  The equilibrium properties of a tangent-hard-sphere polymer chain in a hard
sphere monomer solvent are studied using a Born-Green-Yvon integral equation in
conjunction with a two-site solvation potential. The solvation potential is
constructed using low density results for a hard-sphere trimer in a hard sphere
solvent. The BGY equation has been solved for polymers of lengths up to 100 for
a range of solvent densities and solvent diameters. The theory accurately
describes the compression of the average polymer dimensions with increasing
solvent density. The theory also accurately describes the variation in this
compression as a function of the solvent diameter, predicting a maximum effect
when the solvent diameter is two to three times larger than the polymer site
diameter. Scaling exponents relating the polymer dimensions to chain length and
solvent density are also obtained.
