Measurements of the emission of purposely entrained volatiles (Ar and D2O) during the loading and unloading of a bisphenol-A polycarbonate in vacuum are made by quadrupole mass spectrometry. Transient loading events are accompanied by dramatic increases in emission, reflecting a similar rise in the diffusion constant of the measured species. We attribute this change to an increase in size of molecular voids in the polymer network, which accompany the increase in sample volume under load. The results are interpreted in terms of the Dolittle relation in which the diffusion constant depends exponentially upon upsilon*/upsilon(f0), the ratio between an activation volume for diffusion and the average size of the relevant voids in the polymer network. Our data suggests that upsilon*/upsilon(f0) is unusually low in the D2O-polycarbonate system, which we attribute to a relatively large value of upsilon(f0); this would be consistent with the relatively long distance between flexible links in the polycarbonate structure.