## 3 Results and Discussion
The insufficient mechanical strength leads to incomplete open-cellular structures, as described above. Aiming at the above problems, the strength of the material is enhanced by increasing the molar ratio of DVB or St to obtain higher toughness and open-cellular extent. Five kinds of polyHIPE membranes with different monomer ratios based on stable emulsions are synthesized via RAFT polymerization, as listed in Table 1. When the molar ratio of BA/St/DVB changes from 9/2/1 to 7/2/3, RAFT-6 shows brittle fracture, as shown in Figure 8, indicating that the amount of DVB has a significant effect on the brittleness of the material. By changing the molar ratio of BA/St/DVB from 9/2/1 to 5/6/1, RAFT-3 and RAFT-4 remain intact and the degree of shrinkage is reduced. However, when the molar ratio of BA/St/DVB changes to 3/8/1 in RAFT-5, brittle fracture is observed again, as shown in Figure 8. The SEM image (Figure 9) shows that all polyHIPE membranes have an interconnected open-cellular structure when the molar ratio of BA/St/DVB changes from 9/2/1 to 5/6/1. The changes of molar ratios of BA/St/DVB also cause the P\({}_{\text{C}}\) to increase from 88.80% to 100%, which is consistent with the change of sample size, indicating that the collapse and closure of pores can be avoided effectively by increasing the St content. The specific surface area increases from 3.42 m\({}^{2}\cdot\)g\({}^{-1}\) to 5.19 m\({}^{2}\cdot\)g\({}^{-1}\), as shown in Table 3.  
Figure 6: Illustration of the crosslinking process of (**a**) conventional free radical polymerization and (**b**) RAFT polymerization. A tensile test of polyHIPE membranes with different molar ratios of BA/St/DVB were further conducted. The test results are summarized in Table 3, while the stress-strain curves are shown in Figure 10. When the molar ratio of BA/St/DVB changes from 9/2/1 to 7/4/1, the T\({}_{\rm g}\) of RAFT-3 increases to 18.7 \({}^{\circ}\)C (Figure 7), and a distinct yield point is observed in the stress-strain curve. Because the test temperature is close to the T\({}_{\rm g}\), the yield stress of RAFT-3 is lower than the fracture stress. The frozen chain segment of the glassy RAFT-3 begins to move under external force after the yield point, and the extension of the polymer chain provides significant deformation of the material. Therefore, RAFT-3 exhibits plastic deformation with ductile fracture. Specifically, although elongation at break decreases from 24.00 \(\pm\) 3.26% to 17.50 \(\pm\) 3.90%, Young's modulus and the tensile strength increase to 10.09 \(\pm\) 1.82 MPa and 819.62 \(\pm\) 33.31 kPa, respectively. Accordingly, the M\({}_{\rm T}\) increases from 47.60 \(\pm\) 7.88 kJ\(\cdot\)m\({}^{-3}\) to 93.04 \(\pm\) 12.28 kJ\(\cdot\)m\({}^{-3}\). When the molar ratio of BA/St/DVB changes to 5/6/1, the T\({}_{\rm g}\) of RAFT-4 increases to 41.7 \({}^{\circ}\)C (Figure 7) and  
Figure 8: The optical images of polyHIPE membranes obtained by different molar ratios of BA/St/DVB prepared by RAFT polymerization. Figure 7: The derivative DSC curves of RAFT-2, RAFT-3, and RAFT-4. [PERSON]'s modulus of RAFT-4 increases sharply, indicating that the strength of the polymer skeleton is greatly enhanced. Simultaneously, a large number of macropores with a size of several hundred nanometers to microns appear inside the material, while the mesopores with a size below 10 nm basically disappear, as shown in Figure 11, which is consistent with the research of [PERSON] et al. (2016). The results indicate that the existence of mesopores inside RAFT-2 and RAFT-3 with high BA content may be attributed to the collapse of pores caused by insufficient polymer skeleton strength, rather than structural defects caused by uneven crosslinking. However, because the test temperature is much lower than the T\({}_{\text{g}}\), the yield stress of RAFT-4 is higher than the fracture stress. Thus, elongation at break and toughness of RAFT-4 is sharply reduced, and RAFT-4 responds in an almost linear-elastic manner and fails by brittle fracture.