## 4 Discussion
These rankings do qualitatively agree with those of the MV as presented in Figure 5. It is a clear indication that the differences are not necessarily a sign of reduced crosslink density but, similar to MV, the result of stronger filler-polymer bonding and a larger free volume due to the addition of resins. The replacement of CB by silica and the addition of resins does not result in large crosslink density differences for all systems (Figure 9). The use of resins does neither negatively interfere with the network formation during vulcanization nor with the silanization reaction for systems containing CB/SI and SI; it has a small positive effect. The viscosities of TP and C9 at 150 \({}^{\circ}\)C are 3400 and 650 mPa.s respectively [11; 12]; the viscosity of TDAE oil at 100 \({}^{\circ}\)C is 17.86 mPa.s [14]. Despite a higher viscosity of theresins compared to oil, they impart a similar PE in the CB system. The dispersion of CB in the polymer matrix is relatively easy due to the less developed filler-filler network of CB and the high compatibility of CB with the non-polar polymers. Therefore, replacing an equivalent amount of TDAE oil with resins in CB-filled compounds results in nearly the same PE as the CB-control. The addition of TP and C9 does not negatively interfere with the silanization and shows a slight improvement of silanization. A slight decrease in PE is observed in CB/SI- and SI-filled systems by the addition of resins from their respective controls (Figure 10). Compatible resins and rubbers will shift or broaden the tan \(\delta\) peak region. In the case that resin and rubber are incompatible, two separate Tg-peaks are commonly visible in the tan \(\delta\) curve as a function of temperature [23] located at their original positions, at least if both are present in sufficient quantities. The use of resins shifts the tan \(\delta\) peak of the vulcanizates slightly to a higher temperature compared to the controls (Figure 11). This is clearly due to the addition of resins with high Tg and softening point, more for TP than for C9. As the Tg of the NR-phase as well as of the BR-phase shift with the addition of the resins (Table 7), it may be taken as an indication that the resins have no particular preference for either of the two phases. However, due to the lower amount of BR versus NR in the formulation, the shift in Tg of BR is difficult to discern; thus, the BR-data in Table 7 need to be taken with some reserve. At \(-30\)\({}^{\circ}\)C, the use of TP resin results in only a slightly higher ICT than for C9 in all filler systems. This is related to the shift of the tan \(\delta\) peak as a consequence of using resins with a high Tg and molecular weight. At 5\({}^{\circ}\)C, the C9 resin provides a higher WSR than TP and the respective controls in all filler systems. This seemingly contradictory observation is visible in the cross-over of the tan \(\delta\) curves for TP and C9 around \(-20\)\({}^{\circ}\)C, as seen for all three filler systems in Figure 12. It relates to the structure of C9, which contains methyl groups on the aromatic rings from vinyltoluene and along the polymer chain from \(\alpha\)-methylstyrene groups, providing more flexibility for rotation and movement than the bulky configuration of TP (Figure 2). Thus, the mobility of the chains increases more for C9 than for TP at raised temperature, leading to relatively higher viscoelastic losses. The use of resins for the CB-compounds raises the tan \(\delta\) values at 100 \({}^{\circ}\)C, while for the pure SI-compound, it leads to a small but significant further reduction (Figure 14). The effect in the SI-filled compounds is clearly the result of the chemical bonding of the rubber molecules to the silica surface by the coupling agent TESPT versus far less strong physical adhesion for the CB-reinforced compounds. It restricts release/adhesion or segmental motions of polymer segments on the filler surface and thus reduces mechanical loss phenomena on a molecular scale [24].