A hybrid epoxy resin realized by facile glycidyl-grafting of highly-branched polyurethane toward heat-free structural bonding

In response to the potential issues associated with traditional high-temperature curing epoxy resins, such as significant energy consumption and inconvenience of handling, this study successfully developed a novel room-temperature curing epoxy resin structural adhesive. Herein, we develop a facile approach of synthesizing hybrid epoxy resin by grafting the hydroxyl-containing E51 onto a branched prepolymer. Specifically, a tri-functional polypropylene glycol (PPG) and di-functional polytetramethylene ether glycol (PTMEG) were mixed with 4,4′-dicyclohexylmethane diisocyanate (HMDI) to obtain branching chains terminated with NCO groups, which were ultimately consumed by E51 to obtain a PUEP resin with terminal epoxy groups. This resin was mixed with epoxy resin E51 in different proportions and cured at room temperature using amine curing agents. Notably, PUEP-5 demonstrated a shear strength of 23.2 ± 0.3 MPa on lapped steel plates after 24 h of room-temperature curing, along with the T-peel strength of 5.3 ± 0.2 kN/m. Moreover, the critical stress intensity factor ( K IC ) of the cured samples reached 3.1 ± 0.003 MPa/m 2 , indicating excellent mechanical and interfacial performance. This structural adhesive is suitable for applications in the electronics and automotive industries, offering significant cost savings in manufacturing processes and holding promising industrial prospects. By designing and synthesizing highly-branched polyurethane terminated by epoxy resin for room-temperature structural bonding, the process has demonstrated a significant toughening effect on the epoxy resin, achieving the goals of high shear strength and enhanced toughness.