Nylon 7,10: An odd-even polyamide with a complex melting and a peculiar high temperature polymorphic form
The crystalline structure of nylon 7,10, an odd–even polyamide derived from biobased sebacic acid, has been investigated to elucidate its complex polymorphism and thermal behavior. Solution-crystallized samples display two intense X-ray reflections at 0.439 nm and 0.380 nm, features that challenge a...
| Autores: | , , , |
|---|---|
| Tipo de recurso: | artículo |
| Fecha de publicación: | 2026 |
| País: | España |
| Institución: | Universitat Politècnica de Catalunya (UPC) |
| Repositorio: | UPCommons. Portal del coneixement obert de la UPC |
| Idioma: | inglés |
| OAI Identifier: | oai:dnet:upcommonspor::6d222bb9891b74d289096af6e6718f6d |
| Acceso en línea: | https://hdl.handle.net/2117/460710 https://dx.doi.org/10.1016/j.polymer.2026.129922 |
| Access Level: | acceso abierto |
| Palabra clave: | Aliphatic polyamides Hydrogen bonds Temperature-induced transitions Polymorphism Thermal properties |
| Sumario: | The crystalline structure of nylon 7,10, an odd–even polyamide derived from biobased sebacic acid, has been investigated to elucidate its complex polymorphism and thermal behavior. Solution-crystallized samples display two intense X-ray reflections at 0.439 nm and 0.380 nm, features that challenge a conventional sheet-type arrangement considering the presence of odd diamide units and an extended chain conformation. In contrast, melt-crystallized specimens adopt a well-defined pseudohexagonal structure at room temperature. Upon heating, a-modified crystals evolve toward a pseudohexagonal arrangement through a process involving partial melting, whereas cooling from the melt does not restore the a-modified packing. Close to fusion, an additional monoclinic/triclinic structure emerges, also detectable in the early stages of melt crystallization. Depending on solvent and thermal history, mixed structures are frequently obtained. These findings support the formation of hydrogen-bonded packings in which intermolecular H-bonds can be established in more than one direction. Calorimetric data further reveal a complex behavior, including the appearance of a high-temperature crystalline form that depends strongly on processing conditions. An equilibrium melting temperature of approximately 228 °C was estimated from the evolution of the main melting peak with crystallization temperature. Overall, these results highlight the pronounced structural plasticity of odd–even polyamides and the key role of thermal history in governing their polymorphic behavior. |
|---|