Poly(tert-butylcarbonyloxystyrene) by itself or as a component in a copolymer decomposes at elevated temperatures (about 130-150 degrees C) to give the free phenolic group, isobutylene, and carbon dioxide. It has been found that the isothermal conversion of the ester (the protected phenol) to the free phenol proceeds slowly at first but accelerates with time so that the rate of reaction increases until more than half the reaction is over. Thus, the pattern of conversion with time is typical of an autocatalytic process. Although the classical model of autocatalysis which we reported earlier gave a qualitative representation of the process, two modifications to the model result in a much better approximation to the actual experimental data. These two experimentally rational modifications take into account the very real decrease in the volume of the reacting system as,conversion (deprotection) proceeds and the possibility that the catalyzed (fast) reaction is second order in free phenol.