Alkaline hydrolysis of polymers with ester groups studied by isothermal calorimetry

Alkaline hydrolysis of polymers produces heat that can be measured with isothermal calorimetry to monitor the hydrolysis. We here report on two studies to measure the enthalpy of alkaline hydrolysis of polymers containing esters of carboxylic acids. The heat from the hydrolysis of films of poly(vinyl acetate), PVAc, was followed for up to 42 days and correlated with the amounts of acetic acid produced. The enthalpy per hydrolysed repeat unit was −57.3 kJ mol−1 for PVAc. For poly(lactic acid), PLA, fibres the enthalpy of hydrolysis was determined by integrating the heat produced during complete hydrolysis. For PLA, the result per hydrolysed repeat unit was −57.9 kJ mol−1. The determined values are within a few percent of the enthalpy of neutralization of the carboxylic acids formed, as the hydrolysis itself has a low enthalpy; it is the neutralization of the acid that produces most of the measured heat. Isothermal calorimetry is thus a general quantitative method for the investigation of the rate and extent of alkaline hydrolysis of esters of carboxylic acids in polymers and other organic substances.