## 3 Results and Discussion
### Thermal Stability  
The thermal stability of the polymers was studied by thermogravimetric analysis (TGA). Results for DBI homopolymer and AESO-DBI thermosets are shown in Figure 4, and \(T\)5, \(T\)10, \(T\)50, and char yield values are shown in Table 1. \begin{table}
\begin{tabular}{c c c c c} \hline
**Sample** & _T_**5 (\({}^{\circ}\)C)** & _T_**10 (\({}^{\circ}\)C)** & _T_**50 (\({}^{\circ}\)C)** & **Char yield** \\ \hline DBI homopolymer & 220 & 257 & 333 & 1.74\% \\ AESO:DBI 1:1 & 313 & 336 & 387 & 6.34\% \\ AESO:DBI 2:1 & 324 & 343 & 397 & 6.66\% \\ \hline \end{tabular}
\end{table} 
Table 1: Thermogravimetric data for DBI and EC homopolymers, AESO-DBI, and AESO-EC resins. \(T\)5, \(T\)10, and \(T\)50 temperatures correspond to mass loss of 5%, 10%, and 50% respectively. Char yield is based on residue at 700 \({}^{\circ}\)C.  
Figure 4: Thermogravimetric curves for poly(DBI) and AESO-DBI thermosets. Black traces correspond to mass loss _vs._ temperature; gray traces are the corresponding derivative plots. Figure 3: Infrared spectrum of AESO-EC (1:1) thermoset. For the AESO-DBI blends, the TGA data show that the major degradation process has an onset around 300 \({}^{\circ}\)C, and the maximum rate of degradation occurs at 385-390 \({}^{\circ}\)C, apparently independent of the DBI content. The \(T\)50 values are very similar to that of pure AESO thermoset (398 \({}^{\circ}\)C) [13], for which the major thermal transformation is decomposition of the crosslinked polymer network and random scission of the linear chains [22]. In the case of DBI homopolymer, the sample shows loss of mass in the 150-200 \({}^{\circ}\)C range. GPC data showed that the purified DBI homopolymer still contained residual DBI monomer (\(<\)5%), therefore we attribute the lower-temperature mass loss to the monomer, which was not present in the AESO resins. EC homopolymer (Figure 5) showed two major degradation stages centered at 153 \({}^{\circ}\)C and 355 \({}^{\circ}\)C. TGA of EC monomer showed sharp mass loss centered at 165 \({}^{\circ}\)C; therefore it is likely that the EC homopolymer contained a small amount of unreacted EC. The AESO-EC samples show that unreacted EC was removed by the solvent extraction pre-treatment. Consumption of EC via thermal [2 + 2] dimerization during the cure was not expected due to the higher temperatures (\(>\)200 \({}^{\circ}\)C) that would be required [23]. \(T\)5, \(T\)10, and \(T\)50 values for the two series of thermosets are comparable. The values for AESO-EC are slightly higher than those for the DBI series, suggesting that the aromatic content in EC may provide limited stability, but in general the \(T\)50 values are not significantly different than the \(T\)50 of AESO alone. Char values are low for all materials tested, in agreement with the literature on thermal stability of AESO and AESO blends [13]. The AESO blends were further characterized by dynamic mechanical analysis (DMA). Representative traces of storage modulus as a function of temperature for AESO-EC blends are shown in Figure 6. Tan \(\delta\) curves as a function of temperature (Figures 7 and 8) were used to determine _T_g for AESO-DBI and AESO-EC materials. The results are summarized in Table 2. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sample** & _T_**5 (\({}^{\circ}\)C)** & _T_**10 (\({}^{\circ}\)C)** & _T_**50 (\({}^{\circ}\)C)** & **Char yield** \\ \hline AESO:DBI 3:1 & 325 & 343 & 393 & 5.16\% \\ EC homopolymer & 233 & 296 & 352 & 0.53\% \\ AESO:EC 1:1 & 309 & 337 & 390 & 2.86\% \\ AESO:EC 2:1 & 318 & 344 & 398 & 2.42\% \\ AESO:EC 3:1 & 326 & 348 & 402 & 2.84\% \\ \hline \hline \end{tabular}
\end{table} 
Table 1: _Cont._  
Figure 5: Thermogravimetric curves for poly(EC) and AESO-EC thermosets. Figure 6: Storage modulus as a function of temperature for AESO-EC thermosets. Figure 7: Tan \(\delta\) as a function of temperature for AESO-DBI thermosets.