## 3 Results and Discussion
### Dielectric Properties
Thus, the plasticization effect was weakened, which explained the decrease in the dielectric constant of prepreg samples with higher initiator concentration. On the other hand, however, the dielectric loss at the prepreg stage did not change much with the variation of initiator content and the level of TAIC polymerization, which can be explained by the fact that the TAIC monomers have a highly symmetric structure and poly(TAIC) has a very low dielectric loss [32]. When the samples were cured at elevated temperatures, several changes took place in the system. First, with the advancement of the curing reaction, more and more TAIC molecules reacted with SA9000 and either generated crosslink networks by bridging SA9000 molecules or formed bulky pendant groups by grafting onto SA9000 chains. Both factors caused decreased dipolar mobility, contributed to lower polarizability, and drove the dielectric constants to a lower level. At the same time, the lessening of the plasticizing effects of TAIC were also in favor of the reduction of the dielectric constant. On the other hand, however, there were several new factors generated during the curing which may have promoted an increase in dielectric constants. PPO and TAIC molecules are highly \begin{table}
\begin{tabular}{c c} \hline \hline
**Prepreg Sample** & **Melt Viscosity (cP)** \\ \hline P/T-0.25-L & 10,739 \\ P/T-0.75-L & 20,884 \\ P/T-1.50-L & 23,454 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Melt viscosity of different samples. Figure 10: Dielectric properties of different initiator mass fractions: (a) laminate samples (the resin content was 52 \(\pm\) 3%); (b) casting samples. symmetrical, and the polarity was very low. When PPO and TAIC were copolymerized, the structural symmetry of both components was diminished and the dipole movements were enhanced, which resulted in significantly higher molecular and group polarity. Moreover, short TAIC branches can weaken the interaction force between polymer chains and increase the movability of polymer chains. Furthermore, chain transfer products from free radicals may also contribute to the overall polarizability of a system as polar impurities. For example, the primary radicals from the initiator may have been terminated by taking atoms from the other reactant and producing hydroxyl groups. Although the presence of alcoholic hydroxyl groups was not detected by ATR-FTIR or SSNMR [52], such byproducts from chain transfer reactions were inevitable and contribute to an increase in dielectric properties. Figure 11: DSC curves of P/T-0.25-L and TAIC homopolymerization system (the mass ratio of TAIC: BIPb was 99:1). Figure 12: FTIR spectra of different prepreg samples. Therefore, the overall trends of dielectric constant and dielectric loss were the superposition of these competing factors. It was evident that the factors increasing polarizability prevailed after curing compared to that of the corresponding prepreg samples, which resulted in an increase in dielectric constant and loss. Moreover, the polarizabilities were enhanced with the higher concentration of the initiator which led to the significant ascending of dielectric loss, whereas increases in the dielectric constant were partially offset by the increased free volume and reduced plasticizing effect at higher initiator concentration (Figure 9 and Table 6).