2.2.14. Crosslinking Density

Small square samples were cut from the cured sample sheet (0.5 × 0.8 cm) and immersed in toluene at room temperature to assess the degree of swelling as a function of time. In this case, the swelling degree can be directly related to the crosslinking density. Experiments were done three times. Specimens from each composition were kept completely immersed in 20 mL of toluene throughout the test. The solvent was changed every 24 h. At given times, the specimens were removed from the solvent, had their surface carefully dried, weighed and were placed back into the solvent. Each specimen was kept out of the solvent for less than 20 s. The specimens were weighed in air on a balance with accuracy 0.1 mg. Crosslinking densities were calculated using the Flory-Rehner equation (see in Appendix A.2 for calculation details).