Effect of supercritical carbon dioxide on the crystallization and melting behavior of linear bisphenol A polycarbonate

The crystallization and melting behavior of bisphenol A polycarbonate treated with supercritical carbon dioxide (CO₂) has been investigated with differential scanning calorimetry. Supercritical CO₂ depresses the crystallization temperature (T_c) of polycarbonate (PC). The lower melting point of PC crystals increase nonlinearly with increasing treatment temperature. This indicates that the depression of T_c is not a constant at the same pressure. T_c decreases faster at a higher treatment temperature than at a lower temperature. The leveling off of the depression in T_c at higher pressures is due to the antiplasticization effect of the hydrostatic pressure of CO₂. The melting curves of PC show two melting endotherms. The lower melting peak moves to a higher temperature with increasing treatment temperature, pressure, and time. The higher temperature peak moves toward a higher temperature as the treatment temperature is increased, whereas this peak is independent of the treatment pressure, time, and heating rate. The double melting peaks observed for PC can be attributed to the melting of crystals with different stability mechanisms. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 280–285, 2004