Inherent viscosities were measured for polystyrene (PS) in N,N-dimethylformamide (DMF)/cyclohexane (CH) in the temperature range covered from 65°C close to the upper critical solution temperature T C of the DMF/CH system. It was found that near the critical temperature, the inherent viscosities contracted to about one-third of the value at 65°C. The overall contraction behavior agrees well with de Gennes’ theory and some interesting results have been observed. First, in the far off-critical temperature range (logt ⬎ ¹ 1.5), the strong synergetic, co-solvency effect of the mixed solvent was shown by higher values of the inherent viscosity than those measured in any single solvent. Second, the reduced theta temperature, t v, at which the chain dimension was supposed to have the unperturbed, ideal dimension, weakly depends on the molecular weight. Third, although we observed only the contraction behavior instead of contraction-and-reswelling on approaching the critical point, the expansion factors a3h ( ¼ [h]=[h]v ) for the different molecular weight samples fell on one master curve when plotted as a function of (logt ¹ logtv )Mw1=2 . Here t[ ¼ (T ¹ TC )=TC ] and M w are the reduced temperature and the weight-average molecular weight, respectively.
Посилання на статтю:
Conformational transition of polystyrene chain near the critical point of N,N-dimethylformamide/cyclohexane mixed solvent system / II Hyun Park // Polymer. – 1999. – N 40. – P. 2003–2009.