A thermocouple method of following the non-stationary state of chemical reactions IV. The initial and later stages of the polymerization of methyl methacrylate

Abstract

A study has been made of the changes which occur in the velocity coefficients and energies of activation for the propagation and termination reactions during the first 35 % polymerization of methyl methacrylate, photosensitized with 1. 1'-azo-bis- cyclo hexane carbonitrile. The slight increase in the rate of polymerization during the first 15 % conversion is followed by a threefold increase in rate during the next 10 % conversion. The lifetime of the kinetic chain also increases during the reaction. Between 15 and 25 % conversion there is a decrease in the overall energy of activation for the reaction from 7·2 to — 1·6 kcal/mole, and a very marked increase in the temperature coefficient of the reciprocal of the lifetime. During this stage of the reaction, the intensity exponent falls from the initial value of 0·5 to about 0·3. At later stages, the intensity exponent appears to exceed 0·5, but the results may be subject to considerable errors due to non-adiabatic conditions existing during the measurement of the non-stationary phase of the reaction.