AbstractGlassy polycarbonate has been subjected to sub‐glass‐transition annealing and exposure to high‐pressure CO2. The subsequently measured solubilities of nitrogen, argon, and CO2in these specimens were found to be decreased by the former and increased by the latter. Annealing decreases the enthalpy of polycarbonate and mechanically embrittles it, whereas subsequent exposure to CO2erases these effects of annealing, can make the polymer even more ductile than the untreated material, and can apparently give it a higher enthalpy. Annealing densifies the glass, whereas the CO2treatment dilates it. The gas sorption observations are in accord with the dual‐sorption model, and the effects of prior history are apparently the result of changes in the Langmuir capacity, which evidently is a sorption mechanism that exists as a result of the nonequilibrium nature, or excess volume, of the glass
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