Novel high performance tough hyperbranched epoxy by an A2 + B3 polycondensation reaction

Abstract

High performance tough epoxy thermoset with excellent adhesive strength is one of the most in demand materials for advanced engineering applications. In the present investigation three hyperbranched epoxy resins with varying compositions were synthesized by a single step controlled polycondensation reaction using an A₂ + B₃ approach for the first time. The physical properties like epoxy equivalent, hydroxyl value, viscosity, etc. of the synthesized epoxy resins were determined by different analytical techniques. The hyperbranched structure of the resins was characterized by spectroscopic techniques. The degrees of branching were found to be 0.60, 0.79 and 0.51 for the resins with 10, 20 and 30 wt% of the B₃ moiety respectively, as obtained from the ¹³C NMR study. The poly(amidoamine) cured hyperbranched epoxy thermosets exhibited high thermostability (up to 293, 298 and 296 °C), tensile strength (38, 47 and 26 MPa), elongation at break (43, 21 and 52%), strain energy or toughness (1277, 758 and 1056 MPa), exceptionally high adhesive strength (1987, 2662, 1638 MPa), impact resistance (>100 cm) and scratch hardness (8.5, 9.0, 8.0 kg). The results showed the prominent role of the amount of the B₃ moiety in the performance of the thermosets. The study, therefore, revealed that the unison of the aliphatic–aromatic moiety in the hyperbranched structure can offer a high performance tough epoxy thermoset without any processing difficulty.