Fabrication of polyurethane/polythiourethane core–shell microspheres via thiol-isocyanate click chemistry and their application in toughening epoxy resin

In this study, a novel kind of core–shell microsphere for toughening epoxy resin was developed and investigated. Polyurethane/polythiourethane (PU/PSU)-based core–shell microspheres with polyurethane as the core and polythiourethane as the shell were prepared by dispersion polymerization method via thiol-isocyanate click chemistry. The structure, morphology and particle sizes of PU/PSU core–shell microspheres were investigated by infrared spectroscopy, transmission electron microscopy and scanning electron microscopy. Results showed that the PU/PSU microspheres were successfully fabricated and had a core–shell structure with the particle size of about 0.5–1.5 µm. The PU/PSU core–shell microspheres can be uniformly dispersed in epoxy resin matrix, and the factors which affected the toughening performance of PU/PSU microspheres on the epoxy resin were investigated in detail. When they were used to toughen the epoxy resin, both the tensile strength and impact strength of the epoxy resin can be enhanced simultaneously. When the PU/PSU core–shell ratio was 1:8 and the amount of PU/PSU core–shell microspheres was 8 wt% of epoxy resin, the tensile strength of the epoxy resin toughened by PU/PSU microspheres was 62.5 MPa, which was 1.27 times that of pristine epoxy resin, and the impact strength reached the value of 13.1 kJ/m², which was 2.47 times that of pristine epoxy resin. This study indicates that PU/PSU core–shell microspheres are a kind of novel toughening agent which may find potential applications in toughening thermosetting resins, such as epoxy resin.