SOL-GEL TRANSITION OF POLYACRYLONITRILE PROPYLENE CARBONATE SOLUTION

The thermoreversible gelation of polyacrylonitrile (PAN)/propylene car bonate (PC) solution was investigated by calorimetric, thermomechanica l, optical, and rheological measurements. Two endothermic signals are observed for PAN/PC gels in DSC thermograms, and the peak temperature of the higher melting endotherm coincides with the gel melting tempera ture determined from the TMA thermogram. SEM micrographs show that the overall structure is separated into two phases and is composed of spe rical domains, which may be formed upon passing through the thermodyna mically unstable or metastable state via the liquid-liquid phase separ ation. The gelation rate increases with the aging temperature. This is also discussed on the basis of the elasticity theory of the fishnet g el. (C) 1994 John Wiley & Sons, Inc.