Synthesis and Characterization of a Covalent Polymer Network Based on ESOF and Bismaleimide

The synthesis of the covalent polymer network was performed according to the protocol illustrated in Scheme 1. Bismaleimide (BMI) served as the cross-linker and was initially combined with ESOF. Subsequently, the polymer networks, denoted as ESOF-Ix, were gradually formed through heating at 80℃, facilitated by the formation of Diels-Alder adducts between the furyl and imide moieties. To confirm the presence of covalent cross-links, swelling tests were employed. The solvent resistance of the obtained films was evaluated using toluene. The swelling ratio (SR) and gel fraction (GF) were determined and presented in Figure 2a. The findings indicated that the GF and SR of ESOF-I0.6 were approximately 60% and 621%, respectively. However, an increase in the amount of BMI used resulted in a higher GF for ESOF-I1.0, reaching 92%. This observation suggests that a higher concentration of BMI led to an increased cross-linking density, thereby enhancing the solvent resistance of the resulting cross-linked network.