## 3 Results and Discussion
### Swelling Behavior  
Depicted in Figure 7 are the solvent uptake in mol% and the swelling index (percentage swelling) of the blends cured at different spans of time at 170 \({}^{\circ}\)C.  
It can be seen that the solvent uptake and the swelling index of the blend NR/CR-CV cured at its \(T_{90}\) was considerably higher than the corresponding NR/CR-CVMF\({}_{3}\) cured at its \(T_{90}\). This swelling behavior is quite expected because the \(\Delta M\) value of the \(T_{90}\) cured NR/CR-CV was around 44% lower than the \(T_{90}\) cured NR/CR-CVMF\({}_{3}\). In general, the lower the \(\Delta M\) value, the lower will be the crosslink density and, hence, the higher will be the solvent uptake and swelling index. However, it is interesting to note that the solvent uptake and the swelling index of NR/CR-CVMF\({}_{3}\) cured up to 8 min was also lower than the \(T_{90}\) cured NR/CR-CV even though the \(\Delta M\) produced in NR/CR-CVMF\({}_{3}\) after 8 min of curing and the \(\Delta M\) of NR/CR-CV cured up to its \(T_{90}\) exhibit almost the same value of around 3.0 dNm (Figure 2). Similarly, the solvent uptake of the \(T_{90}\) (10 min) cured  
Figure 6: RPA cure curves at 170 \({}^{\circ}\)C and the corresponding strain-sweep curves at 40 \({}^{\circ}\)C of **(a,b)**\(T_{90}\) cured NR/CR-CV and 8 min cured NR/CR-CVMF\({}_{3}\) and **(c,d)**\(T_{90}\) cured NR/BIR-CV and 5 min cured NR/BIR-CVMF\({}_{3}\).  
Figure 7: Equilibrium swelling index and the solvent uptake of the blends molded at different curing time.  
NR/BIIR-CV was around 23 mol% higher than the 5 min cured NR/BIIR-CVMF\({}_{3}\) even if both these blends cured up to the specified time exhibited the same \(\Delta M\) of around 1.6 dNm.  
From the above-mentioned equilibrium swelling studies of the blends, it has been confirmed that the blends cured with CVMF\({}_{3}\) exhibit a higher swelling resistance in terms of solvent uptake compared to the blends cured with only CV. As already explained, one of the reasons for this might be a tightened network structure formed due to the formation of bismaleimide-based adducts between the chains of NR and CR (or BIIR). To check whether the network is really tightened or not right from the beginning of curing owing to the formation of the bismaleimide bonds as shown in Figure 5, we have monitored the solvent uptake of the blends at different intervals of time. Represented in Figure 8a,b is the solvent uptake in g/cm\({}^{3}\) of the \(T_{90}\) cured NR/CR-CV, 8 min cured NR/CR-CVMF\({}_{3}\), \(T_{90}\) cured NR/BIIR-CV and the 5 min cured NR/BIIR-CVMF\({}_{3}\). It can be seen that the blend NR/CR-CV exhibits a higher speed of swelling in terms of solvent uptake compared to the NR/CR-CVMF\({}_{3}\) even though both these blends cured up to the above-mentioned curing time exhibited the same magnitude of \(\Delta M\). For instance, after 5 min of swelling, the solvent uptake of the \(T_{90}\) cured NR/CR-CV was around 5% higher than NR/CR-CVMF\({}_{3}\). Similarly, after 5 min of swelling, the solvent uptake of the \(T_{90}\) cured NR/BIIR-CV was around 25% higher than the 5 min cured NR/BIIR-CVMF\({}_{3}\). This low amount of solvent uptake at the early stage of swelling of the blends cured with CVMF\({}_{3}\) supports the fact that MF can act as a compatibilizer (co-curing agent) between NR and CR (or BIIR) by utilizing the in situ formed dienes via Diels-Alder reaction, as depicted in Figure 5.