Effect of Oxygen on the Crosslinking and Mechanical Properties of a Thermoset Formed by Free-Radical Photocuring

In this article, we report on the formation of optically transparent photopolymer films from hexanediol diacrylate (HDDA) by inkjet printing, where droplets of monomer approximately 5 mu m in diameter were deposited onto a surface. The films were cured by irradiation with a UV-light-emitting-diode light source. It was found that the inkjet-printed HDDA films picked up a considerable amount of absorbed O(2) during printing. Exposure to increasing amounts of O(2) during photocuring severely restricted both the degree of conversion and the UV dose required for gelation in proportion to the O(2) concentration. Viscoelastic property data indicated that exposure to reduced oxygen concentrations during thermal postcuring (dark reaction) resulted in linear trends of increasing modulus above the glass-transition temperature (T(g)) and increasing Tg itself. Thus, the final crosslink density was greater in fully cured samples that were exposed to atmospheres with increasing inert gas concentrations. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 119: 2359-2370, 2011