Osmotic pressure of solutions containing flexible polymers subject to an annealed molecular weight distribution

The osmotic pressure P of equilibrium polymers (EP) in a good solvent is in vestigated by means of an off-lattice Monte Carlo simulation. Our results c ompare well with conformation space renormalisation group theory and the os motic compressibility K as obtained by recent light scattering measurements of long worm-like micelles. The present study allows for the rst time the mapping of the relevant energy scale of a standard coarse-grained model on data from real experiments. We also con rm the scaling predictions for EP i n the dilute and semidilute limit. In particular, we find P proportional to phi (2.3) for the scaling of the pressure with the volume fraction phi and , hence, K proportional to phi (-0.3) in the semidilute regime in agreement with both theory and laboratory experiment. At higher concentrations where the semidilute blobs become too small and hard-core interactions and packi ng effects become dominant, a much stronger increase is evidenced and, cons equently, a compressibility that decreases much more rapidly with phi than predicted from semidilute polymer theory, but again in agreement with exper iment. Our results apply both to EP systems with and without rings.