Self-crosslinking pyrimidine siloxanes with tunable mechanical and adhesive properties

Abstract

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.