A Mechanistic Study of the Influence of Oxygen on Free Radical Polymerization of Styrene

In commercial production of polystyrene by free radical polymerization, the presence of trace amounts of oxygen can lead to the formation of toxic, volatile side products such as benzaldehyde and formaldehyde as well as peroxides, which can cause safety issues during polymerization, as well as during subsequent application. In an effort to develop strategies to reduce this issue, in this work, the influence of oxygen on the radical polymerization of styrene is explored. First, results from a series of solution polymerizations in the presence of varying oxygen concentrations are shown. The experimental results reveal that while the rate of polymerization is only slightly affected by the presence of oxygen, there is a significant decrease in the molar mass and a significant increase in the concentration of aldehydes produced as the oxygen concentration increases. To complement the experimental findings, a mathematical model is described to predict the effects of oxygen on polymerization in terms of the production of undesirable volatile organic compounds (VOCs), notably benzaldehyde and styrene oxide, as well as the evolution of molar masses and conversion. It is hoped that in the future, this model can help in the development of strategies to minimize the production of VOCs resulting from the presence of trace amounts of oxygen during free radical polymerization of styrene.