Optical/UV radiation from accretion disks in quasars is likely to be partly scattered by a hot plasma enveloping the disk .
We investigate whether the scattering may produce the steep rises in polarization observed blueward of the Lyman limit in some quasars .
We suggest and assess two models .
In the first model , primary disk radiation with a Lyman edge in absorption passes through a static ionized “ skin ” covering the disk , which has a temperature kT \sim 3 keV and a Thomson optical depth \tau _ { T } \sim 1 .
Electron scattering in the skin smears out the edge and produces a steep rise in polarization at \lambda < 912 Å .
In the second model , the scattering occurs in a hot coronal plasma outflowing from the disk with a mildly relativistic velocity .
We find that the second model better explains the data .
The ability of the models to fit the observed rises in polarization is illustrated with the quasar PG 1630+377 .