Crystal Structure of the α-Form of Poly(l-lactide)

Study on the molecular packing of the α-form of poly(l-lactide) has been attempted taking into account packing energy calculations, refinement against new electron diffraction data, and Monte Carlo simulations. Packing energy has been evaluated for a fixed 107 conformation and an antiparallel arrangement of molecular chains. The energetically allowed space seems to be quite restricted, but with several minima of similar energy. One of them corresponds to a P212121 space group and agrees with the structure refined against diffraction data. Moreover, Monte Carlo simulations show a spontaneous evolution toward the refined model when parameters that define the packing, such as chain axis shift and setting orientation angles, are relaxed. On the other hand, the proposed packing shows asymmetric interactions that may lead to a molecular distortion.