Crystalline structure and morphology of poly(L-lactide) Formed under high-pressure CO₂

Crystalline structure and morphology of poly(L-lactide) (PLLA) formed under high-pressure CO₂ were studied by comparing the C0 ²-treated PLLA and the annealed one in terms of the crystallization behavior, crystalline forms, and crystalline superstructures. The crystallization temperature dependence of the diffraction peak position (2θ-16°) and crystallinity for the C0₂-treated PLLA indicates that the crystal modification changes continuously from the disorder α (α ) to a forms not through the a one with increasing temperature. By using light scattering technique, we clarified that the morphological transition from spherulites on a micrometer scale to rodlike crystalline superstructures on a nanometer scale occurs around 15 °C under 7-15 MPa CO₂ and around 30 °C under 3 MPa CO₂. By introducing the parameters Ν and A in the theoretical calculation for Vv light scattering from spherulites, it is indicated that there is a distinct difference in the arrangement of crystalline lamellae within spherulite between the C0 ₂-treated PLLA and the annealed one.