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The mechanical properties of polymer fibers are dependent on the molecular chemical structure and condensed state structure. Effective control over these two structural parameters allows us to study the relationship between fiber structures and properties and thereafter optimizes the material performance. In this work, the copolyamides (CoPAs) are prepared by selecting polyamide 6 (PA6) as the matrix and copolymerizing with the polyamide 66 (PA66) component, and the CoPA/HwPA6 (CoPA-Hw) composites with discrete molecular weight distribution are further fabricated by adding the high-molecular-weight PA6 (HwPA6) component in the CoPA. The CoPA fibers and CoPA-Hw fibers are prepared via melt spinning, and the crystal structures and mechanical properties of the fibers are studied. The mechanical properties cannot be effectively improved by adjusting the content of the PA66 component in the CoPA molecular chains or increasing the molecular weight of the CoPA. However, the addition of the HwPA6 component can effectively inhibit the slippage of molecular chains under stress and maintain the orientation of the molecular chains during annealing. Therefore, the mechanical properties of the CoPA-Hw fibers are significantly improved, and the stress at break can reach 6.86 cN/dtex. It is expected that the molecular chain orientation of polymer materials resulting from discrete molecular weight distribution can be used to improve the mechanical properties of other polymer materials.

Flexible aliphatic poly(lactic acid) is introduced into polyethylene terephthalate through copolymerization to prepare biodegradable copolyester, which aims to solve the non‐degradability of polyethylene terephthalate (PET) and realize the greening of raw materials. In this work, poly(ethylene terephthalate‐co‐lactic acid) random copolyesters (PETLAs) of lactic acid composition from 10 to 50% is synthesized via one‐pot method. The chemical structure and composition, thermal property, and crystallization property of prepared PETLAs resin are characterized. The results shows that the introduction of LA segment forms random copolyester, and the flexible LA segment results in slight decrease in the glass transition temperatures (Tg), melting point (Tm), and crystallinity (Xc) of the copolyesters. The thermal stability of PETLAs is better, and the initial decomposition temperature of PETLA‐10 can reach 394 °C. The PETLAs resin exhibits good processability, and PETLAs fibers are prepared by melt spinning. The strength of PETLA‐10 fiber can reach 260 MPa after drawing treatment, and the elongation at break can reach 130%. Taking advantage of their features, PETLAs as an innovative bio‐based polymer are expected to achieve ecofriendly applications in the fields of fiber, plastic, and film.

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