Thin liquid films of polyfunctional poly(methylhydro-dimethyl)siloxane copolymers (PMDMS) have been investigated using X-ray reflectivity. The electron density of liquids within the films is altered significantly as a function of film thickness and fraction of Si-H groups in the PMDMS molecule, The density profile in the region next to the Si substrate is highly sensitive to the interaction between the liquid molecules and the substrate surface. Increasing the number of Si-H groups interacting with the surface leads to a more pronounced low-density region in the vicinity of the substrate. However, one-dimensional ordering normal to the surface is identical for all PMDMS films.