Three distinct peaks at 80, 175, and 325°C were identified in the dynamic derivative TGA curves of PMVEMA and PMVEMAC at a 10°C/min heating rate. These peaks were attributed to free water removal, anhydride formation, and polymer degradation, respectively. The kinetics of the anhydride formation were studied by isothermal TGA in the temperature range of 150–200°C. It was found to be an endothermic and first-order intramolecular reaction with an activation energy of 18.8 kcal/mol. It was concluded from FT-IR and DSC results that no intermolecular anhydride structure was present in the dehydration of PMVEMAC. This is different from the cases of the dehydration of poly(acrylic acid) and poly(methacrylic acid) in the literature. The limiting glass transition temperatures of PMVEMA and PMVEMAC were found to be 153 and 144°C, respectively. The higher glass transition temperature in PMVEMA as compared to PMVEMAC is attributed to the increase in stiffness in the main polymer chain by the five-membered ring anhydride structure in PMVEMA.