Impact of Oxygen on Photopolymerization Kinetics and Polymer Structure

Abstract

The effects of varying polymerization conditions on the extent of oxygen inhibition of free-radical photopolymerization were investigated using both experimental and modeling efforts. Specifically, sample thickness, initiation rate, and oxygen concentration were varied, and the resulting photopolymerization kinetics were studied using real-time FTIR and a comprehensive photopolymerization model. As the sample thickness was increased, the overall average double-bond conversion increased due to the greater conversion in the lower depths of the films. Because of the dramatic inhibition at the top of the film, this led to heterogeneity in the film's conversion as shown with the comprehensive model. Increasing the initiation rate decreased the inhibition time and increased the overall average double-bond conversion due to an increase in the overall radical production, allowing better competition of the propagation reaction with the inhibition reaction. The oxygen concentration was varied, and as the oxygen concentration increased, the overall inhibition reaction increased, thus lowering the overall double-bond conversion. Finally, the effect of oxygen concentration on the bulk mechanical properties of the film was determined. It was found that no statistical difference was observed in the mechanical properties for films exposed to argon ( P O 2 = 0) as compared to a film exposed to air ( P O 2 = 0.21).