Forces exerted between block poly(vinyl-2-pyridine)/polystyrene (PV2P/PS) copolymer layers adsorbed on mica substrates have been measured over the separation range 0–200 nm between the substrate surfaces. The PV2P block binds strongly to mica in a flattened configuration; the PS block is not bound directly to mica in our experiments. The PS block is held on the surface through its covalent bond to PV2P. The form and range of the force vs. separation curve depend upon block molecular weights and the thermodynamic quality of the immersion solvent for the PS chain. In the good solvent toluene, the PS chains are shown to be stretched away from the surfaces in extended configurations and to exert long-ranged, mutually repulsive forces when two layers are brought to a separation causing overlap of the PS chains. In the θ solvent cyclohexane, the range is reduced considerably due to configurational contraction and due to the diminished effects of binary interactions between polymer segments. The range of the forces observed and their dependence on block molecular weights can be explained by fairly simple arguments about the packing of polymer chains on the surface. © 1986, American Chemical Society. All rights reserved.