Polystyrene/nylon 1212 blends were prepared with supercritical CO2 as the substrate swelling agent and monomer/initiator carrier. Original nylon 1212 and blends were characterized with differential scanning calorimetry (DSC), polarizing microscopy, wide-angle X-ray diffraction, and scanning electron microscopy (SEM). A novel phenomenon, CO2-induced epitaxy, was discovered, and its mechanism was deduced. Thermal analysis performed with DSC indicated that the polystyrene/nylon 1212 blends had thermal stability superior to that of virgin nylon 1212. The DSC and SEM measurements indicated that incorporated polystyrene could notably improve the mechanical performance of nylon 1212. (C) 2004 Wiley Periodicals, Inc.