Designing polymer networks that allow independent control of room‐temperature rigidity and high‐temperature rheological behavior is essential for material recycling. To address physical constraints within semi‐crystalline polyolefins, we constructed polyethylene‐based vitrimers with varying crosslinker ratios and catalyst concentrations via in situ reactive melt blending. Results reveal that large physical spacing in loosely crosslinked networks restricts topological rearrangement. However, combining an equimolar crosslinker ratio with 15 mol% catalyst overcomes these constraints, achieving the lowest activation energy of 94.53 kJ/mol. While increasing the catalyst to 20 mol% plateaus the activation energy at 95.44 kJ/mol, it continues driving the initial static network's densification. Moreover, networks deviating from the equimolar ratio release enhanced local segmental mobility via single‐ended dangling chains, endowing the material with exceptional mechanical recovery. This work provides deep insight into the synergistic regulation between crosslinker and catalyst. It achieves a high degree of decoupling between structural rigidity and rheological activity, offering a core design paradigm for tailored, recyclable polyolefin networks.
Kai Niu, Chenchao Fu, Mingfei Liu et al.· Journal of Applied Polymer S...· 0 citations
Converting polyethylene (PE) into dynamic covalent networks represents a crucial pathway toward achieving sustainability in polyolefins. In this study, PE‐Vitrimers with gradient cross‐link densities were constructed, and their non‐isothermal crystallization behavior was systematically investigated using multiple kinetic models. It was found that the influence of the dynamic cross‐linked network on non‐isothermal crystallization is primarily manifested as a reshaping of the kinetic evolution pathway rather than thermodynamic disruption of the crystal structure. Although the introduction of the cross‐linked network does not alter the inherent orthorhombic crystal system of the PE matrix, the polar cross‐linking nodes enhance the Avrami exponent via heterogeneous nucleation effects and induce anisotropic crystal growth. Meanwhile, the steric hindrance arising from the dense topological network gradually dominates, leading to a monotonic decrease in the overall crystallization rate, accompanied by a global upward shift and a non‐monotonic decrease‐then‐increase evolution of the local crystallization activation energy with conversion. This work elucidates the physical competition mechanism between cross‐link‐induced heterogeneous nucleation and topological constraints, providing important theoretical support for the processing design of semi‐crystalline Vitrimer.
Kai Niu, Chenchao Fu, Xudong Xu et al.· Polymer Engineering & Sc...· 0 citations