Sa. Vshivkov et Ap. Safronov, THE CONFORMATIONAL COIL-GLOBULE TRANSITION OF POLYSTYRENE IN CYCLOHEXANE SOLUTION, Macromolecular chemistry and physics, 198(10), 1997, pp. 3015-3023
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.