Determination of the velocity coefficients for polymerization processes III. Effect of environment on polymerization processes

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Abstract
The kinetics of the photopolymerization of vinyl acetate in ethyl acetate and n-hexane solutions were investigated with a view to studying the effect of environment on the course of the reaction. The ethyl acetate solutions allow the polymer to remain extended so that the course of the reaction is similar to that of the pure monomer. With n-hexane, precipitation of the polymer takes place with the result that a considerable 'gel' effect is observed. The reaction rate in both cases is proportional to the monomer concentration and to the square root of the light intensity. In ethyl acetate solutions the activation energy is 4$\cdot $42 kcal./g.mol., which is virtually the same as for the bulk reaction, while in normal hexane the value found is -1$\cdot $30 kcal./g.mol. Reasons for this have been suggested. The life time of the active polymer in n-hexane solution both before and after the inception of the gel stage has been measured using the sector technique, and the values of the coefficients for the propagation and termination reactions have been computed. It is found that the value of the former is little changed by the change in medium, while that of the termination step falls sharply-the fall being in agreement with the increase in rate. These results confirm present theories on the cause of the gel stage.

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