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To reduce carbon dioxide emissions, the development of sustainable bio-based polyamides with performance advantages has become the focus of widespread attention. 1,5-Pentanediamine (PDA) is a renewable monomer produced by decarboxylation of lysine, which can be used as a sustainable alternative to traditional petroleum-based diamines and play a crucial role in the synthesis of bio-based polyamides. Herein, a series of bio-based aliphatic polyamides (PA5X) synthesized from PDA and aliphatic diacids with different methylene groups were successfully prepared via melt polycondensation. Their chemical structures were characterized, and the effects of diacid chain length on crystallization behavior, memory effect, and thermo-mechanical properties were emphatically investigated. The results show that the melting and crystallization temperatures of PA5X decrease with increasing diacid chain length. Meanwhile, the PA5X exhibits high thermal stability, with T d,5 % exceeding 380 °C. Unlike the even-even polyamide, the crystalline form of PA5X is γ -form, and the crystallization behavior and spherulitic morphology change significantly with diacid chain length, which is attributed to the complex entanglement effects. More particularly, the correlation between the diacid chain length and the melt memory effect is explored. PA56 with shorter methylene groups exhibits stronger melt memory effects due to the memory effects being directly affected by segmental chain interactions. Moreover, PA5X exhibits comparable or even superior tensile strength and ductility compared with hexamethylenediamine-based polyamide (PA6X) and reported fully bio-based PA11. This work provides a comprehensive investigation into the structure-property relationship of the bio-based polyamide PA5X, demonstrating great potential for application in high-performance eco-friendly materials. [Display omitted] • Bio-based polyamides were synthesized based on renewable 1,5-Pentanediamine (PDA) and various aliphatic diacids. • The physical properties of polyamides can be effectively modulated by altering the diacid chain length. • Compared to even-even polyamides, these polyamides exhibit comparable or even superior thermal and mechanical properties. [ABSTRACT FROM AUTHOR]

With bio-renewable and environmentally friendly nature, biobased polyamides have emerged as attractive alternatives to traditional petroleum-derived polymers. However, poor thermal and mechanical performance, high costs, and limited scalability significantly hinder their practical applications. Herein, a series of biobased copolyamides PA6/PA56 (CoPAs) were successfully synthesized from caprolactam, adipic acid, and the lysine-derived biobased monomers 1,5-pentanediamine. The copolyamides were characterized by gel permeation chromatography (GPC), nuclear magnetic resonance spectroscopy (1H NMR), wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA), rheological analysis, mechanical testing, and scanning electron microscopy (SEM). The result shows the α to γ transition in the crystalline form of the copolyamides with comonomer loading. The melting temperature, crystallization temperature, and crystallinity gradually decrease due to the introduction of the odd-even structure, causing deviation in amide positions and reducing hydrogen bond formation between molecular chains. Furthermore, variable-temperature infrared (VTIR) analysis and density functional theory (DFT) calculations further confirm a decrease in intermolecular forces. Importantly, the mobility of the molecular chains in the amorphous region is significantly improved, endowing the copolyamides with sufficient degrees of freedom to cope with externally applied strains. Moreover, significant entanglement facilitates effective stress transfer during stretching. As a result, the synthesized copolyamides achieve a high strength of 51 MPa and a remarkable toughness of 199 MJ/m3, without sacrificing thermal stability and processing properties. These biobased CoPAs show great potential and prospects in the field of high-performance thermoplastic materials, films, and textiles. [Display omitted] • Hydrogen bonding decreased with the introduction of the odd-even structure. • The massive entanglements formed within the copolyamides effectively transferred the stress. • The mechanical properties of biobased copolyamides were remarkably enhanced. [ABSTRACT FROM AUTHOR]

[Display omitted] • The isodimorphism of biobased PA6/PA56 was studied by the thermodynamic model. • The polymorphic crystallization behavior of PA6-type crystals is influenced by the content of 56 units. • The inclusion of 6 units in the crystal led to lower defect excess free energy (ε). A series of semi-crystalline bio-based copolyamides PA6 x 56 y were synthesized via melt polycondensation from caprolactam (6 units) and bio-based Pentamethylene adipamide units (56 units). DSC results show that the melting and crystallization temperature depend on the comonomers composition, and exhibit isodimorphic behavior. Combined with the analysis of WAXD, it is found that the 56 units are more tend to be excluded from rather than incorporated into the PA6 crystals. However, it does not imply a complete exclusion. Unexpectedly, there is a significant relationship between the content of 56 units on the polymorphic crystallization behavior of PA6-type crystals. Moreover, the pseudo-eutectic point appears when 56 units content is 30 mol %, and the spherulite morphology exhibits a strong correlation with the pseudo-eutectic point. In addition, the excess free energy of defects (ε) is calculated by applying the Wending-Suter model, and it is found that the ε -value caused by the insertion of 56 units into the crystal formed by PA6 is higher than that of 6 units into a crystal formed by PA56. Therefore, 6 units are more easily inserted into crystals formed by PA56, i.e., 6 units have better compatibility with PA56 crystals. In summary, this work reveals the involved mechanisms of comonomer units in the crystallization process and provides a potential strategy to guide the development of high-performance copolymers in the future. [ABSTRACT FROM AUTHOR]