A process of preparing a compounded hydrostable poly(aliphatic ester-carbonate) includes providing a hydrostable poly(aliphatic ester-carbonate), compounding in an extruder the hydrostable poly(aliphatic ester-carbonate) and 0.05 wt % to 0.60 wt % of a multifunctional epoxide compounding stabilizer, based on the total weight of the compounded hydrostable poly(aliphatic ester-carbonate), under vacuum of 17000 to 85000 Pascals, and a torque of 30% to 75%, to provide the compounded hydrostable poly(aliphatic ester-carbonate). After compounding, at least one of the following apply: the inter-sample variability in molecular weight is less than 5%, wherein inter-sample variability is determined by comparing five 100 mil chips of the compounded hydrostable poly(aliphatic ester-carbonate); the % weight average molecular weight (MW) difference is less than 5% after hydroaging at 85° C. and 85% humidity; or the compounded poly(aliphatic ester-carbonate) has less than 75 ppm of unreacted —COOH end groups measured by 31P NMR.