Imine or Secondary Amine-Derived Degradable Polyaminal: Low-Cost Matrix Resin with High Performance

In recent years, much effort has focused on the development of degradable thermosets; however, high cost and relatively low performance have become serious barriers to their practical applications. In this work, degradable thermosets based on imine/secondary amine dynamic bonds were prepared by amine aldehyde condensation. Specifically, terephthaldehyde and various diamines were used as monomers, and triethylenetetramine was selected as a novel cross-linker to prepare the degradable polyaminal. Because of the -NH₂ and -NH-CH₂-CH₂-NH- groups in triethylenetetramine, a hybrid imine/imidazolidine cross-linking structure was obtained. Thanks to the rigid ring structure of imidazolidine, the polyaminal represents higher cross-linking density and mechanical properties compared with common thermosets based on Schiff base. Importantly, the present strategy reduced the preparation cost by ∼60% due to the usage of a quite low-priced cross-linker. The results showed that the obtained degradable polyaminal exhibits superior properties, T_g (120-150 °C), T_d (249-277 °C), and tensile strength (52-64 MPa). Moreover, the polyaminal/carbon fiber composite could be completely degraded under mild acidic conditions within 1 h, leading to a rapid and nondestructive recycling of valuable fiber. This study is believed to offer an alternate strategy to set up a green framework for high-performance degradable thermosets that can potentially be used in commercial and industrial production.