# Synthesis and Characterization of Unsaturated Succin Acid Biobased Polyester Resins
## 4 Conclusions  
In this work, we reported the successful synthesis of unsaturated polyester resins with high biobased content, based on monomers from renewable resources such as ethylene glycol and succininic acid. The structure of the materials was verified by the means of \({}^{1}\)H-NMR and FTIR spectroscopies. SEC measurements revealed that the molecular weight of the resins was between 1600 and 3600 g/mol, which is adequate for applications in the adhesives or coatings industry. Rheological examination of the resins showed increased viscosity at ambient temperatures, which drastically decreased at temperatures higher than 40 \({}^{\circ}\)C. For this reason, acrylic acid was used as a potential reactive diluent and cross-linked resins were successfully prepared in the presence of initiators and Co(II) octoate as the accelerator. Additionally, between BPO and MEKP for their properties as initiators, the latter presented better control of the cross-linking and in lower temperatures, achieving curing times down to -4-5 min at a curing temperature of 90 \({}^{\circ}\)C. Apart from DSC studies of the curing of the systems, the cross-linked resins were thoroughly studied by means of FTIR and XPS, and the thermal stability of the materials was also examined via TGA. Overall, the resins presented in this study were prepared for the first time, showing potential as replacements of their fossil-based counterparts. It is apparent that the utilization of biobased monomers can lead to valuable materials. In addition, combining the correct monomers can lead to different attributes, as evidenced by the diol selection and the resulting viscosity of the resins. Nevertheless, more fundamental research needs to be conducted in order to establish such biobased products in the coatings and adhesives industry.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sample** & **T\({}_{\textbf{d,2\%}}\) (\({}^{\circ}\)C)** & **T\({}_{\textbf{d,5\%}}\) (\({}^{\circ}\)C)** & **T\({}_{\textbf{d,max}}\) (\({}^{\circ}\)C)** & **R\({}_{\textbf{600}}\) (\%)** \\ \hline PESM 50-50 & 219 & 278 & 433 & 12.8 \\ PESM 40-60 & 181 & 270 & 440 & 9.3 \\ PESM 25-75 & 216 & 275 & 431 & 12.1 \\ PPEGSM 50-50 & 154 & 266 & 431 & 8.4 \\ PPEGSM 40-60 & 202 & 266 & 426 & 9.2 \\ PPEGSM 25-75 & 195 & 268 & 425 & 11.2 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Characteristic temperatures for the thermal decomposition of the materials.  
Figure 10: Thermogravimetric curves (weight loss and dTG) of the cross-linked PESM (**a**) and PPEGSM (**b**) resins.  
**Supplementary Materials:** The following are available online at [[https://www.mdpi.com/2076-341](https://www.mdpi.com/2076-341)]([https://www.mdpi.com/2076-341](https://www.mdpi.com/2076-341)) 7/11/3/896/s1, Figure S1: SEC elugrams of the resins synthesized in this study, Figure S2: Example of \({}^{1}\)H NMR integration of the signals.  
L.P.: conceptualization, methodology, investigation, writing--original draft preparation; L.M.: investigation, writing--original draft preparation; D.P., A.M., E.P. ([PERSON]), Z.T., and E.P. ([PERSON]): investigation; K.C., C.M., and D.N.B.: conceptualization, methodology, formal analysis, funding, supervision, writing--review and editing. All authors have read and agreed to the published version of the manuscript.  
This research was co-financed by the European Union and Greek national funds through the Operational Program Competitiveness, Entrepreneurship and Innovation, under the call RESEARCH--CREATE--INNOVATE (project code: T1 EDK-01413).  
Not applicable.  
L.P. would like to acknowledge [PERSON] for the performance of the viscosity measurements.  
The authors declare no conflict of interest.