We measure the chemical potential in a polymer melt with a modification of Widom’s insertion method. Our method is based on partial insertion of a testchain by controlling the interaction between the testchain and the melt by means of a control parameter. The chemical potential can be obtained from a single run in a multicanonical-like simulation over a wide range of temperatures and densities. From the chemical potential the osmotic pressure and the entropy are calculated. We study a variant of the bond fluctuation model of a polymer melt where an energy is gained when the bond vector is taken from the set (+/-3,0,0) lattice spacings (or permutations thereof). From extensive previous studies it is known that the model exhibits a glass-like freezing at low temperatures. We show that the configurational entropy decreases strongly when one cools the system through this transition, but it remains distinctly nonzero in the glass phase.