Modeling of 1,6-Hexanediol Diacrylate Photopolymerization with Spatial Gradients and Film Shrinkage

A dynamic model is proposed to account for shrinkage and swelling during the photopolymerization of 1,6-hexanediol diacrylate (HDDA) with the bifunctional initiator bis-acylphosphine oxide (BAPO) in the presence of oxygen. The model is composed of 14 partial differential equations (PDEs) that are used to track changes in film thickness along with time- and spatially-varying concentrations of monomer, initiator, oxygen, pendant vinyl groups, and seven types of radicals. Shrinkage has a noticeable influence on the model predictions. For a variety of simulated photopolymerization experiments, there is ≈9% discrepancy between predicted overall vinyl-group conversions obtained from the current model with shrinkage and a previous model without. Prediction discrepancies become larger for simulated experiments involving thin films (8 µm) or low light intensities (1200 W m⁻²). In the future, it will be important to re-estimate the kinetic parameters used in the shrinkage model to obtain accurate model predictions for use in process improvement studies.