Polyethylene-Like Polyesters Derived from Macrolactones: Structure–Property Relationships and Deformation-Induced Mechanical Instability

Polyethylene-like long-chain aliphatic polyesters (LCAPs) have emerged as promising sustainable alternatives to conventional polyethylene. In this work, poly(ethylene dodecanedioate) (PED) was synthesized via ring-opening transesterification polymerization of a biobased macrolactone (ethylene dodecanedioate), yielding a polyethylene-like polyester with a number-average molecular weight of up to 66.0 kg·mol –1 . Wide-Angle X-ray Scattering (WAXS) analysis reveals that PED crystallizes in an orthorhombic lattice identical to that of polyethylene. Benefiting from its high molecular weight and well-defined crystalline structure, PED exhibits excellent mechanical performance, including a tensile strength of 40.0 ± 1.6 MPa, a yield strength of 24.0 ± 1.5 MPa (significantly higher than those of previously reported LCAPs and approaching that of high-density polyethylene), an elastic modulus of 427.4 ± 35 MPa, and an elongation at break of 696.9 ± 47%. Notably, an unusual mechanical instability characterized by stress oscillations is observed during tensile deformation. The stress oscillation occurs simultaneously with the formation of periodic transparent/opaque bands, and both phenomena exhibit a strong deformation-rate dependence. Under rapid deformation (20–80 mm·min –1 ), they are accompanied by a temperature increase of approximately 6–8 °C, whereas neither stress oscillation nor periodic banding is observed at 5 mm·min –1 in the absence of measurable self-heating. Two-dimensional SAXS/WAXS analysis reveals pronounced crystal reorientation and long-period structural evolution during stretching. Specifically, the transparent bands exhibit reduced crystallinity but enhanced crystal and long-period orientation, whereas the opaque bands show increased crystallinity and crystal orientation but a largely decreased long-period orientation. These findings suggest that the oscillatory behavior and periodic band formation arise from localized crystal reorganization and cyclic stress relaxation/recovery under thermo–mechanical coupling. This work provides new insights into deformation-induced instability in polyethylene-like LCAPs and highlights the importance of hierarchical structural evolution in governing their large-strain mechanical response.