Structure and crystallization of even–odd nylons derived from pimelic acid: Influence of the number of methylene groups in the diamine unit
Nylons 6,7, 8,7 and 10,7 have been synthesized by interfacial polycondensation and characterized. Thermal properties and thermally induced structural transitions have been evaluated to complement the reported data on nylon 4,7. Therefore, the complete even–odd series derived from pimelic acid is her...
| Autores: | , , |
|---|---|
| Tipo de recurso: | artículo |
| Fecha de publicación: | 2025 |
| País: | España |
| Institución: | Universitat Politècnica de Catalunya (UPC) |
| Repositorio: | UPCommons. Portal del coneixement obert de la UPC |
| Idioma: | inglés |
| OAI Identifier: | oai:upcommons.upc.edu:2117/443078 |
| Acceso en línea: | https://hdl.handle.net/2117/443078 https://dx.doi.org/10.3390/fib13070086 |
| Access Level: | acceso abierto |
| Palabra clave: | Aliphatic polyamides Nylons Even–odd series Pimelamide Synchrotron radiation Structural transitions Hydrogen bonds Thermal properties Àrees temàtiques de la UPC::Enginyeria química |
| Sumario: | Nylons 6,7, 8,7 and 10,7 have been synthesized by interfacial polycondensation and characterized. Thermal properties and thermally induced structural transitions have been evaluated to complement the reported data on nylon 4,7. Therefore, the complete even–odd series derived from pimelic acid is here fully characterized, in order to insist on their peculiar structural polymorphism. Real-time WAXD synchrotron experiments were conducted during heating, cooling and reheating processes. Basically, three structures were involved: a modified a-form, a distorted pseudohexagonal form and a pseudohexagonal form. The modified a-form was stable up to relatively low temperatures (i.e., lower than 140 °C), was mainly produced by solution crystallization and was progressively disfavored when the number of methylene groups of the diamine moiety increased. A progressive transition from the modified a-form to the distorted pseudohexagonal structure was observed during heating. Also, a continuous reverse transition was detected on cooling, although the yield on the modified a-form was low. A Brill transition towards a pseudohexagonal structure was observed in all cases. This transition was reversible, although with some hysteresis degree. Oriented fiber patterns corresponding to the distorted pseudohexagonal structure were obtained by melt stretching. In all cases, the 00l reflections appeared with a meridional orientation and indicated a shortening close to 0.05 nm/amide group with respect to the expected values for fully extended conformations. |
|---|