Enhanced Solvent Resistance of Covalent Polymer Networks through Increased Cross-linking Density

A covalent polymer network was constructed using bismaleimide (BMI) as a cross-linker. BMI was mixed with ESOF, and polymer networks, designated as ESOF-Ix, were gradually formed by heating at 80℃. This formation was driven by the Diels-Alder reaction between furyl and imide groups. The presence of covalent cross-linked networks was verified through swelling tests, and the solvent resistance of the resulting films was assessed using toluene. The analysis of swelling ratio (SR) and gel fraction (GF), presented in Figure 2a, revealed that ESOF-I0.6 exhibited a GF of approximately 60% and an SR of 621%. However, increasing the amount of BMI in ESOF-I1.0 led to a GF of 92%. This indicated that a higher concentration of BMI resulted in a denser cross-linking structure, thereby enhancing the solvent resistance of the resulting network.