Accounting for spatial variations during photopolymerization of 1,6-hexane-diol diacrylate in the presence of oxygen

A dynamic model is proposed for photopolymerization of 1,6-hexane-diol diacrylate (HDDA) with bifunctional initiator bis-acylphosphine oxide (BAPO) in the presence of oxygen. This partial-differential-equation model predicts time and spatially varying vinyl-group conversion as well as concentrations of monomer, initiator, oxygen, and seven types of radicals. Experiments to obtain diffusivities of oxygen, BAPO and HDDA are reported. Oxygen-related parameters are estimated using real-time Fourier-transform infrared (FTIR) conversion data. FTIR experiments were conducted using a range of film thicknesses (8 - 17 μm), BAPO levels (1 -4 wt %) and light intensities ( 200 - 6000 W /m²). The model predicts qualitative trends. Conversion predictions for runs with high intensities (≥ 5000 W /m²) and high BAPO (4 wt %) are accurate with a root-mean-squared error (RMSE) of 0.04. Larger RMSE (0.13) for runs with lower intensities and BAPO indicates that improved parameter estimates are required. Parameter estimates will be updated in future using a model that accounts for shrinkage during polymerization.