This paper will discuss a mathematical model developed to predict monomer conversions in a photopolymerization process. The proposed model, which is based on the expression for photobleaching system derived by Wegscheider using Lambert-Beer's law for light absorption in the sample (1), has been validated by experimental data obtained by studying photopolymerization of butyl acrylate and styrene in a narrow channel reactor. Previous mathematical models (2, 3) were based on thin film approximation where the variation of light through the film was neglected. Such a model results in unusually high conversion rates for configurations with high characteristic path lengths.

In establishing our model, experimental data generated by performing a parametric study to investigate the influence of initiator concentration, flow rates, and light intensity, were taken into account. Polymerization was carried out in a narrow channel glass reactor (dia=1.5mm) using UV intensity in the range of 50-150 mW/cm^2. 2,2-dimethoxy-2-phenyl-acetophenone was used as non-photobleaching initiator. Gas Chromatography was used to monitor the conversions and gel permeation chromatography for the molecular weights. This model can also be used for predicting the extent of curing in photolithography applications.

References:

1. Wegscheider, R.; ‘Beitrage Zur Photochemischen Kinetik', Z. Phys. Chem. 1923, 103, 273-306.

2. Boodhoo, K. V. K.; Dunk, W. A. E.; Jassim, M. S.; Jachuck, R. J. J.; ‘Thin film solvent-free photopolymerization of n-butyl acrylate. I. Static film studies', Journal of Applied Polymer Science, 91 (2004), 2079-2095.

3. Decker, C.; ‘The use of UV irradiation in polymerization', Polymer International 45 (1998), 133-141.