The kinetics of the polymerization of methyl methacrylate. I. The bulk reaction

Abstract

AbstractA thermocouple method of following the nonstationary state of chemical reactions has been used to study the changes which occur in the velocity coefficients and energies of activation for the propagation and termination reactions over the whole range of the conversion of methyl methacrylate to polymer. After about 10% conversion the rate and lifetime of the kinetic chain increase as conversion proceeds. These changes are accompanied by a decrease in the overall energy of activation and an increase in the temperature coefficient of the reciprocal of the lifetime. During this stage of the reaction, the intensity exponent falls from an initial value of 0.5 to 0.25. These results are believed to be due to an increase in the activation energy for the diffusion of polymeric radicals in the increasingly viscous medium. Beyond 40% conversion the activation energy for the propagation increases while the corresponding velocity coefficient decreases, possibly due to the monomer addition step becoming diffusion controlled. Simultaneously the intensity exponent increases toward unity.