## 3 Results and Discussion
### Mechanical Properties Measurement  
As we know, whether a material can be put into practical use greatly depends on its physical properties [39]. Figure 6 depicts the tensile stress-strain curves for the samples. The membranes with different contents of the hard segment of polyurethanes showed flexibility and typical nonlinear behaviors. The average values of the obtained numerical data about the tensile strength, elastic modulus, and other corresponding characteristic tensile parameters of the prepared films are given in Table 2. The PCUs showed tensile moduli in the range of 9.4-18.3 MPa and elongation at break in the range of 380%-530%. The mechanical behavior of the polyurethanes were dependent on several factors, such as the degree of crystallinity and microphase separation [40; 41], concentration, and the interconnectivity of hard segments. Here, all samples containing hard segments with the same composition presented an amorphous structure, as already indicated by AFM. The increment in hard segment content brought about a consequent increase in the cross-linked density as well as the degree of ordering structures, and can also be an important factor related to the decreased values of the tensile modulus [42]. The 30%-PCU presented relatively lower ultimate tensile strength and greater elongation at break than the others. Moreover, it is worth noting that when the hard segment was 35%, the flexibility of the films decreased to a great extent. This may mainly result from the loss of the three-dimensional steric effect on the main chain of the macromolecules. Based on the analysis of the above-mentioned points, it was possible to conclude that the inter-molecular interaction provided by the increased crosslinking density (caused by the increased hard segment) tends to generate a secondary crystallization (soft segment) to limit the mobility of the chains, causing an increase in the values of the mechanical properties [43]. In each series, the material will be broken when the local strength is more than the limited strength, giving rise to the rupture of the local molecular chains, which was consistent with the theory [44]. As we know, the elongation is inversely proportional to brittleness. The analysis of the AFM images fully proved that the degree of the microphase separation enhanced with the increase of the hard segment. The deduction of deformability can be derived from the statistics in Table 2, which may be attributed to the increased hard segment phase gathered in the regions. The aggregation could result in a larger degree of microphase separation and a greater crystallization possibility of the soft segment, causing the material to become more brittle and the elongation at break to decrease. To some extent, the results indicated that the mechanical properties of the polymer were influenced by the proportion of the hard segment. In addition, there were other factors influencing the final physical performance, such as the possibility of a localization of shear stresses at the narrow interface occurring and the ratio of the hard/soft segment [45].  
Figure 5: The DSC of the raw material PCDL and the prepared polymer.