As the most produced thermoplastic after polyolefins, an urgent issue for polyesters is to improve their environmentally friendliness in processing, application, and recycling. However, the performance of polyesters significantly deteriorates in the above stages. This work breaks through the difficulties when applying traditional polyesters by the green in situ construction of a novel covalent adaptable network, which has an ultrafast exchange reaction rate attributed to the synergistic catalytic effect of neighboring group participation (NGP) and the tertiary amine structure. This polyester-based vitrimer shows advanced performance in repairability (fast self-healing), foamability (matching fast CO₂ diffusion) and recyclability (efficient reprocessing), due to the ultrafast exchange reaction rate in the system. The obtained vitrimer then possesses excellent self-healing behavior, as the damage was recovered within 32 min at 245 °C, possesses great foamability, as the foam prepared via green scCO₂ foaming technology has a density as low as 0.039 g cm⁻³ and has a thermal conductivity as low as 28 mW/(m K)⁻¹, and, meanwhile, possesses an advanced reprocessing ability without performance loss. Furthermore, the proposed strategy shortens the preparation time of the vitrimer to 3.5 min, providing a practical green method for the continuous process and industrial production of the polyester vitrimer via the synergistic catalytic effect of NGP and the tertiary amine structure, which is also constructive to the improved performance, environmentally friendly upcycling, and green application of the polyester vitrimer.

Considering that environmental friendliness and energy conservation are becoming crucial, it is urgent to advance the sustainability of materials in terms of their lifecycle, including synthesis, processing, and application. Herein, covalent adaptable networks were constructed in a polyethylene terephthalate (PET) matrix via a green, external-catalyst-free method within only 8 min, which was realized by sequential transesterification and crosslinking reaction. This synthesis is environmentally friendly given that no toxic solvents or external catalysts are required, and it avoids energy waste. Meanwhile, the vitrimer exhibited an extremely fast relaxation time of 4.8 s, which was realized through the synergistic catalysis of the tertiary amine structure and neighboring group participation. Therefore, the vitrimer could readily change its configuration via fast exchange reactions during processing, which eliminated the residual stress and suppressed the molecular-chain orientation, avoiding shrinkage and warpage. Further, the vitrimer has potential sustainable applications in repairability and shape memory, where on the one hand, due to its stable state resulting from configuration-change foaming processing, the vitrimer foam has attractive self-healing behavior, which is the first time this is reported for foam materials, whereas other foams tend to shrink in the melt state, and hence fail to realize self-healing. On the other hand, due to the quick rearrangement of the crosslinking networks, the obtained vitrimer could be rapidly shape-programmed repeatedly, where its shape-memory behavior could be strengthened or erased by the synergistic effects of its covalent adaptable networks and physical crystalline networks, making it more regulable and concealed in encryption application. Briefly, the synthesis, processing, and application of this vitrimer are constructive to guide the design of novel polymers with improved performance and sustainability.

Herein, highly thermally conductive and insulating epoxy composites were reported. Firstly uniform alumina-coated graphite flakes were successfully prepared by a two-step coating method of chemical precipitation with the aid of a sodium dodecyl sulfonate (SDS) surfactant using an inorganic precursor (aluminum nitrate) as the starting material. Then the alumina-coated graphite particles were incorporated into the epoxy resin. The thermal conductivity value of epoxy/alumina-coated graphite composite shows a significant increase from 0.22 W mK⁻¹ (neat epoxy) to 0.64 W mK⁻¹ by a factor of approximately 3 at the filler loading of 18.4%. Moreover, due to the presence of the alumina nanolayers coating on the graphite surface, epoxy/alumina-coated graphite composites could retain high electrical volume resistivity of >10¹⁰ Ω cm up to high filler contents, which was much higher than that of epoxy/graphite composites (<10⁵ Ω cm) at the same filler loadings. And they still could be regarded as insulators.