## 3 Results and Discussion
### Dielectric Properties  
As shown in Figure 10a, at 10 GHz with a resin contents of about 52% the cured PPO/TAIC/L-glass composites exhibited dielectric constants from 3.24 to 3.10 and ultralow dissipation factors from 0.0023 to 0.0031, respectively. Before curing, the dielectric constants of prepreg samples decreased significantly with higher initiator concentration, while the dielectric loss stayed almost the same. After curing, the dielectric constant of the laminates kept the same trend as that of prepreg but moved to  
Figure 8: (**a**) The storage modulus (\(E^{\prime}\)) curves of different initiator mass fractions samples; (**b**) the tan\(\delta\) curves of different initiator mass fractions samples. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**BIPb\%** & \(\mathrm{T_{g}}\)**-tans/DMA (\({}^{\circ}\)C)** & \(E\)**/\(\mathrm{T_{g}}\) + 40 \({}^{\circ}\)C (MPa)** & \(v_{e}\)**(mol/m\({}^{3}\))** \\ \hline
0.25 & 172.0 & 9.0 & 814.53 \\
0.50 & 200.5 & 24.7 & 2076.97 \\
0.75 & 213.0 & 37.7 & 3097.26 \\
1.00 & 229.9 & 74.7 & 5937.05 \\
1.25 & 231.6 & 77.3 & 6134.94 \\
1.50 & 236.0 & 1 higher levels compared to the corresponding prepreg samples. The dielectric loss, however, showed an ascending trend at the same time. This trend was further confirmed with the resin cast samples (Figure 10b), indicating that the variation of the dielectric properties of the composites was mainly caused by the intrinsic variation of the resin matrix. For thermosetting polymer systems, it had been commonly agreed that, with the increase in crosslinking density, the orientation of the groups is progressively hindered and usually results in a lower dielectric constant and dielectric loss [43; 44; 45]. In the current PPO/TAIC system, however, it was obvious that more polarization and relaxation mechanisms were involved, and the significance of each mechanism varied depending on the advancement of curing, environment of the functional groups, and crosslinking structures. \begin{table}
\begin{tabular}{c c c c c c} \hline
**BIPb\%** & \(\tau_{3}\) **(ns)** & \(\tau_{3}\) **(Å)** & \(\mathbf{V_{3}\) **(Å)** & \(\mathbf{I_{3}\) **(\%)** & **FFV (\%)** \\ \hline
0.25 & 2.19 & 3.02 & 115.03 & 40.1 & 6.9 \\
0.50 & 2.29 & 3.10 & 125.03 & 38.5 & 7.2 \\
0.75 & 2.33 & 3.14 & 129.06 & 38.4 & 7.4 \\
1.00 & 2.44 & 3.22 & 140.62 & 36.8 & 7.6 \\
1.25 & 2.51 & 3.28 & 147.27 & 33.0 & 8.0 \\
1.50 & 2.57 & 3.32 & 153.42 & 31.5 & 8.5 \\ \hline \end{tabular}
\end{table} 
Table 6: Summary of the PALS analysis results of different samples. Figure 9: Positron lifetime spectra measured for cured samples. When PPO and TAIC were mixed together with a ratio of 4:3, the TAIC could be considered as a reactive plasticizer before curing since the two components were fully miscible at this composition [58]. It has been revealed that plasticizers in polymers can reduce intermolecular interaction, enhance the segmental mobility of polymer chains, and promote the dipole moments, thus increasing the dielectric constant [59; 60]. Such mechanisms may play important roles in the current system. While baked at 150 \({}^{\circ}\)C, some polymerization reactions were initiated which resulted in an increase in melt viscosity (Table 7). The DSC scan of P/T-0.25-L prepreg in Figure 11 showed that the curing reaction started at about 120 \({}^{\circ}\)C and had dual exothermic peaks at 160 \({}^{\circ}\)C and 180 \({}^{\circ}\)C, respectively, whereas that of pure TAIC started at 100 \({}^{\circ}\)C and reached an exothermic peak at 155 \({}^{\circ}\)C. The results revealed that multiple reaction processes are involved in the curing of PPO/TAIC systems. It is most likely that the peak at 160 \({}^{\circ}\)C can be mainly attributed to the curing of pure TAIC, and the reaction between PPO and TAIC occurred later at higher temperature. FTIR spectra in Figure 12 and the calculated results in Table 8 confirmed that, with the increase in initiator content in original compositions, more TAIC participated in homopolymerization and less plasticizer was left in the matrix.