Siloxane-containing epoxy resins derived from magnolol with low dielectric properties, excellent toughness, and flame retardancy

Abstract

The entanglement disorder, highly polar groups and carbon-rich structure of conventional epoxy resins result in high dielectric constants and flammability, posing challenges to the development of high-frequency communications. Therefore, a silicone-containing active ester curing agent (FMAE) derived from magnolol was synthesized via a straightforward two-step process. And a thermosetting resin (FMAE/TGDDM) was then obtained by moisture self-cross-linking as well as curing epoxy N, N, N, N-tetraethoxypropyl-4, 4-diaminodiphenylmethane (TGDDM). The epoxy resin (MAE/TGDDM) cured by MAE that was not undergoing click chemistry was used for comparison. The results showed that the large volume of curing agents (31.86 Å × 14.98 Å × 9.03 Å for FMAE, 16.01 Å × 11.46 Å × 8.09 Å for MAE) and the absence of –OH enabled both resins to have excellent dielectric properties, especially FMAE/TGDDM, with a D_k of 2.78 and a D_f of 0.0066 at 10 MHz. Additionally, FMAE/TGDDM demonstrated favorable impact resistance (43.9 kJ/m²) and lower hygroscopicity (0.56%) than MAE/TGDDM, which due to the introduction of siloxane chain (Si% = 7.08%) and the increase of the crosslinking density (2302 mol/cm³ vs 6751 mol/cm³). Furthermore, the charring rate of FMAE/TGDDM was 39.1%, almost twice that of MAE/TGDDM, and the PHHR and THR were 201.2 W/g and 22.6 kJ/g, 103.9% and 67.7% lower than MAE/TGDDM, respectively, proving that the intrinsic flame retardancy of FMAE/TGDDM. Hence, this paper provides a strategy to synergistically address the limitations of TGDDM and conventional epoxy resins for impact resistance, dielectric properties and flame retardancy through a simple structural design.