Self-crosslinking pyrimidine siloxanes with tunable mechanical and adhesive properties

Silicone rubbers exhibit high and low temperature resistance, electrical insulation, biocompatibility and other superior properties. However, their low mechanical strength is a fatal defect. It is necessary to develop new molecular structures and network architectures that enhance intermolecular interactions and optimize the performance of silicone elastomers. Consequently, this study presents a design strategy based on an “end-functionalized physical crosslinking domain + long covalent main chain” network structure. We develop amino-functionalized polysiloxane (PDMS-NH₂) with embedded photopolymerization sites. PDMS-NH₂ has long polymer chains to provide covalent cross-linking of the main chain. The end-groups of PDMS-NH₂ are modified by 2-ureido-4[1H]-pyrimidinone (UPy). The modified PDMS can self-crosslink to form supramolecular elastomers (UPy-PDMS) by domains of physical bonds of end groups. Meanwhile, thermoset silicone elastomers enhanced with domains of physical bonds are designed and synthesized (r-UPy-PDMS). The storage modulus of UPy-PDMS increases by four orders of magnitude at low frequencies to significantly enhance intermolecular interactions. UPy-PDMS has a siloxane content greater than 96%. Thereby, it exhibits excellent thermal stability (T_5% = 447 °C, T_max = 609 °C) and low temperature resistance. UPy-PDMS demonstrates reversible adhesion–disassembly performance. r-UPy-PDMS exhibits tunable mechanical properties, with tensile strength ranging from 0.41 to 0.87 MPa. This represents a remarkable 443% improvement compared to conventional silicone rubber (r-PDMS). This study aims to design specific end-group architecture and functionality to investigate their modulation of the mechanical properties and emergent functions of silicone elastomers. The goal is to accelerate the development of high-strength silicone rubbers and provide a theoretical foundation.