Phase equilibrium in solutions of star-shaped macromolecules: an improved Okada–Numasawa model

The two-region Okada–Numasawa model for solutions of star-shaped polymers has been improved by means of a change in the integration order and introduction of a concentration-dependent and molar-mass-dependent Flory–Huggins interaction parameter (the second and third approximations of the Flory–Huggins theory). To overcome calculation difficulties, a special algorithm for computing coexistence curves of polymeric systems with an UCST has been used. The agreement between the experimental and calculated coexistence curves for the star-shaped polystyrene (PS)–cyclohexane system has been improved: the difference between Tcs is ∼0.33 K against ∼12 K as given by the original model.