Network evolution mechanism of a heat-resistant recyclable polyimine vitrimer capable of curing below the fully cured glass transition temperature

Vitrimer curing temperatures typically exceed their fully cured glass transition temperature ( T g ), limiting their compatibility with heat-sensitive materials. Herein, a heat-resistant, recyclable polyimine vitrimer is synthesized below the fully cured T g by using polyethyleneimine replacing the commonly used tris(2-aminoethyl)amine as a crosslinker. It attains a gel content of 99 % upon curing at 120 °C, while exhibiting a T g of 155 °C, a thermal expansion coefficient comparable to thermosets (33.8 μm m −1  °C −1 ), and a 5 % weight-loss temperature of 279 °C. Moreover, 99 % of tensile strength is retained after recycling. This mild curing behavior arises from a solvent-thermal synergistic network evolution mechanism that differs from conventional thermosets. Before solvent removal, polyethyleneimine shows higher reaction kinetics than tris(2-aminoethyl)amine, which promotes a more rapid evolution from oligomers to a crosslinked network. The solvent’s plasticizing effect maintains a diffusion-unconstrained state of the network, enabling its sustained growth. After solvent removal, a continuous high-crosslinked network with dispersed low-crosslinked domains is formed, yielding a gel content of 90 %. Subsequent mild heating (120 °C) activates segmental mobility in low-crosslinked domains, enabling their integration into the continuous high-crosslinked network and completing curing. In contrast, tris(2-aminoethyl)amine systems require 180 °C to activate segmental mobility within the discontinuous high-crosslinked domains, enabling interdomain crosslinking to achieve full curing. These findings provide novel network evolution routes and strategies for mild curing of heat-resistant vitrimers.