## 3 Results and Discussion
### Synthesis Development and Optimization
#### 3.1.3 DSC and TGA Analysis  
Following structural and purity analysis, thermal characterization was performed by TGA and DSC to determine thermal stability (thermal degradation, cycling), melting and crystallization points T\({}_{\rm m}\) and T\({}_{\rm c}\), degree of supercooling and enthalpy of fusion \(\Delta\)H of commercial and self-produced MEPA. Commercial MEPA presented an average onset T\({}_{\rm m}\) of 28.2 \({}^{\circ}\)C \(\pm\) 0.2 \({}^{\circ}\)C, and T\({}_{\rm c}\) of 25.3 \({}^{\circ}\)C \(\pm\) 0.1 \({}^{\circ}\)C in accordance to what was stated by the provider, and a supercooling of 2.9 \({}^{\circ}\)C for 10 \({}^{\circ}\)C/min heating rate. The melting and crystallization peaks were calculated by the STAR\({}^{\rm e}\) software through the tangent method, and the enthalpies were obtained by integration of the corresponding peak. The standard deviations were calculated from the results of the cycling tests and repetitions. For determination of phase change temperatures, onset temperatures are reported, and supercooling is calculated as the difference between onset melting temperature and onset crystallization temperature, unless stated otherwise. A high \(\Delta\)H of 204 J/g \(\pm\) 2 J/g was observed for commercial MEPA, indicating its suitability as PCM for LHS applications. As can be seen from Figure 7, synthesized MEPA presents phase change temperatures in accordance with the commercial sample with melting temperature of 26.3 \({}^{\circ}\)C \(\pm\) 0.0 \({}^{\circ}\)C and crystallization temperature of 24.2 \({}^{\circ}\)C \(\pm\) 0.2 \({}^{\circ}\)C, same degree of supercooling and stability over three heating/cooling cycles. The enthalpy of fusion observed from integration of the corresponding peak amounted to 201 \(\pm\) 1 J/g, indicating a high degree of purity in the MEPA produced, thus confirming once again the results previously reported.  
Figure 6: NMR spectra of MEPA produced in the laboratory. No impurities were detected, thus confirming GC-MS results of purity over 98%. The main peaks have been assigned, in particular: the singlet at 3.66 ppm from \(-\)CH\({}_{3}\), the triplet from \(\alpha\)-CH\({}_{2}\) and multiplet from \(\beta\)-CH\({}_{2}\) at 2.28–2.32 and 1.58–1.65 ppm, respectively, the aliphatic chain at 1.26 ppm and finally the shielded \(-\)CH\({}_{3}\) triplet at 0.86–0.90 ppm. The green lines indicate the integral areas, while the normalized values are indicated in blue.  
Figure 7: DSC analysis of MEPA produced in the laboratory for comparison with commercial sample. The results found of T\({}_{\rm m}\) of 26.3 \({}^{\circ}\)C \(\pm\) 0.0 \({}^{\circ}\)C and T\({}_{\rm c}\) of 24.2 \({}^{\circ}\)C \(\pm\) 0.2 \({}^{\circ}\)C and \(\Delta\)H of 201 \(\pm\) 1 J/g are in accordance with the values expected. This indicates a high degree of purity for the sample produced, and its suitability as PCM. The STAR\({}^{\rm e}\) Software version (14.00) is reported on the bottom right.  
Concerning TGA analysis, no residuals of methanol were observed in the sample (boiling point 64.7 \({}^{\circ}\)C), and degradation of the produced sample was complete by 240 \({}^{\circ}\)C in accordance with what was registered for commercial MEPA. The starting temperature of degradation varied between 100 and 110 \({}^{\circ}\)C for laboratory samples, while it was around 150 \({}^{\circ}\)C for commercial MEPA (Figure 8). The mass loss before 150 \({}^{\circ}\)C was less than 5% for all laboratory MEPA samples, and the remaining 95% was lost in the range between 150-240 \({}^{\circ}\)C as for commercial MEPA. Therefore, it could be concluded that no significant differences in the thermal stability between the self-produced sample and commercial one existed.