The influence of oxygen upon polymerization reactions

Abstract

AbstractInvestigations were carried out to measure the influence of varying initial concentrations of oxygen upon the rate of polymerization during the early stages of polymerization of styrene in toluene solution. Likewise, the viscosity‐average molecular weights of the polymers produced were determined and correlated with the changes of the amounts of oxygen initially present.In order to evaluate properly the differences in the length of the inhibition periods caused by the varying amounts of oxygen added, polymerizations of styrene were first carried out in the absence of oxygen. No inhibition period was observed then. The influence of varying amounts of oxygen is shown by an appearance of inhibition periods, the length of which is dependent upon the initial oxygen concentration. The viscosity‐average molecular weights of the resulting polymers also are related to the same quantity. It too can be observed that the velocity of the reactions immediately following the inhibition period is dependent on the amount of oxygen added at the beginning of the reaction.In accordance with evidence produced by other investigators it is assumed that formation of polyperoxides takes place during the inhibition period. All the observed experimental facts can be explained by this assumption. It also is assumed that the decomposition of these polyperoxides causes a decrease in the length of the inhibition periods by producing radicals which can start new polyperoxide chains. The increase in the rate of the polymerizations after the end of the inhibition period above the rate of a thermal polymerization is of course also due to the decomposition of the polyperoxides at that period of the reaction.Thus it is proposed to change the equation, suggested by Bolland and Gee for the relationship between initial oxygen concentration and inhibition period to P = Kt + a where a is a factor dependent on the rate of decomposition of the polyperoxides during the inhibition period, as well as on possible side‐reactions consuming oxygen.