The influences of temperature and pressure on the melting behavior of PC treated by supercritical CO_2 and CO_2 + C_2H_5OH have been studied by differential scanning calorimetry (DSC). Supercritical CO_2 depresses the crystallization temperature of PC and induces crystallization below the glass transition temperature. CO_2 has no dipole moment and only a small quadrupole moment and, therefore, is essentially a nonpolar fluid. The addition of a small amount of a polar cosolvent is equivalent to giving the mixed fluid an overall small dipole moment. Similar annealing condition in the presence of supercritical CO_2 + C_2H_5OH leads to more stable crystals. The addition of a small amount of C_2H_5OH as a cosolvent can induce crystallization at much lower temperature and pressure. In addition to its own plasticizing effect, supercritical CO_2 acting as a carrier which delivers the polar component uniformly into the polymer matrix.

Key words: DSC, CARBON DIOXIDE, SUPER-CRITICAL STATE, DSC, CRYSTALLIZE, POLYCARBONATE