is usually around 0.1-1 wt%. Another one is that the dye generates radicals that can’t initiate the polymerization, but do terminate it. To overcome these two problems, a third redox additive can be added to the PIS, which reacts with the semi-oxidized or semi-reduced form of the dye, so that the ground state of the dye is regenerated.

These photocyclic initiating systems PCIS present at least two advantages with respect to the 2C-PIS. Firstly, the regeneration of the ground state of the dye, which not only removes the potentially terminating dye radicals, but also allows dye molecules to absorb light once again, thus, reentering in the photocycle. In this way, the polymerization reaction is no longer limited by the amount of dye. Secondly, the third component can also generate radicals that initiate the reaction, which increases the amount of radicals generated per photon absorbed.
2013 Conference Photoinitiating systems for use with LED and LASER diodes in the visible.
Author: L. Di Stefano | 7 pages

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