Self-healing bismaleimide resin via “click” reactions: impact of structure on healing efficiency

Aromatic bismaleimide (BMI)-based copolymers composed of alternating BMI and bis(sulfanediylethoxy)ethylene units of short and long lengths are synthesized and crosslinked via the reversible Diels–Alder reaction, resulting in thermoreversible amorphous networks with different structures and hence properties. The structure of BMI-based copolymers was confirmed by ¹H nuclear magnetic resonance (NMR) spectroscopy, and the occurrence of the DA reaction forming networks was followed using Fourier transform infrared (FT-IR) analysis. A comparison of the properties of the networks was obtained vis differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA) and wide-angle powder X-ray diffraction (XRD), optical microscopy, field-emission scanning electron microscopy (FE-SEM) and tensile measurements. Owing to higher mobility of the network structure derived from the long copolymer precursor, the corresponding network exhibits a lower glass transition and much better healing ability of scratches and cuts than for the short precursor-derived one. Efficient healing of complete cut, with strength and ultimate strain recoveries of 80% and 73%, respectively, are achieved for the long precursor-derived material.