Ultralow dielectric, high performing hyperbranched epoxy thermosets: synthesis, characterization and property evaluation

Abstract

In the present report, low viscosity hyperbranched epoxy resins are synthesized using a simple A₂ + B₄ polycondensation reaction between pentaerythritol and the in situ prepared diglycidyl ether of bisphenol-A, with variation of the reaction time and amount of B₄ reactant. The structural features and degree of branching (DB) of the hyperbranched epoxy resins are determined by spectroscopic analyses, such as FTIR, ¹H NMR and ¹³C NMR studies. The highest DB (0.78) with the lowest epoxy equivalent (394 g eq⁻¹), viscosity (2.99 Pa s) and specific gravity (1.03) values is found for the resin formed after a reaction time of 4 h with 10 wt% pentaerythritol. The thermoset of the same resin also exhibits the highest tensile strength (51 MPa), elongation at break (37.5%), toughness (1432 MPa), adhesive strength (3429 MPa) and thermal stability (∼300 °C), as well as the lowest dielectric constant (1.8), dielectric loss (0.009) and moisture absorption (0.09%). The results are also compared with a linear diglycidyl ether of bisphenol-A based epoxy (without the addition of pentaerythritol) prepared under the same conditions. The study also shows that the hyperbranched epoxy is superior in terms of physical properties as well as performance (especially, the toughness value is 800% higher) compared to the linear analog. Thus the synthesized hyperbranched epoxy thermoset can solve the genuine problem of the brittleness character of the conventional epoxy. This epoxy thermoset can also be used efficiently as a low dielectric adhesive material in the field of electronics.