LED-induced thiol-ene photopolymerizations

The photoinduced free radical condensation polymerization of multifunctional thiols with acrylate monomers takes place rapidly and with high efficiency even in the presence of air. These highly photosensitive systems can be effectively cured using long wavelength UV or visible light sources including light emitting diodes (LEDs). The key to this technology was the observation that only relatively small amounts of thiols are effective in reducing the oxygen inhibition effect in acrylate monomers. Particularly significant was the discovery of an especially effective titanium-based photoinitiator that provides very high photosensitivity of these photopolymer systems at the long wavelengths emitted by LED light sources. The photopolymerization reactions were monitored using real-time infra red spectroscopy and an optical pyrometry (OP) apparatus fitted with an InGaN LED array as a light source with an emission centered at 470 nm.