Forces between solid surfaces across polymer melts are poorly understood despite their importance for adhesion and composite materials. Using an atomic force microscope (AFM) this force was measured for poly(dimethyl siloxane) (PDMS) on silicon oxide. The influence of molecular weight (4.0-40 kDa) was studied. Forces are attractive for low and repulsive for high molecular weight. In addition, changing the terminal methyl group for a hydroxyl group leads to an increased probability of bridging.