The conformational coil‐globule transition of polystyrene in cyclohexane solution

Abstract

AbstractThe phase diagram of a monodisperse high molecular weight polystyrene (Mw = 3.3 · 106, Mw/Mn < 1.06) solution in cyclohexane was thoroughly studied by means of light scattering, cloud point, coexisting phases volume ratio, coexisting phases composition and scanning calorimetry methods, and binodal and spinodal curves were obtained. Coordinates of the UCST (T = 306.2 K, ϕ2 = 1.88 · 10−2) determined by different methods were similar. It was found that the first‐order phase transition curve obtained by calorimetric scanning at 10−6 K/s accurately fits the spinodal of the system within the concentration range of semidilute and concentrated solutions and has a horizontal part in dilute solutions where the temperature of phase transition was found to be 303.86 K, independently of concentration. At the same temperature a deflection point was found on the concentrated branch of the spinodal. The results were taken as calorimetric evidence of a coil‐globule phase transition in the polystyrene solution. It was shown that the collapse of the polystyrene coils takes place in the metastable system between the binodal and the spinodal in the same way as in the homogeneous solution above the binodal.