The thermally stimulated current thermal sampling (TSC-TS) technique was used to study the cooperative glass transition like relaxations in different tacticity poly(methyl methacrylates) (PMMAs) including iso-and syndiotactic forms. We use the high sensitivity of the TSC-TS method to study these weak and sometimes overlapping relaxations at a frequency of about 10 -3 Hz where one can resolve cooperative relaxations well below the main glass transition (Tg), even if the species are a minor fraction of the overall relaxing species. The magnitudes of the values of Ea are compared with a theoretical prediction as a function of temperature, showing that the low-temperature tail of the glass transition in conventional atactic (e.g., 45% syndiotriads) extends down to 15 °C, while in our highest syndiocontent PMMA (80% syndiotriads), the glass-transition-like relaxations only extend down to about 80 °C. Results taken from the literature also substantiate the results obtained here for atactic PMMA. The results are contrasted to those for bisphenol-A polycarbonate and other polymers and suggest that compositional heterogeneity, more specifically the presence of low Tg "pockets" of predominantly isotactic sequences, contributes to the broad glass transition extending almost 90 °C below the main glass transition in atactic PMMA.