Using atomic force microscopy, the force between solid surfaces (oxidized silicon) was studied in a melt of end-functionalized polymers (hydroxyl-terminated polyisoprene). The surfaces repelled each other in both approach and retraction. Comparison to results obtained with methyl-terminated polyisoprene shows that the hydroxyl groups bind to the silicon oxide surfaces, and a polymer brush is formed. Thickness and stability of the brush increase with the molecular weight, possibly due to entanglement. With increasing humidity the repulsive force decreases and changes to attraction in the retracting part. This implies that water adsorbs to the interface and destabilizes the bond between the hydroxyl group and the oxidized silicon.