Shape‐memory thermosets: Tailoring the structure for toughness improvement and scratch healability

Abstract A straightforward but effective approach to fabricate shape‐memory polyurethane thermosets by tailoring the soft phase composition of two‐ and four‐armed polycaprolactone (PCL) polyols is described. As the crystallization of the PCL soft phase has an effect on driving the self‐assembly of H‐bonds, a good balance of tensile performance and thermo‐healability can be achieved by regulating the ratio between PCL‐diol and PCL‐tetrol in the soft phase. The inferior ability of crystallization of the segments near the branching point gives rise to enhancement of the both overall healability and toughness of the network. Healings of punctured holes and cuts are assessed using optical microscopy (OM), field‐emission scanning electron microscopy (FE‐SEM), tensile analysis, and two‐electrode impedence characterization. The obtained network with the best healing behavior has a soft phase composition with the PCL‐diol/PCL‐tetrol molar ratio of 2/1, a tensile toughness of 64 MPa J −1 and a healing efficiency (estimated by recovery of tensile strength) of nearly 80%. Highlights The composition of the soft phase of polyurethane networks was tailored. Two‐ and four‐armed polycaprolactones were used for the network structure. A good balance between mechanical and healing performance was obtained. Healing of complete cuts showed tensile strength recovery of nearly 80%.