Reprocessable and Self-Healable Boronic-Ester-Based SBS Vitrimers with Improved Thermomechanical Property and Adhesive Performance

Abstract

As a traditional block copolymer-type elastomer, the poly(styrene−butadiene−styrene) SBS elastomer has limited properties like weak heat/solvent/creep resistance and adhesive performance. In this work, the "melt-blending and ultraviolet (UV) post-treatment" method was used to activate a thiol−ene reaction between thiol-terminated boronic ester cross-linkers (BDB) and vinyl groups of SBS chains. In this way, it can effectively incorporate a dynamic boron−oxygen (B−O) network into SBS elastomers. When increasing the BDB content from 1 to 10 wt %, the gel content of SBS vitrimers varies from 18.76 to 83.91%. At the same time, the glass transition temperature (T g ) of the PB phase in SBS vitrimers increases from −87.87 to −73.25 °C and a rubbery plateau appears instead of an instant rupture when the temperature rises above the T g of the PS phase. The stress relaxation behavior of all SBS vitrimers shows an Arrhenius-type temperature dependence, and the estimated bond-exchange activation energy (E a ) of SBS-BDB10 was 52.28 kJ/mol. Compared to the pure SBS elastomer, SBS vitrimeric elastomers show an increased Young's modulus, creep resistance, and self-healing properties and maintain their rubber elasticity. Furthermore, the adhesive property to the metal was notably improved, achieving a lap-shear strength of up to 1.83 MPa. Therefore, it is demonstrated to obtain good reprocessability and improved physical properties via fabricating SBS vitrimers with dynamic B−O networks.