A thermocouple method of following the non-stationary state of chemical reactions - III. The evaluation of velocity coefficients and energies of activation for the propagation and termination reactions for the initial and later stages of the polymerization of butyl acrylate

Abstract

The changes which occur in the velocity coefficients and energies of activation for the propagation and termination reactions in the polymerization of butyl acrylate photosensitized with I . l'-azo-bis- cyclohexane carbonitrile have been studied. The rate increases slightly during the first 25% conversion and then gradually decreases throughout the remainder of the reaction, while the overall energy of activation increases slightly at later stages of the reaction. Beyond 20% conversion the energy of activation for the propagation reaction remains in the region of 13 kcal/mole and that for the termination reaction at about 17 kcal/mole. The high values of these energies of activation are consistent with both the propagation and termination reactions becoming diffusion controlled by about 20% conversion. The velocity coefficient for the propagation reaction decreases from an initial value of 2100 to 44 l. mole- 1 s- 1 at about 75% polymerization, while that for the termination reaction changes from 3.3 x 10 7 initially to 7.3 x 10 6 1. mole- 1 s- 1 at about 75% conversion.