THE CONFORMATIONAL COIL-GLOBULE TRANSITION OF POLYSTYRENE IN CYCLOHEXANE SOLUTION

The phase diagram of a monodisperse high molecular weight polystyrene ((M) over bar(w) = 3.3.10(6), <(M)over bar (w)>/(M) over bar(n) < 1.06 ) solution in cyclohexane was thoroughly studied by means of light sca ttering, cloud point, coexisting phases volume ratio, coexisting phase s composition and scanning calorimetry methods, and binodal and spinod al curves were obtained. Coordinates of the UCST (T=306.2 K, phi(2) = 1.88.10(-2)) determined by different methods were similar. It was foun d that the first-order phase transition curve obtained by calorimetric scanning at 10(-6) K/s accurately fits the spinodal of the system wit hin the concentration range of semidilute and concentrated solutions a nd has a horizontal part in dilute solutions where the temperature of phase transition was found to be 303.86 K, independently of concentrat ion. At the same temperature a deflection point was found on the conce ntrated branch of the spinodal. The results were taken as calorimetric evidence of a coil-globule phase transition in the polystyrene soluti on. It was shown that the collapse of the polystyrene coils takes plac e in the metastable system between the binodal and the spinodal in the same way as in the homogeneous solution above the binodal.