Ultrathin films of polystyrene (PS) were grown from self-assembled monolayers by the "grafting-from" technique. The initiating system consisted of a dithiol azobisisobutyronitrile-type free-radical initiator that was activated by irradiation at 300 nm. The thickness of the PS films ranged from 7 to 190 nm and could be controlled by varying the reaction time or the monomer concentration. The films were characterized by ellipsometry and Fourier transform-reflection absorption infrared spectroscopy after Soxhlet extraction of residual physisorbed polymer. These films were unstable above 60 degreesC, and a water-jacketed Soxhlet extractor was designed to maintain solvent temperatures below 45 degreesC during extraction.