Structural analyses have been undertaken with the monoclinic and orthorhombic crystalline structures of polyester 4 6. X-ray diffraction patterns performed at 50 degreesC and electron diffraction patterns from single crystals, solution-grown films, and epitaxial crystallizations have been considered. Skew CH2CH2-OC(O) bonds and a P12(1)/n1 space group were postulated for the monoclinic structure (alpha-form). Molecular packing was optimized from electron diffraction data and a final R factor of 0.19 was obtained. The orthorhombic structure (beta-form) is characterized by an extended conformation and a molecular packing similar to polyethylene. Thus, an R factor of 0.11 is calculated for a setting angle of 40degrees, taking into account the electron diffraction data. A regular folding habit is found in the lamellar surfaces of crystals belonging to the beta-form, whereas an irregular folding habit is characteristic of the alpha-form.