## 3 Results and Discussion
### Matrix Toughening by Polymerization-Induced Phase Separation  
We prepared simple formulations with 10 wt-% of PES 5003P with respect to the total amount of matrix precursors and a composite with powdered silica representing 60 wt-% of the whole material to examine the effects of this additive on the cationic polymerization of epoxides. Monomer conversion was measured at various moments of the UV-initiated polymerization of these blends containing 1 wt-% of TAS-SbF\({}_{6}\) with respect to the matrix. The polymerization profiles of Figure 11 show that there is no significant impact on polymerization kinetics, only a possible screening effect due to UV absorption of UV photons by the PES, but no chemical inhibition, no retardation, and only a slightly slower polymerization rate in the presence of silica powder. We have therefore explored the possibility to introduce a PES thermoplastic toughening agent into the EB-curable epoxy blends. This approach has marked differences with respect to the conventional toughening methodology applicable to heat-curable systems. The thermodynamics and kinetics of the two modes of curing are strongly different, being extremely brief and starting from RT for radiation processing, and slow and at high temperature for thermal curing. These distinct features are expected to favor the early occurrence of thermoplastic demixion upon radiation-induced polymerization and should limit the growth of the nucleated thermoplastic domains if the system starts vitrifying in the early stage of curing. This combination of favorable factors proved to be particularly efficient for designing acrylate-based radiation-cured matrices and composites [42; 43; 44; 45]. Figure 10: Sketch representing the gradual formation of a monolithic nano-heterogeneous network upon radiation-initiated cationic polymerization DGEBA-based formulations as supported by AFM imaging [41; 22]. Figure 9: Influence on Tg (based on T\({}_{\alpha}\) determined with the position of E\({}^{\prime\prime}\) maximum in DMA spectra) of various contents in additives effective as internal plasticizers of a DGEBA resin sample containing 0.5 wt-% of DAIS-B after EB irradiation with 4 consecutive 25 kGy passes. To compare materials prepared by the two curing process, we implemented the method utilizing a tandem initiator system with a peroxide and an iodonium salt, as presented earlier in Scheme 3. Two series of DGEBA formulations were prepared with poly(THF)-diol as a transfer agent (DGEBA/poly(THF), 93.3:6.7 \(w/w\)), various amounts of PES 3006P (0, 7.5, 10, 12.5, 15, 17.5, 19 wt-%) and either 0.5 wt-% DAIS only as the initiator for EB curing, or 0.5 wt-% DAIS and 0.125 wt-% Luperox P for the thermally-induced polymerization [46]. Samples cured in the form of 1 mm thick plates by both types of activation (for 90 min at 120 \({}^{\circ}\)C plus 60 min at 170 \({}^{\circ}\)C, or EB dose of 50 kGy) showed high conversion levels (>95%). Comparison of the thermomechanical spectra recorded by DMA analysis of the two series of samples revealed differences that can be interpreted in terms of distinct types of morphology in materials of similar compositions but subject to different curing modes. We focus on the plots representing the variations of the loss factor \(\tan\delta\) as a function of the content in PES and of the curing conditions (Figure 12). In the absence of PES, the epoxy networks present similar DMA spectra, as the peak is centered at 160 \({}^{\circ}\)C for both curing methods.