Effect of Light Intensity on the Free-Radical Photopolymerization Kinetics of 2-Hydroxyethyl Methacrylate: Experiments and Simulations.

The effect of UV light intensity on the kinetics of free-radical polymerization of 2-hydroxyethyl methacrylate (HEMA) triggered with the phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (BAPO) photoinitiator was investigated experimentally and theoretically. The temporal evolution of the conversion yield and polymerization rate was followed by Raman spectroscopy. The experimental data were treated with a kinetic model, which takes into account significant diffusion-controlled processes and termination pathways including bimolecular reaction and primary radical termination. This model showed very good agreement with the experiment in a large range of UV light intensities and shed light on the termination process. In particular, it was shown that the primary radical termination is dominant for relatively low light intensities below 1 mW/cm2, when the photoinitiator is weakly consumed during the polymerization process.