Poly(lactic acid). Группа авторов

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Schematic illustration of comparison between the observed (broken line) and calculated (solid line) X-ray diffraction profiles of PLLA alpha form for the several layer lines (25°C).

      Source: Reproduced from Wasanasuk et al., Macromolecules 2011, 44, 6441–6552.

      As mentioned above, the finally‐determined space group is P21. This symmetry reduction is needed to generate the 00l diffraction peaks of the odd l values (see Figure 6.5a). Strictly speaking, even this model could not reproduce the observed 00l profile perfectly, although most of the hkl diffraction peaks were reproduced satisfactorily enough (Figure 6.4). This situation requires introducing some structural disorder that was not considered in the structural analyses mentioned above. After many trials, the disordered domain model was found to reproduce the data quite well. Figure 6.5b shows that the domains of a specific size are gathered together with the relative height disorder. The relative‐height shift between the domains is small (0.1–0.2 c), but it gives a good reproduction of the 00l diffraction profile as shown in Figure 6.5a. Since the domain size is large enough, the observed X‐ray diffraction profiles of the general hkl peaks are not seriously affected [14].

      6.2.3 Crystal Structure of the δ Form

Image described by caption.

      Source: Reproduced from Wasanusuk et al., Macromolecules 2011, 44, 6441–6452.

      (b) PLLA domain model (several tens Å size along the a axis).

Schematic illustration of temperature dependence of the 1D WAXD profile measured in the phase transition from the delta to alpha form of the unoriented PLLA sample (heating process).

      Source: Reproduced from Zhang et al., Macromolecules 2008, 41, 1352–1357.

Schematic illustration of observed X-ray 00l reflection profiles of PLLA alpha and delta forms.

      Source: Reproduced from Wasanasuk and Tashiro, Polymer 2011, 52, 6097–6109.

      6.2.4 Crystal Structure of the β Form


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