Morphology and enzymatic degradation of poly(ε-caprolactone) single crystals:: does a polymer single crystal consist of micro-crystals?

Solution-grown lamellar single crystals of poly(epsilon-caprolactone) (PCL) were prepared from a dilute solution of n-hexanol by the isothermal crystallization condition or the self-seeding method. Hexagonal-shaped lamellar crystals with and without spiral growth were obtained, and the crystals produced well-resolved electron diffraction diagrams. The chain-packing structure and morphological complexity in lamellar crystals were investigated by bright-field and dark-field diffraction contrast methods of transmission electron microscopy. Based on both diffraction contrast images, it was revealed that both tightly and loosely chain-packing regions exist in one lamellar crystal. Thus, it was emphasized that PCL solution-grown lamellar single crystals consist of micro-crystals with nano-order size for the crystalline core region. Lipase type XIII from Pseudomonas sp was used for the enzymatic degradation of the PCL lamellar crystals. Enzymatic degradation progressed perpendicularly from the crystal lateral sides, without decrease of the molecular weight and lamellar thickness, yielding notched-shaped morphologies to the crystals. These results further indicate that PCL lamellar crystals consist of nano-order micro-crystals, and that enzyme hydrolyzes the loosely chain-packing regions between the tightly chain-packing regions (micro-crystal regions). (C) 2002 Society of Chemical Industry.