## 4 Conclusions  
The addition of functionalized silanes can enhance the cohesion of sealants, provided that their functional groups react with the matrix and crosslink under the influence of moisture. Although butyl rubber exhibits low gas and moisture permeability, crosslinking effects became more prominent after extended immersion (24 h). This underscores the importance of water or humidity exposure for driving silane functionality, especially when targeting improved long-term properties such as peel resistance and cohesion. In the presence of radicals, silanes may act as coagents, facilitating the attachment of silane molecules to the butyl rubber chain, thereby increasing cohesion. While silane-induced crosslinking can raise cohesion and peel resistance, radical-mediated degradation processes occurring simultaneously tend to reduce molecular weight and compromise mechanical properties. The net effect depends on which reaction--crosslinking or degradation--dominates un  
Figure 6: Mooney viscosity ML changes depending on modifier content. Sample compositions in Table 1.  
der specific formulation and processing parameters. The chain degradation process is associated with the reduction in molecular weight, which, in turn, is evident as reduced peel adhesion at a 10 mm/min peel rate. Unreacted silanes in the sealant matrix serve as plasticizers. This behavior is evidenced by higher melt flow rates (MVRs) and lower Mooney viscosity, highlighting how even low concentrations of silanes can alter a sealant's processability. Systems without radical sources exhibited few significant changes, implying that the matrix itself (IIR/PIB) did not strongly interact with the silanes unless a radical pathway was present. The findings suggest that partial silane crosslinking is a promising route to balance cohesive strength and processability in butyl-based systems. By judiciously controlling silane type and concentration--along with radical initiators--manufacturers can tailor sealant formulations for higher-performance end uses. However, excessive silane content can lead to over-plasticization or competing degradation, underscoring the need for formulation optimization. The absence of significant changes in the properties of blends without a radical source suggests a lack of reactivity between the blend components (IIR, PIB) and the modifiers used (MPTES, APTES, VTMOS, GLYEOS). Therefore, the PIB/IIR matrix is a convenient basis for the investigation of potential filler-modifier interactions in further studies. Overall, these findings position silane-modified butyl rubber as a viable pathway for achieving customizable levels of cohesion and tack, provided that careful consideration is given to crosslinking conditions, silane selection, and potential degradation pathways. Conceptualization, J.C., B.S. and R.E.P. ; methodology, J.C. and R.E.P. ; validation, B.S., D.P. and R.E.P. ; formal analysis, J.C.; investigation, J.C.; resources, J.C.; data curation, D.P. ; writing--original draft preparation, J.C.; writing--review and editing, B.S., J.C. and D.P. ; visualization, D.P. ; supervision, B.S. and R.E.P. ; project administration, R.E.P. ; funding acquisition, J.C. and R.E.P. All authors have read and agreed to the published version of the manuscript. This research was funded by the Ministry of Education and Science: implementation doctorate I, registration number DWD/6/0325/2022. This work was also funded by the Smart Growth Operational Programme, project no. POIR.04.02.00-00-D003/20-00; European Funds, project no. RPWP:01.01.00-30-0004/18; and the Ministry of Science and Higher Education, project no. 21/529535/SPUB/SP/2022. Not applicable. The data presented in this study are available upon request from the corresponding author. The authors would like to thank Almara sp. z o.o. sp.k. for providing access to the necessary equipment, materials, and technical support. Author [PERSON] was employed by the company Almara sp. z o.o. sp.k.