Thiol-Ene Photopolymerization under Blue, Green and Red LED Irradiation

Abstract

Photopolymerization allows fast production of materials with special properties; however, a short wavelength of light is required for most commercial photoinitiating systems and the oxygen inhibition effect for the free radical polymerization has limited possible applications. Herein, we investigate thiol-ene photopolymerization with various types of “ene” derivatives and thiols using our previously reported photoinitiator 2-(4-methoxystyryl)-4,6-bis(trichloromethyl)-1,3,5-triazine (triazine) alone or in combination with rubrene or 1,4-bis(isopropylamino)anthraquinone (SB36) as the photoinitiating systems to trigger polymerization under irradiation with blue, green, and red LEDs. An analysis of photopolymerization kinetics and the effects of different light irradiation conditions, chemical structures, composites of “ene” and thiol monomers, and air on the thiol-ene photopolymerization reaction are presented. Specifically, rates of photopolymerization of all thiol-ene formulations decrease as the wavelength of irradiation increases and show no significant difference when polymerization occurs under air or in laminate. Mechanical properties and homogeneity of the photocured samples are analyzed and demonstrated that all thiol-ene formulations appear to have a homogeneous network. Regarding mechanical properties, with a lower amount of thiol incorporated in the network, the storage modulus and the glass transition temperature (T ) of the photocured product increased. Storage stability of thiol-ene formulations is also studied and 5-hydroxy-1,4-naphthoquinone (5HNQ), a naturally derived dye derivative, is found to be successful in inhibiting premature gelation in thiol-ene systems without significantly affecting the photopolymerization performance.