## 3 Results and Discussion
### Synthesis of Methyl and Decyl Esters
Some differences arise compared to the spectra of methyl esters, and in particular: the triplet instead of singlet at 4.05–4.07 ppm (a) from –CH\({}_{2}\) in \(\alpha\) to the oxygen, the integral values of the peaks at 2.27–2.29 ppm (c) from –CH\({}_{2}\) in \(\alpha\) to the carbonyl, at 1.58–1.65 ppm (d) from –CH\({}_{2}\) in \(\beta\) to the carbonyl, at 1.26 ppm (e) from the aliphatic chain of both the alcohol and the acid, and at 0.86–0.90 ppm (f) from shielded –CH\({}_{3}\) groups at the end of the aliphatic chains from both the alcohol and acid side. Impurities from residual alcohol can be observed and quantified through the integral value of the triplet at 3.62–3.66 ppm (b) assigned to the –CH\({}_{2}\) in \(\alpha\) to the hydroxyl groups in the free unreacted alcohol molecules. Similarly as for previous pictures, the green lines indicate the integral areas, while the normalized values are indicated in blue. \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline  & **Structure** &
\begin{tabular}{c} **Carbon** \\ **Number** \\ \end{tabular} & **Purity** & **T\({}_{\text{s}}\) (onset, \({}^{\circ}\)C)** & **T\({}_{\text{m}}\) (onset, \({}^{\circ}\)C)** & **Supercooling** & **AH (\(\text{pg}\))** & **AH** & **T\({}_{\text{degradation}}\)** & **\(T_{\text{degradation}}\)** \\ \hline MEMC (C1-C14) & C\({}_{51}\)H\({}_{50}\)O\({}_{2}\) & 15 & 242.4 & 98\% & 18.5 \(\pm\) 1.2 & 14 \(\pm\) 1.9 & 1.2 & 190 \(\pm\) 2 & 46.1 & 87.2 & 233 \(\pm\) 12 \\ MEPA (C1-C16) & C\({}_{71}\)H\({}_{50}\)O\({}_{2}\) & 17 & 270.5 & 98\% & 24.2 \(\pm\) 0.2 & 26.3 \(\pm\) 0.0 & 2.1 & 201 \(\pm\) 1 & 54.4 & 119 \(\pm\) 10 & 272 \(\pm\) 4 \\ MESA (C1-C18) & C\({}_{51}\)H\({}_{50}\)O\({}_{2}\) & 19 & 298.5 & 98\% & 31.9 \(\pm\) 1.1 & 35.6 \(\pm\) 1.0 & 3.7 & 204 \(\pm\) 1 & 60.9 & 117 \(\pm\) 27 & 287 \(\pm\) 6 \\ MEBE (C1-C22) & C\({}_{52}\)H\({}_{50}\)O\({}_{2}\) & 23 & 354.6 & 98\% & **41.5 \(\pm\) 1.0** & **47.9 \(\pm\) 0.7** & 6.4 & 200 \(\pm\) 5 & 70.9 & 155 \(\pm\) 7 & 308 \(\pm\) 20 \\ DEMP (C1-C14) & C\({}_{51}\)H\({}_{50}\)O\({}_{2}\) & 24 & 368.7 & 98\% & **22.9 \(\pm\) 0.2 & 25.2 \(\pm\) 0.4 & 2.3 & 196 \(\pm\) 3 & 72.3 & 130 \(\pm\) 5 & 318 \(\pm\) 11 \\ DEPA (C10-C16) & C\({}_{52}\)H\({}_{50}\)O\({}_{2}\) & 26 & 396.7 & 89\% & 28.9 \(\pm\) 1.2 & 29.0 \(\pm\) 1.9 & 0.1 & 193 \(\pm\) 6 & 76.6 & 145 \(\pm\) 7 & 310 \(\pm\) 14 \\ DESA (C10-C18) & C\({}_{52}\)H\({}_{50}\)O\({}_{2}\) & 28 & 424.8 & 98\% & 33.8 \(\pm\) 1.3 & 36.2 \(\pm\) 0.8 & 2.4 & 192 \(\pm\) 6 & 81.6 & 205 \(\pm\) 20 & 350 \(\pm\) 14 \\ DESE (C10-C22) & C\({}_{52}\)H\({}_{50}\)O\({}_{2}\) & 32 & 480.9 & 95\% & **44.7 \(\pm\) 0.6** & **41.8 \(\pm\) 0.7** & 0.1 & 193 \(\pm\) 9 & 92.8 & 200 \(\pm\) 20 & 357 \(\pm\) 21 \\ \hline \end{tabular}
\end{table} 
Table 1: Summary of thermal properties of the ester produced. The colors indicate the temperature gradient from the lowest values (blue) to the highest (red). A trend between degradation temperatures and molecular structure is observed, with a progressive growth of the thermal stability together with carbon chain length. This is supposedly due to longer chains’ ability to create more compact crystal packing structures, thus stronger intermolecular forces. No clear correlation between \(\Delta\)H (J/g) and the structure can be deduced, however all AH (J/g) values registered were over 190 J/g, confirming the fatty acid esters’ suitability as PCM. An increase in molar AH (KJ/mol) is observed for increasing molecular weights. A trend can be observed in the degradation temperatures, with the longer chained esters being the most stable and starting to degrade at much higher temperatures compared to shorter ones. This can be explained using literature reports, with longer chain esters being able to create tighter crystal structures and therefore stronger intermolecular bonding, thus requiring higher temperature to break the bonds [15; 16; 17; 18]. A similar behavior would be expected regarding melting temperatures T\({}_{\text{m}}\).