Preparation of hydrogen and boron ester bonded double crosslinking styrene butadiene rubbers and self-healing, adhesive capability

Developing styrene-butadiene rubber (SBR) with integrated functionality of mechanical robust, self-healing, self-welding, adhesive, and conductive properties is of great significance, but it still remains huge challenges. This work successfully prepared a double dynamically crosslinked styrene-butadiene rubber (HSBR-UPy-BE) that integrates excellent mechanical performance and self-healing, self-welding, and adhesion properties with hydroxylated styrene-butadiene rubber (HSBR) as the backbones, 2-ureido-4-pyrimidinone (UPy-NCO) and 4,4’4’’-(1,3,5,2,4,6-trioxaborocyclohexane-2,4,6-triyl) triaryl chlorides (aryl-boronic esters) (BE) serving as hydrogen bond and boronate ester crosslinking agents, respectively. The synergistic effects of dynamic hydrogen and boron ester bonds endow HSBR-UPy_15%-BE_5% with excellent mechanical properties, with a tensile strength of 5.3 MPa, a elongation at break of 281.0%, and a Young’s modulus and toughness reaching 25.9 MPa and 13.3 MJ/m³, respectively. Furthermore, the dynamic boronate ester and hydrogen bonds provide the material with excellent self-healing and welding capabilities. HSBR-UPy_5%-BE_5%, HSBR-UPy_10%-BE_5%, and HSBR-UPy_15%-BE_2% achieve self-healing efficiencies of up to 100% after healing at 60℃ for 24 h, and self-welding efficiencies of 100% at room temperature and 60℃ after welding for 24 h. Additionally, the multiple interactions including hydrogen, coordination, and hydrophobic interactions between HSBR-UPy-BE and the substrate confer the material with excellent adhesion properties to metals, glass, and PE substrates. Furthermore, based on HSBR-UPy_10%-BE_5% and graphite powder as a conductive medium, a conductive double crosslinked SBR composite material (GP/HSBR-UPy-BE) was prepared through ultrasonic dispersion and hot pressing, which can be used as a strain sensor, successfully achieving real-time monitoring of heart rate and electromyographic signals.