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 μm 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 O₂ during printing. Exposure to increasing amounts of O₂ during photocuring severely restricted both the degree of conversion and the UV dose required for gelation in proportion to the O₂ 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 T_g itself. Thus, the final crosslink density was greater in fully cured samples that were exposed to atmospheres with increasing inert gas concentrations. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011