Effect of the oxygen affected layer in multilayered photopolymers

Abstract

Photopolymerization is known to be limited in depth by light absorption. In addition, oxygen inhibition of acrylate films under air leaves some unreacted double bonds at the surface. Both phenomena account for heterogeneity in the conversion of the cured layer. Therefore, it can be relevant to build thick photopolymers through a multilayering process. 450 μm thick-photopolymers were prepared either through a bulk or a layering process, in the presence and in the absence of oxygen. They were compared in terms of conversion and the three point bending test. The results highlight an improvement in the conversion homogeneity with depth and in the mechanical properties of the layered samples. Experiments also showed that the presence (or absence) of an oxygen affected layer (OAL) does not make any mechanical differences. The oxygen inhibition of free radical photopolymerization leaves some unreacted double bonds at the surface of the film which could further bond to the subsequent layers. Therefore, the oxygen inhibition is not detrimental in a multilayer process.