Reprocessable and Self-Healable Boronic-Ester-Based\nSBS Vitrimers with Improved Thermomechanical Property and Adhesive\nPerformance

Abstract

As\na traditional block copolymer-type elastomer, the poly(styrene–butadiene–styrene)\nSBS elastomer has limited properties like weak heat/solvent/creep\nresistance and adhesive performance. In this work, the “melt-blending\nand ultraviolet (UV) post-treatment” method was used to activate\na thiol–ene reaction between thiol-terminated boronic ester\ncross-linkers (BDB) and vinyl groups of SBS chains. In this way, it\ncan effectively incorporate a dynamic boron–oxygen (B–O)\nnetwork into SBS elastomers. When increasing the BDB content from\n1 to 10 wt %, the gel content of SBS vitrimers varies from 18.76 to\n83.91%. At the same time, the glass transition temperature (<i>T</i>_g) of the PB phase in SBS vitrimers increases\nfrom −87.87 to −73.25 °C and a rubbery plateau\nappears instead of an instant rupture when the temperature rises above\nthe <i>T</i>_g of the PS phase. The stress relaxation\nbehavior of all SBS vitrimers shows an Arrhenius-type temperature\ndependence, and the estimated bond-exchange activation energy (<i>E</i>_a) of SBS-BDB10 was 52.28 kJ/mol. Compared to\nthe pure SBS elastomer, SBS vitrimeric elastomers show an increased\nYoung’s modulus, creep resistance, and self-healing properties\nand maintain their rubber elasticity. Furthermore, the adhesive property\nto the metal was notably improved, achieving a lap-shear strength\nof up to 1.83 MPa. Therefore, it is demonstrated to obtain good reprocessability\nand improved physical properties via fabricating SBS vitrimers with\ndynamic B–O networks.