We have investigated the swelling of a polystyrene brush in cyclohexane at
varying temperatures with angle-dependent ellipsometry. The brush was grown
in situ on the base of a high index prism by the "grafting from" technique
. In the dry state it has a thickness of d = 134 nm. At the theta temperatu
re it swells to about 600 nm. In accordance with the predictions from mean
field theory, the brush thickness continuously increases with solvent quali
ty. As the thickness increases, the shape of the segment density profile be
comes smoother with a broad dilute transition region between the brush and
the solvent.