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PEA (─[─OCH₂CH₂OCO(CH₂)₄CO─] _n ─) crystallizes to the α form with the unit cell parameters of a = 5.47 Å, b = 7.23 Å, c (chain axis) = 11.72 Å and β = 113.5° [87–89]. The two chains of almost zigzag type are packed in the unit cell with the P2₁/a space group symmetry.

The spherulite of PEA α form gives a beautiful ring pattern as shown in Figure 6.26. The stepwise WAXD/SAXS measurements at 1 μm step using a synchrotron X‐ray beam of 1 μm size revealed that the lamellae grow radially with the 180° twisting around the a′ axis at 7 μm pitch. On the other hand, the SEM observation of the fractured surface of the spherulite clarified that the spherulite consists of the discontinuous aggregation of the lamellar blocks in the radial direction [90]. These two observations, the lamellar twisting phenomenon and the discontinuous growth of lamellae, must be combined together consistently. In the growing spherulite of PEA α form, the molecular chains are attached on the front surface of the lamella, and the lamella grows with the small twisting of the plane sheet of the extended chain stems. Once when the 180° twisting is completed, a new lamella starts to generate discontinuously on the adjacent lamellar surface and grows with the twisting phenomenon. So far, as a general phenomenon of the ring‐pattern spherulite, the twisted lamellae have been believed to grow continuously from the center. But the study of the PEA spherulite gave us a warning about such an unsound universal concept of the continuously growing process of the twisted lamellae.

FIGURE 6.26 (a) (A) polarized optical microscopic image and (B) and (C) SEM (scanning electron microscope) images measured for PEA spherulite.

Source: Reproduced Woo et al., Macromolecules 2012, 45, 1375–1383.]

(b) Illustration of the stacking structure of the twisted lamellae.

Source: Reproduced from Tashiro et al., Polymer Journal 2019, 51, 131–141.