Application of the steady state method to benzoyl peroxide initiated polymerization of styrene

The steady state method is applied to the benzoyl peroxide initiated polymerization of styrene in toluene at 80°C. The reaction mixture is kept homogeneous by stirring. A theoretical discussion shows that the time needed to reach the steady state concentrations with an accuracy of 1% or better is about seven times the average time which the mixture spends in the reaction vessel; this is confirmed by experiment. The experimental results show that the rate of polymerization can be represented by the formula: where m is the monomer concentration, while k and β are constants. It is found that β = 1.19 liter/mole. The apparent order of the reaction, with respect to monomer, increases from 1.18 when m = 1.8 mole/liter to 1.36 when m = 0.4 mole/liter. An analysis of the limits of experimental error indicates that in the conventional method this change in apparent reaction order would have been of the same order of magnitude as the experimental error. The accuracy of the steady state method, however, is sufficient to establish this change unambiguously. Numerous data from the literature concerning the polymerization of styrene and other monomers are discussed, and are found to be in good agreement with the conclusions reached in the present work. Explanations are offered for a number of discrepancies found in the literature.