## 3 Results and Discussion
### Peel Resistance  
Peel resistance at a 180\({}^{\circ}\) angle is a typical test used to determine the mechanical properties of an adhesive layer. In the case of sealants used for moisture or corrosion protection, cohesive failure in the sealant layer is desirable. The results of the tests are significantly influenced by both the temperature and the peel rate due to the viscoelastic nature of pressure-sensitive materials. Under standard conditions, a peel rate of 300 mm/min allows for the evaluation of the material's adhesion to the surface, while a peel rate of 10 mm/min typically leads to cohesive failure. The adhesive failure modes recognized in conducted test specimens were \"adhesive\", where a clean separation of the adhesive from the adherend was observed; \"cohesive\", where the failure was in the adhesive layer; or \"mixed\", where both adhesive and cohesive failure was observed (Table 2).  
Figure 2: Schematic representation of \(\beta\)-scission of PIB chain.  
Figures 3 and 4 illustrate cohesion changes based on modifier content. The addition of MPTES in the MPTES-1, MPTES-2.5, and MPTES-5 systems resulted in a decrease in peel adhesion values by 10 N/24 mm, 5 N/24 mm, and 2 N/24 mm, respectively, compared to MPTES-0. However, the introduction of the silane did not significantly affect the adhesive properties of the blends, which still exhibited adhesive failure. In contrast, cohesion, measured at a separation rate of 10 mm/min, increased by 27% for the MPTES-1 system and 38% for the MPTES-2.5 system. Water immersion tests, however, did not show an improvement in cohesion compared to the reference sample, as adhesive failure at the steel interface resulted in a low value of 0.68 N/24 mm for the MPTES-1 sample. The addition of 10 PHR MPTES to the MPTES-10 and BIPB samples changed the fracture mode to a mixed failure mode. In the MPTES-10B blend, which contained a radical source (BIPB), cohesion increased significantly, particularly after water immersion, suggesting that the presence of BIPB may have promoted the formation of stronger internal bonds and improved the material's properties under wet conditions.  
The addition of VTMOS did not have a significant impact on the properties of the blends. However, comparing the values of cohesion for VTMOS-10 and VTMOS-10B, the matrix degradation caused by peroxide led to a 50% decrease in cohesion, as evident in Figure 4B. The addition of GLYEOS at concentrations of 0-5 PHR did not significantly alter the cohesion of the blends; however, the 10 PHR addition resulted in a decrease in cohesion. Epoxides generally react with nucleophiles (such as amines or carboxylic acids) or under strongly acidic or basic conditions to open the epoxide ring and form covalent bonds [34; 35]. In a primarily hydrocarbon-based butyl rubber matrix, suitable reactive species are scarce. The matrix lacks polar functional groups or strong nucleophiles under tested conditions. Without an appropriate curing agent or elevated temperatures specifically designed to promote epoxide ring-opening reactions, the glycidyl group remains dormant, preventing GLYEOS from integrating into the polymer network. Both VTMOS and GLYEOS, under this study's given conditions, lacked the necessary chemical reactivity pathways to effectively bond with the butyl rubber matrix. VTMOS's vinyl group and GLYEOS's epoxy group were not readily reactive with the saturated IIR/PIB backbone, especially in the absence of a strong nucleophile, suitable catalyst, or radical initiator designed for their particular functionalities. As a result, these silanes remained mostly unreacted within the matrix, functioning as mild plasticizers rather than crosslinking agents and providing no substantial improvement in mechanical or cohesive properties.