PHASE-SEPARATION IN THE POLY(GAMMA-BENZYL-ALPHA, L-GLUTAMATE) BENZYL ALCOHOL SYSTEM AND ITS ROLE IN GELATION

Gelation in systems containing poly(gamma-benzyl-alpha,L-glutamate) (PBLG) is well known, but two different mechanisms have been proposed to explain it. One attributes the gelation to crystallization, the other to phase separation via spinodal decomposition. In this paper we report a study of PBLG/benzyl alcohol (BA) gels. We have examined the possible types of phase separation that may occur when samples are held above the gel melting point. Three different types of phase separation may occur, corresponding to phase separation within the cap, the chimney and the broad biphasic parts of the Flory phase diagram. When these various phases cool, crystals (revealed by a melting endotherm in the differential scanning calorimetry) are formed in each of them, and the crystal melting point can be identified with the melting point of the unseparated gel. We are led to a picture of gelation in which phase separation occurs followed by crystallization, this picture bringing together the two existing models.