Polymorphism of poly(nonamethyleneoxamide) crystal

Abstract

The crystal structures of poly(nonamethyleneoxamide) (nylon-9,2) were investigated by wide-angle X-ray diffraction (WAXD) and differential scanning calorimetry. Nylon-9,2 shows a polymorphism with two different structures depending on the conditions of sample preparation.Monoclinic form I is the dominant crystalline phase for the solution-crystallized sample. For melt-crystallized samples, form I and new monoclinic form I′ coexist. Variable-temperature WAXD measurements were used to investigate the stability of each crystal form and the phase transition. Form I does not undergo any phase transitions prior to melting, although the orthorhombic molecular chain packing in form I at low temperature comes close to the quasihexagonal one during the heating process. Form I′ shows no phase transition on heating until its melting, too. The crystal lattice simply expands due to the thermal expansion. Form I is believed to be more stable, because the melting temperature of form I is higher than that of form I′.

Temperature‐induced structural changes in even‐odd nylons with long polymethylene segments

“…Nevertheless, X‐ray diffraction patterns of solution crystallized samples usually showed the typical strong reflections of conventional nylons (e.g., those appearing at spacings close to 0.440 and 0.380 nm). This feature has been described for both odd‐even nylons, such as 5 6, 5 10, 9 2, 11 10, 11 12, and 13 6, and even‐odd nylons like 6 5, 12 5, 6 13, 4 7, and 6 9 . Therefore, a new structure based on a molecular chain conformation that causes a slight rotation of consecutive amide groups of the odd diamide unit was proposed.…”

Reversible changes induced by temperature in the spherulitic birefringence of nylon 6 9

“…More complex geometries have been postulated for the room temperature structures of polyamides containing glycine units [14] and also of several odd-even and even-odd 4 nylons [8,[15][16][17][18][19][20][21][22][23][24][25][26]. These structures were characterized by the establishment of hydrogen bonds along three and two directions as a consequence of the conformational preferences of glycine residues and the inability to establish a saturated intrasheet hydrogen bonding scheme when an all-trans molecular conformation was assumed and odd diamine or diacid units were involved (Figure 1a).…”

Synthesis and characterization of poly (1,6‐hexamethylene oxamide‐co‐m‐xylene oxamide) copolymers

“…It has the shortest diacid‐unit and thus the highest amide concentration among the diacid‐based polyamides with a given diamine unit. As a result, POA possesses high melting point, high modulus, and excellent chemical resistance . More interesting is that the saturated water absorption of POA is much lower than common polyamides .…”