# Synthesis of Shape-Memory Polyurethanes: Combined Experimental and Simulation Studies
## 3 Results and Discussion
### Thermal Analyses  
Thermal analyses of BMC, OCDs, and PCUUs were performed using DSC (Table 3, Figure 8, and Figures S43-S54, Supplementary Materials). The results have clearly shown that the crystallization temperature (T\({}_{\rm{c}}\)) is strongly related to the content of hard segments in PCUU structures. The highest T\({}_{\rm{c}}\) of 19 \({}^{\circ}\)C was observed in the case of E_PCUU_5000_2, \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Sample** & **G\({}_{\rm{f}}\)** & **Q\({}_{\rm{m}}\)** & **HS * ** & \(\sigma\) & \(\epsilon\) & **E\({}_{\rm{Young}}\)** \\ \cline{2-7}  & **\%** & **\%** & **wt.\%** & **MPa** & **\%** & **MPa** \\ \hline E\_PCUU3000\_3.5 & 45 \(\pm\) 4 & 8430 \(\pm\) 700 & 21 \(\pm\) 1 & 28 \(\pm\) 3 & 840 \(\pm\) 40 & 67 \(\pm\) 15 \\ E\_PCUU3000\_3 & 0 & - & 18 \(\pm\) 1 & 24 \(\pm\) 3 & 990 \(\pm\) 35 & 91 \(\pm\) 7 \\ E\_PCUU3000\_2.5 & 0 & - & 15 \(\pm\) 1 & 23 \(\pm\) 3 & 950 \(\pm\) 20 & 108 \(\pm\) 11 \\ E\_PCUU3000\_2 & 0 & - & 13 \(\pm\) 1 & 27 \(\pm\) 2 & 960 \(\pm\) 40 & 112 \(\pm\) 9 \\ E\_PCUU3000\_1.5 & 0 & - & 10 \(\pm\) 1 & 34 \(\pm\) 5 & 1070 \(\pm\) 40 & 164 \(\pm\) 58 \\ E\_PCUU5000\_3 & 61 \(\pm\) 18 & 4480 \(\pm\) 670 & 12 \(\pm\) 1 & 23 \(\pm\) 4 & 1100 \(\pm\) 70 & 172 \(\pm\) 30 \\ E\_PCUU5000\_2 & 51 \(\pm\) 12 & 5840 \(\pm\) 290 & 8 \(\pm\) 1 & 22 \(\pm\) 3 & 1020 \(\pm\) 45 & 101 \(\pm\) 22 \\ \hline \end{tabular} G\({}_{\rm{f}}\)–gel fraction content in chloroform. Q\({}_{\rm{m}}\)—mass equilibrium swelling ratio in chloroform. *–calculated based on the amounts of OCD and IPDI used in the synthesis of PCUU.  
\end{table} 
Table 2: Hard segment content (HS), swelling behavior, and mechanical properties of PCUU samples. containing the lowest content of HS among the synthesized PCUUs. In the case of E_PCUU_5000_3, a slightly lower T\({}_{\rm c}\) of 11 \({}^{\circ}\)C was observed. PCUUs based on E_OCD_3000 showed T\({}_{\rm c}\) values in the range of 12 \({}^{\circ}\)C to 0 \({}^{\circ}\)C, which decreased with an increase in HS content in the structure. The T\({}_{\rm c}\) of E_BMC_8 and OCDs were much higher, at around 40 \({}^{\circ}\)C. Enthalpy of crystallization (\(\Delta\)H\({}_{\rm c}\)), in the case of PCUUs, decreased with higher HS content in the samples based on the same OCD. E_PCUU5000_3 and E_PCUU5000_2 exhibited higher \(\Delta\)H\({}_{\rm c}\) values for a similar HS share in samples based on E_OCD_3000. A decrease in the \(\Delta\)H\({}_{\rm c}\) value can be observed with the subsequent steps of the synthesis from 123 J \(\times\) g\({}^{-1}\) for E_BMC_8. After the second step of the synthesis, enthalpy declined to around 80 J \(\times\) g\({}^{-1}\), and then from 13 J \(\times\) g\({}^{-1}\) to 35 J \(\times\) g\({}^{-1}\) for E_PCUU3000_3.5 to E_PCUU5000_2, respectively. As the subsequent steps of the PCUU synthesis were carried out, the less crystalline phase was formed. This may be due to the disturbance of the regular structure introduced by a long chain and the content of rigid segments, which in the case of IPDI are asymmetric. DSC technique provides relatively quick and easy quantitative and qualitative analysis of transitions occurring in tested materials. Although extensive research has been carried out using this technique, studies such as these do not necessarily show subtle changes, or the precision essential for the analysis of shape-memory materials. MDSC applies the sinusoidally modulated heating rates. Therefore, the possibility to determine reversible events associated with glass transition and the melting process, as well as non-reversible changes such as crystal rearrangement, annealing, cold crystallization, and relaxation  
Figure 8: Thermal properties determined based on DSC measurements of PCUUs, OCDs, and BMC: melting points T\({}_{\rm m}\) (pink color) and melting enthalpies \(\Delta\)H\({}_{\rm m}\) (blue color).