Polyoxymethylene oriented crystallization

Figure 1.10. Surface replica of molded polyoxymethylene fractured at liquid nitrogen temperatures. While the lamellae to the lower left are oriented at an angle to the fracture surface, the lamellae elsewhere are nearly parallel to the fracture surface. The important point is that lamellae (resembling those in single crystals) are stacked up like cards or dishes in the bulk state. (Geil, 1963.)...

Other Thermoplastics. Polyoxymethylene (POM) was imaged by afm, revealing oriented polymer chains parallel with the machine axis of sample extrusion (Fig. 15). Atomic scale resolution of the chains demonstrated the helical nature of the polymer chains. Long-range correlation between poljuner chains was observed as well (97). Imaging of extended chain crystals of POM closely matched molecular models for this material, allowing for the molecular packing and order in the extended chain crystal to be well understood. The authors were able to describe the polymer chain orientations with respect to the crystal (98). 

Snetivy D, Vancso GJ. Selective visualization of atoms in extended-chain crystals of oriented polyoxymethylene by atomic force microscopy. Macromolecules 1992 25 3320. 

Figure 8.12 Polymer decoration epitaxial crystallization on the fold surface. Polyethylene vapors were deposited on the surface of single crystals of polyoxymethylene (POM) at room temperature. The resulting PE decoration is made of edge-on lamellae oriented normal to the POM growth faces, with the deposited PE chains parallel to the growth front. The distance between POM fold planes (0.386 nm) imposes the monoclinic (010) PE contact plane, in which chains are separated by =0.4 nm [68].

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