Effect of Supercritical CO_2 on Induced Crystallization and Melting Behavior of Bisphenol-A Polycarbonate

The influences of temperature,pressure and cosolvent on the crystallization and melting behavior of bisphenol-A polycarbonate(BAPC)treated by supercritical CO_2 were studied by means of DSC.The results showed supercritical CO_2 depressed the crystallization temperature of BAPC and induced crystallization below the glass transition temperature.CO_2 had no dipole moment and only a small quadrupole moment and,therefore,was essentially a nonpolar fluid.The addition of a small amount of a polar cosolvent was equivalent to giving the mixed fluid an overall small dipole moment,or come into being hydrogenolysis with solute.Similar annealing condition in the presence of supercritical CO_2+cosolvent led to more stable crystals.The addition of a small amount of cosolvent could induce crystallization at much lower temperature and pressure.